Podcasts about Chemotaxis

Matters Microbial #83: Helicobacter — Passing the Acid Test March 19, 2025 Today, Dr. Karen Ottemann, Professor and Chair of the Department of Microbiology and Environmental Toxicology at the University of California Santa Cruz joins the #QualityQuorum to discuss the fascinating strategies of Helicobacter pylori, which can cause gastric ulcers and even stomach cancer in people. Host: Mark O. Martin Guest: Karen Ottemann Subscribe: Apple Podcasts, Spotify Become a patron of Matters Microbial! Links for this episode An overview of Helicobacter pylori and its relationship to gastric ulcers and gastric cancer. A video on the relationship between Helicobacteri pylori and gastric diseases. The story of how Helicobacter pylori was finally demonstrated to be responsible for gastric ulcers and gastric cancer. The prevalence of Helicobacter pylori world wide. When Helicobacter pylori does not cause disease:  a possible theory. The mechanism by which Helicobacter pylori causes gastric ulcers. The mechanism by which Helicobacter pylori causes gastric cancer. An overview of gastric cancer. An overview of inflammation and cancer. One of the articles from Dr. Ottemann's research group discussed in this episode:  “Bacterial flagella hijack type IV pili proteins to control motility.” Another of the articles from Dr. Ottemann's research group discussed in this episode:  “Helicobacter pylori cheV1 mutants recover semisolid agar migration due to loss of a previously uncharacterized Type IV filament membrane alignment complex homolog.” Dr. Ottemann's faculty website. Dr. Ottemann's research website. Intro music is by Reber Clark Send your questions and comments to mattersmicrobial@gmail.com

Astronomy Daily - The Podcast: S04E32In this episode of Astronomy Daily, host Anna explores a range of captivating developments from the cosmic frontier, featuring groundbreaking research on life detection methods, seismic discoveries on Mars, and the celebration of Pluto's discovery. Join us as we dive into the latest astronomical news and insights that are reshaping our understanding of the universe.Highlights:- Revolutionary Life Detection Method: Discover a new and simple technique developed by researchers in Germany to detect microorganisms' movement towards chemicals, potentially transforming our search for extraterrestrial life on planets like Mars and Europa.- Mars Seismic Highway: Learn about the groundbreaking discovery of a 'seismic highway' on Mars, revealing how seismic waves travel deeper than previously thought, reshaping our understanding of the Martian interior and planetary evolution.- Celebrating Pluto's Discovery: Get the details on the upcoming Weinhardt Pluto Festival at Lowell Observatory, honoring Clyde Tombaugh's historic discovery of Pluto and the 10th anniversary of NASA's New Horizons mission.- Gaia 4B Exoplanet Discovery: Explore the remarkable findings of Gaia 4B, one of the largest exoplanets discovered, and the intriguing questions it raises about the nature of planets and failed stars.- The Enormous Quipu Structure: Uncover the discovery of Quipu, the largest cosmic structure ever observed, and its implications for our understanding of the universe's architecture and the distribution of matter.- NASA's First Live Twitch Stream: Hear about NASA's historic live Twitch stream from the International Space Station, aimed at engaging new audiences and inspiring the next generation of space explorers.For more cosmic updates, visit our website at astronomydaily.io. Join our community on social media by searching for #AstroDailyPod on Facebook, X, YouTubeMusic, Tumblr, and TikTok. Don't forget to subscribe to the podcast on Apple Podcasts, Spotify, iHeartRadio, or wherever you get your podcasts.Thank you for tuning in. This is Anna signing off. Until next time, keep looking up and stay curious about the wonders of our universe.00:00 - Welcome back to Astronomy Daily01:02 - New life detection method using chemotaxis05:30 - Insights from Mars' seismic highway discovery10:15 - Upcoming Weinhardt Pluto Festival details14:00 - Discovery of Gaia 4B exoplanet18:20 - Quipu: the largest cosmic structure discovered22:00 - NASA's first live Twitch stream from the ISS25:00 - Conclusion and upcoming content✍️ Episode ReferencesLife Detection Method Research[Life Detection Method](https://www.scientificreports.com)Mars Seismic Study[Mars Seismic Study](https://www.nasa.gov/insight)Weinhardt Pluto Festival[Weinhardt Pluto Festival](https://www.lowell.edu)Gaia 4B Discovery[Gaia 4B](https://www.esa.int/Science_Exploration/Gaia)Quipu Structure[Quipu Structure](https://www.astrobiology.com)NASA Twitch Stream[NASA Twitch Stream](https://www.nasa.gov/live)Astronomy Daily[Astronomy Daily](http://www.astronomydaily.io)Become a supporter of this podcast: https://www.spreaker.com/podcast/astronomy-daily--5648921/support.

This month, Chris Smith hears how blood-thirsty bacteria sniff out wounds to trigger infections, how ants navigate at night, how male and female brains respond differently to starvation, and inflammation linked to premature labour... Get the references and the transcripts for this programme from the Naked Scientists website

