Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Dr. Deborah MacLatchy

Advisor Role

Supervisor

Abstract

This study investigated ovarian development in Fundulus heteroclitus (mummichog), through molecular characterization of key mediators in the ovarian steroidogenic pathway; these included ovarian StAR (steroidogenic acute regulatory protein), cytochrome P450 enzymes, estrogen receptors (ERα, ERβ1 and ERβ2), and gonadotropin receptors (FSHr and LHr); additionally, hepatic vitellogenin (VTG1) and ERs, and brain P450 aromatase (P450arom; CYP19b) were studied. Fish were staged into cortical alveolus, vitellogenic, early mature, late mature, and ovulating stages of maturation; blood (plasma), ovary (tissue and isolated ovarian follicles per stage), liver, and brains were collected. Testosterone (T), 17β-estradiol (E2) and maturation inducing steroid (MIS), measured from plasma and in vitro ovarian follicle incubations, confirmed that T and E2 production correlate with vitellogenesis and final maturation in mummichog, whereas MIS correlates with only final maturation in mummichog; no E2, as is present in other teleosts, drop prior to maturation was observed. The expression of P450arom (CYP19a1), ERα, StAR, P450 side-chain cleavage, and hepatic VTG1, determined by qPCR methods, were associated with patterns of E2 in maturing mummichog, but did not follow patterns exhibited in other teleosts. CYP17 expression was not associated with E2 patterns in mummichog, or other teleosts. To determine EE2 (17α-ethinyl estradiol) effects during maturation, follicles grouped per stage were exposed to 50 - 250 nM of EE2 in vitro for 24 hours; there was no effect on P450arom or LHr expression, or on T or MIS production. The tolerance exhibited by mummichog to exogenous estrogens in vitro could be partially attributable to continuously high levels of E2 present in the maturing ovary, as EE2 during follicular incubations had no effect on presumed E2-responsive genes.

Convocation Year

2018

Convocation Season

Spring

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