Expression and localization of activin receptors, Smads, and βglycan to the postnatal rat ovary

Despite understanding the molecular basis of activin/TGFbeta and bone morphogenetic protein (BMP) signaling, this study is the first to characterize multiple, sequential elements of these pathways in the ovary concurrently. The expression of activin/BMP receptor, Smad, and betaglycan mRNAs by postnatal rat ovaries were investigated by real-time PCR. Activin/BMP receptors (ActRIA, ActRIB, ActRIIA., and ActRIIB), betaglycan, and Smad 1-8 mRNAs were expressed by the ovary. Activin receptor and Smad 1, 2, 4, 5, and 7 mRNAs declined up to 4-fold between postnatal d 4-8, coinciding with secondary follicle formation. The emergence of antral follicles (postnatal d 12) saw ActRIA, ActRIIB, and Smad 2 mRNA expression return to d 4 levels, whereas ActRIB, ActRIIA, and Smads 1, 4, 5, and 7 remained at lower levels. betaglycan mRNA levels increased 2-fold between d 8 and 12, suggesting expression by the developing theca. Smad 3, 6, and 8 mRNAs were unchanged. Activin receptor and Smad proteins were present in oocytes at all stages of follicular development; granulosa cells of primary-antral follicles, and theca cells. betaglycan protein was present in oocytes, granulosa cells, and theca cells at all stages of folliculogenesis. The colocalization of receptors and Smads supports the notion that activin/TGFbeta and BMP signaling pathways are functional in the cellular compartments of the follicle.