The meiotic arrest of bovine oocytes

Authors: Mayes, Mario
Advisor: Sirard, Marc-AndréFortier, Michel A.
Abstract: Bovine oocytes incubated in vitro resume meiosis, whereas most of those incubated with theca cell monolayers remain at the germinal vesicle (GV) stage. Experiments were carried out using bovine oocytes to understand the factors involved in the control of oocyte maturation. The objectives were 1) to determine whether or not the morphology of cumulus oocyte complexes (COC) is correlated with the kinetics of meiotic resumption following a period of induced meiotic arrest. 2) To investigate the role of type-specific phosphodiesterase (PDE) inhibitors alone or in conjunction with theca cell monolayers on meiotic arrest of bovine oocytes. 3) To study the role of the protein kinase A and protein kinase C signaling pathways in the control of meiotic resumption of bovine oocytes incubated with granulosa cells, theca cell monolayers or both cell types. 4) To further characterize the inhibitory factor secreted by the theca cell monolayers. These studies show that bovine COCs resume meiosis faster following a short period of induced meiotic arrest than untreated COCs. Atretic or denuded oocytes have fewer oocytes at the GV stage at the onset of maturation compared to healthy or slightly atretic COCs. Type 3 phosphodiesterase (PDE) inhibitors maintained bovine oocytes in meiotic arrest, whereas type 4 PDE inhibitors did not have an effect. Furthermore, PDE inhibitors and the theca cell monolayers show an additive effect. COCs incubated with the theca cell monolayer remained in meiotic arrest, whereas those incubated with granulosa cells resumed meiosis. Untreated granulosa cell abrogate the inhibitory effect of the theca cell monolayers on the maturation of COCs. However, COCs remain in meiotic arrest when cAMP analogs are used in conjunction with both granulosa and theca cells. The inhibitory factor(s) secreted by the theca cell monolayers is (a) not sensitive to heat, proteolytic enzymes and charcoal treatment, (b) sensitive to chloroform treatment, (c) has a Mr less than 1000 daltons and (d) the patterns of chromatographic peaks are different in conditioned medium and fresh medium. Further work is needed to fully isolate and identify the factor produced by the theca cells responsible for maintaining bovine oocytes in meiotic arrest.
Document Type: Thèse de doctorat
Issue Date: 2002
Open Access Date: 11 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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