Podcasts about heterochromatin

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2023.08.01.551420v1?rss=1 Authors: Amoiridis, M., Meaburn, K., Verigos, J., Gittens, W. H., Ye, T., Neale, M. J., Soutoglou, E. Abstract: DNA replication and transcription generate DNA supercoiling, which can cause topological stress and intertwining of daughter chromatin fibers, posing challenges to the completion of DNA replication and chromosome segregation. Type II topoisomerases (Top2s) are enzymes that relieve DNA supercoiling and decatenate braided sister chromatids. How Top2 complexes deal with the topological challenges in different chromatin contexts, and whether all chromosomal contexts are subjected equally to torsional stress and require Top2 activity is unknown. Here we show that catalytic inhibition of the Top2 complex in interphase has a profound effect on the stability of heterochromatin and repetitive DNA elements. Mechanistically, we find that catalytically inactive Top2 is trapped around heterochromatin leading to DNA breaks and unresolved catenates, which necessitate the recruitment of the structure specific endonuclease, Ercc1-XPF, in an Slx4- and SUMO-dependent manner. Our data are consistent with a model in which Top2 complex resolves not only catenates between sister chromatids but also inter-chromosomal catenates between clustered repetitive elements. 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/2023.07.06.547894v1?rss=1 Authors: Rajshekar, S., Adame-Arana, O., Bajpai, G., Lin, K., Colmenares, S., Safran, S., Karpen, G. H. Abstract: Nucleoli are surrounded by Peri-Centromeric Heterochromatin (PCH), reflecting a close spatial association between the two largest biomolecular condensates in eukaryotic nuclei. We have investigated how this highly conserved organization is established de novo during early Drosophila development and whether these distinct condensates influence each other's 3D organization. High-resolution live imaging revealed a highly dynamic process in which the PCH progressively surrounds nucleoli through a series of stage-specific intermediates. To assess interplay between the condensates, nucleolus assembly was eliminated by deleting the ribosomal RNA genes (rDNA), resulting in increased PCH compaction and subsequent reorganization to a hollow shell. In addition, in embryos lacking rDNA, some nucleolar proteins were abnormally redistributed into new bodies or 'neocondensates,' including enrichment in the PCH hollow core. These observations, combined with computational modeling, led to the hypothesis that nucleolar-PCH associations are mediated by a hierarchy of affinities between PCH, nucleoli, and 'amphiphilic' protein(s) that interact with both nucleolar and PCH components. We identified the nucleolar protein Pitchoune as a candidate for such an amphiphilic protein because it also contains a PCH-interaction motif and fills the PCH hollow core in embryos lacking rDNA. Together, these results unveil a dynamic program for establishing nucleolar-PCH associations during animal development, demonstrate that nucleoli are required for normal PCH organization, and identify Pitchoune as a likely molecular link for stabilizing PCH-nucleolar associations. Finally, we propose that disrupting affinity hierarchies could cause cellular disease phenotypes by liberating components that form 'neocondensates' or other abnormal structures through self-association and secondary affinities. 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/2023.03.03.531058v1?rss=1 Authors: Miller, J. M., Prange, S., Ji, H., Rau, A. R., Butova, N. L., Lutter, A., Chung, H., Merigliano, C., Rawal, C. C., McVey, M., Chiolo, I. Abstract: Pericentromeric heterochromatin is highly enriched for repetitive sequences prone to aberrant recombination. Previous studies showed that homologous recombination (HR) repair is uniquely regulated in this domain to enable 'safe' repair while preventing aberrant recombination. In Drosophila cells, DNA double-strand breaks (DSBs) relocalize to the nuclear periphery through nuclear actin-driven directed motions before recruiting the strand invasion protein Rad51 and completing HR. End-joining (EJ) repair also occurs with high frequency in heterochromatin of fly tissues, but how different EJ pathways operate in heterochromatin remains uncharacterized. Here, we induce DSBs in single euchromatic and heterochromatic sites using the DR-white reporter and I-SceI expression in spermatogonia. We detect higher frequency of HR repair in heterochromatic insertions, relative to euchromatin. Sequencing of repair outcomes reveals the use of distinct EJ pathways across different euchromatic and heterochromatic sites. Interestingly, synthesis-dependent michrohomology-mediated end joining (SD-MMEJ) appears differentially regulated in the two domains, with a preferential use of motifs close to the cut site in heterochromatin relative to euchromatin, resulting in smaller deletions. Together, these studies establish a new approach to study repair outcomes in fly tissues, and support the conclusion that heterochromatin uses more HR and less mutagenic EJ repair relative to euchromatin. Copy rights belong to original authors. Visit the link for more info Podcast created by Paper Player, LLC

