Date of Award
1995
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
The overall objective of this study was to investigate the role in vitro of epidermal growth factor (EGF) in the regulation of both nuclear and cytoplasmic maturation of the porcine oocyte, and in the expansion of cumulus cells.;Studies aimed at the induction of oocyte maturation and cumulus expansion revealed that EGF is a potent stimulant of the resumption of meiosis in the oocyte and that the addition of FSH, but not LH, to EGF further enhances its effect on germinal vesicle breakdown (GVBD). Both estradiol-17{dollar}\beta{dollar} (E{dollar}\sb2{dollar}) and androstenedione (A{dollar}\sb4{dollar}) inhibited FSH-stimulated GVBD, but had no effect on EGF-stimulated GVBD, suggesting that EGF may be acting through a different mechanism than that of FSH. EGF stimulated cumulus expansion in about 50% of oocyte-cumulus cell complexes (OCC), however FSH was much more effective and induced expansion in {dollar}\sim{dollar}90% of the complexes.;The removal of the oocyte did not impair the ability of porcine cumulus cells to expand in response to EGF, indicating that EGF-induced expansion of porcine cumuli oophori is not dependent on the oocyte. However, the denuded porcine oocytes enabled mouse cumulus cells, which do not undergo expansion in the absence of the oocyte, to expand in response to FSH, indicating that the porcine oocyte is capable of secreting the putative cumulus expansion-enabling factor required for mouse cumulus cell expansion and that this factor is not species specific.;Reverse transcription-polymerase chain reaction (RT-PCR) and immunolocalization studies revealed local follicular production of EGF and the presence of its receptor in the ovarian follicle. From the relative abundance of the mRNAs and immunoreactive peptides, it appeared that, within the follicle, the oocyte is the primary, although not necessarily the exclusive source of EGF, and the somatic cells that of EGF-R, suggesting that an EGF paracrine system may be in place in the porcine ovarian follicle.;Both EGF and FSH influenced cytoplasmic maturation of porcine oocytes as revealed by the success of fertilization and by the changes in the pattern of protein synthesis. Fertilization studies indicated that the effect of EGF is beneficial when added alone to the oocyte maturation media, whereas FSH appeared to influence cytoplasmic maturation adversely. Addition of EGF alone decreased the proportion of polyspermic oocytes and increased the percentage of monospermic oocytes forming male pronuclei, whereas FSH abolished these effects of EGF and increased the percentage of polyspermic oocytes forming more than two pronuclei. Both EGF and FSH altered the synthesis of certain proteins in the oocyte and cumulus cells after different culture periods.;RT-PCR and immunocytochemistry indicated the presence of TGF-{dollar}\alpha{dollar} in the cumulus and granulosa cells. Since EGF was also localized in porcine cumulus and granulosa cells, the presence of two ligands which trigger a similar signal transduction cascade after binding to the EGF-R may indicate ligand redundancy.;In conclusion, evidence is provided that EGF of follicular origin may play a vital role in bringing a complete physiological maturation to the porcine oocyte, including expansion of the surrounding cumulus cells. (Abstract shortened by UMI.)
Recommended Citation
Singh, Balwant, "Epidermal Growth Factor Regulation Of Porcine Oocyte Maturation And Cumulus Cell Expansion In Vitro" (1995). Digitized Theses. 2575.
https://ir.lib.uwo.ca/digitizedtheses/2575