Examination of the role of different classes of progesterone receptors in oocyte maturation in zebrafish, Danio rerio
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The overall goal of this thesis was to investigate the involvement of three potential progestin receptors in the oocyte maturation of a single model species, zebrafish. Potential mediators of oocyte maturation in lower vertebrates include the nuclear intracellular progesterone receptor (nPR) and two membrane bound progestin receptors, a seven-transmembrane progestin receptor (mPR) and a single transmembrane progestin receptor (PGRMC1). Inhibitory G-protein involvement was inspected as well as ligand activation, relative binding of various ligands and expression patterns of membrane receptors. Intracellular inhibitory G (Gi)-protein signal pathways were shown to be necessary for the steroid induction of oocyte maturation by injecting competent oocytes with pertussis toxin. Various native and synthetic steroid ligands were investigated for their ability to promote germinal vesicle breakdown (GVBD). Classical nPR antagonists were potent inducers of GVBD. Ligand effectiveness of various steroids in promoting GVBD in vitro was correlated to the steroids' relative binding affinity for recombinant zebrafish mPR[Greek small letter alpha] The expression of PGRMC1 was investigated and shown not to be correlated with any oocyte developmental stage. Gonadotropin in vitro incubation resulted in a modest but insignificant increase in PGRMC1 mRNA expression levels. Furthermore, abrogating PGRMC1 expression with antisense morpholino oligonucleotide injections did not significantly impair gonadotropin induction of oocyte maturational competence. This research supports the involvement of the seven transmembrane mPR receptor in the oocyte maturation of zebrafish. Though the involvement of nPR and PGRMC1 is not supported, some trends in data require further investigation as to potential involvement of PGRMC1 in oocyte function.