No one is exempt from ageing, and with aging comes diseases and sickness. Decreased performance and cell production also occur because of this phenomenon. Lifestyle changes may be inadequate to help your body function properly. Over the past years, longevity science has been evolving, with the emergence of several anti-ageing supplements in the market. However, the body may not absorb these supplements effectively enough to slow down the effects of ageing. In this episode, Dr Elena Seranova explains how the ageing process works. She details how to use supplements, complemented by lifestyle changes, to reverse ageing. She also shares how NMN can be coupled with TMG to create the ultimate longevity supplement. There's no one supplement to optimise your health, but good habits and lifestyle changes are integral to having a longer and healthier life! If you want to learn how to reverse ageing through supplements and lifestyle changes, then this episode is for you! Here are three reasons why you should listen to the full episode: Understand the aging process, its vicious cycle, and how it affects and changes our bodies.  Learn how you can slow down and reverse the effects of aging. Discover how you can combine TMG with NMN for better results. Get Customised Guidance for Your Genetic Make-Up For our epigenetics health programme, all about optimising your fitness, lifestyle, nutrition and mind performance to your particular genes, go to  https://www.lisatamati.com/page/epigenetics-and-health-coaching/. Customised Online Coaching for Runners CUSTOMISED RUN COACHING PLANS — How to Run Faster, Be Stronger, Run Longer  Without Burnout & Injuries Have you struggled to fit in training in your busy life? Maybe you don't know where to start, or perhaps you have done a few races but keep having motivation or injury troubles? Do you want to beat last year's time or finish at the front of the pack? Want to run your first 5-km or run a 100-miler? ​​Do you want a holistic programme that is personalised & customised to your ability, goals, and lifestyle?  Go to www.runninghotcoaching.com for our online run training coaching. Health Optimisation and Life Coaching Are you struggling with a health issue and need people who look outside the square and are connected to some of the greatest science and health minds in the world? Then reach out to us at support@lisatamati.com, we can jump on a call to see if we are a good fit for you. If you have a big challenge ahead, are dealing with adversity or want to take your performance to the next level and want to learn how to increase your mental toughness, emotional resilience, foundational health, and more, contact us at support@lisatamati.com. Order My Books My latest book Relentless chronicles the inspiring journey about how my mother and I defied the odds after an aneurysm left my mum Isobel with massive brain damage at age 74. The medical professionals told me there was absolutely no hope of any quality of life again. Still, I used every mindset tool, years of research and incredible tenacity to prove them wrong and bring my mother back to full health within three years. Get your copy here: https://shop.lisatamati.com/collections/books/products/relentless. For my other two best-selling books Running Hot and Running to Extremes, chronicling my ultrarunning adventures and expeditions all around the world, go to https://shop.lisatamati.com/collections/books. Lisa's Anti-Ageing and Longevity Supplements  NMN: Nicotinamide Mononucleotide, an NAD+ precursor Feel Healthier and Younger* Researchers have found that Nicotinamide Adenine Dinucleotide or NAD+, a master regulator of metabolism and a molecule essential for the functionality of all human cells, is being dramatically decreased over time. What is NMN? NMN Bio offers a cutting edge Vitamin B3 derivative named NMN (beta Nicotinamide Mononucleotide) that can boost the levels of NAD+ in muscle tissue and liver. Take charge of your energy levels, focus, metabolism and overall health so you can live a happy, fulfilling life. Founded by scientists, NMN Bio offers supplements of the highest purity and rigorously tested by an independent, third-party lab. Start your cellular rejuvenation journey today. Support Your Healthy Ageing We offer powerful third-party tested NAD+ boosting supplements so you can start your healthy ageing journey today. Shop now: https://nmnbio.nz/collections/all NMN (beta Nicotinamide Mononucleotide) 250mg | 30 capsules NMN (beta Nicotinamide Mononucleotide) 500mg | 30 capsules 6 Bottles | NMN (beta Nicotinamide Mononucleotide) 250mg | 30 Capsules 6 Bottles | NMN (beta Nicotinamide Mononucleotide) 500mg | 30 Capsules Quality You Can Trust — NMN Our premium range of anti-ageing nutraceuticals (supplements that combine Mother Nature with cutting edge science) combats the effects of aging while designed to boost NAD+ levels. Manufactured in an ISO9001 certified facility Boost Your NAD+ Levels — Healthy Ageing: Redefined Cellular Health Energy & Focus Bone Density Skin Elasticity DNA Repair Cardiovascular Health Brain Health  Metabolic Health My  ‘Fierce' Sports Jewellery Collection For my gorgeous and inspiring sports jewellery collection, 'Fierce', go to https://shop.lisatamati.com/collections/lisa-tamati-bespoke-jewellery-collection. Episode Highlights [01:53] How Longevity Science Is Growing There are a growing number of anti-ageing products as we understand the ageing process better. Multiple cellular processes decline or become imbalanced as people age. There are 9 hallmarks of ageing, and the study recently added another hallmark to include inflammation.  The top four killer diseases are cancer, cardiovascular disease, neurodegeneration, and diabetes. The older you are, the higher your chance of developing one of these diseases.  Our body peaks at 25 and starts the aging process from there. [06:06] Why Is NMN Important?  NMN stands for nicotinamide mononucleotide and is a Vitamin B3 derivative.  It's a natural molecule that you can get from food, but getting an efficient dosage requires supplementation. NMN is a precursor to help our metabolism, and it boosts NAD levels. NAD serves as fuel for SIRTUIN proteins that are involved in rejuvenation processes.  NAD is vital to keep our cells healthy and ensure they don't lose their identity. [09:23] What Happens in the Body as We Age Cell identity is vital. What differentiates cells is how certain parts of the genomes are read. As we age, this process can become chaotic.  Chromatin is a substance in a chromosome. Lightly packed chromatin under active transcription is called euchromatin. Heterochromatin, on the other hand, is more condensed and transcriptionally silent. Epigenetic changes can dictate which areas will be active or inactive. This defines how a cell can be expressed. Sirtuins are crucial in making sure the right genes are active and mediating DNA repair. However, they become less efficient as we age.  This is how our epigenetic regulation becomes loose, leading to genomic instability and loss of cellular identity.  [15:33] How Aging Can Create a Vicious Cycle NAD is the fuel source of sirtuin genes. When these genes are depleted, our DNA can't be repaired. As we age, NAD production depletes. DNA breaks and genome instability also increase.  This becomes a vicious cycle of needing more energy but with less production.  Furthermore, genome instability can increase senescence or zombie cells. These can further increase genome instability.  Senescent cells are cells that forget how to do their function well and stop replicating. These cells can further drain NAD levels. [18:19] The Link Between Fasting and Cell Autophagy Autophagy is the process where cells can get rid of toxins and other things that are not needed anymore. Autophagy ensures housekeeping and can be triggered by fasting.  12 hours of fasting can start autophagy in the liver, while 20 hours of fasting can start the process in other tissues.    Eating can activate mTOR, which is another vital cell regulator. This process is deactivated through supplements like Berberine. Learn to balance both eating and fasting. Hear about Dr Elena's fasting schedule and supplements in the full episode! [27:48] Why Dr Elena Launched TMG Methylation is vital for the body's most critical functions. These include creating neurotransmitters, cell division, energy production, metabolism, and epigenetics.  Dr Elena launched TMG to boost NMN's effectiveness and metabolism.  Methylation and TMG can control homocysteine levels, which correlate with cardiovascular diseases. TMG may also enhance athletic performance. It also has a good safety profile with no side effects despite higher dosage. Dr Elena recommends a 1:2 or 1:3 ratio of NMN to TMG. For every 500 milligrams of NMN, take 1 to 2 grams of TMG. [33:31] Do We Need to Worry about Hyper-methylation?  It's difficult to hyper-methylate. However, individual genetic factors can affect homocysteine levels.  To check your homocysteine levels, you can undergo a blood test or check your gene variants with a genetic test TMG is an osmoregulator that helps regulate cell balance and can optimize methylation. After taking over 20 grams, a laxative effect may appear. [39:41] Where to Start Dr Elena recommends taking NMN, TMG, and extra virgin olive oil for anti-ageing. NMN can also help increase insulin sensitivity and boost collagen production, as seen in human clinical trial in prediabetic women. The market has a lot of collagen supplements, but not all of them are absorbed by the body effectively. Insulin sensitivity decreases as we age. This is the body's ability to let glucose flow freely into cells. You can reverse ageing problems with a better lifestyle and supplements. Dr Elena recommends avoiding carbohydrates in your diet. [42:55] How to Have a Healthier Diet Around 80% of adults in the West may be pre-diabetic. So many foods nowadays are made to be addictive.  While a vegan diet can help you detox at first, you will eventually experience amino acid depletion. Dr Elena prefers a carnivore diet. She also does fasting with a three-hour eating window. You can start with a longer eating window and slowly reduce it.  You don't want a glucose spike in the morning. [48:06] You Don't Need to Be Perfect  You don't have to be perfect every day, but make sure you stay consistent with your overall longevity routine.  Exercise and saunas activate Sirtuins. Try to have a routine for one or both. Optimize your routine and find out what works for you.  [50:52] NMN Bio's Growth Dr Elena shares that her company has been growing rapidly. They now have a UK warehouse, UK Amazon FBA, and another warehouse in Europe.  They are also expanding to the United States.  Remember that no one supplement will do everything for you. You also need to change your lifestyle, which includes diet, exercise, and even biorhythms.   There's a lot of information about longevity online, and it can become overwhelming. This is why Dr Elena created an online course about longevity.  Dr Elena recommends making sure your circadian rhythm is not disrupted.  Resources Gain exclusive access and bonuses to Pushing the Limits Podcast by becoming a patron! Tune in to more Pushing the Limits episodes on health and ageing! Episode 231: The Immune System and How It Fights Cancer Cells and Viruses with Dr Elizabeth Yurth  Episode 196: Rethinking the Function of Mitochondria for Our Health with Dr Elizabeth Yurth  Episode 189: Understanding Autophagy and Increasing Your Longevity with Dr Elena Seranova  Episode 187: Back to Basics: Slow Down Ageing and Promote Longevity with Dr Elizabeth Yurth Episode 183: Sirtuins and NAD Supplements for Longevity with Dr Elena Seranova  Want to dive deeper into longevity and work out a protocol for yourself? Take the Foundations of Longevity and Life Extension Online Course by Dr Elena Seranova and Jesse Coomer  The Ultimate Anti-Aging Combination: TMG & NMN to Live Significantly Longer? By NMN Bio  The Hallmarks of Aging  Nicotinamide Mononucleotide Increases Muscle Insulin Sensitivity in Prediabetic Women Visit NMN Bio to know more about NMN supplements!      Lifespan by Dr David Sinclair    7 Powerful Quotes [04:28] ‘The older you are, the highest your risk of getting one of these diseases; so if it's not gonna be one of them, it's gonna be the other one… Now we start realising when does aging start, which is actually at quite a young age, basically at the age of 25. Because this is where our hormones peak…' [12:25] ‘There are multiple functions that Sirtuins need to attend to within the cell. With age, this function becomes less and less efficient, basically, because sirtuins become more forgetful.' [16:02] ‘So as we age, the production of NAD is declining. So this means that there is less NAD available for sirtuins to use as their fuel to do their job.' [39:52] ‘There are so many collagen supplements on the market, but not all of them are efficient. And actually not all of them are being absorbed properly because when you do take collagen orally, basically, it's broken down into amino acids in your digestive system. And then those amino acids may or may not be used to produce more collagen.' [47:56] ‘We're all on this road of re-educating ourselves and don't go for perfection. Just go for better, I think is a message as well, you don't have to be perfect.' [52:22] ‘With regards to the longevity field, I think that it's very important for people to understand that there is no such thing as the fountain of youth. There is no one supplement that you're going to take that is going to do everything for you.' [56:40] ‘If your melatonin is disrupted, then you will have less defense against reactive oxygen species and that there is another plethora of processes that melatonin is also implicated in and then you don't have all these benefits. And then you're basically aging faster… Takeaway message from today's podcasts. Make sure that you go to sleep early, everyone.' About Dr Elena  Dr Elena Seranova is a scientist, serial entrepreneur and business mentor. She has now founded multiple innovative biotechnological businesses. She first studied at the University of Ioannina with a major in Psychology. Dr Elena then started a private practice before developing an interest in neuroscience. She continued her studies and earned her Master's Degree in Translational Neuroscience at the University of Sheffield. She now also holds a Doctorate Degree in Stem Cell Biology and Autophagy from the University of Birmingham. Dr Elena's expertise in these fields has led her to become the co-founder of a biotech start-up, SkyLab Bio. She has written several peer-reviewed articles on autophagy throughout her career. In addition to these accomplishments, she started her latest business, NMN Bio. Her own experiences with the use of supplements have inspired her to expand the market to supply the public with cutting-edge anti-ageing supplements. NMN Bio reaches New Zealand, the UK, and Europe. Dr Elena found her passion for drug discovery and autophagy. She has endeavoured to share this with the public through her research and work as an entrepreneur.  To learn more about Dr Elena and her work, visit NMN Bio. Enjoy The Podcast? If you did, be sure to subscribe and share it with your friends! Post a review and share it! If you enjoyed tuning in, then leave us a review. You can also share this with your family and friends so they can know how to optimise sleep.  Have any questions? You can contact me through email (support@lisatamati.com) or find me on Facebook, Twitter, Instagram and YouTube. For more episode updates, visit my website. You may also tune in on Apple Podcasts. To pushing the limits, Lisa  

