Estrogen Receptor 1 (ESR1; ERα), not ESR2 (ERβ), Modulates Estrogen-Induced Sex Reversal in the American Alligator, a Species With Temperature-Dependent Sex Determination

Abstract

All crocodilians and many turtles exhibit temperature-dependent sex determination where the temperature of the incubated egg, during a thermo-sensitive period (TSP), determines the sex of the offspring. Estrogens play a critical role in sex determination in crocodilians and turtles, as it likely does in most nonmammalian vertebrates. Indeed, administration of estrogens during the TSP induces male to female sex reversal at a male-producing temperature (MPT). However, it is not clear how estrogens override the influence of temperature during sex determination in these species. Most vertebrates have 2 forms of nuclear estrogen receptor (ESR): ESR1 (ERα) and ESR2 (ERβ). However, there is no direct evidence concerning which ESR is involved in sex determination, because a specific agonist or antagonist for each ESR has not been tested in nonmammalian species. We identified specific pharmaceutical agonists for each ESR using an in vitro transactivation assay employing American alligator ESR1 and ESR2; these were 4,4',4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT) and 7-bromo-2-(4-hydroxyphenyl)-1,3-benzoxazol-5-ol (WAY 200070), respectively. Alligator eggs were exposed to PPT or WAY 200070 at a MPT just before the TSP, and their sex was examined at the last stage of embryonic development. Estradiol-17β and PPT, but not WAY 200070, induced sex reversal at a MPT. PPT-exposed embryos exposed to the highest dose (5.0 μg/g egg weight) exhibited enlargement and advanced differentiation of the Müllerian duct. These results indicate that ESR1 is likely the principal ESR involved in sex reversal as well as embryonic Müllerian duct survival and growth in American alligators.

Incubation history prior to the canonical thermosensitive period determines sex in the American alligator

“…Expression levels of these transcripts display a clear bimodal distribution in regards to sexual dimorphism and differ between males and females by orders of magnitude. Validation of this molecular sex assessment indicates that there is a 98.7% (213/216) concordance between histology-based sex assignment and that based on expression patterns of sexually dimorphic genes (Kohno et al 2015). RNA isolation, purification, and RT were conducted as previously reported (Kohno et al 2010).…”

Oil Spills and Human Health: Contributions of the Gulf of Mexico Research Initiative

“…The survey sought to evaluate "the role of social networks, risk perception, preparedness measures, individual resilience, and demographics as predictors of preparedness and resilience" for future disasters in the GOM (Lesen et al, 2019, p. 3). GoMRI supported some of the recent research conducted by his lab, including work on the American alligator (e.g., see Kohno et al, 2014, Kohno et al, 2015. McCoy et al (2016) authored a tribute to and a review of the scientific legacy of the late Dr. Louis J. Guillette Jr. and his work as a reproductive biologist.…”

Integrative and comparative reproductive biology: From alligators to xenobiotics

“…This work aided in defining the “E 2 -sensitive period” of induced ovarian differentiation at MPT and explicitly compared mechanistic differences between temperature and estrogenic effects. For example, in A. mississippiensis , E 2 -induced ovaries at MPT exhibited a different mRNA expression pattern than the control ovaries produced at FPT, revealing that temperature and estrogens induce different gonadal mRNA expression patterns in this species (Kohno et al, 2015). …”

“…In ovo experiments provide information regarding the potential roles for ESRs in the sex determination process. For example, in A. mississippiensis , exposure to a selective ESR1 agonist induced ovarian differentiation at MPT whereas exposure to an ESR2 agonist did not (Kohno et al, 2015). …”