Granulosa Cells Promote Differentiation of Cortical Stromal Cells into Theca Cells in the Bovine Ovary

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Formation of a theca cell (TC) layer is an important physiological event occurring during early follicular development. Nevertheless, little is known concerning the nature and regulation of the formation of the TC layer during follicular growth. Using an established co-culture system in this study, we examined the hypothesis that stromal cells differentiate into theca cells during early follicular development and that this process involves interaction with granulosa cells (GC). Ovarian stromal cells from the bovine ovarian cortex (SC) and medulla (SM) were cultured with or without GC from small antral follicles. The presence of GC increased the number of lipid droplets and mitochondria, and stimulated androstenedione production in SC and SM. However, luteinizing hormone/choriogonadotropin receptor (LHCGR) mRNA abundance and hCG-induced cAMP and androstenedione production were increased in SC but not in SM by the presence of GC. The present results indicate that GC are involved in the functional differentiation of and the acquisition of LH responsiveness in stromal cells of the ovarian cortex. We suggest that GC-SC interaction is important in the formation of the TC layer during early follicular development, although the nature of this interaction remains to be determined.