Genome-wide Association Analysis For Number Of Porcine Ribs And The Clone And Expression Of LTBP2

In China,sparerib is one of the most valuable parts of the pork carcass.As a result,candidate gene mining for number of ribs has become an interesting study focus.To examine the genetic basis for this major trait,we genotyped 596 individuals from an F2 Large White × Minzhu intercross pig population using the PorcineSNP60 Genotyping BeadChip.The genome-wide association study identified a locus for number of ribs in a 2.38-Mb region on Sus scrofa chromosome 7.We identified the top significant SNP ASGA0035536,which explained 16.51 % of the phenotypic variance.Haplotype sharing analysis in F1 boars localized the rib number QTL to a 951-kb interval on SSC7.This interval encompassed 15 annotated genes in Sscrofa10.2.To further investigate the QTL for number of ribs on SSC7,We genotyped 596 individuals from an F2 Large White × Minzhu intercross pig population through whole genome re-sequencing.7083 SNPs within 6.8Mb region(102.59-109.39Mb)on SSC7 were significant associated with number of ribs through special GWAS,Furthermore,the 95 % confidence interval of the major locus was defined by a-log(p value)dropoff of 3 from the strongest significant SNP012606.According to this criterion,the critical region for the trait was narrowed to a 800Kb(103.1–103.9 Mb)interval.This interval encompasses 11 annotated genes.Of the 11 candidate genes,LTBP2,which encodes a latent transforming growth factor beta binding protein,was previously reported to indirectly regulate the activity of growth differentiation factor Gdf11,which has been shown to increase the number of ribs in knock-out mice.Thus,we proposed LTBP2 as a good new candidate gene for number of ribs in the pig population.To further identify causative mutations within LTBP2 for number of ribs on SSC7,we firstly cloned the full-length cDNA sequence of LTBP2 using RACE.The full-length of LTBP2 is 7608 bp which contains 34 exons.We detected 73 SNPs by using F0 individuals.Association of these SNPs with number of ribs in the F2 resource population,a total of 14 SNPs(1 in 5,UTR ?2 in ORF and 11 in 3,UTR)were significant associated with number of ribs.Tissue expression profiles of LTBP2 implied that the expression of LTBP2 is extremely high in lung tissue on 180 days.This study revealed LTBP2 as a good outstanding candidate gene for number of ribs through GWAS?fine mapping and whole genome re-sequence.This finding not only has important theoretical significance during the exploration of major gene,but also advances our understanding of the genetic architecture of rib number in pigs.