AbstractEpigenetic modifications, including DNA methylation and histone modifications, are reprogrammed considerably following fertilization during mammalian early embryonic development. Incomplete epigenetic reprogramming is a major factor leading to poor developmental outcome in embryos generated by assisted reproductive technologies, such as somatic cell nuclear transfer. However, the role of histone modifications in preimplantation development is poorly understood. Here, we show that co-knockdown (cKD) of Hdac1 and 2 (but not individually) resulted in developmental failure during the morula to blastocyst transition. This outcome was also confirmed with the use of small-molecule Hdac1/2-specific inhibitor FK228. We observed reduced cell proliferation and increased incidence of apoptosis in cKD embryos, which were likely caused by increased acetylation of Trp53. Importantly, both RNA-seq and immunostaining analysis revealed a failure of lineage specification to generate trophectoderm and pluripotent cells. Among many gene expression changes, a substantial decrease of Cdx2 may be partly accounted for by the aberrant Hippo pathway occurring in cKD embryos. In addition, we observed an increase in global DNA methylation, consistent with increased DNA methyltransferases and Uhrf1. Interestingly, deficiency of Rbbp4 and 7 (both are core components of several Hdac1/2-containing epigenetic complexes) results in similar phenotypes as those of cKD embryos. Overall, Hdac1 and 2 play redundant functions required for lineage specification, cell viability and accurate global DNA methylation, each contributing to critical developmental programs safeguarding a successful preimplantation development.SignificanceSubstantial changes to epigenetic modifications occur during preimplantation development and can be detrimental when reprogrammed incompletely. However, little is known about the role of histone modifications in early development. Co-knockdown of Hdac1 and 2, but not individually, resulted in developmental arrest during morula to blastocyst transition, which was accompanied by reduced cell number per embryo and increased incidence of apoptosis. Additionally, we observed a failure of first lineage specification to generate trophectoderm and pluripotent cells, which were associated with reduced expression of key lineage-specific genes and aberrant Hippo pathway. Moreover, an increase in global DNA methylation was found with upregulated Dnmts and Uhrf1. Thus, Hdac1 and 2 play overlapping roles in lineage development, apoptosis, and global methylation during preimplantation development.
Direct readout of heterochromatic H3K9me3 regulates DNMT1-mediated maintenance DNA methylation
