Comparative mapping of bovine chromosome 13 by fluorescence in situ hybridization J Schla Èpfer, D S Gallagher Jr, J D Burzlaff, J E Womack, D M Stelly, J F Taylor, S K Davis Summary We present chromosomal fluorescence in situ hybridization (FISH) results that both extend the HSA20/BTA13 comparative map as well as cytogenetically anchor two microsatellite mar- kers. A bovine bacterial artificial chromosome (BAC) library was screened for conserved genes (type I loci) previously assigned to HSA10 or HSA20 and BTA13, and for microsatellites selected from two published BTA13 linkage maps. Clones from six out of nine comparative loci and both microsatellites were found repre- sented in the BAC library. These BAC clones were used as probes in single colour FISH to determine the chromosome band position of each locus. As predicted by the human/bovine comparative map, all type I loci mapped to BTA13. Because single colour FISH analysis revealed that the loci were clustered within the distal half of BTA13, dual colour FISH was used to confirm the locus order. Established order was centromere-PRNP-(SOD1L/AVP/OXT)- (BL42/GNAS1)-HCK-CSSM30. The findings con- firm the presence of a conserved HSA20 homo- logous synteny group on BTA13 distal of a HSA10 homologous segment. Keywords: bovine, bovine bacterial artificial chromosome library, cattle, chromosomes, fluorescence in situ hybridization, physical gene mapping Introduction The past 10 years have seen enormous progress in the endeavour to map the bovine genome. Second generation bovine linkage maps contain almost 1600 loci, mostly microsatellites, with an average map resolution of less than 2 . 5 cm between markers (Barendse et al. 1997; Kappes et al. 1997), and approximately 400 genes have been physically mapped to bovine chromo- somes (Womack & Kata 1995). In addition, comparative mapping of selected anchor loci (O'Brien et al. 1993) and other homologous genes (type I) has revealed extensive conserva- tion of synteny between the human and cattle genomes (Womack 1987). As the bovine genome effort continues, comparative gene mapping relative to human and mouse will likely play an increasingly important role due to its strategic function in the `positional candidate cloning' of QTLs (Collins 1995). Several studies using bovine/human Zoo- fluorescence in situ hybridization (FISH) (Hayes 1995; Solinas-Toldo et al. 1995; Chowdhary et al. 1996) have extended our knowledge of the boundaries of syntenic con- servation by identifying approximately 56 homologous chromosome segments between cattle and man. Bovine chromosome 13 (BTA13), for example, was shown to be homo- logous to parts of human chromosomes 10 and 20 (HSA10 and HSA20). BTA13 has been reported to be composed of a HSA10 segment `sandwiched' by centromeric and telomeric HSA20 segments. These Zoo-FISH results cor- roborate comparative mapping data for BTA13. Two HSA10 genes, interleukine 2 receptor a (IL2RA) and vimentin (VIM) have been assigned to BTA13 (Threadgill & Womack 1991), as have the HSA20 genes prion protein (PRNP), haemo- poietic cell kinase (HCK) (Womack et al. 1991), guanine nucleotide binding protein a-subunit (GNAS1), casein kinase 2 a-1 polypeptide (CSNK2A1) (Gao et al. 1997), arginine-vasopres- sin (AVP), oxytocin (OXT) (Dietz et al. 1992), adenosine deaminase (ADA), inosine tripho- sphatase-A (ITPA) (Womack & Moll 1986) and growth hormone-releasing hormone gene (GHRH) (Moody et al. 1995). Bovine soluble superoxide dismutase 1-like (SOD1L), a pseu- dogene of the soluble superoxide dismutase 1 gene (SOD1), has been mapped to BTA13 (Gallagher et al. 1992), but has yet to be identified in human. If present in the human genome, the bovine/human comparative map allows us to predict that it will likely map to either HSA10 or HSA20. Despite extensive conservation of synteny among species, little is known about conserva- Animal Genetics, 1998, 29, 265±272 J Schla È pfer J E Womack Department of Veterin- ary Pathobiology, Crop Sciences, Texas A&M University, College Sta- tion, TX 77843, USA D S Gallagher Jr J D Burzlaff J F Taylor S K Davis Department of Animal Science, Texas A&M University, College Sta- tion, TX 77843, USA D M Stelly Department of Soil and Crop Sciences, Texas A&M University, Col- lege Station, TX 77843, USA ã 1998 International Society for Animal Genetics 265 Correspondence: S K Davis. Accepted 18 March 1998