Summary: Are you telling me a brainless protists has senses? You bet! Join Kiersten as she discusses slime mols senses.   For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean   Show Notes: “Slime Mould Senses” Warwick Life Sciences. https://warwick.ac.uk/fac/sci/lifesci “Phototaxis and Photomorphogenesis in Physarum polycephalum Plasmodia”, by Th. Schereckenbach. Blue Light Effects in Biological Systems pp 463-475. Proceedings in Life Sciences, Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-69767-8_51 “The Intelligence of Slime Mold,” by Hannah Gillespie, The Appalachian Voice. October 11, 2019. https://appvoices.org “Can Slime Molds Think?” By Nancy Walecki. Harvard Magazine, November-December 2021. https://www.harvardmagazine.com   Transcript  (Piano music plays) Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife. (Piano music stops) Welcome to Ten Things I Like About… I'm Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we'll find right out side our doors and some are continents away but all are fascinating.  This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won't regret it. This is episode six of slime mold and today we're talking senses. I know it sounds a little odd to talk about senses in a life form that doesn't even have a brain but the fact that slime mold has senses is the sixth thing I like about it. To be honest, slime mold doesn't have all the traditional senses that we think about creatures having, such as sight, hearing, taste, touch, and smell, but the senses they have are pretty mind-blowing for such a simple organism. Let's look at sight first. He-he, see what I did there? On boy! I'm stuck in a pun-cycle! Seriously, slime mold can't actually see, there is no evidence of an optical nerve or any kind of optical receptors in slime mold. They do have the ability to sense light. Most of the time, slime mold will avoid light. Blue light and UV light can damage DNA and the slime mold consistently moved away from these wavelengths. On the other end of the spectrum, red light influenced the movements of slime mold but to a lesser degree than blue and UV.  Light affects slime mold in various ways. In laboratory experiments, visible light has been shown to inhibit growth, induce a light avoidance response in mobile slime mold, control the change of plasmodial slime mold into resting structures, and trigger a formation of fruiting bodies. Movement influenced by light is called phototaxis. It looks like slime mold may not be able to see light in the traditional sense, but it defiantly has quite the impact on this organism. In the diet episode we already sniffed out slime molds sense of smell, but let's revisit it quickly here. Slime mold doesn't possess an olfactory system in the traditional sense. In mammalians we have a centralized olfactory system that concentrates the cells that collect scent. It's our nose! Slime mold does not have a nose, but it does have olfactory cells all over its form. So, it's kind of like one big nose. It is able to determine, by smell, which direction it wants to go to find high-quality food. It can, somehow make decisions based on the scents in the environment. Chemotaxis is movement influenced by chemical scents in the environment. Slime mold has this ability. In laboratory experiments, slime mold moved toward oats and paprika, both a good source of acceptable food, and moved away from black pepper and turmeric. Sense of smell often goes hand in hand with a sense of taste. Slime mold definitely behaves like it has a sense of taste as well as smell, because it avoids engulfing certain types of food.  Items high in salt, caffeine, and items with a high pH level are all commonly avoided by slime mold. Oats, sugar, and high protein foods all attract slime mold. Now, of course, these items all give off a chemical scent that we know the slime mold can sense, but it's reasonable to believe that it may also have a sense of taste. We'll have to wait for future research to see if it's true. Moving on to the sense of touch. There is really no way for use to truly understand what slime mold feels, but there is research that shows slime mold has preferences for certain surfaces. Like Goldilocks, slime mold wants a surface that is just right. They want something hard but not too hard. They will pick wood over a rock or over a loose patch of moss.  There is no evidence, yet, that slime mold is capable of hearing, but give it some time. I don't think we should rule anything out when it come to slime mold. We do know that slime mold employs mechanosensation to judge objects in the distance without coming into physical contact with them. Researchers at Harvard's Wyss Institute for Biologically Inspired Engineering and the Allen Discovery Center at Tufts University presented challenges to the slime mold in a laboratory setting to see what it was capable of. They placed the slime mold in the center of a petrie dish and placed glass discs on opposite sides of the dish. One side held one disc and the other side held three discs. They turned off the lights and left the slime mold for approximately 12 hours. When they checked on the slime mold, it consistently traveled toward the side contains three discs. Now, they filmed the progression of the slime mold to make sure it hadn't  reached all the way out to each side touching the discs and then determined which way to go. The slime mold never touched any of the discs before it favored the side with the three discs.  To make this even crazier, the slime mold showed a preference for discs that took up more horizontal space than discs that were closer together or stacked on top of one another. They are still not sure how the slime mold is processing this information, but the presence of protein channels called TRP have been found in slime mold. The human brain uses these TRP channels to process mechanosensation input. Notice I said the human brain, and as we know by now, slime mold does not have a brain. So , how is slime mold processing the information that helps it determine the mass of objects on the horizon? I don't know about you, but each episode of this slime mold series amazes me. Slime mold senses is mu sixth favorite thing bout this under appreciated organism.   If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change.    Join me next week for another episode about slime mold.       (Piano Music plays)  This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.

Microbes have existed on Earth for almost 4 billion years; 3x as long as multicellular organisms and 1000x longer than humans. So what does the future hold? Will recent advances in genetic engineering enable us to create bacterial ‘drug-delivery' machines or self-replicating microbial vaccines? What will the first human-created lifeform mean for our understanding of biology? Will humanity end with a ‘microbial bang', or might microbes perhaps be the solution we need to spread our wings beyond this planet?A lecture by Robin May recorded on 10 May 2023 at Barnard's Inn Hall, London.The transcript and downloadable versions of the lecture are available from the Gresham College website: https://www.gresham.ac.uk/watch-now/microbial-futureGresham College has offered free public lectures for over 400 years, thanks to the generosity of our supporters. There are currently over 2,500 lectures free to access. We believe that everyone should have the opportunity to learn from some of the greatest minds. To support Gresham's mission, please consider making a donation: https://gresham.ac.uk/support/Website:  https://gresham.ac.ukTwitter:  https://twitter.com/greshamcollegeFacebook: https://facebook.com/greshamcollegeInstagram: https://instagram.com/greshamcollegeSupport the show

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2023.05.05.539547v1?rss=1 Authors: Dupuy, L., Mimault, M., Ptashnyk, M. Abstract: Movement is critical for bacterial species inhabiting soils because nutrient availability is limited and heterogeneously distributed both in space and time. Recent live microscopy experiments show that bacteria form flocks when navigating through porous medium, and complex cell-cell interactions may be required to maintain such flocks. Here we propose a non-local model to study how peer attraction can affect flocking patterns in a porous medium. We establish the existence and uniqueness of the solution of the problem, propose a numerical scheme for simulations of the non-local convection-diffusion equation, and investigate the numerical convergence of the scheme. Numerical simulations showed that the strength of peer attraction is critical to control the size, shape, and nature of movement of the flocks in a porous network. Copy rights belong to original authors. Visit the link for more info Podcast created by Paper Player, LLC

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2023.01.25.525622v1?rss=1 Authors: Tomioka, M., Umemura, Y., Ueoka, Y., Chin, R., Katae, K., Uchiyama, C., Ike, Y., Iino, Y. Abstract: The nematode Caenorhabditis elegans memorizes various external chemicals, such as ions and odorants, during feeding. Here we find that C. elegans is attracted to the monosaccharides glucose and fructose after exposure to these monosaccharides in the presence of food; however, it avoids them without conditioning. The attraction to glucose requires a left-sided ASE gustatory neuron called ASEL. ASEL activity increases when glucose concentration decreases. Optogenetic ASEL stimulation promotes forward movements; however, after glucose conditioning, it promotes turning, suggesting that after glucose conditioning, the behavioral output of ASEL activation switches toward glucose. We previously reported that chemotaxis toward sodium ion (Na+), which is sensed by ASEL, increases after Na+ conditioning in the presence of food. Interestingly, glucose conditioning decreases Na+ chemotaxis, and conversely, Na+ conditioning decreases glucose chemotaxis, suggesting the reciprocal inhibition of learned chemotaxis to distinct chemicals. The activation of PKC-1, an nPKC {varepsilon}/{eta} ortholog, in ASEL promotes glucose chemotaxis and decreases Na+ chemotaxis after glucose conditioning. Furthermore, genetic screening identified ENSA-1, an ortholog of the protein phosphatase inhibitor ARPP-16/19, which functions in parallel with PKC-1 in glucose-induced chemotactic learning toward distinct chemicals. These findings suggest that kinase-phosphatase signaling regulates the balance between learned behaviors based on glucose conditioning in ASEL, which might contribute to migration toward chemical compositions where the animals were previously fed. Copy rights belong to original authors. Visit the link for more info Podcast created by Paper Player, LLC

