CRL4 is required in activated oocytes for follicle maintenance and ovulation

In mammals, oocytes within the primordial follicles require a number of essential factors tomaintain their survival. However, the survival factors for activated oocytes have been poorly characterized. Recently we reported that damaged DNA binding protein-1 (DDB1), the linker subunit of the cullin ring-finger ubiquitin E3 ligase-4 (CRL4) complex, and its substrate adaptor,DDB1-CUL4 associated factor-1 (DCAF1), were essential for primordial follicle maintenance. In this study we specifically deleted these in the oocytes of growing follicles, to investigate if DDB1 and DCAF1 were also survival factors for activated oocytes. In the ovaries of Ddb1;Zp3-Cre mice, the primordial follicle pool was intact, but awakened oocytes and growing follicles beyond the primary stage were rapidly depleted. In the ovaries of Dcaf1;Pten;Gdf9-Cre and Ddb1;Pten;Gdf9-Cre mice, global primordial follicle activation was stimulated by enhanced PI3K signaling, but the awakened oocytes were rapidly lost due to no CRL4 activity. These mouse models provided original evidence that CRL4 was essential for maintaining oocyte survival, not only those in dormancy at the primordial follicle stage, but also naturally awakened oocytes and those awakened by hyperactivation of PI3K signaling. Interestingly, the oocyte-specificDdb1orDcaf1 knockoutmice had ovulation defects even before oocyte exhaustion. CRL4withinoocyteswas required for cumulus expansion andovulation-related somatic geneexpression in acell non-autonomousmanner. Granulosa cells that surrounded these Ddb1 or Dcaf1-deleted oocytes exhibited increased rates of apoptosis and showed poor responses to ovulation signals. These results suggested that CRL4 in oocytes also regulated granulosa cell functions in a cell non-autonomous manner.