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A Follicle Rupture Assay Reveals an Essential Role for Follicular Adrenergic Signaling in Drosophila Ovulation.

ABSTRACT: Ovulation is essential for the propagation of the species and involves a proteolytic degradation of the follicle wall for the release of the fertilizable oocyte. However, the precise mechanisms for regulating these proteolytic events are largely unknown. Work from our lab and others have shown that there are several parallels between Drosophila and mammalian ovulation at both the cellular and molecular levels. During ovulation in Drosophila, posterior follicle cells surrounding a mature oocyte are selectively degraded and the residual follicle cells remain in the ovary to form a corpus luteum after follicle rupture. Like in mammals, this rupturing process also depends on matrix metalloproteinase 2 (Mmp2) activity localized at the posterior end of mature follicles, where oocytes exit. In the present study, we show that Mmp2 activity is regulated by the octopaminergic signaling in mature follicle cells. Exogenous octopamine (OA; equivalent to norepinephrine, NE) is sufficient to induce follicle rupture when isolated mature follicles are cultured ex vivo, in the absence of the oviduct or ovarian muscle sheath. Knocking down the alpha-like adrenergic receptor Oamb (Octoampine receptor in mushroom bodies) in mature follicle cells prevents OA-induced follicle rupture ex vivo and ovulation in vivo. We also show that follicular OA-Oamb signaling induces Mmp2 enzymatic activation but not Mmp2 protein expression, likely via intracellular Ca2+ as the second messenger. Our work develops a novel ex vivo follicle rupture assay and demonstrates the role for follicular adrenergic signaling in Mmp2 activation and ovulation in Drosophila, which is likely conserved in other species.

SUBMITTER: Deady LD

PROVIDER: S-EPMC4608792 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description: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.

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A Follicle Rupture Assay Reveals an Essential Role for Follicular Adrenergic Signaling in Drosophila Ovulation.

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