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2022.12.07.519354v1?rss=1 Authors: Dowdell, A., Paschke, P., Thomason, P., Tweedy, L., Insall, R. Abstract: Negative chemotaxis, where eukaryotic cells migrate away from repellents, is important throughout biology, for example in nervous system patterning and resolution of inflammation. However, the mechanisms by which molecules repel migrating cells are unknown. Here, we use a combination of modelling and experiments with Dictyostelium cells to show that competition between different ligands that bind to the same receptor leads to effective chemorepulsion. 8-CPT-cAMP, widely described as a simple chemorepellent, is inactive on its own, and only repels cells if it interacts with the attractant cAMP. If cells degrade either competing ligand, the pattern of migration becomes more complex; cells may be repelled in one part of a gradient but attracted elsewhere, leading to populations moving in different directions in the same assay, or converging in an arbitrary place. More counterintuitively still, two chemicals can each attract cells on their own, but repel cells when combined together. We have thus identified a new mechanism that drives reverse chemotaxis, verified by mathematical models and experiments with real cells, and important anywhere several ligands compete for the same receptors. Copy rights belong to original authors. Visit the link for more info Podcast created by Paper Player, LLC

Today's ID the Future continues intelligent design theorist Casey Luskin's conversation with Apologetics 315 podcast hosts Brian Auten and Chad Gross. Here in Part 2, Luskin give a peek behind the scenes of ID 3.0, the current research program inspired by the intelligent design framework. Luskin is then asked to explain his reservations about theistic evolution, and Luskin points out the evidential, rhetorical, and logical problems he sees with the brand of theistic evolution advocated by Francis Collins and Biologos. What about the future of the intelligent design movement? Luskin says he's optimistic, both because of the exciting research and publication breakthroughs of late, and because of the many converts he's seeing to the ID framework. According to Luskin, many of these Read More › Source

Today's ID the Future is Part 2 of a recent live webinar with Eric Cassell fielding questions about his new book, Animal Algorithms: Evolution and the Mysterious Origin of Ingenious Instincts. He and host Casey Luskin explore the engineering wonders of web-spinning spiders and their extraordinary silk, and the challenge of transforming solitary insects into social insects (with their complex and interdependent caste systems) via a blind step-by-step evolutionary process, and the many thousands of genetic changes required. What does Cassell consider the best explanation? He invokes design theorist William Dembski's work with No Free Lunch theorems to argue that blind processes are a no-go for explaining their origin. From there Luskin opens the webinar up to questions from the Read More › Source

Today's ID the Future brings listeners the first half of a recent live webinar featuring author Eric Cassell fielding questions about his intelligent design book, Animal Algorithms: Evolution and the Mysterious Origin of Ingenious Instincts. Center for Science and Culture associate director Casey Luskin hosts. They begin the webinar discussing Cassell's unique set of qualifications for writing the book, and then they move into a conversation about the amazing desert ant, a master navigator from birth, able to integrate multiple navigation sensors despite having an incredibly tiny brain. Cassell argues that these innate skills point to algorithms programmed into the ant's brain and genome, and that such programming is far better explained by intelligent design than by any blind evolutionary Read More › Source

Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Evolution of Modularity, published by johnswentworth on the AI Alignment Forum. Crossposted from the AI Alignment Forum. May contain more technical jargon than usual. This post is based on chapter 15 of Uri Alon's book An Introduction to Systems Biology: Design Principles of Biological Circuits. See the book for more details and citations; see here for a review of most of the rest of the book. Fun fact: biological systems are highly modular, at multiple different scales. This can be quantified and verified statistically, e.g. by mapping out protein networks and algorithmically partitioning them into parts, then comparing the connectivity of the parts. It can also be seen more qualitatively in everyday biological work: proteins have subunits which retain their function when fused to other proteins, receptor circuits can be swapped out to make bacteria follow different chemical gradients, manipulating specific genes can turn a fly's antennae into legs, organs perform specific functions, etc, etc. On the other hand, systems designed by genetic algorithms (aka simulated evolution) are decidedly not modular. This can also be quantified and verified statistically. Qualitatively, examining the outputs of genetic algorithms confirms the statistics: they're a mess. So: what is the difference between real-world biological evolution vs typical genetic algorithms, which leads one to produce modular designs and the other to produce non-modular designs? Kashtan & Alon tackle the problem by evolving logic circuits under various conditions. They confirm that simply optimizing the circuit to compute a particular function, with random inputs used for selection, results in highly non-modular circuits. However, they are able to obtain modular circuits using “modularly varying goals” (MVG). The idea is to change the reward function every so often (the authors switch it out every 20 generations). Of course, if we just use completely random reward functions, then evolution doesn't learn anything. Instead, we use “modularly varying” goal functions: we only swap one or two little pieces in the (modular) objective function. An example from the book: The upshot is that our different goal functions generally use similar sub-functions - suggesting that they share sub-goals for evolution to learn. Sure enough, circuits evolved using MVG have modular structure, reflecting the modular structure of the goals. (Interestingly, MVG also dramatically accelerates evolution - circuits reach a given performance level much faster under MVG than under a fixed goal, despite needing to change behavior every 20 generations. See either the book or the paper for more on that.) How realistic is MVG as a model for biological evolution? I haven't seen quantitative evidence, but qualitative evidence is easy to spot. MVG as a theory of biological modularity predicts that highly variable subgoals will result in modular structure, whereas static subgoals will result in a non-modular mess. Alon's book gives several examples: Chemotaxis: different bacteria need to pursue/avoid different chemicals, with different computational needs and different speed/energy trade-offs, in various combinations. The result is modularity: separate components for sensing, processing and motion. Animals need to breathe, eat, move, and reproduce. A new environment might have different food or require different motions, independent of respiration or reproduction - or vice versa. Since these requirements vary more-or-less independently in the environment, animals evolve modular systems to deal with them: digestive tract, lungs, etc. Ribosomes, as an anti-example: the functional requirements of a ribosome hardly vary at all, so they end up non-modular. They have pieces, but most pieces do not have an obvious distinct function. To sum it up: modul...

Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Evolution of Modularity, published by johnswentworth on the AI Alignment Forum. Write a Review This post is based on chapter 15 of Uri Alon's book An Introduction to Systems Biology: Design Principles of Biological Circuits. See the book for more details and citations; see here for a review of most of the rest of the book. Fun fact: biological systems are highly modular, at multiple different scales. This can be quantified and verified statistically, e.g. by mapping out protein networks and algorithmically partitioning them into parts, then comparing the connectivity of the parts. It can also be seen more qualitatively in everyday biological work: proteins have subunits which retain their function when fused to other proteins, receptor circuits can be swapped out to make bacteria follow different chemical gradients, manipulating specific genes can turn a fly's antennae into legs, organs perform specific functions, etc, etc. On the other hand, systems designed by genetic algorithms (aka simulated evolution) are decidedly not modular. This can also be quantified and verified statistically. Qualitatively, examining the outputs of genetic algorithms confirms the statistics: they're a mess. So: what is the difference between real-world biological evolution vs typical genetic algorithms, which leads one to produce modular designs and the other to produce non-modular designs? Kashtan & Alon tackle the problem by evolving logic circuits under various conditions. They confirm that simply optimizing the circuit to compute a particular function, with random inputs used for selection, results in highly non-modular circuits. However, they are able to obtain modular circuits using “modularly varying goals” (MVG). The idea is to change the reward function every so often (the authors switch it out every 20 generations). Of course, if we just use completely random reward functions, then evolution doesn't learn anything. Instead, we use “modularly varying” goal functions: we only swap one or two little pieces in the (modular) objective function. An example from the book: The upshot is that our different goal functions generally use similar sub-functions - suggesting that they share sub-goals for evolution to learn. Sure enough, circuits evolved using MVG have modular structure, reflecting the modular structure of the goals. (Interestingly, MVG also dramatically accelerates evolution - circuits reach a given performance level much faster under MVG than under a fixed goal, despite needing to change behavior every 20 generations. See either the book or the paper for more on that.) How realistic is MVG as a model for biological evolution? I haven't seen quantitative evidence, but qualitative evidence is easy to spot. MVG as a theory of biological modularity predicts that highly variable subgoals will result in modular structure, whereas static subgoals will result in a non-modular mess. Alon's book gives several examples: Chemotaxis: different bacteria need to pursue/avoid different chemicals, with different computational needs and different speed/energy trade-offs, in various combinations. The result is modularity: separate components for sensing, processing and motion. Animals need to breathe, eat, move, and reproduce. A new environment might have different food or require different motions, independent of respiration or reproduction - or vice versa. Since these requirements vary more-or-less independently in the environment, animals evolve modular systems to deal with them: digestive tract, lungs, etc. Ribosomes, as an anti-example: the functional requirements of a ribosome hardly vary at all, so they end up non-modular. They have pieces, but most pieces do not have an obvious distinct function. To sum it up: modularity in the system evolves to match modularity in the environment. Than...

