SNAP23 is required for constitutive and regulated exocytosis in mouse oocytes

Mammalian oocytes are stored in the ovary for prolonged periods, and arrested in meiotic prophase. During this period, their plasma membranes are constantly being recycled by endocytosis and exocytosis. However, the function of this membrane turnover is unknown. Here, we investigated the requirement for exocytosis in the maintenance of meiotic arrest. Using Trim-away, a newly developed method for rapidly and specifically depleting proteins in oocytes, we have identified the SNARE protein, SNAP23, to be required for meiotic arrest. Degradation of SNAP23 causes premature meiotic resumption in follicle-enclosed oocytes. The reduction in SNAP23 is associated with loss of gap junction communication between the oocyte and surrounding follicle cells. Reduction of SNAP23 protein also inhibits regulated exocytosis in response to a Ca2+ stimulus (cortical granule exocytosis), as measured by lectin staining and cleavage of ZP2. Our results show an essential role for SNAP23 in two key processes that occur in mouse oocytes and eggs. Summary Sentence The SNARE protein, SNAP23, is required to maintain gap junction communication between the oocyte and follicle cells that is needed to maintain oocyte meiotic arrest, as well as for cortical granule exocytosis at fertilization.