Roles of extracellular matrix in follicular development

The cellular biology and changes in the extracellular matrix of ovarian fol licles during their development are reviewed. During growth of the bovine o varian follicle the follicular basal lamina doubles 19 times in surface are a. It changes in composition, having collagen IV alpha 1-26 and laminin alp ha 1, beta 2 and gamma 1 at the primordial stage, and collagen IV alpha 1 a nd alpha 2, reduced amounts of alpha 3-alpha 5, and a higher content of lam inin alpha 1, beta 2 and gamma 1 at the antral stage. In atretic antral fol licles laminin alpha 2 was also detected. The follicular epithelium also ch anges from one laver to many layers during follicular growth. It is clear t hat not all granulosal cells have equal potential to divide, and we have ev idence that the granulosal cells arise from a population of stem cells. Thi s finding has important ramifications and supports the concept that differe nt follicular growth factors can act on different subsets of granulosal cel ls. In antral follicles, the replication of cells occurs in the middle laye rs of the membrana granulosa, with older granulosal cells towards the antru m and towards the basal lamina. The basal cells in the membrana granulosa h ave also been observed to vary in shape between follicles. In smaller antra l follicles, they were either columnar dr rounded,and in follicles > 5 mm t he cells were all rounded. The reasons for these changes in matrix and cell shapes are discussed in relation to follicular development.