Ontogenic expression pattern and genetic polymorphisms of the retinol-binding protein 4 (RBP4) gene in Erlang mountainous chickens

Retinol-binding protein 4 (RBP4) is the only circulatory transport protein for vitamin A. Based on the essential role of vitamin A in chicken reproduction, we measured RBP4 mRNA abundance in Erlang mountainous chickens. We also identified and analyzed the gene polymorphism and its effect on reproduction traits among 349 chickens. The expression of RBP4 mRNA showed specific developmental changes and striking differences among tissues. The mRNA abundance was greatest (P < 0.05) in the liver, intermediate in the ovary, kidney, small intestine, oviduct and heart, and lowest in the hypothalamus and pituitary, as compared to all other tissues (P < 0.05). We detected one single nucleotide polymorphism (g.19942455C>G) in intron 2 of the RBP4 gene. Three genotypes (CC, CG and GG) were identified, with a significant effect of genotype on the age at first egg (AFE), first egg weight (FEW), total eggs at 300 days (TE300), highest continuous laying days (HCLD) and average laying interval (ALI). The GG genotype, where chickens display earlier AFE, more TE300, longer HCLD and shorter ALI, would be genetically advantageous and its selection may improve reproduction traits. These results suggested that the RBP4 gene might play an important role in reproduction traits in chickens.