The Identification of SNPs in BCDO2 Gene for Skin Color in Chinese Indigenous Chicken

Significant genomic introgression from grey junglefowl (Gallus sonneratii) to domestic chickens (Gallus gallus domesticus)

BACKGROUND

Chicken is one of the most numerous and widely distributed species around the world, and many studies support the multiple ancestral origins of domestic chickens. The research regarding the yellow skin phenotype in domestic chickens (regulated by BCO2) likely originating from the grey junglefowl serves as crucial evidence for demonstrating the multiple origins of chickens. However, beyond the BCO2 gene region, much remains unknown about the introgression from the grey junglefowl into domestic chickens. Therefore, in this study, based on whole-genome data of 149 samples including 4 species of wild junglefowls and 13 local domestic chicken breeds, we explored the introgression events from the grey junglefowl to domestic chickens.

RESULTS

We successfully detected introgression regions besides BCO2, including two associated with growth trait (IGFBP2 and TKT), one associated with angiogenesis (TIMP3) and two members of the heat shock protein family (HSPB2 and CRYAB). Our findings suggest that the introgression from the grey junglefowl may impact the growth performance of chickens. Furthermore, we revealed introgression events from grey junglefowl at the BCO2 region in multiple domestic chicken breeds, indicating a phenomenon where the yellow skin phenotype likely underwent strong selection and was retained. Additionally, our haplotype analysis shed light on BCO2 introgression event from different sources of grey junglefowl into domestic chickens, possibly suggesting multiple genetic flows between the grey junglefowl and domestic chickens.

CONCLUSIONS

In summary, our findings provide evidences of the grey junglefowl contributing to the genetic diversity of domestic chickens, laying the foundation for a deeper understanding of the genetic composition within domestic chickens, and offering new perspectives on the impact of introgression on domestic chickens.

Genome-wide association study revealed the genomic regions associated with skin pigmentation in an Ogye x White Leghorn F2 chicken population

Skin color in chickens is an economically important trait that determines the first impression of a consumer toward a broiler and can ultimately affect consumer choice in the market. Therefore, identification of genomic regions associated with skin color is crucial for increasing the sales value of chickens. Although previous studies have attempted to reveal the genetic markers associated with the skin coloration in chickens, most were limited to investigations of candidate genes, such as melanin-related genes, and focused on case/control studies based on a single or small population. In this study, we performed a genome-wide association study (GWAS) on 770 F2 intercrosses produced by an experimental population of 2 chicken breeds, namely Ogye and White Leghorns, with different skin colors. The GWAS demonstrated that the L* value among the 3 skin color traits is highly heritable, and the genomic regions located on 2 chromosomes (20 and Z) were detected to harbor SNPs significantly associated with the skin color trait, accounting for most of the total genetic variance. Particular genomic regions spanning a ∼2.94 Mb region on GGA Z and a ∼3.58 Mb region on GGA 20 were significantly associated with skin color traits, and in these regions, certain candidate genes, including MTAP, FEM1C, GNAS, and EDN3, were found. Our findings could help elucidate the genetic mechanisms underlying chicken skin pigmentation. Furthermore, the candidate genes can be used to provide a valuable breeding strategy for the selection of specific chicken breeds with ideal skin coloration.

Characterization of Chicken Skin Yellowness and Exploration of Genes Involved in Skin Yellowness Deposition in Chicken

Skin color is an important economic trait in meat-type chickens. A uniform bright skin color can increase the sales value of chicken. Chickens with bright yellow skin are more popular in China, especially in the broiler market of South China. However, the skin color of chickens can vary because of differences in breeds, diet, health, and individual genetics. To obtain greater insight into the genetic factors associated with the process of skin pigmentation in chickens, we used a colorimeter and high-resolution skin photographs to measure and analyze the skin color of chickens. By analyzing 534 chickens of the same breed, age, and feed condition, we found that the yellowness values of the chickens varied within this population. A significant positive correlation was found between the cloacal skin yellowness values before and after slaughter, and the cloacal skin yellowness value of live chickens was positively correlated with the overall body skin yellowness value. Additionally, chicken skin yellowness exhibited low heritability, ranging from 0.07 to 0.27. Through RNA sequencing, 882 genes were found to be differentially expressed between the skin with the highest and lowest yellowness values. Some of these differentially expressed genes may play an important role in yellow pigment deposition in chicken skin, which included TLR2B, IYD, SMOC1, ALDH1A3, CYP11A1, FHL2, TECRL, ACACB, TYR, PMEL, and GPR143. In addition, we found that the expression and variations of the BCO2 gene, which is referred to as the yellow skin gene, cannot be used to estimate the skin yellowness value of chickens in this population. These data will help to further our understanding of chicken skin yellowness and might contribute to the selection of specific chicken strains with consistent skin coloration.