The lysine deacetylase activity of histone deacetylases 1 and 2 is required to safeguard zygotic genome activation in mice and cattle.

The genome is transcriptionally inert at fertilization and must be activated through a remarkable developmental process called zygotic genome activation (ZGA). Epigenetic reprogramming contributes significantly to the dynamic gene expression during ZGA; however, the mechanism has yet to be resolved. Here, we find histone deacetylases 1 and 2 (HDAC1/2) can regulate ZGA through lysine deacetylase activity. Notably, in mouse embryos, overexpression of a HDAC1/2 dominant-negative mutant leads to developmental arrest at the two-cell stage. RNA-seq reveals that 64% of downregulated genes are ZGA genes and 49% of upregulated genes are developmental genes. Inhibition of the deacetylase activity of HDAC1/2 causes a failure of histone deacetylation at multiple sites, including H4K5, H4K16, H3K14, H3K18 and H3K27. ChIP-seq analysis exhibits an increase and decrease of H3K27ac enrichment at promoters of up- and downregulated genes, respectively. Moreover, HDAC1 mutants prohibit the removal of H3K4me3 by impeding expression of Kdm5 genes. Importantly, the developmental block can be greatly rescued by Kdm5b injection and by partially correcting the expression of the majority of dysregulated genes. Similar functional significance of HDAC1/2 is conserved in bovine embryos. Overall, we propose that HDAC1/2 are indispensable for ZGA by creating correct transcriptional repressive and active states in mouse and bovine embryos.

TEAD4 regulates KRT8 and YAP in preimplantation embryos in mice but not in cattle.

In brief: Lineage specification plays a vital role in preimplantation development. TEAD4 is an essential transcription factor for trophectoderm lineage specification in mice but not in cattle. Abstract: Tead4, a critical transcription factor expressed during preimplantation development, is essential for the expression of trophectoderm-specific genes in mice. However, the functional mechanism of TEAD4 in mouse preimplantation development and its conservation across mammals remain unclear. Here, we report that Tead4 is a crucial transcription factor necessary for blastocyst formation in mice. Disruption of Tead4 through base editing results in developmental arrest at the morula stage. Additionally, RNA-seq analysis reveals dysregulation of 670 genes in Tead4 knockout embryos. As anticipated, Tead4 knockout led to a decrease in trophectoderm genes Cdx2 and Gata3. Intriguingly, we observed a reduction in Krt8, suggesting that Tead4 influences the integrity of the trophectoderm epithelium in mice. More importantly, we noted a dramatic decrease in nuclear Yap in outside cells for Tead4-deficient morula, indicating that Tead4 directly regulates Hippo signaling. In contrast, bovine embryos with TEAD4 depletion could still develop to blastocysts with normal expression of CDX2, GATA3, and SOX2, albeit with a decrease in total cell number and ICM cell number. In conclusion, we propose that Tead4 regulates mouse blastocyst formation via Krt8 and Yap, both of which are critical regulators of mouse preimplantation development.

Linker histone H1FOO is required for bovine preimplantation development by regulating lineage specification and chromatin structure†.

Linker histone H1 binds to the nucleosome and is implicated in the regulation of the chromatin structure and function. The H1 variant H1FOO is heavily expressed in oocytes and early embryos. However, given the poor homology of H1FOO among mammals, the functional role of H1FOO during preimplantation embryonic development remains largely unknown, especially in domestic animals. Here, we find that H1FOO is not only expressed in oocytes and preimplantation embryos but granulosa cells and spermatids in cattle. We then demonstrate that the interference of H1FOO results in preimplantation embryonic developmental arrest in cattle using either RNA editing or Trim-Away approach. H1FOO depletion leads to a compromised expression of critical lineage-specific genes at the morula stage and affects the establishment of cell polarity. Interestingly, H1FOO depletion causes a significant increase in the expression of genes encoding other linker H1 and core histones. Concurrently, there is an increase of H3K9me3 and H3K27me3, two markers of repressive chromatin and a decrease of H4K16ac, a marker of open chromatin. Importantly, overexpression of bovine H1FOO results in severe embryonic developmental defects. In sum, we propose that H1FOO controls the proper chromatin structure that is crucial for the fidelity of cell polarization and lineage specification during bovine preimplantation development.

Overlapping functions of RBBP4 and RBBP7 in regulating cell proliferation and histone H3.3 deposition during mouse preimplantation development.

Preimplantation development is critical for reproductive successes in mammals. Thus, it is important to understand how preimplantation embryogenesis is regulated. As a key event of preimplantation development, epigenetic reprogramming has been widely studied, yet how epigenetic complexes regulate preimplantation development remains largely unknown. Retinoblastoma binding protein 4 (RBBP4) and 7 (RBBP7) are integral components of epigenetic complexes including SIN3A, NuRD, and CoREST. Here, we demonstrate that double knockdown of Rbbp4 and 7, but not individually, causes embryonic lethality during the morula-to-blastocyst transition. Mechanistically, depletion of RBBP4 and 7 results in dysregulation of genes related to cell cycle, lineage development, and regulation of transcription, which is accompanied by cell cycle block, disrupted lineage specification and chromatin structure. Interestingly, RBBP4/7 depletion leads to a dramatic increase in H3.3 and H3K27ac abundance during morula-to-blastocyst transition. ChIP-seq analysis in early embryos and embryonic stem cells reveals enrichment of H3.3 at the promoter regions of RBBP4/7 target genes. In summary, our studies demonstrate the compensatory role of RBBP4/7 and reveal its potential mechanisms in preimplantation development.Summary sentence:RBBP4 and RBBP7 play a compensatory role in regulating cell proliferation, apoptosis, and histone H3.3 deposition during preimplantation development.