Expression Analysis of the PITX2 Gene and Associations between Its Polymorphisms and Body Size and Carcass Traits in Chickens

Abstract

PITX2 is expressed in and plays an important role in myocytes of mice, and it has effects on late myogenic differentiation in chickens. However, the expression profile and polymorphisms of PITX2 remain unclear in chickens. Therefore, the aim of the present study was to detect its expression and investigate single nucleotide polymorphisms (SNPs) within its exons and then to evaluate whether these polymorphisms affect body size as well as carcass traits in chickens. The expression analysis showed that the expression level of chicken PITX2 mRNA in the leg muscle and hypophysis was significantly higher (p < 0.01) than those in other tissues. The results of polymorphisms analysis identified two SNPs (i.e., g.9830C > T and g.10073C > T) in exon 1 and 10 SNPs (i.e., g.12713C > T, g.12755C > T, g.12938G > A, g. 3164C > T, g.13019G > A, g.13079G > A, g.13285G > A, g.13335G > A, g.13726A > G and g.13856C > T) in exon 3, including four novel SNPs (i.e., g.9830C > T, g.12713C > T, g.12938G > A and g.13856C > T). In the loci of g.10073C > T and g.12713C > T, chickens with the CT genotype had the highest (p < 0.05 or p < 0.01) breast depth and breast angle, respectively. For the locus of g.13335G > A, chickens with the GG genotype had the highest (p < 0.05 or p < 0.01) breast angle and shank circumference. For the locus of g.13726A > G, chickens with the GG genotype had the highest breast width, fossil keel bone length and shank circumference. The locus of g.12713A > G had significant effects on the PITX2 mRNA expression level in leg muscle. The H1H7 diplotype showed the highest shank circumference, and the H2H8 diplotype showed the highest breast muscle rate. The present research suggested that polymorphisms of the exons of the PITX2 gene were significantly associated with the body size and carcass traits of Wuliang Mountain Black-bone chickens and the PITX2 gene could be a potential candidate gene for molecular marker-aided selection in Wuliang Mountain Black-bone chickens and other chicken breeds.

Chronological Expression of PITX2 and SIX1 Genes and the Association between Their Polymorphisms and Chicken Meat Quality Traits

“…In the present study, 12 SNPs (g.9830C > T and g.10073C > T in exon 1, g.12713C > T, g.12755C > T, g.12938G > A, g.12961C > T, g.13019G > A, g.13079G > A, g.13285G > A, g.13335G > A, g.13726A > G and g.13856C > T in exon 3) were detected in the PITX2 gene, and one SNP (g.564C > T in exon) was detected in the SIX1 gene. In our previous studies, all mutations of PITX2 and SIX1 genes were synonymous [ 16 , 17 ]. As shown in Table 2 , except for g.13079G > A and g.13856C > T of the PITX2 gene, all SNPs exhibited three genotypes.…”

“…Combined with our previous results, individual with the CT genotype of g.10073C > T at the PITX2 gene had higher breast width, pH and lower drip loss; individuals with the GG genotype of g.13335G > C at PITX2 gene had higher breast angle, shank circumference and lower drip loss; individuals with the GG genotype of g.564G > A at the SIX1 gene had higher breast muscle weight, percentage of breast muscle and pH. Therefore, the CT genotype of g.10073C > T and the GG genotype of g.13335G > C at PITX2 may serve as molecular markers to improve both body size and meat quality traits of WLMB chickens; and the GG genotype of g.564G > A at the SIX1 gene may serve as a molecular marker to improve both carcass and meat quality traits [ 16 , 17 ].…”

“…Primers [ 16 , 17 ] to amplify the exons of PITX2 and SIX1 genes are shown in Table 1 . Since the second exon of the SIX1 gene has a high GC content and POLY N (A, T, and C), amplification is extremely difficult.…”

“…Some studies have shown that the polymorphisms of PITX2 and SIX1 genes were associated with pig meat quality [ 14 , 15 ]. In our previous studies, the polymorphisms of PITX2 and SIX1 genes were significantly associated with chicken carcass and body size traits [ 16 , 17 ]. However, the association between their polymorphisms and meat quality traits of chicken has not been reported before, nor has the chronological expression profiles of them in the post-hatching pectoral muscle.…”

“…Therefore, in the present study, the chronological expression profiles of PITX2 and SIX1 genes in the post-hatching pectoral muscle were detected, as well as the association between their polymorphisms and meat quality traits in Wuliang Mountain Black-Bone (WLMB) chickens. WLMB chicken is a Chinese indigenous breed that has good meat quality, feathered feet, green ear lobes, black bones, and a lower growth rate than the commercial broiler, which provides a valuable genetic resource for scientific research and further genetic improvement in the chicken industry [ 16 ]. The PITX2 gene (Gene ID: 427549) of chicken is located on chromosomes 4 with 3 exons, and the SIX1 gene (Gene ID: 693262) is located on chromosome 5 with 2 exons.…”