Today's ID the Future spotlights the new book Animal Algorithms: Evolution and the Mysterious Origin of Ingenious Instincts. The author, Eric Cassell, joins host and Baylor computer engineering professor Robert J. Marks to discuss the groundbreaking book and, in particular, the chapters on some of the animal kingdom's most stunning navigators—the arctic tern, homing pigeons, the monarch butterfly, and the desert ant, among others. Cassell has degrees in biology and engineering, and he draws on these and his decades of professional expertise in aircraft navigation systems to show that these creatures instinctively employ navigational technologies that humans have only recently mastered. According to Cassell, their skills are driven by sophisticated algorithms embedded in their brains. But what created these algorithms Read More › Source

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.11.11.379230v1?rss=1 Authors: Nakai, T., Ando, T., Goto, T. Abstract: Many kinds of peritrichous bacteria that repeat runs and tumbles by using multiple flagella exhibit chemotaxis by sensing a difference in the concentration of the attractant or repellent between two adjacent time points. If a cell senses that the concentration of an attractant has increased, their flagellar motors decrease the switching frequency from counterclockwise to clockwise direction of rotation, which causes a longer run in swimming up the concentration gradient than swimming down. We investigated the turn angle in tumbles of peritrichous bacteria swimming across the concentration gradient of a chemoattractant because the change in the switching frequency in the rotational direction may affect the way tumbles. We tracked several hundreds of runs and tumbles of single Salmonella typhimurium cells in the concentration gradient of L-serine, and found that the turn angle depends on the concentration gradient that the cell senses just before the tumble. The turn angle is biased toward a smaller value when the cells swim up the concentration gradient, whereas the distribution of the angle is almost uniform (random direction) when the cells swim down the gradient. The effect of the observed bias in the turn angle on the degree of chemotaxis was investigated by random walk simulation. In the concentration field where attractants diffuse concentrically from the point source, we found that this angular distribution clearly affects the reduction of the mean square displacement of the cell that has started at the attractant source, that is, the bias in the turn angle distribution contributes to chemotaxis in peritrichous bacteria. Copy rights belong to original authors. Visit the link for more info

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.08.19.257477v1?rss=1 Authors: Elangovan, R., Soman, V., Kumari, S., Nath, S. Abstract: Many species of bacteria use flagella to navigate in its environment. The flagellum is a 7-10 m long helical filament with a rotary motor at its base embedded in the cell membrane and almost a dozen stator complexes. Proton motive force across the cell membrane powers the flagellar motors of E.coli and Salmonella. The motor stochastically switches between clockwise and counter-clockwise direction. A chemotaxis system causes the motor to change its direction, but the process is more complex as the switch is sensitive to load and proton motive force as well. NaCl is significant with regard to the flagellar motor as it affects the stator dynamics, proton motive force, and osmotaxis at higher concentration. Chemotaxis helps the bacteria for its growth and survival. E.coli's natural habitat has high osmolarity and the organism uses use various mechanisms for osmoregulation. However, the role of flagellar motor to adapt to the changes in osmolarity, or osmotaxis, is not well studied. In this work, we dissipated the membrane potential of bacteria in pH 7 using step-wise increase in concentration of NaCl in motility buffer and studied the output of E.coli's flagellar motor using tethered bead assay and swimming Salmonella enteritidis cells. We observed decrease in motor speed and switching rates with stepwise increase in NaCl concentration in the motility buffer. The mean speed of the motors decreased with NaCl concentration. The population of swimming cells tumbled more with increase in concentration of NaCl. At the single motor level, the motors biased to CCW rotation with decrease in membrane potential. In this study, we present our observations of the flagellar motor in high NaCl concentration, and explore how NaCl can be used to study various aspects of the bacterial flagellar motor. Copy rights belong to original authors. Visit the link for more info

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.05.19.104109v1?rss=1 Authors: Laprell, L., Brehme, M.-L., Oertner, T. G. Abstract: Microglia react to danger signals by rapid and targeted extension of cellular processes towards the source of the signal. This positive chemotactic response is accompanied by a hyperpolarization of the microglia membrane. Here we show that optogenetic depolarization of microglia has little effect on baseline motility, but significantly slows down the chemotactic response. Reducing the extracellular Ca2+ concentration mimics the effect of optogenetic depolarization. As the membrane potential sets the driving force for Ca2+ entry, hyperpolarization is an integral part of rapid stimulus-response coupling in microglia. Compared to other excitable cells, the sign of the activating response is inverted in microglia, leading to inhibition by depolarizing channelrhodopsins. Copy rights belong to original authors. Visit the link for more info

Researchers have gained new insights into how bacteria move in complex environments. Bacteria move using a system called "swim-and-tumble": they swim in a straight line for a bit, then tumble in a circle, which gives them a chance to correct their course. They can't see where they're going - they can't see at all - but they can sense and follow gradients of increasing concentration of food, like following a delicious smell into the kitchen. This type of movement is called chemotaxis, and it's been well studied in bacteria moving in a clear area. But in the real world, such as inside the human... Like this podcast? Please help us by supporting the Naked Scientists

Researchers have gained new insights into how bacteria move in complex environments. Bacteria move using a system called "swim-and-tumble": they swim in a straight line for a bit, then tumble in a circle, which gives them a chance to correct their course. They can't see where they're going - they can't see at all - but they can sense and follow gradients of increasing concentration of food, like following a delicious smell into the kitchen. This type of movement is called chemotaxis, and it's been well studied in bacteria moving in a clear area. But in the real world, such as inside the human... Like this podcast? Please help us by supporting the Naked Scientists

