MacroH2A1 Regulates the Balance between Self-Renewal and Differentiation Commitment in Embryonic and Adult Stem Cells

Abstract

e One of the most striking epigenetic alterations that occurs at the level of the nucleosome is the complete exchange of the canonical H2A histones for the macroH2A variant. Here, we provide insight into the poorly recognized function of macroH2A in transcriptional activation and demonstrate its relevance in embryonic and adult stem cells. Knockdown of macroH2A1 in mouse embryonic stem (mES) cells limited their capacity to differentiate but not their self-renewal. The loss of macroH2A1 interfered with the proper activation of differentiation genes, most of which are direct target genes of macroH2A. Additionally, macroH2A1-deficient mES cells displayed incomplete inactivation of pluripotency genes and formed defective embryoid bodies. In vivo, macroH2A1-deficient teratomas contained a massive expansion of malignant, undifferentiated carcinoma tissue. In the heterogeneous culture of primary human keratinocytes, macroH2A1 levels negatively correlated with the self-renewal capacity of the pluripotent compartment. Together these results establish macroH2A1 as a critical chromatin component that regulates the delicate balance between self-renewal and differentiation of embryonic and adult stem cells.

Mice without MacroH2A Histone Variants

“…These effects on important physiological processes can explain the evolutionary conservation of macroH2A histones. We did not see evidence that macroH2As have a crucial role in differentiation or morphogenesis during embryonic development, in contrast to some studies of in vitro ES cell differentiation and early zebrafish development (20)(21)(22). Interestingly, other studies of ES cells (42) or induced pluripotent stem cells (43) found that macroH2As are not required for in vitro differentiation and thus appear to be compatible with our results with macroH2A KO mice.…”

“…Other studies indicate that macroH2As have a critical role in early development and differentiation. A knockdown of macroH2A2 in developing zebrafish embryos led to severe developmental defects (20), and some studies of embryonic stem (ES) cells found that knockdown of macroH2A1 and/or macroH2A2 impaired the expression of differentiation genes and the inactivation of pluripotency genes during in vitro differentiation (21,22). In contrast, our studies of macroH2A1 knockout (KO) mice showed no obvious defects in development or X inactivation (23).…”

Epo-induced erythroid maturation is dependent on Plcγ1 signaling

“…31,32 Loss of function approaches revealed a critical role for these histone variants in the differentiation but not the self-renewal of embryonic and adult stem cells. 34 Although macroH2As have well-characterized repressive functions, their influence on differentiation of embryonic stem cells is at least in part dependent on a pro-activating function of macroH2A1 on important differentiation regulatory genes such as Gata2 and Brachyury. 34 In line with the proposed pro-differentiation function of macroH2A, knockdown of mH2A2 in proerythroblasts resulted in delayed erythroid maturation after Epo stimulation.…”

“…34 Although macroH2As have well-characterized repressive functions, their influence on differentiation of embryonic stem cells is at least in part dependent on a pro-activating function of macroH2A1 on important differentiation regulatory genes such as Gata2 and Brachyury. 34 In line with the proposed pro-differentiation function of macroH2A, knockdown of mH2A2 in proerythroblasts resulted in delayed erythroid maturation after Epo stimulation. These data resemble almost identically the morphological and immunophenotypical differentiation process of Plcγ1-deficient cells as shown before.…”

“…[33][34][35] Thus, we decided to investigate whether mH2A2 has a functional role in erythroid differentiation. Therefore, we infected the pro-erythroblast cell line I/11 with control shRNA or one of two different mH2A2 shRNAs ( Figure 6a) and then analyzed for differentiation by flow cytometry.…”