p300/CBP inhibition promotes apoptosis in mouse embryos by impairing H1K75ac-associated DNA repair during the 4-cell-to-blastocyst transition

Defective pre-implantation embryonic development is a major cause of implantation failure and early embryonic arrest. E1A-associated protein p300 ( p300)/ CREB-binding protein ( CBP ) is known to influence blastocyst formation; however, the molecular mechanisms underlying its role in mouse embryonic development during the 4-cell-to-blastocyst transition remain poorly understood. Here, we show that pharmacological inhibition of p300/CBP markedly reduced morula and blastocyst formation rates, increased embryonic fragmentation, and altered the expression of markers associated with compaction, polarization, and first lineage segregation during the 4-cell-to-blastocyst transition. GO enrichment analysis of the Smart-seq2 data revealed that differentially expressed genes were enriched in biological processes associated with the intrinsic apoptotic signaling pathway in response to DNA damage, cell-cycle regulation, and embryonic development. Consistently, immunofluorescence analyses showed that p300/CBP inhibition promoted DNA damage accumulation, increased apoptosis, and suppressed cell proliferation. Mechanistically, p300/CBP inhibition was associated with reduced histone H1 lysine 75 acetylation (H1K75ac), attenuation of the ataxia telangiectasia mutated (ATM)-associated DNA damage response, impaired DNA repair, DNA damage accumulation, and subsequent p38 MAPK activation. Collectively, these findings support a working model linking these molecular alterations to compromised genome integrity, increased apoptosis, and impaired developmental competence in mouse preimplantation embryos.