Distribution patterns of TGF-α, laminin and fibronectin and their relationship with folliculogenesis in rat ovary

Many growth factors are considered to be involved in regulatory functions in the ovary. Specific factors mediate local cell-cell interactions in relation to follicle development. As a result of the complexity of the estrous cycles in experimental models, it is not easy to determine the role of a growth factor such as transforming growth factor alpha (TGF-alpha) in the system. Moreover, little is known about possible interactions of TGF-alpha and laminin and fibronectin in basement membranes during estrous cycles in relation to follicle development. Therefore, the present study was designed to investigate distribution patterns of TGF-alpha, laminin and fibronectin and their possible roles during follicle maturation in normal rat ovary. Ovaries were obtained from 6 adult virgin female rats and fixed in buffered neutral formalin. TGF-alpha, laminin, and fibronectin distribution patterns were evaluated using 5-7-mum-thick serial sections using the immunoperoxidase method. It was found that TGF-alpha was predominantly localised in nuclei of oocytes. Varying amounts of TGF-alpha were found in granulosa cells and interstitial thecal cells which form follicles. In addition, laminin and fibronectin were found predominantly in vascular walls, outer layers of granulosa cells and basement membranes of cuboidal/columnar surface epithelium of rat ovary. Therefore, we suggest that TGF-alpha is involved in follicular maturation. Moreover, because laminin was found to be present in between parenchymal follicle cell layers, we suggest that they were attached to supportive stromal cells by fibronectin. As TGF-alpha is associated with follicles and their relationship with the extracellular matrix, TGF-alpha. may also induce formation of basement membranes which contains laminin and fibronectin components.