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Symposium 1: Functional Genomics, Proteomics and Bioinformatics 1.1 Symposium Abstracts SYMPOSIUM 1: FUNCTIONAL GENOMICS, PROTEOMICS AND BIOINFORMATICS 1.1. Epigenetics: DNA Methylation and Far Beyond IL 1.1–1 where through epigenetic means nonequivalent sister chromatids The role of MeCP2 in the brain are generated by chromosome replication. Second, epigenetic states controlling gene repression are inherited in mitosis and A. Bird, P. Skene, R. Illingworth and J. Guy Wellcome Trust Centre for Cell Biology, University of Edinburgh, meiosis as remarkably stable conventional Mendelian markers (1). Edinburgh, UK We propose that likewise asymmetric cell divisions in higher eukaryotes might result by further postulating biased segregation The DNA of every cell in the body carries a pattern of chemical of differentiated sister chromatids of both copies of a specific modifications due to the methylation of cytosine in the dinucleo- chromosome to daughter cells (2,3). Can we explain hitherto tide sequence 5¢CG. It is thought that these chemical marks help unexplained developmental traits/disorders in humans and verte- to define the pattern of gene expression that is appropriate for brates by invoking such principles? The causes of schizophrenia each cell type. The nuclear protein MeCP2 was originally discov- and bipolar human psychiatric disorders are unknown. A novel ered because of its ability to specifically bind to methylated CG somatic cell genetics, SSIS (Somatic Strand-specific Imprinting sites, but not to CGs lacking the methyl moiety. Because of its and Selective strand segregation) model, postulated biased segre- DNA binding preference, it was hypothesised that MeCP2 inter- gation of differentiated older ‘Watson’ versus ‘Crick’ DNA chains prets the DNA methylation signal. A considerable body of of a chromosome to specific daughter cells. Such an oriented evidence indicates that DNA methylation causes gene silencing asymmetric cell division in embryogenesis may constitute the and, in line with this view, early evidence established that MeCP2 mechanism for development of healthy, functionally nonequiva- can attract molecular machinery that contains enzymes capable lent brain hemispheres in humans. For evidence, genetic translo- of altering chromatin structure, for example by removing acetyl cations of the relevant chromosome might therefore cause disease groups from histone tails. A plausible hypothesis is therefore that by disrupting the chromosome-specific biased chromatid segrega- MeCP2 binds to methylated DNA and recruits deacetylase activ- tion process. This way the epialleles of a hypothetical gene ity so that the chromatin environment becomes incompatible with controlling brain laterality development in the translocation- efficient transcription. This scenario predicts that the absence of containing chromosome will be randomly distributed to sister MeCP2, as in neurons of patients with the autism spectrum dis- cells. Accordingly, the model predicts that symmetrical brain order Rett Syndrome, will cause inappropriate gene expression hemispheres might develop in 50% of translocation carriers. due to relaxed repression. Decisive evidence supporting this Thus, the observation of only 50% of chromosome 1/6/9;11 trans- prediction has proven elusive so far and other potential functions location carriers that do develop disease is in accord with the for MeCP2 have been proposed – for example that it is an acti- model (4). Likewise, the SSIS model is also advanced for visceral vator of transcription or a regulator of messenger RNA splicing. laterality development in mice. The functional significance of MeCP2 will be assessed in the light References: of studies of the structure and dynamics of the interaction 1. Klar AJS. Lessons learned from studies of fission yeast between MeCP2 and methylated DNA at the molecular level. At mating-type switching and silencing. Annual Review of the level of brain physiology, the unexpected reversibility of Rett Genetics 2007; 41: 213–36. Syndrome-like symptoms in Mecp2-null mice has important 2. Armakolas A and Klar AJS. Cell type regulates selective implications, as it demonstrates that MeCP2 can assume its nor- segregation of mouse chromosome 7 DNA strands in mitosis. mal functions in a brain that developed and acquired severe Science 2006; 311: 1146–1149. neurological symptoms in the complete absence of MeCP2. These 3. Armakolas A and Klar AJS. Left-right dynein motor impli- results challenge the long-held view that Rett Syndrome is a cated in selective chromatid segregation in mouse cells. Science ‘neurodevelopmental disorder’. Taken together, the molecular 2007; 315:100–1. and neurobiological information implicate MeCP2 as a protein 4. Klar AJS. A genetic mechanism implicates chromosome 11 in that is essential for the tight maintenance and stability of gene schizophrenia and bipolar diseases. Genetics 2004; 167: expression programs in mature nerve cells. 