Fine mapping the number of corpora lutea quantitative trait loci on SSC3: Analysis of the porcine follicle-stimulating hormone receptor gene

A haplotype variant of Hu sheep follicle-stimulating hormone receptor promoter region decreases transcriptional activity

In sheep, increased expression of the follicle-stimulating hormone receptor (FSHR) in the ovary is a common feature of ewes that carry the prolific allele. In this study, we demonstrated that polymorphisms in the core promoter of the FSHR gene are associated with the reproductive performance of Hu sheep and are involved in the transcriptional activity of FSHR. An approximately 1.5-kb region of the 5' flanking sequence of the Hu sheep FSHR gene was isolated and characterized, and its core promoter was located in the 5' regulatory region, from nucleotides -580 to -342. Four variants (c.-518T>C, c.-466C>T, c.-414A>G and c.-365C>T) were detected in this region, and six genotypes and three haplotypes were found in the Hu sheep population (n = 245). An association analysis revealed that these polymorphisms are associated with the litter size of Hu ewes. Furthermore, a luciferase assay showed that the T-C-A-C- and C-T-G-T-type core promoters have higher transcriptional activity than does the T-C-G-C type. Notably, the putative binding site for the transcription factor Yin Yang 1 (YY1) was present at the A allele of nucleotide -414, but YY1 can significantly increase the transcriptional activity of the FSHR core promoter, which contains three different haplotypes. Taken together, our results establish that these variants might be involved in regulating the transcriptional activity of FSHR and litter size in Hu ewes and may provide a novel candidate marker for marker-assisted selection in sheep breeding.

A polymorphism in the transcriptional regulatory region strongly influences ovine FSHR mRNA decay

Follicle-stimulating hormone receptor (FSHR) is an important G protein-coupled receptor, which is required for steroidogenesis, follicular development and female infertility. Here, we report a novel polymorphism in the 3'-UTR that strongly influences ovine FSHR mRNA decay. The partial 3'-UTR sequence of Hu sheep FSHR gene was isolated and characterized, and a polymorphism (c.2327A>G) was identified. Luciferase assay and qRT-PCR showed that c.2327A>G polymorphism in the 3'-UTR exerts a strong regulatory role in FSHR transcription. This regulatory role is achieved by affecting FSHR mRNA decay. Furthermore, the c.2327A>G mutation in the 3'-UTR influences ARE (AU-rich element, a cis-acting element promoting mRNA decay)-mediated mRNA decay of Hu sheep FSHR gene. Together, our study identified a novel polymorphism and elucidated a new mechanism underlying transcriptional regulation of FSHR in mammals.

Genome-Wide Association Study of Piglet Uniformity and Farrowing Interval

Piglet uniformity (PU) and farrowing interval (FI) are important reproductive traits related to production and economic profits in the pig industry. However, the genetic architecture of the longitudinal trends of reproductive traits still remains elusive. Herein, we performed a genome-wide association study (GWAS) to detect potential genetic variation and candidate genes underlying the phenotypic records at different parities for PU and FI in a population of 884 Large White pigs. In total, 12 significant SNPs were detected on SSC1, 3, 4, 9, and 14, which collectively explained 1–1.79% of the phenotypic variance for PU from parity 1 to 4, and 2.58–4.11% for FI at different stages. Of these, seven SNPs were located within 16 QTL regions related to swine reproductive traits. One QTL region was associated with birth body weight (related to PU) and contained the peak SNP MARC0040730, and another was associated with plasma FSH concentration (related to FI) and contained the SNP MARC0031325. Finally, some positional candidate genes for PU and FI were identified because of their roles in prenatal skeletal muscle development, fetal energy substrate, pre-implantation, and the expression of mammary gland epithelium. Identification of novel variants and candidate genes will greatly advance our understanding of the genetic mechanisms of PU and FI, and suggest a specific opportunity for improving marker assisted selection or genomic selection in pigs.

TGF-β signaling controls FSHR signaling-reduced ovarian granulosa cell apoptosis through the SMAD4/miR-143 axis

Follicle-stimulating hormone receptor (FSHR) and its intracellular signaling control mammalian follicular development and female infertility. Our previous study showed that FSHR is downregulated during follicular atresia of porcine ovaries. However, its role and regulation in follicular atresia remain unclear. Here, we showed that FSHR knockdown induced porcine granulosa cell (pGC) apoptosis and follicular atresia, and attenuated the levels of intracellular signaling molecules such as PKA, AKT and p-AKT. FSHR was identified as a target of miR-143, a microRNA that was upregulated during porcine follicular atresia. miR-143 enhanced pGC apoptosis by targeting FSHR, and reduced the levels of intracellular signaling molecules. SMAD4, the final molecule in transforming growth factor (TGF)-β signaling, bound to the promoter and induced significant downregulation of miR-143 in vitro and in vivo. Activated TGF-β signaling rescued miR-143-reduced FSHR and intracellular signaling molecules, and miR-143-induced pGC apoptosis. Overall, our findings offer evidence to explain how TGF-β signaling influences and FSHR signaling for regulation of pGC apoptosis and follicular atresia by a specific microRNA, miR-143.

Evaluation of quantitative trait loci affecting intramuscular fat and reproductive traits in pigs using marker-assisted introgression

We investigated the effects of previously identified quantitative trait loci (QTL) in an experimental backcross (BC) between Chinese Meishan pigs and commercial Duroc pigs. We performed marker-assisted introgression of two QTL for intramuscular fat (IMF) content (IMF population) and three QTL for reproductive traits (reproduction population) from a donor Meishan pig into a recipient Duroc pig. At the fourth BC generation of the IMF population and third BC generation of the reproduction population, carrier animals were selected for the production of animals homozygous for the QTL. Our previous studies have shown that the presence of a Meishan allele on the IMF QTL is associated with low IMF values, and the Meishan allele on the reproductive QTL is associated with large litters. In this study, the presence of a Duroc allele at the IMF QTL on SSC9 resulted in a 0.27% increase in IMF (additive effect = 0.27 ± 0.08), whereas the presence of a Meishan allele at the IMF QTL on SSC7 resulted in a 0.34% increase in IMF (additive effect = -0.34 ± 0.09). The presence of the Meishan allele at the IMF QTL on SSC7 thus had the opposite effect to our previous studies, that is, increased IMF. In the reproduction population, we observed no differences between the genotypes of the three QTL in regard to number of corpora lutea or litter size. Marker-assisted introgression at these QTL is thus unlikely to result in an associated increase in litter size. These results show that it is possible to introgress alleles from other breeds into a selection population using molecular markers; any unexpected results might be associated with the genetic background.