The regulation of oocyte maturation and ovulation in the closest sister group of vertebrates

Abstract

Ascidians are the closest living relatives of vertebrates, and their study is important for understanding the evolutionary processes of oocyte maturation and ovulation. In this study, we first examined the ovulation of Ciona intestinalis Type A by monitoring follicle rupture in vitro, identifying a novel mechanism of neuropeptidergic regulation of oocyte maturation and ovulation. Ciona vasopressin family peptide (CiVP) directly upregulated the phosphorylation of extracellular signal–regulated kinase (CiErk1/2) via its receptor. CiVP ultimately activated a maturation-promoting factor, leading to oocyte maturation via germinal vesicle breakdown. CiErk1/2 also induced expression of matrix metalloproteinase (CiMMP2/9/13) in the oocyte, resulting in collagen degradation in the outer follicular cell layer and liberation of fertile oocytes from the ovary. This is the first demonstration of essential pathways regulating oocyte maturation and ovulation in ascidians and will facilitate investigations of the evolutionary process of peptidergic regulation of oocyte maturation and ovulation throughout the phylum Chordata.

Cionin, A Vertebrate Cholecystokinin/Gastrin Homolog, Induces Ovulation in the Ascidian Ciona Intestinalis Type A.

“…A 300-ng aliquot of DNasetreated total RNA was used for rst-strand cDNA synthesis. Real-time PCR was performed using a CFX96 Touch Real-Time PCR Detection System (Bio-Rad Laboratories, Inc., Hercules, CA) as previously described 19,29 . The primers used for real-time PCR analyses are listed in Table 1.…”

Comparative and Evolutionary Physiology of Vasopressin/ Oxytocin-Type Neuropeptide Signaling in Invertebrates

“…CiVpr is expressed by oocytes and investigation of the mechanisms of CiVP action indicates that it causes CiVpr-mediated upregulation of the phosphorylation of extracellular signal-regulated kinase (CiErk1/2) and activation of a maturation-promoting factor, leading to oocyte maturation via germinal vesicle breakdown. Activated CiErk1/2 also induces oocyte expression of a matrix metalloproteinase (CiMMP2/9/13) and it is hypothesized that secretion of this enzyme causes digestion of collagens in the outer follicular cell layer, leading to the rupture of the follicular layer and ovulation (120).…”

“…Evidence that VP/OT-type neuropeptides regulate reproductive processes and behaviors is a prevalent finding, consistent with the roles of OT, and to a lesser extent VP, in vertebrates. Perhaps most notable are the actions of annetocin in inducing egg-laying related behaviors in annelids (105,109), evidence that nematocin signaling is required for normal male mating behavior in the nematode C. elegans (42) and the recent discovery that VP/OT-type signaling regulates oocyte maturation and ovulation in the urochordate C. intestinalis (120). Furthermore, the discovery that VP/OT-type signaling acts differentially to control male and female reproductive systems in the mollusc L. stagnalis illustrates how an ancient signaling system has been adapted to regulate reproduction in the context of hermaphroditism (37, 38).…”

Fractionation of Ovarian Follicles and in vitro Oocyte Maturation and Ovulation Assay of Ciona intestinalis Type A

“…Note: Immature/pre-ovulatory follicles can be isolated from the 150-μm or 90-μm fraction of stage IV-removed samples, when follicles are used for maturation and ovulation (see Figure 2B in Matsubara et al, 2019). 6.…”

“…Repeat Steps B3-B5 and collect developmental-stage follicles of interest. Note: Representative images of entire developmental stages of fractionated follicles (including stages I-IV) are shown inFigure 2AinMatsubara et al (2019).…”