CCAAT/enhancer-binding proteins alpha and beta directly regulate ovulation and selectively regulate gene expression in granulosa cells by preovulatory stage- and dose-dependent mechanisms

The preovulatory luteinizing hormone surge orchestrates complex cellular and molecular events leading to ovulation. CCAAT/enhancer-binding proteins alpha and beta are transcription factors acutely induced by the luteinizing hormone surge and crucial for ovulation and granulosa cell luteinization. However, biological processes and their regulatory mechanisms downstream of C/EBPa/b in the preovulatory ovary are not completely understood. To address this knowledge gap, we generated Cebpa/bfl/fl;Pgr-Cre mutants and compared them with Cebpa/bfl/fl;Cyp19a1-Cre mutant female mice. The Cebpa/bfl/fl;Cyp19a1-Cre mutants have undetectable levels of C/EBPa/b throughout preovulatory stages and no ovulation, aligning with previous reports, while Cebpa/bfl/fl;Pgr-Cre mutants presented gradual deletion of C/EBPa/b during late preovulatory stage and reduced ovulation rate. Comparison of these two models indicates that sustained expression of C/EBPa/b throughout preovulatory stages is necessary for successful ovulation. This provides a unique opportunity to interrogate gene regulatory mechanisms by C/EBPa/b during different preovulatory time windows and the impact of dysregulating C/EBPa/b on ovulation-associated biological processes. Our study revealed that C/EBPa/b regulate gene expression and distinct biological functions via preovulatory stage-, dose-, and/or potentially isoform ratio- dependent mechanisms. These findings shed new light on the intricate gene regulation mechanisms by C/EBPa/b downstream of the LH surge.