Objective  To study the morphological characteristics of pig ovarian follicles at different developmental stages and possible roles of key genes of phosphoinositide 3-kinase (PI3K) signaling pathway in follicular development.

Method  The morphological changes in follicles of 12-, 30-, 70-day postpartum, 20-month follicular phase, 20-month luteal phase and 48-month luteal phase of landrace×large white sows were observed using HE staining. The expressions of key genes of PI3K pathway in these periods were detected by qRT-PCR. The expression of p-rpS6, a downstream effector, was detected by Western blot assay in porcine ovaries at different stages.

Result  A large number of primordial follicles were observed at the cortical edges of ovaries for 12-day-old pigs, and a small amount of primary follicles and a few secondary follicles were found at the junction of cortex and medulla. The number of secondary follicles increased in 30-day-old pigs. Tertiary follicles appeared in ovaries of 70-day-old pigs. At 20 months of age, a large number of mature follicles and bulked corpus luteum were found at follicular and luteal phases, respectively. It was difficult to observe primary follicles at 48 months of age. For PI3K pathway, the ovarian mRNA expression of inhibitors PTEN, TSC1, TSC2 and activators PDK1, AKT1, mTOR showed the highest levels at 12 days of age, followed by 70 days and 48 months of ages, and the lowest levels at 30 days and 20 months of ages. The downstream effector gene rpS6 of PI3K pathway exhibited the highest level of ovarian mRNA expression at 30 days of age, and the lowest level at 20 and 48 months of ages, while p-rpS6 protein had higher ovarian expression level at 12 days, 20 and 48 months of ages, and no expression at 30 and 70 days of ages.

Conclusion  The key genes of PI3K pathway have different expression levels at different developmental stages of porcine ovary, which indicates that the pathway is involved in the processes of porcine follicular generation and maturation.