The TWiV hosts present two potentially seminal papers, on long-distance chemoattraction of a host by a chlorovirus, and replication of a nanovirus across multiple cells in a plant. Hosts: Vincent Racaniello, Dickson Despommier, Alan Dove, Kathy Spindler, and Brianne Barker Subscribe (free): iTunes, Google Podcasts, RSS, email Become a patron of TWiV! Links for this episode Paul Has Measles now in German (virology blog) Chloroviruses lure hosts (J Virol) Multicellular replication in plants (eLife) Image credit Letters read on TWiV 539 Timestamps by Jolene. Thanks! Weekly Science Picks Brianne - Why Do So Many Scientists Want to be Filmmakers Alan- Better boarding method airlines won’t use Dickson- Mass timber building Kathy- What organisms to study flow chart Vincent - World Pulls Andon Cord on 737 MAX Listener Pick Richard- The Real Cost of Knowledge Islam- 200 icosahedral viruses poster Mike- Post-Doc Me Now Intro music is by Ronald Jenkees. Send your virology questions and comments to twiv@microbe.tv

The TWiV hosts present two potentially seminal papers, on long-distance chemoattraction of a host by a chlorovirus, and replication of a nanovirus across multiple cells in a plant. Hosts: Vincent Racaniello, Dickson Despommier, Alan Dove, Kathy Spindler, and Brianne Barker Subscribe (free): iTunes, Google Podcasts, RSS, email Become a patron of TWiV! Links for this episode Paul Has Measles now in German (virology blog) Chloroviruses lure hosts (J Virol) Multicellular replication in plants (eLife) Image credit Letters read on TWiV 539 Timestamps by Jolene. Thanks! Weekly Science Picks Brianne - Why Do So Many Scientists Want to be Filmmakers Alan- Better boarding method airlines won’t use Dickson- Mass timber building Kathy- What organisms to study flow chart Vincent - World Pulls Andon Cord on 737 MAX Listener Pick Richard- The Real Cost of Knowledge Islam- 200 icosahedral viruses poster Mike- Post-Doc Me Now Intro music is by Ronald Jenkees. Send your virology questions and comments to twiv@microbe.tv

Microbes, such as the fungi-like kauri dieback disease, use chemicals to sense their world - and understanding this might help us to develop new treatments.

Microbes, such as the fungi-like kauri dieback disease, use chemicals to sense their world - and understanding this might help us to develop new treatments.

Alan Smrcka explains the distinct contributions that different heterotrimeric G protein subunits make to neutrophil migration.

In this lecture, Prof. Jeff Gore continues his discussion of bacterial chemotaxis, or how bacteria find food. The principle is a biased random walk of runs and tumbles, and is a shown to display perfect adaptation.

Min Zhao and Peter Devreotes discuss the results from a genetic screen to identify genes important for electrotaxis in the slime mold Dictyostelium discoideum.

  Vincent, Elio, and Michael reveal that a soil-dwelling nematode can recognize and respond to a bacterial quorum sensing molecule through a sensory neuron.

Inflammation is at the very heart of many disease processes, from infection and trauma to ageing and cancer. Split across 4 episodes, David Semeraro talks to Jon Lund about acute inflammation, covering definitions, mechanisms and progress with many examples from clinical cases, histopathological and macroscopic inflamed organ specimens. Listening to this series of podcasts will tell you all you need to know about the basics of acute inflammation, a thorough knowledge of which is essential for pre-clinical and clinical medical students and doctors in training in all specialities and at all levels. David Semeraro is a Consultant Histopathologist at the Royal Derby Hospital, UK and Jon Lund is Associate Professor of Surgery at the University of Nottingham, UK.

Thu, 9 Oct 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17530/ https://edoc.ub.uni-muenchen.de/17530/1/Schreyer_Anna-Chi.pdf Schreyer, Anna-Chi ddc:610, ddc:600, Medizinische Fakultät

Blebs lead the way in Dictyostelium chemotaxis Membrane blebs can help the leading edge of migrating cells protrude forwards, but the contribution of blebs to the motility of Dictyostelium cells is unclear. Zatulovskiy et al. reveal that blebs form at the front of chemotaxing Dictyostelium cells, particularly when the cells are faced with a mechanically resistant environment, and that this process is guided by a PI3-kinase-dependent signaling pathway. This biosights episode presents the paper by Zatulovskiy et al. from the March 17, 2014, issue of The Journal of Cell Biology and includes an interview with senior author Robert Kay (MRC Laboratory of Molecular Biology, Cambridge, UK). Produced by Caitlin Sedwick and Ben Short. See the associated paper in JCB for details on the funding provided to support this original research. Subscribe to biosights via iTunes or RSS View biosights archive The Rockefeller University Press biosights@rockefeller.edu

Milena Lazova onderzocht het simpele netwerk dat bacteriën in staat stelt om chemische stoffen waar te nemen en de juiste richting te kiezen. Zij kreeg inzicht in hoe biologische systemen zijn ontworpen en functioneren. Een beter begrip van het reactievermogen van bacteriën naar chemicaliën kan worden toegepast in de geneeskunde of industrie. Zo zou bijvoorbeeld bacteriën kunnen worden gebruikt om medicijnen aan specifieke delen van het lichaam toe te dienen of bacteriën kunnen worden ingezet om vervuilde vloeistoffen te zuiveren. Promotor: prof.dr. P.R. ten Wolde, dr. T.S. Shimizu. Faculteit: Faculteit der Exacte Wetenschappen. Datum: 11-06-2013

Milena Lazova onderzocht het simpele netwerk dat bacteriën in staat stelt om chemische stoffen waar te nemen en de juiste richting te kiezen. Zij kreeg inzicht in hoe biologische systemen zijn ontworpen en functioneren. Een beter begrip van het reactievermogen van bacteriën naar chemicaliën kan worden toegepast in de geneeskunde of industrie. Zo zou bijvoorbeeld bacteriën kunnen worden gebruikt om medicijnen aan specifieke delen van het lichaam toe te dienen of bacteriën kunnen worden ingezet om vervuilde vloeistoffen te zuiveren. Promotor: prof.dr. P.R. ten Wolde, dr. T.S. Shimizu. Faculteit: Faculteit der Exacte Wetenschappen. Datum: 11-06-2013

The chemokine scavenging activity of an atypical chemokine receptor requires signaling through β-arrestin.

