CDK2 Is Required for the DNA Damage Response During Porcine Early Embryonic Development

Cyclin-dependent kinase (CDK) 2 inhibition plays a central role in DNA damage-induced cell cycle arrest and DNA repair. However, whether CDK2 also influences early porcine embryo development is unknown. In this study, we examined whether CDK2 is involved in the regulation of oocyte meiosis and early embryonic development of porcine embryos. We found that disrupting CDK2 activity with RNAi or an inhibitor did not affect meiotic resumption or meiosis II arrest. However, CDK2 inhibitor-treated embryos showed delayed cleavage and ceased development before the blastocyst stage. Disrupting CDK2 activity is able to induce sustained DNA damage, as demonstrated by the formation of distinct gammaH2AX foci in nuclei of Day-3 and Day-5 embryos. Inhibiting CDK2 triggers a DNA damage checkpoint by activation of the ataxia telangiectasia mutated (ATM)-P53-P21 pathway. However, the mRNA expression of genes involved in nonhomologous end joining or homologous recombination pathways for double-strand break repair were reduced after administering CDK2 inhibitor to 5-day-old embryos. Furthermore, CDK2 inhibition caused apoptosis in Day-7 blastocysts. Thus, our results indicate that an ATM-P53-P21 DNA damage checkpoint is intact in the absence of CDK2; however, CDK2 is important for proper repair of the damaged DNA by either directly or indirectly influencing DNA repair-related gene expression.