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

SIMPLE SUMMARY: The production of chickens plays an increasingly important role in people’s daily life because of the high nutritional quality and relatively low cost. Meanwhile, with the improvement of living standards, the requirements for meat quality have also increased significantly. Thus, the improvement of meat quality is becoming more and more important in chicken breeding. Studies have shown that meat quality is closely related to the development of skeletal muscle, which is a complex process regulated by many genes. Paired-like homeodomain transcription factor 2 (PITX2) and SIX homeobox 1 (SIX1) genes are involved in skeletal muscle development, and their polymorphisms were significantly associated with the carcass and body size traits of chickens in our previous studies. The objective of the present study was to detect the chronological expression of them on the pectoral muscles, and evaluate whether their single nucleotide polymorphisms (SNPs) are associated with the meat quality traits in chickens. Our results could provide useful information for the functional research of regulatory mechanisms of meat quality and marker assisted-selection for chicken production and quality. ABSTRACT: Meat quality is closely related to the development of skeletal muscle, in which PITX2 and SIX1 genes play important regulatory roles. The present study firstly provided the data of chronological expression files of PITX2 and SIX1 genes in the post-hatching pectoral muscle and analyzed the association of their polymorphisms with the meat quality traits of Wuliang Mountain Black-bone (WLMB) chickens. The results showed that both PITX2 and SIX1 genes were weakly expressed in the second and third weeks, and then increased significantly from the third week to the fourth week. Furthermore, there was a significant positive correlation between the expression levels of the two genes. Twelve and one SNPs were detected in the chicken PITX2 and SIX1 genes, respectively, of which four SNPs (g.9830C > T, g.10073C > T, g.13335G > A, g.13726A > G) of the PITX2 gene and one SNP (g.564G > A) of the SIX1 gene were significantly associated with chicken meat quality traits. For the PITX2 gene, chickens with the CT genotype of g.9830C > T showed the highest meat color L*, shear force (SF), pH, and the lowest electrical conductivity (EC), and drip loss (DL) (p < 0.05 or p < 0.01); chickens with the CC genotype of g.10073C > T had the lowest L*, pH, and the highest DL (p < 0.01). For the SIX1 gene, chickens with the GG genotype of g.564G > A had the highest (p < 0.05) SF and pH. Furthermore, pH had a significant correlation with all the other meat quality traits. The current study could contribute to the research of regulatory mechanisms of meat quality and lay the foundation for improving meat quality based on marker-assisted selection in chickens.