Primordial germ cell 7 (PGC7)(Dppa3 or Stella) is a small inherently disordered protein that is mainly expressed in oocytes and plays a vital role in the regulation of DNA methylation reprogramming in imprinted loci through interaction with other proteins. Most of PGC7-deficient zygotes are blocked at two-cell stage with an increased tri-methylation at lysine 27 of histone H3 (H3K27me3) level in the nucleus. Our previous work has indicated that PGC7 interacts with yin-yang1 (YY1) that is essential for the recruitment of enhancer of zeste homolog 2 (EZH2)-containing Polycomb repressive complex 2 (PRC2) to H3K27me3 modification sites. Here, we found that the presence of PGC7 weakened the interaction between YY1 and PRC2 without disrupting the assembly of core subunits of the PRC2 complex. In addition, PGC7 promoted AKT to phosphorylate serine 21 of EZH2, resulting in inhibition of EZH2 activity and the dissociation of EZH2 from YY1, thereby decreasing H3K27me3 level. In zygotes, the PGC7-deficient and AKT inhibitor MK2206 both promoted EZH2 to enter the pronuclei but without disturbing the subcellular localization of YY1 and caused an increase in the level of H3K27me3 in the pronuclei, as well as inhibition of the expression of zygote-activating genes regulated by H3K27me3 in two-cell embryos. In summary, PGC7 could affect zygotic genome activation during early embryonic development by regulating the level of H3K27me3 through regulation of PRC2 recruitment, EZH2 activity, and subcellular localization.NEW & NOTEWORTHY PGC7 and YY1 interaction inhibits recruitment of PRC2 by YY1. PGC7 promotes AKT and EZH2 interaction to increase pEZH2-S21 level, which weakens YY1 and EZH2 interaction, thereby decreasing H3K27me3 level. In zygotes, the PGC7-deficient and AKT inhibitor MK2206 promote EZH2 to enter the pronuclei, and increase H3K27me3 level in the pronuclei, as well as inhibition of the expression of zygote-activating genes regulated by H3K27me3 in two-cell embryos, which ultimately affects early embryo development.
Keywords: H3K27me3 modification; PGC7-deficient zygotes; YY1; recruitment of PRC2; two-cell arrest.