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

Abstract

Transforming growth factor-beta (TGF-beta) 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-beta isoforms in the developing bovine follicle was examined using both immunohistochemistry and quantitative reverse transcription-polymerase chain reaction (RT-PCR) procedures. TGF-beta1 protein was found to be present in the granulosa cells of early pre-antral, early antral, and 1-2 mm follicles. Interestingly, there was no visible staining of granulosa cells of 3-5 or 5-10 mm follicles. There was also no TGF-beta1 staining of theca cells. TGF-beta2 and TGF-beta3 staining were present in the granulosa and theca cells of all follicle stages examined. The levels of TGF-beta 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-beta3 mRNA levels were much higher than those of TGF-beta1 and TGF-beta2 in both granulosa and theca. Expression levels were higher in theca than in granulosa for TGF-beta2 and TGF-beta3. FSH was found to decrease TGF-beta1 mRNA expression in granulosa cells, but had no effect on TGF-beta2 and TGF-beta3. Bovine ovarian follicles were found to have a unique pattern of TGF-beta 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-beta in the ovary. In summary, observations demonstrate that as antral follicles develop, TGF-beta3 is the most abundant TGF-beta isoform and TGF-beta1 protein levels decline in large follicles. Granulosa cell TGF-beta1 expression was decreased by FSH and this correlated with reduced levels in large antral follicles. TGF-betas involved in antral follicular growth and development appear to act as paracrine/autocrine signaling molecules having a species-specific pattern of expression.

Transforming growth factor-β1 inhibits luteinization and promotes apoptosis in bovine granulosa cells

“…Conversely, TGFB1 inhibited granulosa cell secretion of E 2 and P 4 from pigs and ruminants (Chang et al 1996, Wandji et al 1996, Ford & Howard 1997, Juengel et al 2004, Ouellette et al 2005, Zheng et al 2008. In the bovine species, TGFB1 expression was observed in granulosa cells of small but not of large antral follicles (Nilsson et al 2003). In agreement with this finding, a previous study showed a negative relationship between follicular fluid TGFB1 and E 2 concentrations and between TGFB1 levels and follicle size (Ouellette et al 2005).…”

“…The bovine ovarian cycle is characterized by the recruitment of waves of small follicles, which proceed to grow until a poorly understood selection process designates a dominant follicle to continue development, while the remaining recruited follicles undergo atresia (Ireland 1987, Fortune et al 2001. TGFB1 is expressed in the granulosa cells of bovine small antral follicles (Nilsson et al 2003) A recent study has suggested that TGFB1 increases atresia in primary and preantral follicles (Rosairo et al 2008). Given the pro-apoptotic properties of TGFB1 that we have observed in cultured bovine granulosa cells, it seems reasonable to speculate that its relative abundance in a given small follicle may be a determinant if it will undergo atresia (i.e.…”

“…One possible way to achieve this effect could be down-regulation of TGFB1 action. Indeed, some studies provide evidence that FSH treatment decreases TGFB1 and TGFBR1 (activin receptor-like kinase 5) mRNA expressions in cultured bovine granulosa cells (Nilsson et al 2003, Jayawardana et al 2006. Further studies, including experiments involving manipulation of TGFB1 activity in vivo and in vitro, will be required explore these possibilities.…”

Role of transforming growth factor-β1 in gene expression and activity of estradiol and progesterone-generating enzymes in FSH-stimulated bovine granulosa cells

“…TGFB1, which is the most extensively studied factor of this family, is present in granulosa and theca cells and in the vascular system of the ovary in many species (Nilsson et al 2003, Juengel & McNatty 2005, and has been shown to either stimulate or inhibit E 2 and P 4 synthesis. For instance, TGFB1 stimulated E 2 and P 4 secretion from rodent granulosa cells (Zachow et al 1999, Knight & Glister 2006, whereas TGFB1 inhibited granulosa cell secretion of E 2 and P 4 from pigs and ruminants (Chang et al 1996, Wandji & Fortune 1996, Ford & Howard 1997, Juengel et al 2004, Ouellette et al 2005.…”

The local regulation of folliculogenesis by members of the transforming growth factor superfamily and its relevance for advanced breeding programmes

“…In cattle, TGFB1, 2 and 3 were all detected in oocytes, granulosa and theca cells, with TGFB3 being the most strongly expressed (Nilsson et al, 2003). TGFB1 has also been detected in oocytes of goat preantral follicles (Rodrigues et al, 2014).…”