The proto-oncogene C-KIT maps to canid B-chromosomes Alexander S. Graphodatsky 1 , Anna V. Kukekova 2 , Dmitry V. Yudkin 1 , Vladimir A. Trifonov 1 , Nadezhda V. Vorobieva 1 , Violetta R. Beklemisheva 1 , Polina L. Perelman 1 , Daria A. Graphodatskaya 1 , Lyudmila N. Trut 1 , Fengtang Yang 3 , Malcolm A. Ferguson-Smith 3 , Gregory M. Acland 2 & Gustavo D. Aguirre 4 1 Institute of Cytology and Genetics, SB RAS, Novosibirsk, 630090 Russia; Tel: þ 007-3832-333857; Fax: þ 007-3832-331278; E-mail: graf@bionet.nsc.ru; 2 James A. Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, 14853, USA; 3 Centre for Veterinary Science, Department of Clinical Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 OES, United Kingdom; 4 School of Veterinary Medicine University of Pennsylvania, PA 19104, USA Received 5 October 2004. Received in revised form and accepted for publication by Wendy Bickmore 1 December 2004 Key words: B-chromosome, Canidae, C-KIT, oncogene Abstract 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. Introduction B-chromosomes are small dispensable super- numerary chromosomes found in certain species, in addition to the standard complement of A-chromosomes. The number of B-chromosomes (Bs) per cell may vary among different tissues, individuals, and populations. They do not pair and recombine with any A-chromosomes at meio- sis and are often heterochromatic. Although it is generally believed (Jones & Rees 1982, Camacho et al. 2000, Dhar et al. 2002) that most B-chromosomes lack major genes, this hypothesis has not been rigorously tested (Camacho et al . 2000). Canidae species exhibit at least two unusual phe- nomena of karyotype evolution. First, their chro- mosomes are extremely rearranged in comparison with other mammals (Yang et al. 1999, 2000, Graphodatsky et al. 2000, 2001) (only rodent species have more reshu¥ed karyotypes). Second, within the Carnivora order, only some canids were found to possess supernumerary chromosomes. B-chromosomes of canids were studied using both conventional and molecular cytogenetic Chromosome Research 13: 113–122, 2005. 113 # 2005 Springer. Printed in the Netherlands