Abstract
BackgroundIn chickens, three mutant alleles have been reported at the C locus, including the albino mutation, and the recessive white mutation, which is characterized by white plumage and pigmented eyes. The albino mutation was found to be a 6 bp deletion in the tyrosinase (TYR) gene. The present work describes an approach to identify the structural rearrangement in the TYR gene associated with the recessive white mutation.ResultsMolecular analysis of the chicken TYR gene has revealed a major structural difference (Restriction Fragment Length Polymorphism, RFLP) in the genomic DNA of the recessive white chicken. A major size difference of 7.7 kb was found in intron 4 of the TYR gene by long-range PCR. Molecular cloning and sequencing results showed the insertion of a complete avian retroviral sequence of the Avian Leukosis Virus (ALV) family. Several aberrant transcripts of the tyrosinase gene were found in 10 week old recessive white chickens but not in the homozygous wild type colored chicken. We established a rapid genotyping diagnostic test based on the discovery of this retroviral insertion. It shows that all homozygous carriers of this insertion had a white plumage in various chicken strains. Furthermore, it was possible to distinguish heterozygous carriers from homozygous normal chickens in a segregating line.ConclusionIn this study, we conclude that the insertion of a complete avian retroviral sequence in intron 4 of the tyrosinase gene is diagnostic of the recessive white mutation in chickens. This insertion causes aberrant transcripts lacking exon 5, and we propose that this insertion is the causal mutation for the recessive white allele in the chicken.
Highlights
In chickens, three mutant alleles have been reported at the C locus, including the albino mutation, and the recessive white mutation, which is characterized by white plumage and pigmented eyes
Probe TyrC which contained exon 5, revealed the same diagnostic bands between normal and mutant chickens as did the full cDNA probe. This result showed that the structural difference of the TYR gene between the recessive white mutant and the wild type chicken was located in the 3' terminal region of the TYR cDNA (Figure 3)
The structural change (RFLP) initially identified in the TYR gene of recessive white chickens has been shown to result from the insertion of a complete avian retroviral sequence of 7.7 kb in intron 4 of the gene
Summary
Three mutant alleles have been reported at the C locus, including the albino mutation, and the recessive white mutation, which is characterized by white plumage and pigmented eyes. The albino mutation was found to be a 6 bp deletion in the tyrosinase (TYR) gene. The present work describes an approach to identify the structural rearrangement in the TYR gene associated with the recessive white mutation. A chicken carrying the wild type allele at the C locus exhibits a colored plumage as determined by other feather color loci. We performed a molecular analysis of the tyrosinase gene in recessive white chickens in order to investigate the gene polymorphism and localize the causal mutation. We identified an avian retroviral sequence insertion in the tyrosinase gene of recessive white chickens in complete association with the mutant phenotype. We established a rapid, sensitive and accurate diagnostic genotyping test that would be very helpful for breeders to identify heterozygous carriers of this recessive mutation
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