Immunoelectron microscopic localization of laminin in rat ovarian follicles.
We studied the immunohistochemical and ultrastructural distribution of laminin in ovaries of immature and mature rats. When sections from 1-8-week-old rat ovaries were labeled directly with conjugates of affinity purified anti-laminin IgG-horseradish peroxidase (HRP), the antibodies bound to all ovarian basement membranes including those surrounding follicles in different stages of maturation. In addition, intracellular labeling was seen in granulosa and theca cells of follicles undergoing rapid development (preantral and antral stages) and in basement membrane-like structures of the Call-Exner bodies. Intracellular laminin was generally not detected, however, in any cells of primordial or atretic follicles. Tissue processed for immunoelectron microscopy 1 hour after the intravenous injection of anti-laminin IgG-HRP showed binding of antibody in linear patterns along endothelial and follicular epithelial basement membranes. Discontinuous strands of laminin-positive, extracellular matrices were also seen between theca cells of all follicles. In addition, injected anti-laminin IgG labeled perisinusoidal basement membranes located within corpora luteae and patches of basement membrane material between granulosa lutein cells. When ovaries were examined 5 d after the intravenous injections of anti-laminin IgG-HRP, uneven or segmented labeling was found in subepithelial basement membranes surrounding developing follicles. Our results therefore indicate that granulosa and theca cells participate directly in basement membrane laminin biosynthesis and suggest that this new laminin is spliced into existing basement membranes during follicular growth.