<p> In selected locations offshore of urban southern California, male hornyhead turbot <i>(Pleuronichthys verticalis)</i> exhibit elevated plasma concentrations of the female sex steroid, 17&beta;-estradiol (E2). Males sampled from Santa Monica Bay have consistently elevated E2 concentration (>1000 pg/ml), as much as 10 times higher than males from locations offshore of Orange County. Since estrogens, including E2, are at undetectable levels in the ocean discharge of regional WWTPs, it was of interest to determine whether testicular expression of steroidogenic enzymes and other proteins impacting estrogen production may be altered and linked to endogenous E2 production. In this study, proteomics was used to screen for changes in testicular protein expression. In addition, proteomes of fish experimentally treated with E2 were compared to a control. These experiments resulted in the molecular characterization of 30 unique proteins, and provided some insight into potential underlying molecular mechanisms associated with this aberrant E2 phenotype.</p>

<p> The uterus is essential for mammalian reproduction as it provides environment for conceptus implantation and subsequent development. Endometrial glands synthesize and secrete or transport substances critical for conceptus survival and implantation, demonstrated by the fact that female sheep and mice containing no uterine glands are infertile mainly due to impaired implantation and early pregnancy loss. FOXA2, a transcription factor, has been showed indispensable for not only the development of uterine glands in the neonate but also its differentiated function in the adult. The goal of the current study is to (1) generate a mouse model for the conditional overexpression of FOXA2, and to (2) determine the effects of FOXA2 overexpression on uterine morphogenesis and female fertility.</p><p> In this thesis, Chapter 1 will review the early pregnancy of mice and discuss in detail how the early pregnancy events including blastocyst activation, uterine receptivity, apposition, attachment, penetration, stromal cell decidualization are regulated by different factors and signaling pathways. Chapter 1 will also introduce FOXA2 including its finding, structure, functions in organ development and differentiated function, functions in carcinogenesis and the regulation of its expression. Chapter 2, the research chapter, shows that we developed a mouse model which could express FOXA2 continuously only in the cells with expression of Cre recombinase. By applying two different mouse strains with special Cre expression, we found that misexpression of FOXA2 in the neonatal mouse uterus alters or inhibits normal differentiation and genesis of endometrial glands and function of the adult uterus, leading to female infertility. It also suggests that regulatory elements may localize inside the <i>Foxa2</i> coding sequence and can be targeted by some unknown epigenetic mechanism. This chapter has been recently published in a journal: Endocrinology.</p><p>

<p> Environmental pollutants can act as endocrine disruptors to affect the biology of organisms including, development, reproduction, behavior, and overall health. Many endocrine disrupting chemicals (EDCs) can mimic or inhibit functions of sex steroids which are critical for the development and maintenance of vertebrate reproductive systems. Sex steroids also interact with arginine vasotocin (AVT)/arginine vasopressin (AVP; mammalian homologue) systems to mediate vertebrate social and sexual behaviors, including vocalizations in male anurans. I used the Western clawed frog, <i>Xenopus tropicalis, </i> as an amphibian model species to evaluate the effects of exposure to EDCs on AVT-regulated behaviors and on brain AVT and sex steroid signaling systems. </p><p> In order to understand the role of neurohormones and social stimuli in behavior of <i>X. tropicalis,</i> I studied the effect AVT and human chorionic gonadotropin (hCG) administration and the influence of different social contexts on sexual behaviors, including calling, in males. I found that AVT and hCG treatment alone and in combination induces male sexual behavior, and the presence of a female is necessary to stimulate this behavior. I also analyzed the expression of genes related to AVT and sex steroid signaling in the brain of male and female <i>X. tropicalis</i> to identify genes that are expressed sexually dimorphically and could be potentially altered by EDC exposure. </p><p> Then I utilized the behavior and gene expression assays I developed to study the effects of developmental exposure to the synthetic androgen 17&beta;-trenbolone (17&beta;-TB) on behavior, fecundity, morphology, and brain gene expression in adult <i>X. tropicalis.</i> Developmental 17&beta;-TB exposure reduced sexual behavior and inhibited female egg release during breeding trials. Exposure to 17&beta;-TB also blocked oviduct development and altered AVT-related brain gene expression in females. </p><p> In another study I evaluated the effects of adult exposure to the common EDCs bisphenol A (BPA), nonylphenol (NP), and triclosan (TCS) or a mixture of the three on sexual behavior, morphology, and brain gene expression in adult male <i>Xenopus tropicalis.</i> Behavior and brain gene expression were not significantly affected, but TCS-exposed animals had a lower normalized liver weight than animals exposed to BPA or the chemical mixture. Males exposed to BPA, NP, and the mixture also exhibited increased oviduct development compared to TCS-exposed males, and the source of the animals influenced oviduct development. </p><p> Results from my dissertation research demonstrate that exposure to endocrine disruptors can affect multiple levels of physiology. Gender, timing of exposure and nature of the chemical are also critical factors in determining these physiological effects. Importantly, because there is evolutionary conservation in vertebrates for the role of sex hormones in regulating the reproductive system as well as the AVT/AVP system and related social behaviors, my work has important broader implications for endocrine-disrupting effects from environmental chemical exposure for all wildlife and humans.</p>

