Identification and Genetic Effect of Haplotypes in the Distal Promoter Region of Chicken CCT6A Gene Associated with Egg Production Traits

The chaperonin containing TCP-1 complex protein 1 subunit zeta (CCT6A) is the only cytosolic chaperonin in eukaryotes assisting in the folding of cytoplasmic proteins. Previous study revealed that the mRNA expression of chicken CCT6A gene was remarkably elevated in the sexually mature ovaries. However, the mechanism underlying chicken CCT6A expression changes remains largely unknown. In this study, haplotypes caused by two single nucleotide polymorphisms (SNPs) of chicken CCT6A gene promoter (g.-2215 T>C and g.-1959 T>C) were identified and their associations with egg production traits as well as effects on gene expression were analyzed. Altogether four haplotypes including A (C-2215-T-1959), B (C-2215-C-1959), C (T-2215-T-1959) and D (T-2215-C-1959) were detected in all of the five chicken populations. Diplotypes AA, AD and DD were predominant in Xinyang brown hens, among which diplotype AD was associated with higher egg number at the age of 28 weeks old (E28) (P <0.05). In addition, diplotype AD was also predominant in Xinyang brown and Hy-line brown chicken populations with high egg production; whereas in Wenchang and Shouguang chicken populations which are Chinese indigenous chicken breeds and relatively lower in egg production, diplotype AA was predominant. Compared with diplotypes AA and DD, the mRNA expression of CCT6A in diplotype AD birds is the highest in F, F5, and POF1 follicles of Hy-line brown hens (P<0.05). These results suggest that the two SNPs in chicken CCT6A promoter region are potential DNA marker for improving egg production trait.