DNMT3b's Role in Hematopoietic Stem Cells

Hematopoiesis proceeds from a bone marrow resident population of stem cells responsible for generation of all lineages within the blood. Distinct molecular programs within hematopoietic stem cells regulate maintenance of this population under homeostatic conditions, however the coordination of these programs remains largely undefined. DNA methylation is an epigenetic means of gene regulation in a mammals carried out by a family of DNA methyltransferases. Of these, the de novo methyltransferase is highly expressed in hematopoietic stem cells as compared to other members of this family and somatic mutations in DNMT3b lead to a syndrone characterized by immunodeficiency. Therefore we hypothesized that DNMT3b regulates hematopoietic stem cells via its ability to methylate DNA. By knock-down of DNMT3b with a retrovirally delivered shRNA or Cre mediated recombination of floxed DNMT3b alleles work presented in this thesis demonstrates a critical role for DNMT3b in hematopoiesis in mice. Loss of DNMT3b leads to limited reconstitution of hematopoiesis in irradiated recipients associated with a proliferative defect in vitro and a failure of hematopoietic stem cell self-renewal in vivo. Targeted deletion of DNMT3b in hematopoietic stem cells leads to decreased engraftment following transplantation and decreased proliferation in vitro. DNMT3b's function in hematopoietic cells requires the methyltransferase activity of the enzyme and the defects in hematopoiesis are associated with loss of DNA methylation and decreased expression of MLL. Therefore DNMT3b is necessary for maintenance of the proliferative ability and engraftment capacity of hematopoietic cells and hematopoiesis is dependent upon appropriate DNA methylation