Georgian white coat color of red fox (Vulpes vulpes) maps to fox chromosome 2 in the region containing KIT gene

The farm breeding of red foxes began in Eastern Canada in the late 19th century.¹ Through fox farm breeding, several new coat color variants have been identified, with the Georgian white (GW) morph first being described at Bakuriany farm in Georgia in 1943.^2,3 GW foxes are produced by breeding GW and standard silver foxes and are heterozygous for the GW allele. They are characterized by white coat color, brown eyes, a black nose and black spots on the head, along the spine and on some other parts of the body (Fig. 1). In a breeding between two GW foxes, offspring homozygous for the GW allele are underrepresented, which was attributed to the death of some homozygous embryos before implantation.³ The offspring homozygous for the GW allele that are born alive are almost completely white and die at 1–2 months of age.³ Interestingly, the shortage of GW homozygous offspring in breedings between GW foxes can be reduced by additional illumination of the dam during pregnancy.³

Figure 1.

Fox heterozygous for the Georgian white allele.

Blood samples were collected from 13 three-generation pedigrees produced by breeding GW and standard silver foxes (88 individuals, including 55 foxes in the third generation) at the Institute of Cytology and Genetics of the Russian Academy of Sciences in Novosibirsk, Russia. DNA was extracted using DNA Maxi Blood Kit (Qiagen). The pedigrees were genotyped with 224 dog microsatellites (Table S1) as described.^4–6 All genotypes were checked for Mendelian segregation and manually corrected for errors. Linkage mapping using the Twopoint function of CRI-MAP version 2.503^7,8 identified the most significant linkage between GW and markers on fox chromosome 2 (VVU2): FH2890 (θ = 0.0; LOD = 16.26), FH3006 (θ = 0.0; LOD = 13.85) and AHT121 (θ = 0.0; LOD = 11.44) (Table S2). Multipoint linkage mapping and haplotype analysis placed the GW locus in the interval defined by markers REN278L10 and REN150M24 (Fig. 2; Fig. S1). This is a region with a suppressed recombination rate, and the marker REN150M24 could not be assigned a unique location. On the fox map constructed with a larger number of pedigrees,⁶ the interval between markers REN278L10 and REN150M24 spans 16.1 cM.^4,6 This interval is syntenic to three dog chromosomes: CFA2, 9, and 13 (Table S3).⁶

Figure 2.

Meiotic linkage map fox chromosome 2 (VVU2) constructed with pedigrees informative for the Georgian white phenotype. The most likely location of the GW locus on VVU2 with LOD support 2.0 is indicated on the left. The map is aligned against the dog genome; positions of markers and the KIT gene (chr13: 47,108,519-47,190,020 bp) in CamFam3.1 are shown on the right.

The part of CFA13 that is syntenic to the GW interval on VVU2 includes the KIT gene (Fig. 2), mutations in which are responsible for white spotting in multiple mammalian species.⁹ Recently, we have shown that a mutation in the KIT gene causes platinum coat color in foxes.¹⁰ Allelic interaction among the GW and platinum coat colors has previously been established through cross-breeding of GW and platinum foxes.³ The mapping of the GW allele to this interval on VVU2 is thus consistent with the results of the experimental breedings³ and suggests that GW is also caused by a mutation in the KIT gene. Little is known about the role of light in regulating gene expression in mammals, and further analysis of the GW phenotype could contribute to our understanding of these mechanisms.

Supplementary Material

Supp Fig S1

Figure S1 Haplotype analysis of the Georgian white phenotype. Representative three-generation pedigrees segregating for the Georgian white phenotype are shown. The markers are listed in the order defined on the fox meiotic linkage map (Kukekova t al., 2007; 2012). Haplotype shading indicates parental origin. The haplotype in dark brown corresponds to the chromosome carrying the GW allele, which is represented by +. The GW locus is positioned between REN278L10 and REN150M24 in recombinant individuals 11, 17, and 25. The GW interval is marked by light gray horizontal block.

Supp Table S1

Table S1 Microsatellite markers used for the genome-wide scan of fox pedigrees. Markers assigned to each fox chromosome and listed in alphabetical order. Location of these markers on the fox meiotic linkage map is presented in Kukekova et al., 2011; 2012.^5,6

Supp Table S2

Table S2 Results of best two-point linkage analysis between the Georgian white (GW) locus and markers from fox chromosome 2.

Supp Table S3

Table S3 Positions of microsatellite markers on the fox meiotic linkage map and in the dog genome.