In this episode of the Epigenetics Podcast, we caught up with Serena Sanulli from Stanford University to talk about her work on Heterochromatin Protein 1 (HP1), the structure of chromatin on the atomic-scale and the meso-scale, and phase separation. The Laboratory of Serena Sanulli is interested in finding connections between changes that happen on the nucleosomal level and the resulting impact on chromatin conformation on the meso-scale. They combine methods like NMR and Hydrogen-Deuterium Exchange-MS with Cell Biology and Genetics. This enables them to dissect how cells use the diverse biophysical properties of chromatin to regulate gene expression across length and time scales. A second focus of the lab is HP1, which interacts with the nucleosome and changes its conformation, enabling the compaction of the genome into heterochromatin, effectively silencing genes in that region. A high concentration of HP1 leads to the phenomenon of phase separation in the nucleus, which the Sanulli lab is now investigating.   References Sanulli, S., Justin, N., Teissandier, A., Ancelin, K., Portoso, M., Caron, M., Michaud, A., Lombard, B., da Rocha, S. T., Offer, J., Loew, D., Servant, N., Wassef, M., Burlina, F., Gamblin, S. J., Heard, E., & Margueron, R. (2015). Jarid2 Methylation via the PRC2 Complex Regulates H3K27me3 Deposition during Cell Differentiation. Molecular Cell, 57(5), 769–783. https://doi.org/10.1016/j.molcel.2014.12.020 Sanulli, S., Trnka, M. J., Dharmarajan, V., Tibble, R. W., Pascal, B. D., Burlingame, A. L., Griffin, P. R., Gross, J. D., & Narlikar, G. J. (2019). HP1 reshapes nucleosome core to promote phase separation of heterochromatin. Nature, 575(7782), 390–394. https://doi.org/10.1038/s41586-019-1669-2 Sanulli, S., & Narlikar, G. J. (2021). Generation and Biochemical Characterization of Phase‐Separated Droplets Formed by Nucleic Acid Binding Proteins: Using HP1 as a Model System. Current Protocols, 1(5). https://doi.org/10.1002/cpz1.109   Related Episodes Transcription and Polycomb in Inheritance and Disease (Danny Reinberg) Heterochromatin and Phase Separation (Gary Karpen)   Contact Active Motif on Twitter Epigenetics Podcast on Twitter Active Motif on LinkedIn Active Motif on Facebook Email: podcast@activemotif.com

