Changes in Localization of Type I, III and IV Collagens and Their mRNA Expression During Follicular Atresia in Bovine and Porcine Ovaries.

Determination of the expression level and localization of extracellular matrix (ECM) components is crucial for understanding the mechanism of maintenance and remodeling of the ovarian follicle structure. Previously, we demonstrated species-specific differences in the process of apoptosis in granulosa and theca cells during follicular atresia. In the present study, we histochemically compared the localization of type I, III and IV collagens and the expression of their mRNA. In healthy porcine or bovine follicles, type III and IV collagens were mainly distributed in theca interna layers, and strong to moderate expression of their mRNAs were observed in granulosa and theca interna layers, respectively. During follicular atresia, marked decreases in type I and IV collagens were observed in porcine follicles, while no changes were seen in bovine follicles. These findings indicate that these ECMs have important roles in follicular development and/or degeneration, and that species-specific differences in their production reflect differences in the regulatory mechanism of granulosa cell apoptosis between atretic porcine and bovine follicles.