1833–1840. IL 1.1–2 IL 1.1–3 Asymmetric cell division through epigenetic Epigenomic programs and reprogramming in differentiation of sister chromatids and their mammals selective segregation in mitosis J. Walter A. Klar Genetics/Epigenetics, Universitat de Saarlandes, Saarbru¨cken, National Cancer Institute, GRCBL, Frederick, USA GERMANY Our studies with the model system of fission yeast have discovered Epigenetic programs play an essential role for the establishment two new principles of biology. First, developmental asymmetry of of pluri-and totipotency of cells in the early embryo. In mammals sister cells simply results from the inheritance of older ‘Watson’ histone modificatons and DNA-methylation patterns are rapidly versus older ‘Crick’ chain-containing chromatids at the mat1 locus changed on the parental chromosomes merged from from the egg FEBS Journal 276 (Suppl. 1) 5–84 (2009) ª 2009 The Authors Journal compilation ª 2009 Federation of European Biochemical Societies 5 Abstracts Symposium and the sperm. This reprogramming begins rapidly after fertiliza- molecular trigger, the non-coding Xist RNA, and its antisens tion and predominantly affects the paternal (sperm) chromo- cis-repressor Tsix. Nanog, Oct4 and Sox2 (the triumvirate of somes in the first cell cycle. The reprogramming is apparently factors underlying pluripotency) all cooperate to repress Xist in crucial to reset the chromatin for developmentally regulated undifferentiated ES cells. Additionally, Rex1 (a well-known mar- genetic programs. Comparative immunofluorescence based analy- ker of pluripotent cells), Klf4 and c-Myc (which in conjunction sis of chromatin changes reveals a striking conservation of the with Oct4 and Sox2 are required to generate iPS cells) are dynamic and specificty of such epigenetic reprogramming events involved in conferring maximal transcriptional activity to Tsix in in early mammalian embryos. Of particular interest are enzymatic undifferentiated ES cells. Our results provide a molecular frame- mechanisms which trigger a rapid replication independent elimi- work linking X-inactivation reprogramming to the control of plu- nation of DNA-methylation from the paternal chromosomes in ripotency, and shed light on how pluripotency and genome the zygote. Such ‘active’ demethylation mechanisms occur in a reprogramming factors reset established epigenetic states. time window of about 4–7 hours postfertilization. We investi- gated the potential involvement of DNA-repair mechanisms in this DNA-demethylation process and identified a striking accu- mulation of strand breaks and repair markers around the early OP 1.1-1 phases of zygotic development. We furthermore observe that Recognition of monomethylated histone potential repair activities can be separated from DNA-replication peptides by the malignant brain tumor repeats processes. We conclude that epigenetic reprogramming is indeed of human SCML2 partially linked to DNA repair processes. I will discus the poten- C. M. Santiveri1, B. C. Lechtenberg2, M. D. Allen2, A. Sathya- tial mechanisms of such DNA-demethylation processes and some murthy2, A. M. Jaulent2, S. M. V. Freund2 and M. Bycroft2 of their general implications for genetic and epigenetic variation. 1Instituto Quimica-Fisica Rocasolano, CSIC, Espectroscopia y Estructura Molecular, Madrid, SPAIN, 2Medical Research IL 1.1–4 Council, Centre for Protein Engineering, Cambridge, UK Molecular coupling of X-inactivation regulation SCML2 (Sex Comb on Midleg-like 2) is a constituent of the and pluripotency Polycomb repressive complex 1, a large multiprotein assembly P. Navarro1, I. Chambers2, V. Karwacki-Neisius2, C. Chureau1, involved in the long term silencing of gene expression required to C. Morey1, A. Dubois1, A. Oldfield3, C. Rougeulle3 and maintain cell identity. SCML2 contains two N-terminal 100-resi- P. Avner1 due malignant brain tumor (MBT) repeats, a protein module 1Institut Pasteur, Developmental Biology, Paris, France, 2MRC adopting a beta-barrel core similar to that of chromatin-binding Centre Development in Stem Cell Biology, Institute for Stem Cell domains like chromo- and Tudor domains. All are members of Research, Edinburgh, UK, 3Universite´ Paris Diderot, UMR 7216 the Royal superfamily of effector modules able to ‘‘read’’ differ- Epige´ne´tique et Destin Cellulaire, Paris, FRANCE ent types of histone post-translational modifications. We have used NMR spectroscopy to investigate the binding specificity of The integration of X-chromosome inactivation into the develop- the MBT repeats of human SCML2. Our data show that they mental process is a crucial aspect of this paradigm of epigenetic preferentially recognize histone
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