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The red fox (Vulpes vulpes) demonstrates a variety of coat colors including platinum, a common phenotype maintained in farm-bred fox populations. Foxes heterozygous for the platinum allele have a light silver coat and extensive white spotting, whereas homozygosity is embryonic lethal. Two KIT transcripts were identified in skin cDNA from platinum foxes. The long transcript was identical to the KIT transcript of silver foxes, whereas the short transcript, which lacks exon 17, was specific to platinum. The KIT gene has several copies in the fox genome: an autosomal copy on chromosome 2 and additional copies on the B chromosomes. To identify the platinum-specific KIT sequence, the genomes of one platinum and one silver fox were sequenced. A single nucleotide polymorphism (SNP) was identified at the first nucleotide of KIT intron 17 in the platinum fox. In platinum foxes, the A allele of the SNP disrupts the donor splice site and causes exon 17, which is part of a segment that encodes a conserved tyrosine kinase domain, to be skipped. Complete cosegregation of the A allele with the platinum phenotype was confirmed by linkage mapping (LOD 25.59). All genotyped farm-bred platinum foxes from Russia and the US were heterozygous for the SNP (A/G), whereas foxes with different coat colors were homozygous for the G allele. Identification of the platinum mutation suggests that other fox white-spotting phenotypes, which are allelic to platinum, would also be caused by mutations in the KIT gene., (© 2015 Stichting International Foundation for Animal Genetics.)

B chromosomes are often considered to be one of the most mysterious elements of karyotypes (Camacho, 2004). It is generally believed that mammalian B chromosomes do not contain any protein coding genes. The discovery of a conserved KIT gene in Canidae B chromosomes has changed this view. Here we performed analysis of sequences surrounding KIT in B chromosomes of the fox and raccoon dog. The presence of the RPL23A pseudogene was shown in canid B chromosomes. The 3' end fragment of the KDR gene was found in raccoon dog B chromosomes. The size of the B-specific fragment homologous to the autosome fragment was estimated to be a minimum of 480 kbp in both species. The origin and evolution of B chromosomes in Canidae are discussed., (Copyright 2007 S. Karger AG, Basel.)

Plant and animal karyotypes sometimes contain variable elements, that are referred to as additional or B-chromosomes. It is generally believed that B-chromosomes lack major genes and represent parasitic and selfish elements of a genome. Here we report, for the first time, the localization of a gene to B-chromosomes of mammals: red fox (Vulpes vulpes) and two subspecies of raccoon dog (Nyctereutes procyonoides). Identification of the proto-oncogene C-KIT on B-chromosomes of two Canidae species that diverged from a common ancestor more than 12.5 million years ago argues against the current view of B-chromosomes. Analyses of fox B-chromosomal C-KIT gene from a flow-sorted fox B-chromosome-specific library revealed the presence of intron-exon boundaries and high identity between sequenced regions of canine and fox B-chromosomal C-KIT copies. Identification of C-KIT gene on all B-chromosomes of two canid species provides new insight into the origin and evolution of supernumeraries and their potential role in the genome.