LOCALIZATION OF LAMININ PROTEINS DURING EARLY FOLLICULAR DEVELOPMENT IN PIG AND RABBIT OVARIES

Laminin, a major component of the basal lamina, is known to be importa nt in the differentiation of epithelial cells. The outer granulosa cel l layer of ovarian follicles is attached to a basal lamina surrounding the follicle and it has been demonstrated that proteins of the basal lamina can alter the steroidogenic capacity and cytoskeletal compositi on of mature granulosa cells. The present studies were carried out to evaluate the developmental expression of laminin proteins in the basal lamina of ovarian follicles during early stages of granulosa cell dif ferentiation. Ovaries from sexually immature pigs (0-20 weeks of age) and rabbits (0-12 weeks of age) were used for this study because forma tion of primordial follicles and initiation of follicular growth occur partially or completely postnatally. Specific antibodies were made ag ainst laminin beta 1/gamma 1 chains using protein purified by high res olution two-dimensional polyacrylamide gel electrophoresis. These anti bodies were used in immunohistochemical localization studies to demons trate that laminin is associated with the basal lamina surrounding egg clusters and their connections to the ovarian surface epithelium and ovarian rete during early ovarian development. In addition, laminin wa s observed to associate with a continuous matrix that surrounds formin g primordial follicles as they are isolated from the egg clusters. Lam inin is localized in the basal lamina of primordial, primary, secondar y, and tertiary follicles of both pig and rabbit ovaries. Laminin prot eins are not only expressed throughout early follicular development in pigs and rabbits, but are also found surrounding the germ cell compar tments prior to initiation of meiosis and formation of primordial foll icles. These results demonstrate that laminin proteins are deposited i n the basal lamina well before granulosa cells undergo morphological d ifferentiation. This pattern of expression suggests that laminin prote ins alone do not control changes in granulosa cell morphology during e arly development but may be required to maintain cell lineage commitme nt.