Differential expression of mRNAs encoding BMP/Smad pathway molecules in antral follicles of high- and low-fecundity Hu sheep.

The Hu sheep is world-famous for its hyper-prolificacy and the bone morphogenetic protein (BMP)/Smad pathway and several other closely related molecules (GDF9, TGF-betaRI) have been shown to have a close relationship with reproduction in sheep. In order to investigate the mechanism of high fecundity in Hu sheep and its relationship with the BMP/Smad pathway, 147 Hu sheep were blood sampled for detection of the FecB mutation (A746G) in the BMPRIB gene by PCR-SSCP, and sixteen adult Hu ewes classified as either high-fecundity (HF) or low-fecundity (LF) animals were sacrificed for tissue and antral follicle sampling. The tissue distribution patterns of mRNAs encoding BMP/Smad pathway molecules including BMPs (BMP2, BMP4, BMP6, BMP7 and BMP15), BMP receptors (BMPRIA, BMPRIB and BMPRII), intracellular transducers (Smad1, Smad5 and Smad4) and closely related molecules (GDF9 and TGF-betaRI) were detected by RT-PCR and the gene expression levels in antral follicles were investigated by real-time PCR. The results showed that all experimental animals were homozygous for the BMPRIB (A746G) mutation, and all detected genes related to the BMP/Smad pathway and GDF9 and TGF-betaRI were expressed in the ovary. In addition, BMP4, BMPRIB, BMPRII, Smad4, GDF9 and TGF-betaRI mRNAs were more abundant in the antral follicles of HF animals than those of LF animals (P<0.05), but BMP15 mRNA was less abundant (P<0.01). This suggests that there could be an unidentified genetic mutation in BMPRIB, or other unidentified genes and unknown factors, which controls ovarian number by changing the expression patterns of genes known to regulate ovulation rate via the BMP/Smad pathway and closely related molecules (GDF9 and TGF-betaRI).