Early ovarian differentiation in the tammar wallaby and the effects of exposure to bisphenol A

Ovarian differentiation in tammar wallabies begins after birth, allowing direct experimental manipulation during the period of differentiation. Using this unique model, we demonstrate that the environmental endocrine-disrupting chemical bisphenol A (BPA) interferes with normal morphological development and gene expression in the developing ovary.

BPA, an environmental endocrine disruptor, is used widely in the manufacturing of various plastics. While BPA can have detrimental effects on fertility and reproductive health, the effects of BPA on early ovarian differentiation in mammals remain unclear. Marsupials have undifferentiated gonads at birth, so this study investigated the gross morphology, protein localisation of FOXL2 and FST and the expression profile of key ovarian differentiating genes FOXL2, WNT4, FST, ESR1 and ESR2 every 2 days from the day of birth to day 10 postpartum (pp) in the marsupial tammar wallaby. A second group of newborn female pouch young were treated with 50 μg/kg of BPA daily from day 0 to day 10 pp, and the morphology and gene expression were examined at day 10 pp. Ovigerous cords in tammar ovaries were first formed between day 2 and day 4 pp. FOXL2 localisation became nuclear by day 4 in pre-granulosa cells. FST was initially in the cytoplasm of pre-granulosa cells at day 2 pp but was then secreted into the extracellular matrix in ovaries by day 10 pp. FOXL2, FST, ESR1 and ESR2 mRNA were upregulated in ovaries around day 2-4 pp, indicating that ovarian differentiation in the tammar begins from day 2 to day 4 pp. Interestingly, BPA treatment from day 0 to day 10 pp blocked the morphological differentiation of the cortex and medulla and ovigerous cord formation and downregulated the expression of FST and FOXL2 at day 10 pp.