The Effect of Slit homolog 2 (SLIT2) on Populations of Preantral Follicles in Cultured Cortical Tissue from Pig Ovaries

SLIT guidance ligands are secreted glycoproteins involved in organogenesis. SLIT proteins and their receptor have been linked to ovarian development in fetal sheep and luteal function in adult humans. In pigs, SLIT proteins have been associated with age at puberty (GWAS) and as a major node in genomic pathway analysis for total number of piglets born. It is hypothesized that SLIT affects formation or growth of preantral follicles in the porcine ovary. The objective was to determine the number of preantral follicles in cortical tissue from porcine ovaries cultured in vitro and treated with SLIT2. Ovaries were collected from 4 gilts at 50 d of age, and were dissected into 1 mm cubes. Some cortical tissue was immediately fixed (Day 0) and the remaining tissue was cultured (medium 199, 37^oC, 5% CO₂) for 24 h (Day 1) in the presence of 0, 5, or 500 ng of SLIT2. Ovarian cortical tissue was then collected into fixative and embedded in paraffin. Three sections (minimum of 6 μm apart) were collected and stained (hematoxylin/Eosin). The number of primordial (3.9 ± 4.6), primary (0.8 ± 1.6), and secondary (1.4 ± 1.8) follicles were quantified in each section. Follicle populations were quantified in a total of 106 sections. There were more (P < 0.05) primordial and secondary follicles on Day 0 compared with Day 1, but the number of primary follicles did not differ with Day. At Day 1, there were more (P < 0.05) primordial follicles in tissue treated with 500 ng of SLIT2 than in tissue from the 0 and 5 ng treatments, which were not different from each other. There was no effect of SLIT2 on the number of primary follicles at Day 1, but the number of secondary follicles were greater (P < 0.05) in ovarian tissue treated with 5 ng SLIT2 than in tissue from 0 or 500 ng SLIT2, which did not differ from each other. The reduction in follicles after 24 h of culture may indicate follicle activation followed by atresia. The greater number of follicles in ovarian cortical tissue treated with SLIT2 may indicate a rescue from this atresia. USDA is an equal opportunity provider and employer.