SMAD2/3 signaling regulates initiation of mouse Wolffian ducts and proximal differentiation in Müllerian ducts.

Male and female reproductive tracts develop from anterior intermediate mesoderm with similar differentiation processes. The anterior intermediate mesoderm develops into the mesonephros, and the Wolffian duct initiates by epithelialization in the mesonephros. The Müllerian duct invaginates from the coelomic epithelium of the cranial mesonephros for ductal formation and is then regionalized into proximal to caudal female reproductive tracts.

Multiple lines of evidence for identifying potential hazards to fish from contaminants of emerging concern in Great Lakes tributaries.

Contaminants of emerging concern (CECs; e.g., pharmaceuticals, flame retardants, pesticides, and industrial chemicals) are omnipresent throughout tributaries to the Great Lakes.

Can Xenobiotics Alter the Sex Ratio of Crocodilians in the Wild?

All crocodilians exhibit temperature-dependent sex determination without sex chromosomes. This temperature dependency can be overridden by exposure to estrogen via estrogen receptor 1. Thus, the sex ratio of crocodilian species is vulnerable to estrogenic xenobiotics.

N-terminal domain regulates steroid activation of elephant shark glucocorticoid and mineralocorticoid receptors.

Orthologs of human glucocorticoid receptor (GR) and human mineralocorticoid receptor (MR) first appear in cartilaginous fishes. Subsequently, the MR and GR diverged to respond to different steroids: the MR to aldosterone and the GR to cortisol and corticosterone. We report that cortisol, corticosterone and aldosterone activate full-length elephant shark GR, and progesterone, which activates elephant shark MR, does not activate elephant shark GR.

Estrogen-induced ovarian development is time-limited during the temperature-dependent sex determination of the American alligator.

Many reptiles, including the American alligator, exhibit temperature-dependent sex determination (TSD), whose thermo-sensitive period for the female alligator begins at stages-15 and ends at stage-24. Estrogen signaling plays a central role in TSD, which can be overridden by an estrogen-exposure during the thermo-sensitive period. As some environmental contaminants are estrogenic, there is growing concern about their effects on the sex ratio and reproductive health of TSD-species.

Stress responses in the chemistry and mRNA abundance of the peripheral blood in the American alligator.

To monitor physiological and toxicological conditions in an endangered species, noninvasive to minimally invasive sampling methods are needed. We analyzed peripheral blood cells to determine if we could monitor some physiological responses of the American alligator following capture stress. Juvenile American alligators were restrained for 16 h to examine the stress response in plasma and blood cells.

Oil dispersant Corexit 9500 is weakly estrogenic, but does not skew the sex ratio in Alligator mississippiensis.

During the Deepwater Horizon oil spill, vast quantities of a chemical dispersant Corexit 9500 were applied in remediation efforts. In addition to the acute toxicity, it is essential to evaluate Corexit further with a broader scope of long-term sublethal endocrine endpoints. The American alligator (Alligator mississippiensis) is an excellent organism for such an endeavor.

Estrone exposure interacts with temperature to alter predator evasion performance and systemic mRNA abundances.

Environmental estrogens from anthropogenic activities are ubiquitous in aquatic ecosystems. Ambient temperature in these systems also fluctuates in daily, seasonal, and long-term rhythms. While both factors have been studied extensively, their interaction on aquatic life is critical to understand.

Transcriptional activation of elephant shark mineralocorticoid receptor by corticosteroids, progesterone, and spironolactone.

The mineralocorticoid receptor (MR) is a nuclear receptor and part of a large and diverse family of transcription factors that also includes receptors for glucocorticoids, progesterone, androgens, and estrogens. The corticosteroid aldosterone is the physiological activator of the MR in humans and other terrestrial vertebrates; however, its activator is not known in cartilaginous fish, the oldest group of extant jawed vertebrates. Here, we analyzed the ability of corticosteroids and progesterone to activate the full-length MR from the elephant shark ().

Land Use Contributions to Adverse Biological Effects in a Complex Agricultural and Urban Watershed: A Case Study of the Maumee River.

Agricultural and urban contaminants are an environmental concern because runoff may contaminate aquatic ecosystems, resulting in stress for exposed fish. The objective of the present controlled, field-based study was to assess the impacts of high-intensity agriculture and urban land use on multiple life stages of the fathead minnow (Pimephales promelas), using the Maumee River (Toledo, OH, USA) as a case study. Laboratory cultured adult and larval fathead minnows were exposed for 21 d, and embryos were exposed until hatching to site-specific water along the lower reach of the Maumee River.

In utero effects of maternal phthalate exposure on male genital development.

Background: Phthalates are used extensively in commercial and personal care products and maternal exposure is ubiquitous. Phthalates are anti-androgenic, but the potential effects of phthalates on male penile development have not been assessed in utero.

Objective: The study aims to investigate the association between early pregnancy phthalate exposure and fetal penile development, overall and by race.

Functional distinctions associated with the diversity of sex steroid hormone receptors ESR and AR.

Sex steroid hormones including estrogens and androgens play fundamental roles in regulating reproductive activities and they act through estrogen and androgen receptors (ESR and AR). These steroid receptors have evolved from a common ancestor in association with several gene duplications. In most vertebrates, this has resulted in two ESR subtypes (ESR1 and ESR2) and one AR, whereas in teleost fish there are at least three ESRs (ESR1, ESR2a and ESR2b) and two ARs (ARα and ARβ) due to a lineage-specific whole genome duplication.

Divergent responsiveness of two isoforms of the estrogen receptor to mixtures of contaminants of emerging concern in four vertebrates.

