Abstract
BackgroundBirds have various plumage color patterns, and spot is a common phenotype. Herein, we conducted genome-wide association studies (GWAS) in a population of 225 ducks with different sized black spots to reveal the genetic basis of this phenomenon.Results First, we quantified the black spot phenotype within the duck population. The results showed that the uncolored area of the body surface first appeared on the ventral side. With increasing duck age, the area of the black spots was highly conserved across the whole body surface. The GWAS results identified a 198 kb (Chr4: 10,149,651 bp to 10,348,068 bp) genetic region that was significantly associated with the black spot phenotype. The conditional GWAS and linkage disequilibrium (LD) analysis further narrowed the ultimate candidate region to 167 kb (Chr4: 10,180,939 bp to 10,348,068 bp). A key gene regulating melanoblast migration and differentiation, EDNRB2 (Endothelin B receptor-like), was found in the candidate region and having significant mRNA expression level changes in embryonic duck skin tissue with different spot sizes. The significant SNPs (single nucleotide polymorphisms) associated with the EDNRB2 gene were annotated, and two mutations (Chr4: 10,180,939 T > C and Chr4: 10,190,671 A > T) were found to result in the loss of binding sites for two trans-factors, XBP1 and cMYB. The phenotypic effect of these two mutations suggested that they can regulate the size of black spots in a dose-dependent manner, and Chr4: 10,180,939 T > C was the major allele locus.ConclusionsOur results revealed that EDNRB2 was the gene responsible for the variation in duck body surface spot size. Chr4: 10,180,939 T > C was the major allele that explained 49.5 % (dorsal side) and 32.9 % (ventral side) of the variation in duck body surface spot size, while 32.1 % (dorsal side) and 19.1 % (ventral side) of the variation could be explained by Chr4: 10,190,671 A > T. The trans-factor prediction also suggested that XBP1 and cMYB have the potential to interact with EDNRB2, providing new insights into the mechanism of action of these genes.
Highlights
Birds have various plumage color patterns, and spot is a common phenotype
The results showed that the expression level of Endothelin B receptor-like (EDNRB2) increased with increasing melanic areas on the body surface of duck embryos (Fig. 5d)
The results showed that 2 potential trans-acting factor binding sites for XBP1 (X-box binding protein 1) and cMYB (v-myb avian myeloblastosis viral oncogene homolog) disappeared (Chr. 4: 10,180,939 T > C corresponded to XBP1 and Chr. 4: 10,190,671 A > T corresponded to cMYB) (Fig. 5e, Table S8)
Summary
Birds have various plumage color patterns, and spot is a common phenotype. Birds constitute one of the most diverse classes of animals on Earth, presenting a wide variety of body types, vocalizations, and plumage displays. Revealing the genetic basis underlying plumage color is helpful for cultivating breeds that can conform to consumption demands and provides a reference for studying the origin and evolution of poultry and the protection of poultry genetic resources. The distribution of pigment on the body, reflecting the absence of mature melanocytes, is caused by defects at various stages of melanocyte development, including proliferation, survival, migration, invasion of the integument, hair follicle entry and melanocyte stem cell renewal [10, 11]. According to Cieslak’s research, the spotted phenotype is mainly caused by a migration disorder of melanoblast cells. The genes responsible for melanoblast migration and melanocyte development include EDN3, EDNRB, EDNRB2, KIT and KITLG [12]
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