Sexual maturation and sex differentiation comprise facets of a common theme: reproduction. The endocrine system regulates many of the critical physiological processes necessary for reproduction and offers a framework within which technologies can be developed for controlling sexual maturation and sex differentiation. The studies described in this thesis were undertaken to improve the understanding of the endocrine control of these critical stages of development in salmonids. Final ovarian maturation in salmon is accompanied by dynamic changes in plasma hormone levels. Ovulation can be accelerated through the use of hormones such as gonadotropin releasing hormone or its analogs (GnRHa). The effectiveness of GnRHa often depends on the timing of treatment. To determine if plasma concentrations of steroids can be used to predict the sensitivity of adult female coho salmon (Oncorhynchus kisutch) to GnRHa, circulating levels of testosterone, 17α,20β-dihydroxyprogesterone (DHP), and estradiol were measured before and after injection with GnRHa to accelerate ovulation. We found that high levels of testosterone were predictive of early response of coho salmon to GnRHa treatment. The correlation between testosterone and ovulatory response to GnRHa suggested a possible functional relation. However. implantation or injection of testosterone. 17α-methyltestosterone (MT), or the antiandrogen, cyproterone acetate (CA), before or with GnRHa treatment did not affect the ovulatory response of coho or chinook salmon ( 0. tshawytscha) to GnRHa. Chinook salmon treated with MT alone had accelerated ovulation in comparison to controls. If steroids are involved in sex differentiation. steroids must be produced early in development. In vitro production of steroids in both coho salmon and rainbow trout (0. mykiss) was assessed from hatch through sex differentiation. Cortisol, androstenedione, testosterone, and estradiol were produced just after hatching by tissue explants that contained anterior kidneys and gonads of coho salmon. To circumvent the problem of not knowing the sex of individuals until after sex differentiation, single-sex populations of rainbow trout were produced by gynogenesis or androgenesis. Tissue explants produced more androstenedione than testosterone or estradiol. More androgens were produced by testes and more estradiol was produced by ovaries within 6 to 10 weeks of hatching. Dietary treatment with estradiol or MT inhibited gonadal steroid secretion. Electrophoresis of gonadal homogenates from salmonids revealed several sex-specific bands. In particular, a prominent band of about 50,000 daltons was apparent in ovaries but not testes. Production of sex-specific proteins may be affected by dietary steroid treatment. / Graduation date: 1991

Many reptiles, including the red-eared slider turtle (Trachemys scripta elegans), exhibit temperature-dependent sex determination (TSD). Temperature determines sex during a temperature sensitive period (TSP), when gonadal sex is labile to both temperature and hormones -- particularly estrogen. Estrogen production is a key step in ovarian differentiation for many vertebrates, including TSD reptiles, and temperaturebased differences in aromatase expression during the TSP may be a critical step in ovarian determination. Steroidogenic factor-1 (Sf1) is a key gene in vertebrate sex determination and regulates steroidogenic enzymes, including aromatase. The biological actions of steroid hormones are mediated by their receptors, defined here as the classic transcriptional regulation of target genes. To elucidate the mechanism of estrogen action estrogen during sex determination, I examined aromatase, Sf1, ER[alpha], ER[beta], and AR expression in slider turtle gonads before, during and after the TSP, as well as following sex reversal via temperature or steroid hormone manipulation by administering exogenous estradiol (E2) or aromatase inhibitor (AI) to the eggshell. Sf1 is expressed at higher levels during testis development and following maleproducing temperature shift and AI treatment, while aromatase increases during ovary determination and feminizing temperature shift and E2 treatment. My results do not lend support to a role for Sf1 in the regulation of aromatase expression during slider turtle sex determination, but do support a critical role for estrogen in ovarian development. Estrogen receptor [alpha] and AR levels spike at the female-producing temperature just as aromatase levels are increasing during ovarian sex determination, while ER[beta] remains constant and only increases late in ovarian differentiation -- well after estrogen levels have increased, indicating that ER[alpha] and ER[beta] may have distinct roles in slider turtle ovarian development. Estrogen receptor [alpha] and ER[beta] are expressed along developing sex cords in the absence of estrogen (AI treatment). When shifted to female-producing temperatures, embryos maintain medullary ER[alpha] and AR expression while ER[beta] is reduced. By contrast, ER[alpha] and ER[beta] redirect to the cortex in E2-created ovaries. Warmer temperature and E2 result in the same endpoint (ovarian development), but may entail different steroid signaling patterns between temperature- and estrogen-induced feminization. / text