Paracrine regulation of the resumption of oocyte meiosis by endothelin-1.
ABSTRACT Mammalian oocytes remain dormant in the diplotene stage of prophase I until the resumption of meiosis characterized by germinal vesicle breakdown (GVBD) following the preovulatory gonadotropin stimulation. Based on genome-wide analysis of peri-ovulatory DNA microarray to identify paracrine hormone-receptor pairs, we found increases in ovarian transcripts for endothelin-1 and endothelin receptor type A (EDNRA) in response to the preovulatory luteinizing hormone (LH)/human chorionic gonadotropin (hCG) stimulation. Immunohistochemical analyses demonstrated localization of EDNRA in granulosa and cumulus cells. In cultured preovulatory follicles, treatment with endothelin-1 promoted oocyte GVBD. The stimulatory effect of endothelin-1 was blocked by cotreatment with antagonists for the type A, but not related type B, receptor. The stimulatory effect of hCG on GVBD was partially blocked by the same antagonist. The endothelin-1 promotion of GVBD was found to be mediated by the MAPK/ERK pathway but not by the inhibitory G protein. Studies using cumulus-oocyte complexes and denuded oocytes demonstrated that the endothelin-1 actions are mediated by cumulus cells. Furthermore, intrabursal administration with endothelin-1 induced oocyte GVBD in preovulatory follicles. Our findings demonstrate a paracrine role of endothelin-1 in the induction of the resumption of meiosis and provide further understanding on the molecular mechanisms underlying the nuclear maturation of oocytes induced by the preovulatory LH surge.
Article: Effect of Droplet Size and Number of Oocytes Examined on Mouse Oocyte Quality in In Vitro Maturation[show abstract] [hide abstract]
ABSTRACT: The number of cumulus—oocyte complexes (COCs) in a droplet is known to affect oocyte maturation rates. In this study, we investigated whether droplet size or the number of COCs examined in in vitro maturation (IVM) affect mouse oocyte maturation, fertilization, or early embryonic development. Moreover, we aimed to determine the optimal, practical culture condition of IVM that could be achieved without changing the culture medium composition. The droplet sizes used were 20, 50, 100, and 200 µl, and the numbers of COCs examined were 1, 5, 10, 20, and 50. The groups with oocyte maturation rates exceeding 75% were treated with in vitro fertilization and in vitro culture. Compared with in vivo-matured oocytes, the 20 COCs/100-µl group did not exhibit significant differences in developmental competence and quality. We also observed progression to blastocysts in the 5-COC group, but the zygotes were likely to form multiple pronuclei. The results indicate: (1) droplet size and numbers of COCs examined in IVM affect oocyte quality; (2) the 20 COCs/100-100-µl condition effectively stimulated maturation in all experiments in this study; and (3) culture of 5 COCs in IVM can also produce blastocysts.Journal of Mammalian Ova Research 06/2011;
[show abstract] [hide abstract]
ABSTRACT: Optimal maturation of oocytes and successful development of preimplantation embryos is essential for reproduction. Mammalian oocytes remain dormant in the diplotene stage of prophase I until the resumption of meiosis characterized by germinal vesicle breakdown (GVBD) following preovulatory gonadotropin stimulation. In response to the preovulatory luteinizing hormone (LH) increase, oocytes undergo GVBD, followed by first polar body extrusion. Although the preovulatory surge of LH is the primary event responsible for the induction of maturation of the oocyte, LH does not act directly on the oocyte due to the absence of functional LH receptors in germ cells. Instead, actions of LH are mediated either by paracrine factors secreted by LH-responsive somatic cells or by the transport of cellular messengers from granulosa/cumulus cells to oocytes through intercellular gap junctions. In addition to the nuclear maturation exemplified by GVBD and extrusion of the first polar body to complete the first meiotic division, oocytes also undergo cytoplasmic maturation characterized by cytoplasmic changes essential for monospermic fertilization, processing of the sperm, and preparation for development to preimplantation embryos. In this review, we summarize our recent works on the identification and characterization of novel LH-inducible ovarian factors for nuclear and cytoplasmic maturation of oocytes.Journal of Mammalian Ova Research 06/2011;