Nearly 20% of U.S. children are reported to have neurobehavioral deficits in part linked to environmental exposure to industrial chemicals like polychlorinated biphenyls (PCBs). PCB exposure is associated with neurotoxicity including both reduced IQ and response inhibition. PCBs may affect normal brain development by acting on the thyroid hormone (TH) system, either by reducing serum TH levels and/or by interfering with TH receptors (TRs). A critical endpoint, dependent upon sufficient TH, is maturation of oligodendrocytes during development and therefore subject to disruption by PCBs. Due to the complexity of the brain we used both in vitro and in vivo approaches to understand the mechanism of PCBs interfering with TH action. Previous work in our lab has demonstrated that metabolism of PCB congeners is necessary for them to act on the TR in vitro. In neonatal rat livers, we evaluated the TR-agonistic properties of PCBs on TR-dependent gene expression in the presence and absence of metabolism. We found that expression of TH target genes in PCB-exposed livers varied between different congener combinations and was independent of the PCB-induced reduction in circulating T4 levels. Further evaluation of global changes in gene expression between a commercial PCB mixture A1254 and hypothyroidism revealed that only 25% of TH-responsive genes also respond to PCB exposure. Individual congeners accounted for only half of the A1254 effects on TH-regulated genes, suggesting that unidentified congeners or metabolites are affecting TH action. In the neonatal brain, we evaluated the congener-specific effects on a TH- sensitive endpoint during development, the white matter cell numbers in the corpus callosum (CC). In the CC, hypothyroidism decreased oligodendrocytes by about 80%. A1254 achieved a 35% reduction in oligodendrocytes; an effect mediated by a mixture of individual congeners. Hypothyroidism and A1254 exposure increased astrocyte numbers by 30%, but the effect of A1254 seems to be mediated by yet another subset of PCB congeners independent of the TH serum levels. PCB exposure has a differential effect on glial cell differentiation in the CC compared to hypothyroidism that is congener-specific as well as region-specific. Both changes in glia cells during development are not observed in adulthood. The disruption of glia cell ratio in the CC by PCBs could lead to diminished CNS functionality during a critical window of neonatal development.

