Transcriptional control of genes mediating ovarian follicular growth, differentiation, and steroidogenesis in pigs

The pig is an agriculturally important species, so understanding its follicular dynamics and the transcriptional events that accompany such changes is critical to optimizing reproductive outcomes. Numerous small- to medium-size antral follicles are recruited and continue growth under the influence of gonadotropins and growth factors during the follicular phase of the porcine estrous cycle. Several of these follicles are selected to mature into large preovulatory follicles whose granulosa cells acquire luteinizing hormone (LH) receptors. Healthy preovulatory follicles that have not been exposed to the LH surge are estrogenic, expressing the genes, and proteins needed for estradiol synthesis. Exposure to the LH surge, however, causes a dramatic decline in their estrogen production and a transient decrease in mRNAs for genes encoding the steroidogenic machinery, followed by a considerable rise in the expression of genes directing progesterone biosynthesis. This review provides a general overview of pig follicular development and the transcriptional regulation of genes critical to this process in the pig ovary, including those for gonadotropin receptors and steroidogenesis. Where data are lacking, related information from other species has been included, with the caveat that similar regulation has yet to be demonstrated for the pig.