Follicle rupture and luteinization during mammalian ovulation are informed by functionally and molecularly distinct regions of the ovarian follicle wall

Ovulation refers to the process when the ovarian surface-facing wall of a preovulatory follicle ruptures and releases the cumulus oocyte complex (COC) into the oviduct or fallopian tube in response to hormonal cues. In parallel, the unruptured wall of the follicle within the ovary transitions to becoming a progesterone-producing corpus luteum. Ovulation is essential for fertilization and eventual pregnancy. Disruption of ovulation, whether purposefully through contraceptive intervention or idiopathically in cases of anovulatory infertility, has translational implications for human health. Importantly, key processes of ovulation, including follicle rupture and luteinization, are recapitulated in models of ex vivo ovulation despite the absence of an intact hypothalamic-pituitary-gonadal axis and intra-ovarian cues. In our study, we used an ex vivo ovulation model to identify functional and molecular differences between distinct regions of the follicle wall, which we refer to as the ruptured and unruptured sides. We observed that the unruptured side of the follicle wall exhibits hallmarks of luteinization after ovulation while the ruptured side exhibits signs of cell death. RNA-sequencing of these specific follicle regions revealed 2,099 differentially expressed genes between follicle sides without hCG exposure and 1,673 between follicle sides 12 hours post-hCG, which were further validated in vivo. We found enriched pathways that recapitulate known ovulation biology, including oxidative stress on the ruptured side and angiogenesis on the unruptured side. We also identified previously unappreciated pathways that may play an important role in ovulation, such as amino acid transport and Jag-Notch signaling on the ruptured side, as well as metal ion processing and IL-11 signaling on the unruptured side. Ultimately our studies demonstrate that our ex vivo model recapitulates known in vivo ovarian biology, identifies pathways that may be novel regulators of ovulation and luteinization, and may have future translational applications for the study of ovulatory disorders and the development of novel non-hormonal contraceptives. Single oocytes and somatic cells from CD-1 mice at various stages of ovarian follicle development were collected. Eight to twelve P6 ovaries were used to obtain all oocytes and somatic cells. In this study we included samples from the the primordial , transitioning from primordial to primary, primary, and secondary stages of follicular development. For the single oocytes, we included 14 primordial stage, 19 transitioning to primary, 20 primary, and 7 secondary replicates. There were a greater number of replicates for somatic cells with 40 primordial, 47 tranisitioning to primary, 56 primary, and 51 secondary being included in our study.Profiling of 54 tissue pieces from cumulus-oocyte complexes. These were extracted from an ex vivo mouse model that involves the isolation and culturing of mouse ovaries in an alginate hydrogel to gain insights into follicle-intrinsic, asymmetric functioning and molecular signaling within distinct regions of the follicle wall.