Contaminants of emerging concern (CECs) are ubiquitous in aquatic environments with well-established endocrine-disrupting effects. A data matrix of 559 water samples was queried to identify two commonly occurring CECs mixtures in Great Lakes tributaries. One mixture consisted of eight agricultural CECs (AG), while another contained 11 urban CECs (UB).

Feminizing effects of exposure to Corexit-enhanced water-accommodated fraction of crude oil in vitro on sex determination in Alligator mississippiensis.

Deepwater Horizon spilled over 200 million gallons of oil into the waters of the Gulf of Mexico in 2010. In an effort to contain the spill, chemical dispersants were applied to minimize the amount of oil reaching coastal shorelines. However, the biological impacts of chemically-dispersed oil are not well characterized, and there is a particular lack of knowledge concerning sublethal long-term effects of exposure.

Improved genome assembly of American alligator genome reveals conserved architecture of estrogen signaling.

The American alligator, , like all crocodilians, has temperature-dependent sex determination, in which the sex of an embryo is determined by the incubation temperature of the egg during a critical period of development. The lack of genetic differences between male and female alligators leaves open the question of how the genes responsible for sex determination and differentiation are regulated. Insight into this question comes from the fact that exposing an embryo incubated at male-producing temperature to estrogen causes it to develop ovaries.

Evolution of corticosteroid specificity for human, chicken, alligator and frog glucocorticoid receptors.

We investigated the evolution of the response of human, chicken, alligator and frog glucocorticoid receptors (GRs) to dexamethasone, cortisol, cortisone, corticosterone, 11-deoxycorticosterone, 11-deoxycortisol and aldosterone. We find significant differences among these vertebrates in the transcriptional activation of their full length GRs by these steroids, indicating that there were changes in the specificity of the GR for steroids during the evolution of terrestrial vertebrates. To begin to study the role of interactions between different domains on the GR in steroid sensitivity and specificity for terrestrial GRs, we investigated transcriptional activation of truncated GRs containing their hinge domain and ligand binding domain (LBD) fused to a GAL4 DNA binding domain (GAL4-DBD).

Toxic effects of chemical dispersant Corexit 9500 on water flea Daphnia magna.

In 2010, approximately 2.1 million gallons of chemical dispersants, mainly Corexit 9500, were applied in the Gulf of Mexico to prevent the oil slick from reaching shorelines and to accelerate biodegradation of oil during the Deepwater Horizon oil spill. Recent studies have revealed toxic effects of Corexit 9500 on marine microzooplankton that play important roles in food chains in marine ecosystems.

Molecular cloning and characterization of the aryl hydrocarbon receptors and aryl hydrocarbon receptor nuclear translocators in the American alligator.

Aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, binds to a variety of chemical compounds including various environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin. This receptor regulates expression of target genes through dimerization with the AHR nuclear translocator (ARNT). Since AHR-ARNT signaling pathways differ among species, characterization of AHR and ARNT is important to assess the effects of environmental contamination and for understanding the molecular mechanism underlying the intrinsic function.

Characterization of evolutionary trend in squamate estrogen receptor sensitivity.

Steroid hormones are a key regulator of reproductive biology in vertebrates, and are largely regulated via nuclear receptor families. Estrogen signaling is regulated by two estrogen receptor (ER) subtypes alpha and beta in the nucleus. In order to understand the role of estrogen in vertebrates, these ER from various species have been isolated and were functionally analyzed using luciferase reporter gene assays.

Integrative and comparative reproductive biology: From alligators to xenobiotics.

Dr. Louis J. Guillette Jr.

In ovo treatment with an estrogen receptor alpha selective agonist causes precocious development of the female reproductive tract of the American alligator (Alligator mississippiensis).

The molecular signaling processes involved the differentiation of the Müllerian duct (MD) into the female reproductive tract, or oviduct, in non-mammalian vertebrates are not well understood. Studies in mammals and birds indicate that steroid hormones play a role in this process, as the embryonic MD has been shown to be vulnerable to exogenous estrogens and progestins and environmental endocrine disrupting contaminants. In a previous study, developmental treatment with an estrogen receptor α (ERα) agonist, 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT), induced significant enlargement of the MD in alligator embryos incubated at a male-producing temperature, which was not observed in embryos treated with an estrogen receptor β (ERβ) agonist, 7-bromo-2-(4-hydroxyphenyl)-1,3-benzoxazol-5-ol (WAY 200070), or with 17β-estradiol (E).

TRPV4 associates environmental temperature and sex determination in the American alligator.

Temperature-dependent sex determination (TSD), commonly found among reptiles, is a sex determination mode in which the incubation temperature during a critical temperature sensitive period (TSP) determines sexual fate of the individual rather than the individual's genotypic background. In the American alligator (Alligator mississippiensis), eggs incubated during the TSP at 33 °C (male producing temperature: MPT) yields male offspring, whereas incubation temperatures below 30 °C (female producing temperature: FPT) lead to female offspring. However, many of the details of the underlying molecular mechanism remains elusive, and the molecular link between environmental temperature and sex determination pathway is yet to be elucidated.

Identification and Characterization of the Androgen Receptor From the American Alligator, Alligator mississippiensis.

Androgens are essential for the development, reproduction, and health throughout the life span of vertebrates, particularly during the initiation and maintenance of male sexual characteristics. Androgen signaling is mediated by the androgen receptor (AR), a member of the steroid nuclear receptor superfamily. Mounting evidence suggests that environmental factors, such as exogenous hormones or contaminants that mimic hormones, can disrupt endocrine signaling and function.