The histone 3 lysine 4 methyltransferase Setd1b is a maternal effect gene required for the oogenic gene expression program

Abstract

Germ cell development involves major reprogramming of the epigenome to prime the zygote for totipotency. Histone 3 lysine 4 (H3K4) methylations are universal epigenetic marks mediated in mammals by six H3K4 methyltransferases related to fly Trithorax, including two yeast Set1 orthologs: Setd1a and Setd1b. Whereas Setd1a plays no role in oogenesis, we report that Setd1b deficiency causes female sterility. Oocyte specific Gdf9iCre conditional knockout (Setd1bGdf9cKO) ovaries develop through all stages however follicular loss accumulated with age and unfertilized metaphase II (MII) oocytes exhibited irregularities of the zona pellucida and meiotic spindle. Most Setd1bGdf9cKO zygotes remained in the pronuclear stage and displayed polyspermy in the perivitelline space. Expression profiling of Setd1bGdf9cKO MII oocytes revealed (i) that Setd1b promotes the expression of the major oocyte transcription factors including Obox1, 2, 5, 7, Meis2 and Sall4; and (ii) two-times more up- than downregulated mRNAs suggesting that Setd1b also promotes the expression of negative regulators of oocyte development with multiple Zfp-KRAB factors implicated. Together, these findings indicate that Setd1b serves as maternal effect gene through regulation of the oocyte gene expression program.