Distinct functions of Dnmt3a and Dnmt3b de novo DNA methyltransferases in ES cell proliferation and differentiation

Abstract

Two de novo DNA methyltransferases, Dnmt3a and Dnmt3b, have been identified in humans and mice\rto contribute to the methylation of unmodified DNA. We recently showed a transition\rof de novo DNA methyltransferase expression from Dnmt3b to Dnmt3a during mouse embryogenesis and in\rtissue-specific stem cells, suggesting distinct functions of Dnmt3a and Dnmt3b during these processes. In\rthis study, to characterize the functions of Dnmt3a and Dnmt3b in pluripotent stem cells, we exogenously\rtransfected ES cells with Dnmt3a\rand Dnmt3b cDNAs linked to an internal ribosome entry site-green fluorescent\rprotein gene, and then analyzed the effects of expression of these de novo DNA\rmethyltransferases on ES cell growth and differentiation. ES cells expressing\rDnmt3b showed specific downregulation of pluripotency marker genes such as\rNanog and Oct 3/4. In addition, Dnmt3a-transfected\rES cells showed a specific increase in mitotic index, while Dnmt3b-transfected\rES cells showed a decrease in mitotic index. These results suggest that Dnmt3b\rhas important physiological roles in the initial process of stem cell\rdifferentiation and that Dnmt3a\rhas a function in stem cell proliferation.