The Role of DOT1L Methyltransferase Activity in Fetal Hematopoiesis

Early mammalian erythropoiesis requires the DOT1L methyltransferase. We demonstrated that loss of DOT1L in mutant mice resulted in lethal anemia during midgestation. The molecular mechanisms by which DOT1L regulates embryonic erythropoiesis have not yet been elucidated. In this study, a methyltransferase mutant mouse line ( Dot1L -MM) was generated to determine whether the methyltransferase activity of DOT1L is essential for erythropoiesis. Dot1L- MM mice displayed embryonic lethality between embryonic days 10.5 and 13.5, similar to Dot1lL knockout ( Dot1L- KO) mice. However, when examined at E10.5, unlike the Dot1L- KO, Dot1L- MM embryos did not exhibit evidence of anemia. In ex vivo hematopoietic differentiation cultures, Dot1L- KO and Dot1L- MM yolk sac (YS) cells both formed reduced numbers of myeloid, and mixed hematopoietic colonies. Erythroid colonies were able to be formed in numbers equal to wildtype embryos. Extensively self-renewing erythroblast (ESRE) cultures were established using YS cells from E10.5 embryos. Dot1L- KO and Dot1L- MM cells expanded significantly less than wild-type cells and exhibited increased cell death. Strikingly, Dot1L- KO and Dot1L- MM cells of YS origin exhibited profound genomic instability, implicating DOT1L methyltransferase activity in maintenance of the genome as well as viability of hematopoietic progenitors. Our results indicate that the methyltransferase activity of DOT1L plays an important role early murine hematopoiesis. ### Competing Interest Statement The authors have declared no competing interest.