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.08.19.254706v1?rss=1 Authors: Eeftens, J. M., Kapoor, M., Brangwynne, C. P. Abstract: Structural organization of the genome into transcriptionally active euchromatin and silenced heterochromatin is essential for eukaryotic cell function. Heterochromatin is a more compact form of chromatin, and is associated with characteristic post- translational histone modifications and chromatin binding proteins. Phase-separation has recently been suggested as a mechanism for heterochromatin formation, through condensation of heterochromatin associated proteins. However, it is unclear how phase-separated condensates can contribute to stable and robust repression, particularly for heritable epigenetic changes. The Polycomb complex PRC1 is known to be key for heterochromatin formation, but the multitude of Polycomb proteins has hindered our understanding of their collective contribution to chromatin repression. Here, we take a quantitative live cell imaging approach to show that PRC1 proteins form multicomponent condensates through hetero-oligomerization. They preferentially seed at H3K27me3 marks, and subsequently write H2AK119Ub marks. Using optogenetics to nucleate local Polycomb condensates, we show that Polycomb phase separation can induce chromatin compaction, but phase separation is dispensable for maintenance of the compacted state. Our data are consistent with a model in which the time integral of historical Polycomb phase separation is progressively recorded in repressive histone marks, which subsequently drive chromatin compaction. These findings link the equilibrium thermodynamics of phase separation with the fundamentally non-equilibrium concept of epigenetic memory. Copy rights belong to original authors. Visit the link for more info

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.07.19.210518v1?rss=1 Authors: Singh, P. B., Belyakin, S. N., Laktionov, P. P. Abstract: The hallmarks of constitutive heterochromatin, HP1 and H3K9me2/3, assemble heterochromatin-like domains/complexes outside canonical constitutively heterochromatic territories where they regulate chromatin-templated processes. Domains are more than 100kb in size; complexes less than 100kb. They are present in the genomes of organisms ranging from fission yeast to man, with an expansion in size and number in mammals. Some of the likely functions of the domains/complexes include silencing of the donor mating type region in fission yeast, regulation of mammalian imprinted genes and the phylotypic progression during vertebrate development. Far cis- and trans-contacts between micro-phase separated domains/complexes in mammalian nuclei contribute to the emergence of epigenetic compartmental domains (ECDs) detected in Hi-C maps. We speculate that a thermodynamic description of micro-phase separation of heterochromatin-like domains/complexes will require a gestalt shift away from the monomer as the "unit of incompatibility", where it is the choice of monomer that determines the sign and magnitude of the Flory-Huggins parameter, {chi}. Instead, a more dynamic structure, the oligo-nucleosomal "clutch", consisting of between 2 to 10 nucleosomes is both the long sought-after secondary structure of chromatin and its unit of incompatibility. Based on this assumption we present a simple theoretical framework that enables an estimation of {chi} for domains/complexes flanked by euchromatin and thereby an indication of their tendency to phase separate. The degree of phase separation is specified by {chi}N, where N is the number of "clutches" in a domain/complex. Our approach may provide an additional tool for understanding the biophysics of the 3D genome. Copy rights belong to original authors. Visit the link for more info

Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.06.23.158014v1?rss=1 Authors: Ravel-Godreuil, C., Massiani-Beaudoin, O., Mailly, P., Prochiantz, A., Joshi, R. L., Fuchs, J. Abstract: Heterochromatin disorganization is a key hallmark of aging and DNA methylation state is currently the main molecular predictor of chronological age. The most frequent neurodegenerative diseases like Parkinson disease and Alzheimer's disease are age-related but how the aging process and chromatin alterations are linked to neurodegeneration is unknown. Here, we investigated the consequences of viral overexpression of Gadd45b, a multifactorial protein involved in active DNA demethylation, in the midbrain of wild-type mice. Gadd45b overexpression induces global and stable changes in DNA methylation, particularly on gene bodies of genes related to neuronal functions. DNA methylation changes were accompanied by perturbed H3K9me3-marked heterochromatin and increased DNA damage. Prolonged Gadd45b expression resulted in dopaminergic neuron degeneration accompanied by altered expression of candidate genes related to heterochromatin maintenance, DNA methylation or Parkinson disease. Gadd45b overexpression rendered midbrain dopaminergic neurons more vulnerable to acute oxidative stress. Heterochromatin disorganization and DNA demethylation resulted in derepression of mostly young LINE-1 transposable elements, a potential source of DNA damage, prior to Gadd45b-induced neurodegeneration. Our data implicate that alterations in DNA methylation and heterochromatin organization, LINE-1 derepression and DNA damage can represent important contributors in the pathogenic mechanisms of dopaminergic neuron degeneration with potential implications for Parkinson disease. Copy rights belong to original authors. Visit the link for more info

In this episode of the Epigenetics Podcast, we caught up with Leonid Mirny, Ph.D., from MIT to talk about his work on biophysical modeling of the 3-D structure of chromatin. Leonid Mirny was part of the initial Hi-C paper titled "Comprehensive Mapping of Long-Range Interactions Reveals Folding Principles of the Human Genome" that was published in 2009 in the journal Science. Since then, technology has evolved and Dr. Mirny's group has developed a method called Micro-C that improves the Hi-C protocol by using MNase digestion to increase the resolution to nucleosomal level. This led to the visualization of interactions that were already predicted by his previous biophysical models. Furthermore, Leonid Mirny worked on finding the mechanism by which chromatin loops are formed. He and his team proposed that loop extrusion underlies TAD formation. In this process, factors like cohesin and CTCF form progressively larger loops but stall at TAD boundaries due to interactions of CTCF with TAD boundaries. He used polymer simulations to show that this model produces TADs and finer-scale features of Hi-C data. Each TAD emerges from multiple loops dynamically formed through extrusion, contrary to typical illustrations of single static loops. In this interview, we chatted with Dr. Mirny about the details of Hi-C, the development of Micro-C and how it compares to Hi-C, and how biophysical modeling helps to unravel the mechanisms behind loop extrusion.    References Grigory Kolesov, Zeba Wunderlich, … Leonid A. Mirny (2007) How gene order is influenced by the biophysics of transcription regulation (Proceedings of the National Academy of Sciences) DOI: 10.1073/pnas.0700672104  Erez Lieberman-Aiden, Nynke L. van Berkum, … Job Dekker (2009) Comprehensive mapping of long-range interactions reveals folding principles of the human genome (Science (New York, N.Y.)) DOI: 10.1126/science.1181369  Geoffrey Fudenberg, Maxim Imakaev, … Leonid A. Mirny (2016) Formation of Chromosomal Domains by Loop Extrusion (Cell Reports) DOI: 10.1016/j.celrep.2016.04.085  Johannes Nuebler, Geoffrey Fudenberg, … Leonid A. Mirny (2018) Chromatin organization by an interplay of loop extrusion and compartmental segregation (Proceedings of the National Academy of Sciences) DOI: 10.1073/pnas.1717730115  Martin Falk, Yana Feodorova, … Leonid A. Mirny (2019) Heterochromatin drives compartmentalization of inverted and conventional nuclei (Nature) DOI: 10.1038/s41586-019-1275-3   Contact  Active Motif on Twitter Epigenetics Podcast on Twitter Active Motif on Linked-In Active Motif on Facebook eMail: podcast@activemotif.com