Phosphoinositide 3-kinase (PI3K) and its phospholipid products are polarized toward the front of migrating fibroblasts, but their exact function in persistent motility remains unclear. Welf et al. reveal that PI3K signaling helps reorient migrating fibroblasts by stabilizing branched protrusions at the leading edge, allowing the cell to pivot and move in a different direction. This biosights episode presents the paper by Welf et al. from the April 2, 2012, issue of The Journal of Cell Biology and includes an interview with senior author Jason Haugh (North Carolina State University, Raleigh, NC). Produced by Caitlin Sedwick and Ben Short. See the associated paper in JCB for details on the funding provided to support this original research. Subscribe to biosights via iTunes or RSS View biosights archive The Rockefeller University Press biosights@rockefeller.edu

Chemotaxis, the ability of cells to detect and migrate directly towards a source of a chemically active agent, is the result of a sophisticated interplay of proteins within a complex regulatory network. However, partially redundant pathways that simultaneously mediate chemotaxis and dynamic protein distributions complicate the experimental identication of distinct signaling cascades and their inuence on chemotactic migration. Yet, increasingly precise generation and rapid modication of chemotactic stimuliin microuidic devices promise further insight into the basic principles of cellular feedback signaling. I developed a Chemotactic Gradient Generator (CGG) for the exposure of living cells to chemotactic gradient elds with alternating gradient direction based on a double T-junction microuidic chamber. A large extension of the concentration gradients enables the parallel exposure of several dozens of cells to identical chemotactic stimuli, allowing for a reliable quantitative analysis of the chemotactic migration behavior. Two pressure pumps and a syringe pump facilitate accurate control of the inow velocities at the individual ow chamber inlets, pivotal for precise manipulation of the chemotactic stimuli. The CGG combines homogeneous gradients over a width of up to 300 µm and rapid alterations of gradient direction with switching frequencies up to 0.7 Hz. Fast gradient switching in our experimental design facilitates cell stimulation at the intrinsic time scales of their chemotactic response as demonstrated by a gradual increase in the switching frequency of the gradient direction. We eventually observe a "chemotactically trapped" state of Dictyostelium discoideum (D. discoideum) cells at a switching rate of 0.01 Hz. Here, gradient switching proves too fast for the cells to respond to the altered gradient direction by migration. In contrast, we observe oscillatory runs at switching frequencies of less than 0.02 Hz. We distinguish between re-polymerizing cells that exhibit an internal re-organization of the actin cortex in response to chemotactic stimulation and stably polarized cells that gradually adjust their leading edge when the gradient is switched. To experimentally characterize both response types, we record cell shape and the intracellular distribution of actin polymerization activity. Cell shape is readily described by the eccentricity of the cell and to record F-actin polymerization dynamics we introduce a fluorescence distribution moment (FDM). Accurate description of the migratory response behavior facilitates a quantitative analysis of the inuence of both the experimental boundary conditions such as gradient shape, ongoing starvation of the cells, and in particular the inuence of distinct signaling cascades on chemotactic migration. Here, we demonstrate this ability of the GCC by inhibition of PI3-Kinase with LY 294002. PI3-Kinase initiates the formation of fresh pseudopods in the direction of the chemotactic gradient and therefore is one of the key signaling pathways mediating the chemotactic response. In shallow gradients and with ongoing starvation of the cells, we find a decreased ratio of re-polymerizing cells, pointing towards a diminished influence of PI3-Kinase. After inhibition of PI3-Kinase, cell re-polymerization in response to a switch in gradient direction is hindered at 5h of starvation, whereas at 7h of starvation evidence is found that chemotactic migration is more efficient. We observe the astonishing result that in dependency of the boundary conditions of the experiment inhibition of PI3-Kinase promotes an effective chemotactic response. Thus, the CGG for the rst time facilitates a quantitative analysis of the starvation time dependent effect of PI3-Kinase inhibition on D. discoideum chemotaxis.

Mon, 24 Oct 2011 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/13999/ https://edoc.ub.uni-muenchen.de/13999/1/Huetz_Annemarie.pdf Hütz, Annemarie dd

Bournaveas, N (Edinburgh) Wednesday 08 September 2010, 15:30-16:10

Calvez, V (École Normale Supérieure) Wednesday 08 September 2010, 16:10-16:50

In this current study, we are investigating the influence of 6-bromo-indirubin-3’oxime (6BIO) and 7-bromo-indirubin-3’oxime (7BIO) on induction of apoptosis, cell proliferation, and anti-migratory effects in the well characterized pancreatic carcinoma L3.6pl and breast carcinoma Skbr3 tumor cell lines and characterize underlying mechanisms. 6BIO and 7BIO at doses of 10 µM were shown to significantly reduce the proliferation and viability as well as induce apoptosis in both cell lines. In addition, 6BIO, but not 7BIO, significantly reduced the migration of both cell lines, nearly halting them completely in the Skbr3 wound healing assay at sub-apoptotic doses (3 µM). Chemotaxis was dramatically disrupted and tumor cells significantly lost their ability to invade through membranes or MatrigelTM layers in response to chemoattractants. An increase of the phosphorylation site S785 of beta1 integrin is seen upon 6BIO which has been linked to decreased motility of carcinoma cells. Additionally, adhesion of Skbr3 tumor cells to fibronectin was reduced by 6BIO stimulation. The effects of 6BIO can be attributed to its reduction of the T308 phosphorylation site of Akt, most likely through its direct inhibition of PDK1, ultimately causing long term alterations to the actin cytoskeleton. Erk, FAK and Rac1 levels are unaffected, but cycling of these signaling molecules appears to be disrupted upon treatment. Finally 6BIO reduced the metabolic capabilities of Skbr3 spheroids at low doses, caused the dissolution of spheroid structures at higher doses and significantly blocked the migration of Skbr3 spheroids. Taken together, the results of this study strongly suggest that the indirubin derivative 6BIO operates by inhibiting different mechanisms in human tumor cells to exert their potent anti-tumor efficacy.

Dictyostelium cells migrate in an orderly head-to-tail arrangement. They do this by leaving a trail of vesicles (thought to contain chemoattractant) for their fellow cells to follow. This biosights episode presents a paper by Kriebel et al. in the Journal of Cell Biology, and includes excerpts from an interview with senior author Carole Parent. Produced by Justin Paul and Ruth Williams.   Subscribe to biosights via iTunes or RSS View biosights archive The Rockefeller University Press biosights@rockefeller.edu

Background: The mechanisms by which tumor-specific T cells induce regression of established metastases are not fully characterized. In using the poorly immunogenic B16BL6-D5 (D5) melanoma model we reported that T cell-mediated tumor regression can occur independently of perforin, IFN-gamma or the combination of both. Characterization of regressing pulmonary metastases identified macrophages as a major component of the cells infiltrating the tumor after adoptive transfer of effector T cells. This led us to hypothesize that macrophages played a central role in tumor regression following T-cell transfer. Here, we sought to determine the factors responsible for the infiltration of macrophages at the tumor site. Methods: These studies used the poorly immunogenic D5 melanoma model. Tumor-specific effector T cells, generated from tumor vaccine-draining lymph nodes (TVDLN), were used for adoptive immunotherapy and in vitro analysis of chemokine expression. Cellular infiltrates into pulmonary metastases were determined by immunohistochemistry. Chemokine expression by the D5 melanoma following co-culture with T cells, IFN-gamma or TNF-alpha was determined by RT-PCR and ELISA. Functional activity of chemokines was confirmed using a macrophage migration assay. T cell activation of macrophages to release nitric oxide (NO) was determined using GRIES reagent. Results: We observed that tumor-specific T cells with a type 1 cytokine profile also expressed message for and secreted RANTES, MIP-1 alpha and MIP-1 beta following stimulation with specific tumor. Unexpectedly, D5 melanoma cells cultured with IFN-gamma or TNF-alpha, two type 1 cytokines expressed by therapeutic T cells, secreted Keratinocyte Chemoattractant (KC), MCP-1, IP-10 and RANTES and expressed mRNA for MIG. The chemokines released by T cells and cytokine-stimulated tumor cells were functional and induced migration of the DJ2PM macrophage cell line. Additionally, tumor-specific stimulation of wt or perforin-deficient (PKO) effector T cells induced macrophages to secrete nitric oxide (NO), providing an additional effector mechanism for T cell-mediated tumor regression. Conclusion: These data suggest two possible sources for chemokine secretion that stimulates macrophage recruitment to the site of tumor metastases. Both appear to be initiated by T cell recognition of specific antigen, but one is dependent on the tumor cells to produce the chemokines that recruit macrophages.

