Assessing impacts of precocious steroid exposure on thyroid physiology and gene expression patterns in the American alligator (Alligator mississippiensis).

The thyroid gland is sensitive to steroid hormone signaling, and many thyroid disrupting contaminants also disrupt steroid hormone homeostasis, presenting the possibility that thyroid disruption may occur through altered steroid hormone signaling. To examine this possibility, we studied short-term and persistent impacts of embryonic sex steroid exposure on thyroid physiology in the American alligator. Alligators from a lake contaminated with endocrine disrupting contaminants (Lake Apopka, FL, USA) have been shown to display characteristics of thyroid and steroid hormone disruption.

Modelling defined mixtures of environmental oestrogens found in domestic animal and sewage treatment effluents using an in vitro oestrogen-mediated transcriptional activation assay (T47D-KBluc).

There is growing concern of exposure of fish, wildlife and humans to water sources contaminated with oestrogens and the potential impact on reproductive health. Environmental oestrogens can come from various sources including concentrated animal feedlot operations (CAFO), municipal waste, agricultural and industrial effluents. US EPA's drinking water contaminant candidate list 3 (CCL3) includes several oestrogenic compounds.

Sex steroid and thyroid hormone receptor expressions in the thyroid of the American alligator (Alligator mississippiensis) during different life stages.

The expression of estrogen receptors, ESR1 (ERα) and ESR2 (ERβ), and androgen receptors (AR) in the thyroid gland has been reported in few vertebrate species other than a few mammals. This study reports the presence of sex steroid hormone receptors and thyroid receptors (ERα, ERβ, AR, TRα, and TRβ) in the thyroid gland of the American alligator at several life stages. It provides a semiquantification and distribution of ERα in the thyroid follicle cells using an immunohistochemical approach as well as reports quantitative differences in mRNA expression of ERα, ERβ, TRα, TRβ, and AR in the same tissue using quantitative real time-PCR (Q-PCR) with primers designed specifically for alligators.

Modeling the interaction of binary and ternary mixtures of estradiol with bisphenol A and bisphenol AF in an in vitro estrogen-mediated transcriptional activation assay (T47D-KBluc).

Exposure to xenoestrogens occurs against a backdrop to physiological levels of endogenous estrogens. Endogenous estrogen levels vary from low levels in early childhood to high levels during pregnancy and in young women. However, few studies have addressed how xenoestrogens interact with endogenous estrogens.

Gene expression patterns in juvenile American alligators (Alligator mississippiensis) exposed to environmental contaminants.

Reproductive and developmental abnormalities have been reported in the American alligator (Alligator mississippiensis) population from Lake Apopka, FL, that is chronically exposed to a complex mixture of environmental contaminants. To begin to understand the molecular mechanisms that could lead to the observed abnormalities of the reproductive and endocrine system, we quantified concentrations of the steroid hormones testosterone (T) and estradiol-17beta (E(2)) and expression of steroid hormone receptors and genes relating to steroidogenesis in gonadal tissue from juvenile alligators from three lakes in Florida using enzyme immunoassay and quantitative real-time polymerase chain reaction. Alterations of ESR2 (estrogen receptor beta) and SF1 (steroidogenic factor 1) mRNA expression in male gonadal tissue, without an observed difference in plasma concentrations of T, from the different lakes, begin to provide insight into potential mechanisms underlying the alterations of the reproductive system previously observed.

Characterization of Inhibitor of Growth 2 tumor suppressor in Alligator mississippiensis, its conservation in Archosauria, and response to thyroid stimulating hormone.

Inhibitor of growth 2 (ING2) belongs to a family of tumor suppressors that are important regulators of a wide range of cellular processes including proliferation, apoptosis, and DNA repair. ING family members are found in yeast, plants, invertebrates and many vertebrate species. However, to date, ING has not been characterized in reptiles.

Isolation of the alligator (Alligator mississippiensis) thyroid hormone receptor alpha and beta transcripts and their responsiveness to thyroid stimulating hormone.

Thyroid hormones (THs) play key regulatory roles in growth, development and metabolism in vertebrates. Modulation of the cellular hormonal response is largely through the activity of two nuclear TH receptors, TRalpha and TRbeta, which act as transcription factors and alter gene expression programs. Little information is available regarding their structure and regulation in reptiles.

