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A Means to Adapt, a Means to Disrupt: Epigenome-by-Environment Dynamics Underlying Sex Determination and Reproductive Perturbations in the American Alligator

Ben Parrott, Savannah River Ecology Lab & Odum School of Ecology, University of Georgia

24 February 2017

Unlike traditional models for reproductive health, the American alligator is a long-lived apex predator that undergoes temperature-dependent sex determination (TSD). Further, these animals are oviparous and field collected eggs allow for the investigation of environmental effects on developmental processes. Here, we use the alligator as a model to (1) examine the role of DNA methylation patterning during TSD and (2) investigate how exposures to endocrine-disrupting contaminants (EDCs) during this period may alter the epigenetic landscape in a manner that influences subsequent reproductive function. When compared to their counterparts living in relatively pristine environments, alligators undergoing natural exposures to EDCs display a severely abated ovarian transcriptional response to gonadotropin stimulation. Here, we employ reduced-representation bisulfite sequencing to explore the sexually dimorphic DNA methylome in gonads from embryos exposed to either male- or female-promoting temperatures. We identify numerous temperature-dependent methylated regions within the alligator genome. In addition, we use targeted bisulfite sequencing on the Illumina platform to examine how DNA methylation status of the CYP19A1 promoter, a gene displaying sexually dimorphic expression and DNA methylation patterns, varies in field-collected embryos originating from contaminated environments. We find that the robustness of sexually dimorphic CYP19A1 promoter methylation is reduced in embryos originating from a site contaminated with EDCs. We next probe the consequences of developmentally inappropriate Estrogen Receptor activity on subsequent CYP19A1 expression and find that treatment with a selective ESR1 agonist prior to gonadal differentiation results in down regulation of CYP19A1 in stage 27 ovaries. Results presented here suggest that DNA methylation patterning may play an integral role in mediating the effects of incubation temperature on sex determination and that EDCs may exert their effects by compromising sexually dimorphic epigenetic patterns acquired during development.