Background: Previously, we reported that adoptively transferred perforin k/o (PKO), and IFN-gammak/o (GKO), or perforin/IFN-gamma double k/o (PKO/GKO) effector T cells mediated regression of B16BL6-D5 (D5) pulmonary metastases and showed that TNF receptor signaling played a critical role in mediating tumor regression. In this report we investigated the role of lymphotoxin-alpha (LT-alpha) as a potential effector molecules of tumor-specific effector T cells. Methods: Effector T cells were generated from tumor vaccine-draining lymph node (TVDLN) of wt, GKO, LT-alpha deficient (LKO), or PKO/GKO mice and tested for their ability to mediate regression of D5 pulmonary metastases in the presence or absence of LT-beta R-Fc fusion protein or anti-IFN-gamma antibody. Chemokine production by D5 tumor cells was determined by ELISA, RT-PCR and Chemotaxis assays. Results: Stimulated effector T cells from wt, GKO, or PKO/GKO mice expressed ligands for LT-beta receptor (LT-beta R). D5 tumor cells were found to constitutively express the LT-beta R. Administration of LT-beta R-Fc fusion protein completely abrogated the therapeutic efficacy of GKO or PKO/GKO but not wt effector T cells (p < 0.05). Consistent with this observation, therapeutic efficacy of effector T cells deficient in LT-alpha, was greatly reduced when IFN-gamma production was neutralized. While recombinant LT-alpha 1 beta 2 did not induce apoptosis of D5 tumor cells in vitro, it induced secretion of chemokines by D5 that promoted migration of macrophages. Conclusion: The contribution of LT-alpha expression by effector T cells to anti-tumor activity in vivo was not discernable when wt effector T cells were studied. However, the contribution of LT-beta R signaling was identified for GKO or PKO/GKO effector T cells. Since LT-alpha does not directly induce killing of D5 tumor cells in vitro, but does stimulate D5 tumor cells to secrete chemokines, these data suggest a model where LT-alpha expression by tumor-specific effector T cells interacts via cross-linking of the LT-beta R on tumor cells to induce secretion of chemokines that are chemotactic for macrophages. While the contribution of macrophages to tumor elimination in our system requires additional study, this model provides a possible explanation for the infiltration of inate effector cells that is seen coincident with tumor regression.

Die Infiltration mit leukozytären Zellen spielt eine entscheidende Rolle in der Pathogenese glomerulärer Erkrankungen der Niere und wird durch sequentielle und sich überschneidende Interaktionen verschiedener Signalmoleküle gesteuert. In dieser Arbeit wurde die Adhäsionsmolekül- und Chemokinexpression von Mesangialzellen (MC) und glomerulären Endothelzellen (GEC untersucht) und deren Regulation durch verschiedene NF-kappaB Inhibitoren bestimmt. Die Zytokinstimulation der MC mit TNF-alpha induzierte die Transkription und Proteinexpression der Adhäsionsmoleküle ICAM-1 und VCAM-1 sowie der Chemokine GRO-alpha, IL-8, MCP-1, aber nicht Fractalkine. GRO-alpha und IL-8 wurden auf der MC Oberfläche über Heparanproteoglykane immobilisiert, MCP-1 und auch IL-8 als lösliche Moleküle sezerniert. Fractalkine hingegen war nur geringfügig induzierbar konstitutiv auf der MC Oberfläche exprimiert. Diese Induktion der Adhäsionsmoleküle und Chemokine durch Zytokinstimulation der MC war assoziiert mit einer vermehrten Monozytenadhäsion und Transmigration. Dabei vermittelte ICAM-1 und VCAM-1, der GRO-alpha Rezeptor CXCR2 und in geringerem Maße auch Fractalkine den festen monozytären Arrest, während der MCP-1 Rezeptor CCR2 die transendotheliale Chemotaxis von Monozyten auf aktivierte MC zu steuerte. Die transkriptionelle Hochregulation der untersuchten Moleküle wurde über eine Inhibition der IkappaB-alpha Degradation durch den Proteaseninhibitor TLCK, den Proteosomeninhibitor MG132 und durch die adenovirale IkappaB-alpha Überexpression gehemmt. Dies war assoziiert mit der Inhibition der monozytären Adhäsion auf aktivierten MC sowie der transendothelialen Migration auf stimulierte MC zu. Im Gegensatz zu MC wurde Fractalkine auf mRNA wie Proteinebene in transformierten GEC deutlich induziert, und sowohl CXCR2 also auch CX3CR vermittelten den Monozytenarrest auf aktivierten GEC unter Flussbedingungen. Die Relevanz dieser Ergebnisse konnte in einem akzelerierten Glomerulonephritis-Modell an der Ratte bestätigt werden, in dem die Blockade von CCR2 deutlich, und die Blockade von CXCR2 fast komplett die akute glomeruläre Makrophagenrekrutierung inhibierte. Dies unterstreicht die Bedeutung von CXCR2 für die Makrophageninfiltration in den frühen Phasen der NTN. Zusammenfassend erschließt sich ein mehrstufiges Modell, das die inflammatorische Monozytenrekrutierung durch funktionell spezialisierte Adhäsionsmoleküle und Chemokine zeigt.

