Ultra-structural characteristics of bovine granulosa cells associated with maintenance of oestradiol production in vitro.

We investigated whether the maintenance of oestradiol production by bovine granulosa cells (GC) in vitro was related to GC ultra-structure, and studied the effects of inclusion of serum as a cell attachment factor on oestradiol secretion, cell morphology and ultra-structure. Bovine granulosa cells from medium-sized follicles (4-8 mm diameter), in a serum-free (SF) culture system, maintained oestradiol production for 6 days, whereas oestradiol secretion by cells cultured in serum-coated (SC) wells declined rapidly with time, in culture. SF cells formed clumps consisting of two types of cells. Cells within clumps presented a phenotype similar to GC in vivo, being spherical, tightly joined by extensive gap junctions and interdigitated pseudopodia/microvilli, had abundant rough and smooth endoplasmic reticulum (ER) and mitochondria with trabecular cristae. In contrast, cells cultured in either SC wells or in the flattened base of cell clumps from SF cultures were enlarged, containing less rough ER, had fewer mitochondria (which tended to be round) and contained endosome-like structures, morphological characteristics suggestive of early luteinisation.