The presence of GH receptors along with increased cumulus expansion and embryos progressing to the 9-16 cell stage supports the hypothesis that r-hGH may be involved in oocyte maturation.
The developmental competence of in vitro-matured (IVM) rhesus macaque cumulus oocyte complexes (COCs) is deficient compared with in vivo-matured (IVM) oocytes. To improve oocyte quality and subsequent embryo development following IVM, culture conditions must be optimized. A series of experiments was undertaken to determine the role of epidermal growth factor (EGF) during IVM of rhesus macaque COCs. The addition of Tyrphostin AG-1478 (a selective inhibitor of the EGF receptor EGFR) to the IVM medium yielded fewer oocytes maturing to metaphase II of meiosis II (MII), decreased cumulus expansion, and a lower percentage of embryos that developed to the blastocyst stage compared with untreated IVM controls, indicating that EGFR activation is important for IVM maturation in the rhesus macaque. However, the addition of recombinant human EGF (r-hEGF) to the IVM medium did not enhance outcome. The expression of mRNAs encoding the EGF-like factors amphiregulin, epiregulin, and betacellulin in cumulus cells indicates that these factors produced by cumulus cells may be responsible for maximal EGFR activation during oocyte maturation, precluding any further effect of exogenous r-hEGF. Additionally, these results illustrate the potential futility of exogenous supplementation of IVM medium without prior knowledge of pathway activity.
Growth hormone (GH) in rhesus macaque in vitro oocyte maturation (IVM) has been shown to increase cumulus expansion and development of embryos to the 9-16 cell stage in response to 100 ng/ml recombinant human GH (r-hGH) supplementation during IVM. Although developmental endpoints for metaphase II (MII) oocytes and embryos are limited in the macaque, gene expression analysis can provide a mechanism to explore GH action on IVM. In addition, gene expression analysis may allow molecular events associated with improved cytoplasmic maturation to be detected. In this study, gene expression of specific mRNAs in MII oocytes and cumulus cells that have or have not been exposed to r-hGH during IVM was compared. In addition, mRNA expression was compared between in vitro and in vivo-matured MII oocytes and germinal vesicle (GV)-stage oocytes. Only two of 17 genes, insulin-like growth factor 2 (IGF2) and steroidogenic acute regulator (STAR), showed increased mRNA expression in MII oocytes from the 100 ng/ml rhGH treatment group compared with other IVM treatment groups, implicating insulin-like growth factor (IGF) and steroidogenesis pathways in the oocyte response to GH. The importance of IGF2 is notable, as expression of IGF1 was not detected in macaque GV-stage or MII oocytes or cumulus cells.
Study Objective
To compare cumulus cell structure and timing of oocyte maturation of in vitro and in vivo matured nonhuman primate oocytes.
Design
In vivo (VVM) and in vitro (IVM) maturation of oocytes.
Setting
Animal cell culture laboratory.
Animal(s)
48 female rhesus macaques.
Interventions
15 females were administered FSH and aspirated oocytes were cultured in vitro for 0, 3, 6, 12 or 24 hours (IVM). 33 females were administered FSH and hCG and oocytes were collected 3, 6, 12, or 28–30 hours following hCG (VVM).
Main Outcome Measures
Nuclear maturation and microtubule scores of oocytes and actin and tubulin transzonal processes of cumulus cells. Embryo development was observed for VVM oocytes.
Results
The rate of nuclear maturation was faster for IVM oocytes compared to VVM oocytes. Actin transzonal processes decreased 0 to 12 hours post hCG for VVM oocytes. Tubulin transzonal processes of IVM and VVM oocytes decreased from 0 to 24 hours and 0 to 3 hours respectively. Embryo development improved as VVM time increased.
Conclusions
Nuclear maturation and remodeling of cumulus oocyte complex structural components associated with IVM do not parallel that of oocyte maturation in vivo, indicating that in vitro culture conditions continue to be sub-optimal.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.