<p> Population based descriptive studies, clinical trials, and evidence analysis of the literature have identified regular breakfast consumption as opposed to breakfast omission, as a habit independently associated with a more healthy weight. Recent studies have identified differences in insulin sensitivity and satiety hormones between breakfast eating and skipping groups, which help to explain the association between breakfast consumption and weight regulation. Evaluation of fasting insulin sensitivity, behavior, and the postprandial satiety response between breakfast groups were used to further elucidate the physiologic response to skipping breakfast. </p><p> First, through a review of the literature the proposed physiologic response to consuming breakfast as well as omitting breakfast is presented. A connection is made between the satiety hormone response and key components of the breakfast meal, which include composition, caloric load, energy density, volume, and time of day. The review findings suggest that breakfast consumption as opposed to breakfast omission stimulates a physiologic response that may help promote a healthy body weight. </p><p> Chapter 2 examines if self reported habitual breakfast skipping was related to fasting insulin resistance in a sample of 321 adults. Participants completed a questionnaire that focused on eating occurrences throughout the day and were then classified by how frequently they ate breakfast. Breakfast eating was related to fasting insulin and HOMA2-IR, both before and after adjusting for age, sex, BMI, and exercise. These data suggest that fasting insulin resistance is affected by breakfast omission, and supports previous intervention studies that report a decline in postprandial insulin action after breakfast omission. </p><p> Chapter 3 evaluates the relationship between cognitive perception and the satiety hormone response. In a crossover intervention, satiety hormones (insulin and GLP-1), the hunger hormone ghrelin, and subjective ratings of meal satisfaction and eating behavior were compared before and after a low or high fiber breakfast meal. We found that reported perceptions of meal satisfaction, the perception of the breakfast meal, and the behavioral description of cognitive restraint can influence the physiologic regulation of satiety hormones measured in response to meal ingestion. Further evaluation of food consumption habits should consider cognitive perception as it may be important for optimal satiety and influence food intake regulation. </p><p> Lastly, chapter 4 was a cross-sectional study to assess the hormones insulin, leptin, GLP-1, and glucagon following a standard lunch meal in 30 women who were habitual breakfast eaters or habitual skippers. We found clear differences in circulating hormones between breakfast eaters and breakfast skippers even though all participants had similar hormone values at the start of the protocol. Our data further support the idea that regularly eating breakfast promotes changes in the postprandial pattern of satiety hormones.</p>

<p> There are two main patterns of development within animals: direct and indirect. Direct developers are animals such as humans, whose offspring are basically smaller versions of the adult. Indirect developers have a larval stage that can be dramatically different than the adult, and consequently go through a transformation known as metamorphosis. Frogs are a well-known example of vertebrate indirect development, developing first into an aquatic, herbivorous tadpole that later transforms into a terrestrial, carnivorous frog. This transformation is largely regulated by a single hormone&mdash;thyroid hormone (TH). Changes in TH play a vital role in tissue transformations such as, differentiation and growth of the limbs, remodeling of the gut tube and liver, as well as resorption of larval features such as the tail. In addition, the timing of metamorphic changes can differ substantially among species. For instance, the average rate of metamorphosis for a majority of frogs/toads (anurans) is between 3-5 weeks, yet there are a multitude of frogs and toads that take several months or even years to go through this process (Duellman and Trueb, 1994; Gilbert, 2010; Petranka, 2007; Provenzano and Boone, 2009). At the other extreme are frogs that have reduced or even eliminated the free-living larval period such as the Eastern Spadefoot toad, <i>Scaphiopus holbrookii, </i> which has one of the shortest larval periods found in metamorphosing frogs or direct developing frogs, like <i>Eleutherodactylus coqui</i> which have no free-living larval stage. This diversity of developmental patterns sparks many questions about the precise molecular and developmental roles TH has on metamorphosis in frogs. How can a single regulator produce such a wide range of responses, not only between species that differ in metamorphic timing, but also among tissues within a single individual? The vast majority of recent studies that examine tissue specific responses to TH have focused on the genes that code for TH binding proteins or for TH receptors (Hollar et al., 2011; Buchholz et al., 2011). However, a very important aspect is being overlooked in these studies, which is the actual level of the TR proteins themselves. </p><p> There are three distinct mechanisms that regulate tissue responses to TH: deiodinase enzymes, cytosolic thyroid hormone binding proteins (CTHBPs), and thyroid hormone receptors (TRs) (Morvan-Dubois <i>et al.,</i> 2008: Buchholz <i>et al.,</i> 2006). The overall objective of the current study is to develop a technique that will allow protein level analysis of two of the three components implicated in the regulation of tissue specific responses to TH during tadpole metamorphosis: CTHBPs and TRs. I hypothesize that changes in the affinity and/or capacity of thyroid hormone receptors and cytosolic thyroid hormone binding proteins to bind TH throughout metamorphosis underlie the timing and extent of tissue remodeling. In fresh tissue, saturation binding assays suggest a difference in binding capacity among tissues.</p>

