Immunohistochemical localization of testin in the female reproductive system of the rat is consistent with its involvement in the turnover of specialized junctional complexes.

The distribution of testin in the female reproductive system of rats throughout the estrous cycle was examined immunohistochemically. In ovarian follicles, immunostainable testin was localized at the junctions between adjacent granulosa cells. During follicular development, immunostainable testin surrounding the granulosa cells increased in every follicle but was reduced drastically when the follicle was undergoing atresia. Testin was also found in the junctions between adjacent germinal epithelial cells that covered the surface of the ovary, at the lower or the lower lateral borders of each cell. In the uterus and oviduct, immunostainable testin was detected only in the luminal and glandular epithelium, where it formed a polygonal network encircling the apical border of the epithelial cells. During the estrous cycle, there was no drastic change in the distribution of testin in the epithelial cells of the ovary. In the vaginal mucosa, testin was found to be localized only at the junction of the epithelial cells on the surface layer of the stratified epithelium; at different stages of the estrous cycle, distinctive staining for testin could be found at proestrus, metestrus, and diestrus, but not at estrus. It is postulated that testin is a cell junction-associated protein in the female reproductive system.