Genome-wide search for candidate genes determining vertebrae number in pigs

Longer porcine carcasses may be expected to have more vertebrae. Therefore, vertebrae number in pigs is an economically important trait. To examine the genetic basis of this trait, we genotyped 578 F-2 Large White x Minzhu pigs using the Porcine SNP60K BeadChip. A genome-wide association study (GWAS) identified 36 significant single nucleotide polymorphisms (SNPs) on the chromosomes SSC1 (294.28-300.32 Mb) and SSC7 (102.22-109.39 Mb). A 6.04-Mb region that contained all 13 significant SNPs on SSC1 also contained the gene NR6A1, previously reported to influence the number of vertebrae in pigs. However, the reported putative casual mutation of NR6A1 c. 748C > T showed no genome-wide significant association with the trait, suggesting it was not a causal mutation in our population. The remaining 23 significant SNPs on SSC7 were concentrated in a 7.17-Mb region, which was within a quantitative trait locus interval for number of vertebrae. TMED10 was the closest gene to the most significant SNP and might be a candidate. Haplotype sharing and block analysis refined the QTL to an interval of about 3 Mb containing 29 candidate genes. Of these 29 genes, the previously reported possible casual mutation of VRTN g. 19034A > C was not found to be a causal mutation in our population. Exploration of these genes via additional genetic and functional studies in mammals revealed that TGF beta 3 could be a good candidate on SSC7. A mutation of TGF beta 3 c. 1749G > A was detected by GWAS and could be proposed as a candidate causal mutation, or as closely linked to a causal mutation, for the number of vertebrae in pigs.