Podosomen sind aktinreiche Strukturen des Zytoskeletts primärer humaner Makrophagen. Für Adhäsion, Polarisation und Chemotaxis sind diese Strukturen von essentieller Bedeutung. Ihr ständiger Umbau und ihre Regulation unterliegt einer fein abgestimmten Balance der Rho GTPasen Rho, Rac und Cdc42. Pathogene Yersinien spp. haben Aktinzytoskelett von Wirtszellen durch Modulation von Rho GTPasen als Angriffsobjekt gewählt. Mit ihrem plasmidkodierten Typ III Sekretions- und Translokationsapparat werden wichtige Immunfunktionen paralysiert. In dieser Arbeit wurde in primären humanen Makrophagen der Einfluss von Yersinien-Effektoren auf Podosomen untersucht. Konkret interessierte die Frage, welchen Effekt YopE auf diese Strukturen hat. Hierzu wurden in einem standardisierten Verfahren gewonnene und gereinigte Makrophagen gesunder Spender mit unterschiedlichen Mutanten der Spezies Yersinia enterocolitica für verschiedene Zeiten infiziert. Nach Färbung der Zellen mit Rhodamin-Phalloidin wurde die Anzahl der verbliebenen Zellen mit Podosomen im konfokalen Mikroskop ermittelt und statistisch ausgewertet. Es konnte erstens gezeigt werden, daß ein voll virulenter Yersinien Stamm in der Lage ist, nach einer Infektion von bereits 30 min die podosomalen Strukturen der Makrophagen vollkommen zu zerstören. Zweitens sind an diesem Effekt verschiedene Yersinien-Effektoren und zusätzlich der Typ III Sekretions- und Translokationsapparat beteiligt. Drittens reicht YopE für die Zerstörung von Podosomen alleine aus. Viertens ist die GAP-Aktivität von YopE für die Destruktion von Podosomen nicht notwendig und lässt auf GAP-unabhängige Mechanismen von YopE schliessen. Zusammenfassend lassen die Ergebnisse dieser Arbeit vermuten, daß YopE ein wichtiger aber nicht der alleinige Effektor der Yersinien bei der Paralyse von menschlichen Makrophagen und insbesondere der Zerstörung podosomaler Adhäsionsstrukturen ist.

Wed, 12 Feb 2003 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/798/ https://edoc.ub.uni-muenchen.de/798/1/Schaer_Andreas.pdf Schaer, Andreas ddc:540, ddc:500, Fakultät für Chemie

Methoden der multidimensionalen konfokalen Mikroskopie wurden für die in vivo Beobachtung dynamischer Prozesse in der Amöbe Dictyostelium discoideum verwendet. Um diese Vorgänge sichtbar zu machen, wurde Grün Fluoreszierendes Protein (GFP) als Reporter von Genexpression und als Fusionsprotein eingesetzt. Mit Hilfe von 4D-Mikroskopie und Mehrkanal-Detektion konnten dabei in vivo die Zellsortierung in vielzelligen Aggregaten und die intrazelluläre Lokalisierung des Zytoskelett-Proteins Severin visualisiert und analysiert werden. Es wurde eine Methode entwickelt, spektral unterschiedliche GFP-Varianten im Konfokalmikroskop simultan zu detektieren und verläßlich zu trennen. Aufgrund der Anregungswellenlänge und der Verwendung nur eines Aufnahmevorgangs zur Erfassung beider GFP-Varianten eignet sich dieser Ansatz zur schonenden Beobachtung lebender Zellen auch über längere Zeiträume. Diese Eigenschaften ermöglichen darüber hinaus die Verwendung dieser Konfiguration bei den wiederholten Aufnahmen einer 4D-Messung. In D. discoideum-Slugs wurde die Lokalisierung von Prestalk-Zellen (pstA- und pst0-Zellen) während der Migration und der Spitzenneubildung mit GFP als Reporter für spezifische Genexpression untersucht. In migrierenden Slugs fallen Prestalk-Zellen aus dem pstA-Bereich der Spitze in den Prespore-Bereich zurück. Dieses Zurückfallen in der zentralen Längsachse läßt sich durch die Organisation der Spitzenregion durch cAMP-Spiralwellen mit einem Zentrum in der Längsachse erklären. Prestalk-Zellen gelangen über diesen Weg aus der Spitze in den Prespore-Bereich. An der Neubildung von Spitzen im Prespore-Bereich sind ehemalige Prestalk-Zellen gemeinsam mit den Anterior-like-Zellen des Prespore-Bereichs maßgeblich beteiligt. Diese Zelltypen bewegen sich an die Slugoberseite und bilden dort rotierende Zentren, aus denen sich neue Spitzen bilden. Das Verhalten dieser Zellgruppen und die 4DTrajektorien einzelner Zellen deuten auf eine Organisation dieser Zentren durch cAMPSignale. Darüber hinaus konnte gezeigt werden, daß es innerhalb dieser Zellen Gruppen gibt, die zu unterschiedlichen Zeiten in neue Spitzen rekrutiert werden. PstA-Zellen sind in neuen Spitzen wieder im vordersten Bereich lokalisiert, obwohl sie aus dem Prespore-Bereich kommen, während pst0-Zellen im gesamten Prestalk-Bereich zu finden sind. Artspezifische Zellsortierungsprozesse gemeinsam vorkommender Dictyostelium-Arten wurden mittels der Markierung von Zellen der beteiligten Arten untersucht. Es konnte gezeigt werden, daß die Sortierung von D. discoideum/D. mucoroides-Mischungen schon in den Aggregationsströmen anfängt und im Mound abgeschlossen wird. Die Trennung erfolgt über Unterschiede in der Zelladhäsion. Erheblich beschleunigt wird dieser Sortierungsvorgang durch die gerichtete chemotaktische Bewegung beider Arten auf dieselben Signale, die bei den sich in den Zellströmen schneller bewegenden D. mucoroides-Zellen zu einer Anreicherung im Moundzentrum führt. Somit sind in vivo zwei Faktoren gemeinsam für die artspezifische Sortierung von D. discoideum und D. mucoroides verantwortlich. In Mischungen von D. discoideum und Polysphondylium spec. geschieht die Aussortierung über die Nutzung unterschiedlicher Botenstoffe für die Chemotaxis, so daß die Arten getrennt aggregieren. Es konnte gezeigt werden, daß diese getrennte Aggregation sehr spezifisch ist und es dennoch zu einer Interaktion zwischen D. discoideum und fortgeschrittenen Polysphondylium-Aggregaten kommt, da in Polysphondylium in späten Aggregationsphasen cAMP für die interzelluläre Kommunikation verwendet wird. In dieser Phase wird von Polysphondylium sowohl cAMP als auch Glorin sekretiert. Severin ist ein mit Gelsolin verwandtes 40 kDa Protein, das F-Aktin-Filamente fragmentiert und an das (+)-Ende des entstehenden Fragments bindet. Mit Hilfe eines GFP-Fusionsproteins wurde die intrazelluläre Lokalisierung dieses Proteins in vivo während einer Vielzahl zellulärer Aktivitäten untersucht. Severin ist in den aktiven Bereichen des F-Aktin Zellkortex angereichert. Obwohl die Morphologie von D. discoideum-Zellen in den verschiedenen Phasen der Entwicklung sehr unterschiedlich ist, ist die Lokalisierung von Severin in allen Stadien primär von der Bildung neuer Zellfortsätze trennbar. Die Anreicherung von Severin ist hingegen mit der Bewegung der Zelle in diese neu gebildeten Fortsätze assoziiert. Erstmals wurde im Rahmen dieser Arbeit der Effekt von cAMP-Signalen auf das Zytoskelett einzelner Zellen in Aggregationsströmen ausführlich dargestellt.

For Bradyrhizobiumjaponicum, the chemotactic and the nod gene-inducing effects of hydroxycinnamic acids and two of their derivatives were compared with those of isoflavonoids. Only the hydroxycinnamic acids were strong chemoattractants, while the other substances tested were chemotactically inactive. Besides the known nod gene induction by isoflavonoids, a weak nod gene induction by coniferyl alcohol, chlorogenic acid, and ferulic acid was found.