SMCHD1 terminates the first embryonic genome activation event in mouse two-cell embryos and contributes to a transcriptionally repressive state.

Embryonic genome activation (EGA) in mammals begins with transient expression of a large group of genes (EGA1). Importantly, entry into and exit from the 2C/EGA state is essential for viability. family member genes play an integral role in EGA1 by activating other EGA marker genes such as family members. We previously reported that structural maintenance of chromosomes flexible hinge domain-containing protein 1 () is expressed at the mRNA and protein levels in mouse oocytes and early embryos and that elimination of expression inhibits inner cell mass formation, blastocyst formation and hatching, and term development. We extend these observations here by showing that siRNA knockdown of in zygotes results in overexpression of and in two-cell embryos, with continued overexpression of at least through the eight-cell stage as well as prolonged expression of . These results are consistent with a role for SMCHD1 in promoting exit from the EGA1 state and establishing SMCHD1 as a maternal effect gene and the first chromatin regulatory factor identified with this role. Additionally, bioinformatics analysis reveals that SMCHD1 also contributes to the creation of a transcriptionally repressive state to allow correct gene regulation.