Transforming growth factor-beta isoform expression during bovine ovarian antral follicle development

Abstract

Transforming growth factor-beta (TGF-β) isoforms are important paracrine and autocrine signaling molecules for the regulation of ovarian follicle growth and physiology. Effective communication between the epithelial granulosa cells, the mesenchymal theca cells, and the oocyte is vital for ovarian function and reproductive success. The expression, localization, and regulation of TGF-β isoforms in the developing bovine follicle was examined using both immunohistochemistry and quantitative reverse transcription-polymerase chain reaction (RT-PCR) procedures. TGF-β1 protein was found to be present in the granulosa cells of early pre-antral, early antral, and 12 mm follicles. Interestingly, there was no visible staining of granulosa cells of 3-5 or 5-10 mm follicles. There was also no TGF-β1 staining of theca cells. TGF-β2 and TGF-β3 staining were present in the granulosa and theca cells of all follicle stages examined. The levels of TGF-β mRNA expression in granulosa and theca cells from antral follicles was measured using quantitative RT-PCR. For each isoform mRNA expression levels did not change in different sized antral follicles. TGF-β3 mRNA levels were much higher than those of TGF-β1 and TGF-β2 in both granulosa and theca. Expression levels were higher in theca than in granulosa for TGF-β2 and TGF-β3. FSH was found to decrease TGF-β1 mRNA expression in granulosa cells, but had no effect on TGF-β2 and TGF-β3. Bovine ovarian follicles were found to have a unique pattern of TGF-β isoform expression and regulation when compared to other species (i.e., rodent, pig, quail, and human). The similarities and differences between the various species is discussed to help elucidate common functions of TGF-β in the ovary. In summary, observations demonstrate that as antral follicles develop, TGF-β3 is the most abundant TGF-β isoform and TGF-β1 protein levels decline in large follicles. Granulosa cell TGF-β1 expression was decreased by FSH and this correlated with reduced levels in large antral follicles. TGF-βs involved in antral follicular growth and development appear to act as paracrine/autocrine signaling molecules having a species-specific pattern of expression. © 2003 Wiley-Liss, Inc.