Formation of ovarian follicles, germ cells surrounded by a cohort of supporting somatic cells, is critical of later female reproductive health. As a follicle matures, it fosters the production of a viable egg that, after ovulation, is available for fertilization. Follicles can form improperly. When two or more germ cells become enclosed a single follicle this malformation is a multioocytic follicle (MOF). In laboratory experiments, estrogenic treatments of female rodents before follicle assembly increase MOF frequencies. Further, this estrogenic treatment appears to interfere with appropriate activin signaling. Interactions between estrogen and activin signaling modulate follicle assembly processes. Yearling alligators from Lake Apopka, a site extensively contaminated with endocrine disrupting compounds, show elevated MOF frequencies. Here, we investigate ovarian follicle assembly dynamics and activin signaling in hatchling alligators to understand possible causation and characterize mechanism underlying these malformations of alligator ovaries.

Results demonstrated that alligator follicle assembly occurs over many months following hatching. Complete follicles were not observed under laboratory conditions until three months after hatching. This prolonged developmental process putatively results in a larger window of time in which follicle assembly could be disrupted. Gonadal expression levels of some activin signaling factor mRNA are sexually dimorphic. In 13-month old contaminant exposed alligators, we observed diminished or lost sexual dimorphisms in both male and female alligator gonads. Additionally, these sexually dimorphic expressions of these factors are also present in hatchling animal gonads, both before and during the period of follicle assembly in females. Further, contaminant exposure altered mRNA expression levels of some of these factors. In some gene expressions, mRNA expression levels differences between contaminant exposed and reference site animals became more pronounced when ovaries were gonadotrophin challenged. Ovaries in contaminant-exposed animals showed both greater and lesser expression levels of factors vital for female reproductive health when compared to ovaries from reference site alligators. Therefore, these reproductive differences could affect later hypothalamus-pituitary-gonadal signaling dynamics after puberty. Taken together, these studies demonstrate that exposure to contaminants found in Lake Apopka, even before hatching, can have lasting effects on gonadal endocrine activity and may comprise the causation of Lake Apopka alligator ovarian MOFs.