Role of Polycomb-group genes in adult stem cells and their expansion

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Hematopoietic stem cell (HSC) transplantation is now routinely performed in clinical practice for the treatment of patients with hematological malignancies and bone marrow failure. And new strategies with HSCs are developed for the treatment of patients with the other malignancies and vascular failure including myocardial infarction, attracting further attention to HSCs. However, molecular mechanisms regulating HSCs still remain unclear.In this study, focusing on Polycomb-group genes we attempted to uncover the role underlying sternness.Polycomb-group genes (PcG) were uncovered by Drosophila genetics as genes supporting the cellular memory system during development. We for the first time reported that PcG are required for sustaining HSC activity. Although PcG are recently reported to support sternness through the repression activity to ink4A locus encoding p16CDKI and p19ARF, so far the molecular bases underlying PcG functions supporting sternness are not fully understood. We found tha … More t licensing of DNA replication was impaired in mice lacking PcG. And PcG complexes interact with Geminin, an inhibitor of a DNA replication licensing factor Cdtl through Scmhl, a member of PcG, which we originally identified based on the conserved protein structure in mammals. We also found Hoxb4, a well known factor regulating HSCs, also interacts with Geminin.Furthermore, by using retrovirus-mediated gene transfer method, we examined in detail the effect of affected Geminin regulation on HSCs. And we showed that PcG complexes regulate Geminin at the level of protein through ubiquitination and that Geminin regulation is pivotal in hematopoiesis and HSC regulation.These results indicate that DNA replication licensing is pivotal in sustaining HSC activity. And PcG complexes play a crucial role in regulation of Geminin. Now by using in vitro reconstituting system further detailed analysis of PcG complexes are in progress. These findings may help future progress in regenerative medicine with stem cells. Less