Heterochromatin plays a pivotal role in organizing our genome in the nucleus and separating active from inactive genomic regions. In this Podcast Episode our Guest Gary Karpen from UC Berkeley sits down with our Host Stefan Dillinger to talk about the regulation of this chromatin structure and how DNA repair mechanisms function in this densely packed nuclear compartment. Furthermore, they also discuss how phase separation might be an important part in how heterochromatin domains are formed. References Jamy C. Peng, Gary H. Karpen (2009) Heterochromatic Genome Stability Requires Regulators of Histone H3 K9 Methylation (PLoS Genetics) DOI: 10.1371/journal.pgen.1000435 Peter V. Kharchenko, Artyom A. Alekseyenko, … Peter J. Park (2011) Comprehensive analysis of the chromatin landscape in Drosophila melanogaster (Nature) DOI: 10.1038/nature09725 Aniek Janssen, Serafin U. Colmenares, … Gary H. Karpen (2019) Timely double-strand break repair and pathway choice in pericentromeric heterochromatin depend on the histone demethylase dKDM4A (Genes & Development) DOI: 10.1101/gad.317537.118  Amy R. Strom, Alexander V. Emelyanov, … Gary H. Karpen (2017) Phase separation drives heterochromatin domain formation (Nature) DOI: 10.1038/nature22989 Contact https://twitter.com/activemotif https://twitter.com/epigenetics_pod https://www.linkedin.com/company-beta/35651/ https://www.facebook.com/ActiveMotifInc/ https://activemotif.com/blog podcast@activemotif.com

Eukaryotic genomes are organized inside the cell nucleus in a structured macromolecular DNA-protein polymer named chromatin, formed by single discrete unites called Nucleosomes. The packing of the genetic information into chromatin allows the efficient regulation of several nuclear processes, such as gene expression and transcription, DNA replication, cell cycle progression, chromosome segregation and DNA damage repair. Chromatin comes in two flavors: a transcriptionally active, more loosened state, called euchromatin and a transcriptionally silent or low expressed, more compact state, called heterochromatin. The assembly of silent chromatin or heterochromatin is fundamental for the regulation of every nuclear process and it is driven in most Eukaryotes by the deposition and the read-out of the histone H3 lysine 9 methylation (H3K9me) post-translational modification (PTM). H3K9me on the nucleosome is specifically bound by chromatin readers called chromodomains (CD) and this recognition is fundamental for the downstream processes that lead to the formation of heterochromatin and shut down the expression of single genes or entire gene clusters. Despite several studies have been done on different chromodomains binding to H3K9me histone tail peptides, to date there was no structural information on how chromodomains interact with their natural binding partners, the H3K9me3 Nucleosomes. In a preliminary structural study carried out in our laboratory we solved the cryo-electron microscopy (Cryo-EM) structure of the chromodomain of the fission yeast Chp1 protein (Chp1CD) in complex with an H3K9me nucleosome. The structure showed that the Chp1CD interacts not only with the histone H3 tail but also with the histone globular domains in the Nucleosome core, primarily with histone H3. Mutations in the residues of Chp1CD that form the binding interface with the Nucleosome core (two loops in the β-sheet of the domain) caused a drop of the affinity in vitro for the H3K9me Nucleosome, which was independent from the histone H3K9me tail interaction. Cells harboring the same Chp1CD loop mutations were defective in silencing centromeric transcripts and maintain the deposition of the H3K9me mark for heterochromatin formation. This indicated that Chp1CD-nucleosome core interaction is fundamental for heterochromatin formation in fission yeast and opened up to the possibility that chromodomains could read multiple histone PTMs, on both the recruiting histone tail and on the nucleosome core. This study substantially contributes to understand how chromodomains interact with chromatin, how much the nucleosome core interaction is conserved among different CDs and how different chromodomain proteins are regulated at the same loci. Understanding how chromodomain readers recognize nucleosomes is fundamental to uncover the basics of gene silencing and heterochromatin formation.

Silvano RIVA, Institute for Biochemical and Evolutionary Genetics/CNR, Pavia - ITALY speaks on "Stress conditions induce transcriptional activation of constitutive heterochromatin - RNA Structure and Function 2014". This seminar has been recorded at ICTP Trieste by ICGEB Trieste

Thu, 2 May 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16320/ https://edoc.ub.uni-muenchen.de/16320/1/Hahn_Matthias.pdf Hahn, Matthias ddc:570, ddc:500, Fakultät für Biologie

Thu, 4 Apr 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16321/ https://edoc.ub.uni-muenchen.de/16321/1/Dambacher_Silvia.pdf Dambacher, Silvia ddc:570, ddc:500, Fakultät für Biologie

