Medical genetic research on molecular basis of epigenetic regulation and human diseases

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The project focused on the investigations of epigenetic gene regulation and related genetic phenomena including human diseases, and discovered a lot of new findings on DNA methyltransferases (DNMT), methylated DNA binding proteins (MBD proteins), chromatin insulator, genomic imprinting, and differentiation of mouse germ cells and embryonic stem cells (ES cells). Dr. Sasaki's group developed germ cell-specific knockout mice for DNMT3A and DNMT3B, and reported that these mice were sterile, and that DNMT3A-mediated DNA methylation during gametogenesis is required for establishing genomic imprinting. This result had a great impact on the imprinting mechanisms. In addition, studies of mutant mice deficient for DNMT3A or its associated factor named DNMT3L showed that aberrations of meiosis and transcriptional repression of transposons occurred in their testis, and that embryos derived from eggs of these mutant mice had abnormal placenta, resulting in the miscarriage. Further, Sasaki's group … More studied the distribution of CpG dinucleotides in male or female germ cell-specific methylated regions, and showed that DNMT3L or related factors can be implicated in development of ICF syndrome.MBD1 functions as a DNA methylation-mediated transcriptional repressor. Nakao's group reported that MBD1 recruits histone methyltransferase SETDB1 and its activating factor MCAF1 (MBD1-containing chromatin associated factor), resulting ir transcriptional repression and heterochromatin formation that is marked with trimethylation of 9th lysine of histone H3. In this case, SUMOylation of MBD1 is important for forming the MBD1-MCAF1-SETDB1 repressive complexes. It was also found that MBD1 and polycomb group proteins have overlapping roles in transcriptional repression and heterochromatin formation. In addition, MBD domain of MeCP2, another type of MBD proteins, is frequently mutated in Rett syndrome, and most MBD mutants lost the ability to bind methylated DNAs. Nakao group found that some MBD mutants retained the methylated DNA binding, suggesting the presence of unidentified mechanisms to develop this disease. Further, in the boundary elements of human genome, insulator binding protein CTCF was found to cooperate with chromatin remodeling factor CHD8, resulting in the enhancer blocking effect on H191IGF2 imprinted region. This is a first evidence for insulator linked to epigenetic remodeling. In neural differentiation of mouse ES cells, PML bodies and chromocenters were found to be remarkably reorganized, and Oct3/4 gene locus was differentially marked with histone acetylation and methylation, and DNA methylation at each stage of ES cells, neural precursor cells and terminally differentiated neurons. Less