CHK1 controls zygote pronuclear envelope breakdown by regulating F-actin through interacting with MICAL3

CHK1 mutations could cause human zygote arrest at the pronuclei stage, a phenomenon that is not well understood at the molecular level. In this study, we conducted experiments where pre-pronuclei from zygotes with CHK1 mutation were transferred into the cytoplasm of normal enucleated fertilized eggs. This approach rescued the zygote arrest caused by the mutation, resulting in the production of a high-quality blastocyst. This suggests that CHK1 dysfunction primarily disrupts crucial biological processes occurring in the cytoplasm. Further investigation reveals that CHK1 mutants have an impact on the F-actin meshwork, leading to disturbances in pronuclear envelope breakdown. Through co-immunoprecipitation and mass spectrometry analysis of around 6000 mouse zygotes, we identified an interaction between CHK1 and MICAL3, a key regulator of F-actin disassembly. The gain-of-function mutants of CHK1 enhance their interaction with MICAL3 and increase MICAL3 enzymatic activity, resulting in excessive depolymerization of F-actin. These findings shed light on the regulatory mechanism behind pronuclear envelope breakdown during the transition from meiosis to the first mitosis in mammals. CHK1 mutations disrupt its closed auto-inhibitory conformation and elevate MICAL3 monooxygenase activity, which in turn dismantles F-actin meshwork of the zygote and impairs pronuclear envelope breakdown (PNEB).Pre-pronuclei transfer to replace the cytoplasm of patient derived zygotes by normal cytoplasm rescues the zygote arrest caused by the CHK1 mutation.F-actin contributes to the regulation of PNEB process in the zygote, while CHK1 mutants disturb the F-actin meshwork in the zygote, leading to disturbances in PNEB.An interaction between CHK1 and MICAL3, a key regulator of F-actin disassembly, is identified in the zygotes.Mutants of CHK1 alter their auto-inhibitory conformation and enhance their interaction with MICAL3 to increase the MICAL3 enzymatic activity, resulting in excessive depolymerization of F-actin. CHK1 mutations disrupt its closed auto-inhibitory conformation and elevate MICAL3 monooxygenase activity, which in turn dismantles F-actin meshwork of the zygote and impairs pronuclear envelope breakdown (PNEB).