<p> Aging is broadly defined as the deterioration of bodily tissues over time. Excluding death due to infectious disease or accidents, aging is what ultimately places finite limits on lifespan and healthspan, the time in which in individual remains active and in good health. Although healthspan and lifespan are intimately linked, it is the extension of human healthspan that is a major goal of gerontological research. Such an achievement would have broad social and economic benefits and importantly would mitigate the dire consequences of the predicted future rise in the prevalence of age-related diseases due to the growing proportion of the population that is of advanced age (65yr and over). A broad understanding of the physiological, metabolic, hormonal, cellular and molecular factors that contribute to aging and lifespan determination will allow for the development of strategies to extend healthspan. </p><p> The work presented herein describes the use of three unique mouse models of extended healthspan and maximum lifespan, including calorie restricted (CR), Snell Dwarf and rapamycin-treated mice, to investigate several factors linked to healthspan and lifespan determination in mammals. These factors include reduced insulin-like growth factor-1 (IGF-1) expression, reduced cell proliferation, reduced protein synthesis and enhanced proteome stability. Using these three models the following conclusions have been drawn: 1) Physiological adaptations to CR previously suggested to confer the healthspan and lifespan benefits of CR in rodents cannot account for the global cell proliferation rate-lowering effect of CR; 2) Fibroblast growth factor 21 (FGF21) is not necessary for the reduction in IGF-1 or the reduction in global cell proliferation rates in response to moderate CR in adult mice; 3) A reduction in global cell proliferation rates is not a consistent predictor of maximum lifespan extension in mice; 4) A reduction in hepatic protein replacement rates is a sensitive and early predictor of maximum lifespan extension in mice and likely reflects a more stable and functional proteome.</p>

<p> Ovulation requires neural circuits in the brain to be sequentially exposed to estradiol and progesterone in the female rat. Estradiol-induced neuroprogesterone is essential for the luteinizing hormone (LH) surge and subsequently, ovulation to occur. The LH surge is regulated by gonadotropin-releasing hormone (GnRH) neurons in the diagonal band of Broca (DBB) which do not express progesterone receptors (PR), but are closely associated with anteroventral periventricular nucleus (AVPV) PR-expressing kisspeptin neurons. I tested the hypothesis that estradiol-induced neuroprogesterone activates AVPV kisspeptin neurons to trigger the LH surge. Inhibiting progesterone synthesis blocked estradiol induction of the LH surge that was rescued by subsequent treatment with either progesterone or DBB kisspeptin infusion. Estradiol treatment triggered a robust LH surge that was blocked by AVPV kisspeptin asODN infusion. These results support the hypothesis that neuroprogesterone induces kisspeptin release from AVPV neurons to activate DBB GnRH neurons and trigger the LH surge.</p>

<p> The neural dimorphisms in the zebra finch present one of the most unique examples of sexual differentiation observed in vertebrates. Although knowledge of these differences has been established for over 45 years, the exact mechanism by which they arise is not known. This dissertation provides additional support for estrogens' involvement in brain development. Specifically, blocking of estrogen receptors with ICI 182,780 decreased neuron soma size of song control regions in both sexes during development. These results are distinctive since previous attempts to block estrogen receptors failed to see the large degree of difference my work displayed. I further supported the role of estrogens in neural brain dimorphisms by decreasing the synthesis of aromatase, an enzyme needed for estradiol production, with the administration of Fadrozole. This successfully decreased neuron soma sizes, neuron number, and nuclear volume in song control regions in males and females, which had not been seen in prior attempts from other laboratories. I have concluded that the route of delivery used in these experiments is likely the largest contributing factor to generating these unique results. I also provide evidence of a potential role for ER alpha by displaying its presence at an early post-hatching age in two auditory processing regions. Taken together, my work provides further support for the role of estrogens in the dimorphic development of the brain, and establishes that it is unlikely that ER alpha contributes to neural dimorphisms in the zebra finch.</p>

Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2009. / Title from PDF t.p. (viewed on Jul 8, 2010). Source: Dissertation Abstracts International, Volume: 70-10, Section: B, page: 5920. Adviser: Gregory E. Demas.