Date of Award

January 2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Turk Rhen

Abstract

Neural control of the endocrine system originates in the hypothalamus in all vertebrates. The hypothalamus signals directly to the pituitary gland to maintain homeostasis by releasing hormones directly into the bloodstream. Hormones travel to peripheral endocrine organs, and regulate widespread activities including growth, metabolism, stress response, circadian rhythms, water balance, and reproduction. Many of these functions have sex-specific aspects, and therefore sexual dimorphism in morphology and function of the hypothalamus is present. Sex-specific genetic background and morphology is established during pre- and peri-natal development, during which sexually dimorphic cellular differentiation occurs and hormonal profiles are set. Disruption of development can therefore have widespread sex-specific effects. A thorough understanding of underlying molecular regulation of sex-specific development is therefore important for understanding disease and dysfunction. Here, we present four studies investigating the sex-specific development of the hypothalamus and pituitary gland in the common snapping turtle, a species with temperature-dependent sex determination. First, we tracked morphological development of the pituitary gland from its origin early in embryogenesis through hatching. Development is a highly conserved process between vertebrate species. Next, we analyzed sex differences in gene expression within the hypothalamus and pituitary gland in embryonic and hatchling turtles. We specifically analyze expression of genes involved in reproductive neuroendocrine function, and also use RNA-seq to identify all differentially expressed genes between sexes and development to further understanding of the underlying mechanisms of development and function. We identified overrepresented functional categories of the differentially expressed gene sets between sexes, and identify protein modification as a potential mechanism underlying sexual dimorphism. Last, we analyzed changes in neuroendocrine gene expression following embryonic exposure to the widely used herbicide atrazine, an endocrine disrupting chemical. Our results indicate an acute, embryonic exposure to atrazine can have persistent changes in expression of genes involved in stress response and reproduction in both the hypothalamus and pituitary gland. This dissertation adds to the body of literature on comparative neuroendocrine development, provides background information for numerous future experiments, and identifies the snapping turtle as another species with potential impacts from atrazine exposure.

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