Galligan Thomas M, Hale Matthew D, McCoy Jessica A, Bermudez Dieldrich S, Guillette Louis J, Parrott Benjamin B
Medical University of South Carolina, Hollings Marine Laboratory, 331 Fort Johnson Road, Charleston, SC 29412, USA; Virginia Polytechnic Institute and State University, College of Natural Resources and the Environment, Department of Fish and Wildlife Conservation, 101 Cheatham Hall, 310 West Campus Drive, Blacksburg, VA 24060, USA.
Medical University of South Carolina, Hollings Marine Laboratory, 331 Fort Johnson Road, Charleston, SC 29412, USA; University of Georgia, Savannah River Ecology Laboratory, PO Drawer E, Aiken, SC 29802, USA; University of Georgia, Eugene P. Odum School of Ecology, 140 E. Green Street, Athens, GA 30602.
Gen Comp Endocrinol. 2019 Jan 15;271:61-72. doi: 10.1016/j.ygcen.2018.11.002. Epub 2018 Nov 5.
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. Previous studies suggest these alterations arise during development and raise the possibility that exposure to maternally deposited contaminants might underlie persistent organizational changes in both thyroidal and reproductive function. Thus, this population provides a system to investigate contaminant-mediated organizational thyroid disruption in an environmentally-relevant context. We assess the developmental expression of genetic pathways involved in thyroid hormone biosynthesis and find that expression of these genes increases prior to hatching. Further, we show that nuclear steroid hormone receptors are also expressed during this period, indicating the developing thyroid is potentially responsive to steroid hormone signaling. We then explore functional roles of steroid signaling during development on subsequent thyroid function in juvenile alligators. We exposed alligator eggs collected from both Lake Apopka and a reference site to 17β-estradiol and a non-aromatizable androgen during embryonic development, and investigated effects of exposure on hatchling morphometrics and thyroidal gene expression profiles at 5 months of age. Steroid hormone treatment did not impact the timing of hatching or hatchling size. Furthermore, treatment with steroid hormones did not result in detectable impacts on thyroid transcriptional programs, suggesting that precocious or excess estrogen and androgen exposure does not influence immediate or long-term thyroidal physiology.
甲状腺对类固醇激素信号敏感，许多干扰甲状腺的污染物也会破坏类固醇激素稳态，这表明甲状腺功能紊乱可能通过改变类固醇激素信号传导而发生。为了研究这种可能性，我们研究了胚胎期性类固醇暴露对美国短吻鳄甲状腺生理的短期和长期影响。来自受内分泌干扰污染物污染的湖泊（美国佛罗里达州阿波普卡湖）的短吻鳄已被证明表现出甲状腺和类固醇激素紊乱的特征。先前的研究表明，这些改变在发育过程中出现，并增加了母体沉积污染物的暴露可能是甲状腺和生殖功能持续组织变化的基础的可能性。因此，这个种群提供了一个系统，用于在与环境相关的背景下研究污染物介导的组织性甲状腺功能紊乱。我们评估了参与甲状腺激素生物合成的基因途径的发育表达，发现这些基因的表达在孵化前增加。此外，我们表明在此期间核类固醇激素受体也有表达，这表明发育中的甲状腺可能对类固醇激素信号有反应。然后，我们探讨了发育过程中类固醇信号对幼年短吻鳄后续甲状腺功能的功能作用。我们在胚胎发育期间将从阿波普卡湖和一个参考地点收集的短吻鳄卵暴露于17β-雌二醇和一种不可芳香化的雄激素，并研究了暴露对5个月大的幼鳄孵化形态和甲状腺基因表达谱的影响。类固醇激素处理不影响孵化时间或幼鳄大小。此外，类固醇激素处理未对甲状腺转录程序产生可检测到的影响，这表明早熟或过量的雌激素和雄激素暴露不会影响即时或长期的甲状腺生理。