Im Zellkern einer jeden Zelle besteht eine gewisse Ordnung der darin vorhandenen DNA und Proteine. Diese Ordnung wird unter dem Begriff „Zellkernarchitektur“ zusammengefasst. In der vorliegenden Arbeit ging es um die nähere Betrachtung einiger Aspekte der Zellkernarchitektur. Diese Aspekte betrafen 1. die Anordnung von Genen, 2. die Anordnung von Chromatin mit Hilfe unterschiedlicher Histonmodifikationen und 3. die Anordnungen von Chromosomenabschnitten, die mit komplexen messenger RNA-Sonden hybridisiert werden. Im ersten Teil der vorliegenden Arbeit wurde mittels 3D FISH die dreidimensionale Positionierung von drei auf dem Chromosom 1 lokalisierten Genen in Zellkernen der Burkitt- Lymphom Zelllinie DG75 bestimmt. Diese Zelllinie wurde von Stefan Bohlander zur Verfügung gestellt und enthielt einen induzierbaren episomalen Vektor für das CALM-AF 10 Gen. Messungen der Genexpression, die in der Bohlander Gruppe mit Hilfe eines Affymetrix- Chips durchgeführt wurden, zeigten das die Induktion des Transgens zu genomweiten Veränderungen der Expressionsmuster hunderter Gene in dieser Zelllinie führten. Die für die 3D FISH Experimente ausgewählten Markergene zeigten nach der Induktion eine signifikant veränderte Expression. Dennoch änderte sich die radiale Positionierung dieser Gene, darunter versteht man die mehr innere oder mehr periphere Position der Gene, nicht. Dieses Ergebnis schien zuerst darauf hinzuweisen, dass die Transkriptionsstärke keine bedeutsamer Faktor im Hinblick auf die radiale Positionierung ist. Die Befunde der Affymetrix-Chip Analyse für diese Gene konnten jedoch in einer anschließende Untersuchungen der Genexpression mit Real-Time-PCR nicht bestätigt werden, obwohl der Vergleich von Affymetrix-Chip und Real- Time-PCR Daten insgesamt eine klare Korrelation zwischen den Datensätzen zeigte. Bei Diskrepanzen gehen wir davon aus, dass Real-Time-PCR die zuverlässigeren Ergebnisse liefert. Bei der hier durchgeführten Real-Time-PCR Untersuchung wurden auch die Expressionsstärken aller in einer Nachbarschaft von etwa 1 Mbp um die Markergene annotierten Gene ermittelt. Dieses Fenster wurde gewählt, weil Untersuchungen in der Arbeitsgruppe von Thomas Cremer und anderen Gruppen gezeigt haben, dass ~1 Mbp Chromatindomänen die Basisstruktur der Chromatinorganisation darstellen. Als Maß für die gesamte Genexpression einer Chromatindomäne wurde eine „Total Expression Strength“ (TES) berechnet. Dieser Wert basiert auf den Real-Time-PCR Werten der annotierten Gene und berücksichtigt auch die Länge der ungespleissten RNA, die von einem Gen transkribiert wird. Dabei zeigte sich, dass das Markergen in der Domäne mit dem höchsten TES Wert am weitesten innen im Zellkern lokalisiert ist. Dieser Befund unterstützt Befunde aus der wissenschaftlichen Literatur, dass die radiale Positionierung von individuellen Genen von Eigenschaften der lokalen Umgebung abhängt. Da sich die Nachbarschaft der untersuchten Markergene nicht nur im Hinblick auf die TES Werte sondern auch im Hinblick auf die Dichte der dort annotierten Gene und den GC-Gehalt unterscheidet, bleibt offen, welcher dieser Parameter als Prädiktor für die zu erwartende radiale Position individueller Gene eine entscheidende Rolle spielt. Möglich ist auch, dass alle Parameter zusammenwirken oder dass je nach den speziellen Umständen einer Untersuchung verschiedene Parameter die radiale Positionierung eines Gens bevorzugt beeinflussen. Die Stabilität der radialen Positionierung der Markergene trotz einer genomweiten Veränderung des Genexpressionsmusters nach CALM-AF 10 Induktion stimmt mit Befunden verschiedener Arbeitsgruppe überein, die für einen hohen Grad an räumlicher Stabilität der Chromatinanordnung während der Interphase sprechen; ~1 Mbp Chromatindomänen zeigen dementsprechend meist nur sehr begrenzte lokale Bewergungen (

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Thu, 21 Oct 2010 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/13128/ https://edoc.ub.uni-muenchen.de/13128/1/Becker_Annette.pdf Becker, Annette ddc:570, ddc:500, Fakultät für Biologie

Mon, 16 Mar 2009 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/12935/ https://edoc.ub.uni-muenchen.de/12935/1/Agarwal_Noopur.pdf Agarwal, Noopur ddc:570, ddc:500, Fakultät für

