Variations in BCO2 Coding Sequence Causing a Difference in Carotenoid Concentration in the Skin of Chickens

Background: Carotenoid consumption decreases the risk of cancer, osteoporosis, or neurodegenerative diseases through interrupting the formation of free radicals. Carotenoid-pigmented egg yolk, skin, legs, beak, comb, and feathers in broilers give consumers the impression that they are healthier than none-pigmented ones. Deposition of carotenoids in chicken skin makes the skin color turn from white into yellow. The enzyme β-carotene oxygenase 2 (BCO2) plays a key role during the degradation process of carotenoids in skin. How does the BCO2 affects the skin color of chicken, and whether it is the key factor resulted in the phenotypic difference between yellow- and white- skin chickens are still unclear. Three female chickens of the Guangxi Huang and Qingjiao Ma breed were slaughtered and used for carotenoid concentration and BCO2 expression level analysis. The carotenoid concentration in chicken skin was determined by HPLC. A total of 1054 DNA samples from seven different chicken breeds were genotyped and allele frequencies analysis.Results: In the present study, we measured the concentration of carotenoids in chicken skin showed that the carotenoid concentration in chicken with a yellow skin was significantly higher than that with white skin chicken. Then we analyzed the expression profile of BCO2 in different tissues and observed significant differences in gene expression in the back skin between yellow- and white- skin chicken. Scanning the SNPs in BCO2 gene, it revealed a G/A mutation in exon 6, which was confirmed by PCR-RFLP. Copy number variation (CNV) was also detected; the copy number in white yellow skin chicken was almost 2-fold of that than in yellow skin chicken. These results implied that the G/A mutation and CNV in chicken skin may play a key role in regulating the carotenoids degradation. Conclusions: Generally, reduced expression of the BCO2 gene due to lower CVNs may be responsible for the deposition of carotenoids and as a consequence a yellow skin color in yellow skin chicken. One SNP c.890A>G was found to be associated with the chicken skin color and may be used as a genetic marker in breeding for yellow skin in chicken in the future.