P-210 LC3B mediates the decay of maternal mRNAs through autophagy to affect ZGA and early embryonic development

Study question The mechanism of LC3B mediated degradation of maternal mRNAs. Effects of failure of critical maternal mRNAs degradation on ZGA and embryonic development. Summary answer In early embryos, LC3B binds to maternal decay mRNAs and carries them into the lysosome for degradation. What is known already It has been reported that LC3B has RNA binding function and can promote mRNAs degradation in HEK 293T cells. Failure of degradation of maternal mRNAs in early embryos results in failure of ZGA initiation and arrest of embryonic development. Study design, size, duration In this study, the expression of LC3B and the dynamic changes of autophagy activity in early embryos were identified firstly. Subsequently, the mRNAs targeted by LC3B were detected. After knockdown or overexpression of LC3B and activation or inhibition of autophagy in embryos, the expression of maternal mRNAs and ZGA genes as well as embryonic development were examined. Finally, the co-localization of maternal mRNAs, LC3B and lysosome were detected. The study lasted for nearly two years. Participants/materials, setting, methods Female and male ICR mice aged 6-8 weeks were selected for this study. PN5, early 2 cell and late 2 cell embryos were collceted for RIP seq. Control group and LC3B knockdown group, control group and LC3B overexpression group, control group and autophagy activation group, control group and autophagy inhibition group were set up, and late 2 cell embryos were collected for RNA seq. The blastocyst rate was calculated by culture embryos in vitro. Main results and the role of chance In this study, we found that autophagy activity changes dynamically in different stages of early embryos, and autophagy activity as well as the expression of LC3B are higher in late 2 cell embryos. By performing RIP seq in early embryos, we found that LC3B, a key protein of autophagy, can binding to maternal mRNAs and promotes the decay process. Further experiments indicated that autophagy inhibition or LC3B knockdown leads to maternal decay failure and ZGA failure, while autophagy activation or LC3B overexpression promotes maternal decay and ZGA. We found that LC3B mediates the degradation of maternal mRNAs through the autophagy pathway. Limitations, reasons for caution This study needs to further explore whether LC3B mediated maternal mRNAs degradation has other pathways or whether it is synergistic with classical maternal mRNAs degradation pathways. Wider implications of the findings Autophagy activity is decreased in aged embryos. The reason for the decreased developmental potential of aged embryos may be the failure of maternal mRNAs degradation, which leads to the failure of ZGA and the decrease of embryonic developmental potential. Activating autophagy in aged embryos may improve embryonic development. Trial registration number No