Physiological role of the aryl hydrocarbon receptor in mouse ovary development

The aryl hydrocarbon receptor (AhR) regulates the toxicity of environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). As the physiological role of the AhR in the ovary is unknown, the purpose of this study was to test the hypothesis that the AhR regulates the appearance and numbers of ovarian follicles. Ovaries were harvested from AhR- deficient (AhRKO) and wild-type mice on gestational day 18 (GD 18) and postnatal days (PND) 2-3, 8, 32-35, and 53. Complete serial sections of ovaries were evaluated histologically for the presence of germ cells and follicles. On GD 18, there was no difference in the number of germ cells per ovary between AhRKO and wild-type fetuses. However, by PND 2-3, AhRKO mice had significantly more fully formed primordial follicles (AhRKO = 38,440 ± 3632 versus wild-type = 21,120 ± 2688) and fewer single germ cells than wild-type mice (AhRKO = 12,696 ± 1192 vs. wild-type = 18,160 ± 720). On PND 8 and 32-35, there was no difference in the number of follicles between AhRKO and wild-type mice but by PND 53, AhRKO mice had significantly fewer antral follicles than wild-type (AhRKO = 3416 ± 480 vs. wild-type = 6776 ± 1024). Taken together, these results suggest that the AhR may play a role in the formation of primordial follicles and the regulation of antral follicle numbers.