Dynamics of the membrana granulosa during expansion of the ovarian follicular antrum

As an endocrine organ, the ovary has some unique characteristics. The forma tion, the maturation and the regression of the hormone producing cells real ly determine the timing, the amount and the type of hormone secreted. Here, we focus on the granulosa cells of ovarian follicles which express 17 beta -hydroxysteroid dehydrogenase type 1 and cytochrome P450 aromatase. Follic les only produce estradiol late in follicular development before tither ovu lation or atresia ensues. We discuss the evidence that the membrana granulo sa has many characteristics in common with other epithelia, including that it arises from stem cells, The corollary of this is that individual cells w ithin the membrana granulosa are of different ages or stages of specializat ion. This is evident as regional differences across the membrana granulosa in terms of cell ages, shapes, gene expression, and even behaviour on cell death. We discuss theoretical considerations of the effects of antrum forma tion on the behavior of the membrana granulosa, and show evidence for diffe rences between follicles in cell shapes, basal lamina phenotypes and locati on of younger cells, which we speculate is due to different rates of antrum expansion. Clearly, the membrana granulosa is dynamic, and this could expl ain much about the differences in the behaviors of cells From within the me mbrana granulosa, and between ovarian follicles. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.