Altered neonatal development and endocrine function in Alligator mississippiensis associated with a contaminated environment.

Reduced reproductive success, altered reproductive tract development, and differences in circulating hormones have been documented in American alligators (Alligator mississippiensis) from Lake Apopka, FL, compared to less contaminated sites, such as the Lake Woodruff National Wildlife Refuge, FL. Comparative studies among alligators of varying size and age suggest that in ovo contaminant-induced alterations of endocrine function are further modified during postembryonic development and/or through environmental exposure. In the present study, we examined developmental and endocrine-related indices in neonatal (age, <1 mo) alligators from Lake Apopka in comparison to those of a reference population (Lake Woodruff), thereby limiting contaminant exposure to that derived via maternal contribution.

Contaminant-induced feminization and demasculinization of nonmammalian vertebrate males in aquatic environments.

Many chemicals introduced into the environment by humans adversely affect embryonic development and the functioning of the male reproductive system. It has been hypothesized that these developmental alterations are due to the endocrine-disruptive effects of various environmental contaminants. The endocrine system exhibits an organizational effect on the developing embryo.

Seasonal variation in plasma thyroxine concentrations in juvenile alligators (Alligators mississippiensis) from three Florida Lakes.

Circulating concentrations of thyroxine (T(4)) vary seasonally in many vertebrates. This study examined the seasonal variation in plasma concentrations of T(4) in juvenile American alligators (Alligator mississippiensis) from three populations in central Florida, USA. One site, Lake Woodruff National Wildlife Refuge, is considered a reference site whereas the other two lakes, Lake Apopka and Orange Lake, are significantly impacted by human activity.

Variation in sex steroids and phallus size in juvenile American alligators (Alligator mississippiensis) collected from 3 sites within the Kissimmee-Everglades drainage in Florida (USA).

This 3-year study was designed to examine variation in plasma sex steroids, phallus size, and the standard error (S.E.) associated with these endpoints in juvenile alligators collected from 3 sites within the Kissimmee-Everglades drainage (Florida, USA) with varying concentrations of sediment organochlorine contaminants.

Abnormal bone composition in female juvenile American alligators from a pesticide-polluted lake (Lake Apopka, Florida).

Reproductive disorders have been found in pesticide-exposed alligators living in Lake Apopka, Florida (USA). These disorders have been hypothesized to be caused by exposure to endocrine- disruptive estrogen-like contaminants. The aim of this study was to expand our analysis beyond previous studies by investigating whether bone tissue, known to be affected by sex steroid hormones, is a potential target of endocrine disruptors.

Molecular cloning of the estrogen and progesterone receptors of the American alligator.

Steroid hormones perform many essential roles in vertebrates during embryonic development, reproduction, growth, water balance, and responses to stress. The estrogens are essential for normal reproductive activity in female and male vertebrates and appear to have direct actions during sex determination in some vertebrates. To begin to understand the molecular mechanisms of estrogen action in alligators, we have isolated cDNAs encoding the estrogen receptors (ER) from the ovary.

Altered histology of the thymus and spleen in contaminant-exposed juvenile American alligators.

Morphological differences in spleen and thymus are closely related to functional immune differences. Hormonal regulation of the immune system has been demonstrated in reptilian splenic and thymic tissue. Spleens and thymus were obtained from juvenile alligators at two reference sites in Florida, USA: Orange Lake and a National Wildlife Refuge, Lake Woodruff, as well as from a contaminated lake, Lake Apopka.

Temporal and spatial variation in plasma thyroxine (T4) concentrations in juvenile alligators collected from Lake Okeechobee and the northern Everglades, Florida, USA.

We examined variation in plasma thyroxine (T4) in juvenile American alligators (Alligator mississippiensis) collected from three sites within the Kissimmee River drainage basin (FL, USA). Based on historical sediment data, Moonshine Bay served as the low contaminant exposure site, Water Conservation Area 3A served as an intermediate contaminant exposure site, and Belle Glade served as the high contaminate exposure site. In May 1999, alligators (n = 22) from Water Conservation Area 3A exhibited higher T4 concentrations than animals from both Belle Glade (n = 22; p = 0.