Anti-Müllerian Hormone Regulation by the Bone Morphogenetic Proteins in the Sheep Ovary: Deciphering a Direct Regulatory Pathway

Abstract

In the ovary, anti-Müllerian hormone (AMH) is produced by the granulosa cells of growing follicles and can modulate the recruitment of primordial follicles and the FSH-dependent development of follicles. However, the regulation of its production remains poorly understood. Recently, a stimulating effect of the bone morphogenetic proteins (BMPs) on AMH production by granulosa cells has been shown in vitro, but the molecular mechanisms implicated in this regulation and its physiological importance in ovarian function have not yet been established. In the hyperprolific Booroola ewes carrying the FecB(B) partial loss-of-function mutation in the fecundity gene encoding the FecB/BMP receptor, type 1B, the granulosa cells of antral follicles expressed and secreted low AMH amounts, resulting in low AMH concentrations in blood, despite high numbers of AMH-secreting follicles in ovaries. The presence of the FecB(B) mutation impaired the granulosa cell response to the stimulating action of BMP4 on AMH production, indicating a crucial role of the BMP receptor, type 1B in AMH regulation. In ovine granulosa cells, BMP4 enhanced the transcriptional activity of the human AMH promoter, and this action depended on the presence of SMAD1, acting on a promoter sequence located between -423 and -202 bp upstream of the AMH transcription start site. SMAD1 and SF1 acted in concert to mediate BMP4 action on the AMH promoter. Among the 2 SF1 binding sites present on the AMH promoter, the most proximal site, located at -92 bp upstream of the AMH transcription start site, was found to be critical for ensuring the response of the AMH promoter to BMP4. In conclusion, AMH could mediate the actions of BMPs in regulating follicular development and contributing to the determination of ovulation numbers. A molecular model of regulation of the AMH promoter transactivation by BMP signaling is proposed.

Flow cytometric analysis of FSHR, BMRR1B, LHR and apoptosis in granulosa cells and ovulation rate in merino sheep

“…Recently, quantitative findings have shown the level of BMPR1B mRNA in 1-3 mm follicles to be equivalent in BB sheep (Estienne et al 2015), but this is not consistent with the present findings. In the Estienne et al (2015) study, the follicles were divided into small (1-3 mm) and large (3-5 mm) groups, which prevented an accurate comparison of the genotype effect because of the large range of development within the 1-3 mm range and because of the down-regulation of the leading dominant follicle in the 3-5 mm range (Gasperin et al 2014). It has been reported previously (McNatty et al 1986b) that BB follicles reach steroidogenic capacity at 2-2.5 mm as compared to the WT follicles at 4-4.5 mm.…”

“…Previously, qualitative data reported that the level of BMPR1B mRNA in follicles from 1 to 3 mm antral follicles indicated that BMPR1B mRNA was not reduced in BB sheep (Mulsant et al 2001). Recently, quantitative findings have shown the level of BMPR1B mRNA in 1-3 mm follicles to be equivalent in BB sheep (Estienne et al 2015), but this is not consistent with the present findings. In the Estienne et al (2015) study, the follicles were divided into small (1-3 mm) and large (3-5 mm) groups, which prevented an accurate comparison of the genotype effect because of the large range of development within the 1-3 mm range and because of the down-regulation of the leading dominant follicle in the 3-5 mm range (Gasperin et al 2014).…”

“…There are several ways in which a high prolificacy breed increases ovulation rate, and it appears that BB follicles may mature early because of an increased receptor density and a reduction in atretic follicles or apoptosis, as was reported in the present study and previous studies (Driancourt et al 1985, McNatty et al 1986b, Estienne et al 2015. The increased FSHR and the ability to wait up to 2 days allowed the subordinate follicles to continue to grow, which resulted in the threefold increase in the terminal end follicles that was reported in the present study (Fig.…”

“…In both the BB sheep and the WT sheep, the leading dominant follicle (4.4-7 mm) had a significantly reduced density of receptors, which demonstrated the presence of a hierarchical organization of the follicles that has been reported to be present in sheep (Figs 6B and 7B) (Evans et al 2002, Gasperin et al 2014. Chen et al (2009) and Estienne et al (2015) have also reported that the WT granulosa cells have increasing BMPR1B with increased follicle size, which is consistent with the present finding of an increased density of BMPR1B in subordinate follicles from 1.8 to 4.6 mm, which was the largest size of the subordinate follicles (P!0.010, Fig. 6B).…”

Postnatal pituitary and follicular activation: a revisited hypothesis in a sheep model

“…AMH concentration was measured in sheep plasma by using the AMH Gen II ELISA kit (Beckman Coulter, Inc., Brea, CA, USA) as previously described (Lahoz et al 2012, Estienne et al 2015. AMH concentrations were determined in 50 ml aliquots of undiluted plasma.…”