Die vorliegende Arbeit hatte zum Ziel, die komplexen Zusammenhänge zwischen der Kernlokalisation, der transkriptionellen Aktivität und dem Replikationsverhalten von Zelltyp-spezifisch regulierten Genen in menschlichen Zellen besser zu verstehen. Im ersten Teil dieser Arbeit wurde die Kernlokalisation der drei benachbarten, jedoch funktionell unabhängigen Gene GASZ, CFTR und CORTBP2 der humanen CFTR-Region auf Chromosom 7q31 ermittelt und mit dem Expressionsverhalten verglichen. Durch eine 2D-Erosionsanalyse wurde die radiale Positionierung dieser Gene in einer Reihe von Zelllinien und primären Zelltypen untersucht. Die Ergebnisse haben gezeigt, dass transkriptionell aktive Gene der CFTR-Region bevorzugt im Zellkerninneren lokalisierten, nicht exprimierte Gene waren dagegen eng mit der Kernperipherie assoziiert. Die benachbarten Genloci wiesen dabei eine voneinander weitgehend unabhängige Lokalisation auf. Unter Verwendung hoch auflösender konfokaler Mikroskopie und dreidimensionaler Bildrekonstruktion konnte diese Korrelation durch eine 3D-Erosionsanalyse im Wesentlichen bestätigt werden. Um zu ermitteln, ob die unterschiedlich positionierten Genloci mit verschiedenen Chromatin-Fraktionen assoziiert sind, wurde eine Kolokalisationsanalyse vorgenommen. Die Daten haben gezeigt, dass inaktive Genloci der CFTR-Region zu einem hohen Anteil mit dem perinukleären Heterochromatin assoziiert sind, aktive Genloci lokalisierten dagegen bevorzugt in dem hyperazetylierten Euchromatin im Kerninneren. Mehrfarben-FISH Experimente haben gezeigt, dass die eng benachbarten Genloci entsprechend ihrer transkriptionellen Aktivität simultan mit unterschiedlichen Bereichen im Zellkern assoziiert sein können und vermutlich die intergenischen Bereiche zwischen den Genen als flexible Linker dienen. Die Ergebnisse dieser Arbeit legen im Gegensatz zu früheren Studien (Sadoni et al., 1999; Volpi et al., 2000; Williams et al., 2002; Mahy et al., 2002) die Vermutung nahe, dass die Positionierung subchromosomaler Regionen auf der Ebene einzelner Gene reguliert wird. Durch die Behandlung der Zellen mit TSA wurde außerdem gezeigt, dass eine erhöhte Histonazetylierung zu der Dissoziation eines inaktiven Genlokus von heterochromatischen Bereichen führt, die transkriptionelle Aktivität davon jedoch nicht beeinflusst wird. Im zweiten Teil dieser Arbeit wurde untersucht, welcher funktionelle Zusammenhang zwischen dem Replikationsverhalten von GASZ, CFTR und CORTBP2 und der transkriptionellen Aktivität und Kernlokalisation dieser Gene besteht. Die Bestimmung der Replikationszeitpunkte wurde durch die Untersuchung des Auftretens von FISH-Dubletten während definierter S-Phase Stadien vorgenommen. Da bei dieser Analyse die Möglichkeit besteht, den Anteil an Dubletten durch eine verlängerte Schwester-Chromatid Kohäsion zu unterschätzen (Azuara et al., 2003), wurden die ermittelten Zeitpunkte darüber hinaus durch verschiedene Fixierungsmethoden überprüft. Die Ergebnisse haben gezeigt, dass transkriptionell aktive Genloci, die in dem hyperazetylierten Euchromatin lokalisierten, zu einem früheren Zeitpunkt replizierten als nicht exprimierte Genloci, die eng mit dem perinukleären Heterochromatin assoziiert waren. Durch eine TSA-Behandlung der Zellen wurde nachgewiesen, dass vor allem die Assoziation mit definierten Chromatin-Fraktionen einen Einfluss auf das Replikationsverhalten ausübt, die transkriptionelle Aktivität und das Replikationsverhalten jedoch nur indirekt miteinander in Zusammenhang stehen. Auf der Basis dieser Daten und früherer Studien wurde ein Modell erstellt, das die epigenetischen Mechanismen zueinander in Beziehung setzt, die an der Aktivierung Zelltyp-spezifisch regulierter Gene beteiligt sind. Der letzte Teil dieser Arbeit war der Frage gewidmet, ob Komponenten der Zellkernlamina an der perinukleären Positionierung des reprimierten CFTR-Lokus beteiligt sind. Dazu wurden HeLa S6 Zellen mit Lamin A/C-, Lap2- oder Emerin-siRNAs transfiziert. Nach erfolgreichem Knockdown wurde die Kernlokalisation des CFTR-Lokus durch Erosionsanalysen und Abstandsmessungen zu der Kernperipherie ermittelt. Die Ergebnisse haben gezeigt, dass nach dem Knockdown von Lamin A/C, Lap2 oder Emerin der CFTR-Lokus signifikant weiter im Kerninneren lokalisierte. Dabei schienen Lamin A/C und Lap2 einen stärkeren Einfluss auf die Lokalisation von CFTR auszuüben als Emerin. Auch wenn in früheren Arbeiten bereits gezeigt wurde, dass die Kernlamina für die Positionierung peripheren Chromatins von Bedeutung ist (Sullivan et al., 1999; Goldman et al., 2004; Zastrow et al., 2004), konnte hier zum ersten Mal ein direkter Einfluss auf die Lokalisation eines einzelnen Genlokus demonstriert werden. In einem ergänzenden Ansatz wurde die Kernlokalisation von CFTR in Fibroblasten von HGPS-Patienten untersucht, die auf Grund der Akkumulation von mutiertem Lamin A/C Deformationen der Zellkernlamina und Zellzyklus-Defekte aufwiesen (Eriksson et al., 2003; Goldman et al., 2004). Durch Abstandsmessungen zu der Kernperipherie und durch Kolokalisationsanalysen wurde gezeigt, dass der CFTR-Lokus in HGPS-Zellen einen größeren Abstand zur Kernperipherie aufwies und häufiger im hyperazetylierten Euchromatin lokalisierte als in Fibroblasten eines gesunden Probanden. Insgesamt unterstützen diese Daten die Vermutung, dass die Misslokalisation von reprimierten Genen in ein verändertes Chromatin-Umfeld an dem Krankheitsbild dieser und anderer Laminopathien beteiligt sein könnte.

