Academic journal article Genetics

Recessive Black Is Allelic to the Yellow Plumage Locus in Japanese Quail and Associated with a Frameshift Deletion in the ASIP Gene

Academic journal article Genetics

Recessive Black Is Allelic to the Yellow Plumage Locus in Japanese Quail and Associated with a Frameshift Deletion in the ASIP Gene

Article excerpt

ABSTRACT

The recessive black plumage mutation in the Japanese quail (Coturnix japonica) is controlled by an autosomal recessive gene (rb) and displays a blackish-brown phenotype in the recessive homozygous state (rb/rb). A similar black coat color phenotype in nonagouti mice is caused by an autosomal recessive mutation at the agouti locus. An allelism test showed that wild type and mutations for yellow, fawn-2, and recessive black in Japanese quail were multiple alleles (*N, *Y, *F2, and *RB) at the same locus Y and that the dominance relationship was Y*F2 > Y*Y > Y*N > Y*RB. A deletion of 8 bases was found in the ASIP gene in the Y*RB allele, causing a frameshift that changed the last six amino acids, including a cysteine residue, and removed the normal stop codon. Since the cysteine residues at the C terminus are important for disulphide bond formation and tertiary structure of the agouti signaling protein, the deletion is expected to cause a dysfunction of ASIP as an antagonist of α-MSH in the Y*RB allele. This is the first evidence that the ASIP gene, known to be involved in coat color variation in mammals, is functional and has a similar effect on plumage color in birds.

THE yellow mutation in the Japanese quail (Coturnix japonica) is controlled by an autosomal incomplete dominant gene (Y). Adult heterozygotes (Y/+, yellow) display a straw plumage color but the dominant homozygotes (Y/Y) display an early embryonic lethality (Homma et al. 1967). The fawn-2 mutation at the Y locus is also controlled by an autosomal incomplete dominant gene (Yf2), which is allelic to and incompletely dominant over the Y gene. Adult homozygotes (Yf2/Yf2, fawn-2) show a whitish light-brown color in males and a creamier plumage color in females than in males. The hetero-zygotes (Yf2/1, dark fawn-2) show a deeper brown color than the homozygotes in each sex (Tsudzuki et al. 1996). The recessive black plumage color in the Japanese quail is controlled by an autosomal recessive gene (rb) and gives a blackish-brown plumage to homozygotes (rb/rb, recessive black) (Fujiwara et al. 2005), which is very similar to that of homozygotes for the extended brown plumage mutation controlled by an autosomal incomplete dominant gene (E) (Somes 1979) at the MC1R locus (Nadeau et al. 2006).

There are interesting similarities between the phenotypic effects and dominance relationships of mutations at the agouti locus in the house mouse (Mus musculus). In nonagouti mice, a black coat color phenotype (a/a) is caused by an autosomal recessive mutation at the agouti (ASIP) locus (Silvers 1979). Embryonic lethality of a dominant homozygous yellow mutation (Ay/Ay) is associated with a deletion upstream of agouti that removes the coding exons of the Raly (hnRNP protein that is associated with the lethal yellow) gene (Michaud et al. 1993). The plumage color of the yellow (Y/1) Japanese quail is similar to the coat color of the yellow (Ay/+) mouse. The Y locus in the Japanese quail was mapped on the QL10 linkage group homologous to GGA20 in chicken (Gallus gallus) (Miwa et al. 2005), where an ASIP-like sequence was found (Klovins and Schiöth 2005). Recently we studied the growth of yellow quails and found that they shared similar phenotypic characteristics (increased body fat, decreased body tempera-ture) with lethal yellow mice (Minvielle et al. 2007). Because of these points, the ASIP gene was considered to be a candidate gene for the yellow mutation in the Japanese quail.

Mutations in the ASIP gene have been shown to cause a wide variety of coat colors in mammals. For instance, standard silver color in red foxes (Vulpes vulpes), non-agouti black in Norway rats (Rattus norvegicus), recessive black in horses (Equus caballus), and black coloration in cats (Felis catus) are all associated with deletions in exon 2 of ASIP that cause a loss of the agouti function (Va°ge et al. 1997; Kuramoto et al. 2001; Rieder et al. 2001; Eizirik et al. …

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