In der vorliegenden Arbeit wurden die beiden Histon-Methyltransferasen Su(var)3-9 und E(Z) aus Drosophila melanogaster charakterisiert. Die Histonmethylierung als Modifikation war schon länger bekannt gewesen, bis zum Jahr 2000 war jedoch vor allem die Acetylierung etwas genauer untersucht worden. Su(var)3-9 war die einzige bekannte Histon-Lysin-Methyltransferase, als diese Arbeit begonnen wurde. Zur Charakterisierung wurde das myc-getagte Enzym aus Drosophila-Kernextrakt durch Affinitätschromatographie aufgereinigt und zunächst die Substratspezifität festgestellt. Wie das humane Enzym Suv39H1 methyliert es ebenfalls spezifisch H3-K9 (Lysin 9 im Histon H3). Das aus den Kernextrakten aufgereinigte Enzym besitzt aber auch die Fähigkeit, ein an H3-K9 präacetyliertes Substrat zu methylieren. Die Vermutung, dass Su(var)3-9 mit einer Histondeacetylase assoziiert ist, konnte durch Verwendung von TSA als HDAC-Inhibitor bestätigt werden. Es stellte sich heraus, dass HDAC1 (Rpd3) mit Su(var)3-9 assoziiert ist. Um das Enzym besser untersuchen zu können, wurde es als Volllängenprotein und als Deletionsmutante in E. coli exprimiert. Die Aufreinigung des rekombinanten Enzyms sowie seine Lagerbedingungen wurden optimiert. Das Volllängenprotein Su(var)3-9 liegt – wie durch Gelfiltration festgestellt - als Dimer vor, die Interaktion mit sich selbst ist über den N-Terminus vermittelt. Su(var)3-9 bindet an sein eigenes, bereits methyliertes Substrat. Dies wurde an Peptiden untersucht, die den ersten 20 Aminosäuren des Histons H3 entsprechen, und entweder an Lysin 9 dimethyliert oder unmodifiziert waren. Die Interaktion mit dem methylierten Substrat ist auf die Chromodomäne von Su(var)3-9 zurückzuführen, ist jedoch schwächer als die Wechselwirkung von HP1 mit methyliertem H3-K9. Des weiteren wurde eine Drosophila-Zelllinie stabil mit Su(var)3-9 transfiziert. Das überexprimierte Protein ist jedoch nur schwach aktiv. Die Tatsachen, dass Su(var)3-9 mit HDAC1 interagiert sowie mit seinem eigenen Substrat assoziiert, ermöglichen die Aufstellung von Hypothesen über die bis jetzt kaum erhellte Ausbreitung von Heterochromatin in euchromatische Bereiche. Durch die Wechselwirkung mit der Deacetylase könnte Su(var)3-9 auch in aktiv transkribierte Bereiche vordringen und diese methylieren. Die Acetylierung, Zeichen für aktive Transkription, würde durch die Methylierung ersetzt werden. Die Interaktion mit seinem umgesetzten Substrat könnte verhindern, dass das Enzym sich nach der Reaktion entfernt, vielmehr könnte Su(var)3-9 entlang eines DNA-Stranges sukzessive alle Nukleosomen methylieren. Die darauffolgende Bindung von HP1 an methyliertes H3-K9 könnte den heterochromatischen Charakter des Chromatins verstärken und für längere Zeit festlegen. Aus Drosophila-Kernextrakten gelang es weiterhin, den E(Z)/ESC-Komplex über Säulenchromatographie aufzureinigen. Dieser enthält neben E(Z), ESC, p55 und Rpd3 auch Su(z)12. E(Z), ESC und Su(z)12 gehören der Polycomb-Gruppe an. Deren Funktion ist die dauerhafte Repression der homöotischen Gene. Sie spielen daher eine wichtige Rolle im „Zellgedächtnis“ während der frühen Entwicklung von Drosophila. Es konnte gezeigt werden, dass der E(Z)/ESC-Komplex Lysin 9 sowie Lysin 27 im Histon H3 methyliert. Außerdem wurde in vitro ein Teilkomplex aus rekombinantem E(Z), p55 und ESC rekonstituiert, der das Histon H3 methylieren kann. Ein Teilkomplex, der E(Z) mit mutierter SET-Domäne enthält, ist nicht in der Lage, H3 zu methylieren. Die Vorhersage, dass E(Z) aufgrund seiner SET-Domäne eine Methyltransferase sein müsse, konnte durch vorliegende Untersuchungen bestätigt werden. Polycomb ist ein weiteres Protein aus der Polycomb-Gruppe. In dieser Arbeit konnte gezeigt werden, dass dieses Protein spezifisch an das Histon H3 bindet, das an K27 trimethyliert ist. Polycomb besitzt wie HP1 eine Chromodomäne. Aus den vorliegenden Daten kann folgendes Modell aufgestellt werden: Nach der Methylierung von H3-K9 sowie H3-K27 durch den E(Z)/ESC-Komplex in homöotischen Genen, die schon abgeschaltet sind und weiterhin reprimiert werden müssen, bindet Polycomb an dieses Methylierungsmuster. Polycomb befindet sich in einem großen Komplex mit weiteren Polycomb-Gruppen-Proteinen. Die Bindung dieses Komplexes an Chromatin könnte ein denkbarer Mechanismus sein, wie die dauerhafte Repression der homöotischen Gene vermittelt wird. Um den E(Z)/ESC-Komplex genauer untersuchen zu können, wurden Viren für das Baculosystem hergestellt, so dass eine Einzel- oder auch Coexpression der Proteine möglich ist. Die Aktivität von E(Z), das im Baculosystem exprimiert wurde, ist nicht besonders hoch. Es bindet unter den in dieser Arbeit verwendeten Bedingungen weder an DNA, noch an Histone noch an H3-Peptide, die methyliert sind. Innerhalb des E(Z)/ESC-Komplexes bindet E(Z) an p55, Rpd3, ESC sowie Su(z)12. Su(z)12 interagiert mit p55, Rpd3 und E(Z). Die weiteren Interaktionen werden am besten durch eine bildliche Darstellung (siehe Abb. 86) vermittelt. In einem Luciferase-Assay wurde eine repressive Wirkung von E(Z) festgestellt. Dieses Experiment bedarf allerdings eines aktivierten Systems. Ferner muss durch Mutationsanalysen sichergestellt werden, dass die repressive Wirkung auf die Methyltransferase-Aktivität von E(Z) zurückzuführen ist. Kürzlich wurde entdeckt, dass E(Z) sowie Su(z)12 in verschiedenen Tumoren überexprimiert sind. Noch ist weder deren Funktion in den Tumorzellen klar, noch weiss man, ob die Überexpression der Grund oder eine Folge der Tumorbildung ist, noch kennt man alle Zielgene, die durch eine Überexpression von E(Z) und Su(z)12 beeinflusst werden. In nächster Zeit sind hier Einsichten in die Wirkungsweise von E(Z), Su(z)12 und anderen Polycomb-Gruppen-Proteinen zu erwarten.

Previous studies revealed changes of pericentromeric heterochromatin arrangements in postmitotic Purkinje cells (PCs) during postnatal development in the mouse cerebellum (Manuelidis, 1985; Martou and De Boni, 2000). Here, we performed vibratome sections of mouse cerebellum (vermis) at P0 (day of birth), at various stages of the postnatal development (P2-P21), as well as in very young (P28) and 17-months-old adults. FISH was carried out on these sections with major mouse satellite DNA in combination with immunostaining of the nucleolar protein B23 (nucleophosmin). Laser confocal microscopy, 3D reconstructions and quantitative image analysis were employed to describe changes in the number and topology of chromocenters and nucleoli. At all stages of postnatal PC development heterochromatin clusters were typically associated either with nucleoli or with the nuclear periphery, while non-associated clusters were rare (

In situ hybridization of human chromosome 18 and X-specific alphoid DNA-probes was performed in combination with three dimensional (3D) and two dimensional (2D) image analysis to study the interphase distribution of the centric heterochromatin (18c and Xc) of these chromosomes in cultured human cells. 3D analyses of 18c targets using confocal laser scanning microscopy indicated a nonrandom disposition in 73 amniotic fluid cell nuclei. The shape of these nuclei resembled rather flat cylinders or ellipsoids targets were preferentially arranged in a domain around the nuclear center, but close to or associated with the nuclear envelope. Within this domain, however, positionings of the two targets occurred independently from each other, i.e., the two targets were observed with similar frequencies at the same (upper or lower) side of the nuclear envelope as those on opposite sides. This result strongly argues against any permanent homologous association of 18c. A 2D analytical approach was used for the rapid evaluation of 18c positions in over 4000 interphase nuclei from normal male and female individuals, as well as individuals with trisomy 18 and Bloom's syndrome. In addition to epithelially derived amniotic fluid cells, investigated cell types included in vitro cultivated fibroblastoid cells established from fetal lung tissue and skin-derived fibroblasts. In agreement with the above 3D observations 18c targets were found significantly closer (P < 0.01) to the center of the 2D nuclear image (CNI) and to each other in all these cultures compared to a random distribution derived from corresponding ellipsoid or cylinder model nuclei. For comparison, a chromosome X-specific alphoid DNA probe was used to investigate the 2D distribution of chromosome X centric heterochromatin in the same cell types. Two dimensional Xc-Xc and Xc-CNI distances fit a random distribution in diploid normal and Bloom's syndrome nuclei, as well as in nuclei with trisomy X. The different distributions of 18c and Xc targets were confirmed by the simultaneous staining of these targets in different colors within individual nuclei using a double in situ hybridization approach.

Wed, 1 Jan 1986 12:00:00 +0100 https://epub.ub.uni-muenchen.de/9323/1/9323.pdf Pearson, P.; Cornelisse, J. L.; Stevenson, A. F. G.; Hager, H. D.; Scholl, Hans Peter; Bakker, E.; Slagboom, P.; Cremer, Thomas; Devilee, P.