A comparative approach to physical and linkage mapping of genes on canine chromosomes using gene-associated simple sequence repeat polymorphisms illustrated by studies of dog chromosome 9.

We describe and illustrate a comparative approach to creating physical and linkage maps of genes on dog chromosomes. The approach is particularly useful in species, like the dog, which have a rudimentary gene map not integrated with microsatellite loci. Human or mouse cDNAs for genes to be mapped are used to isolate cosmid or phage clones from dog genomic libraries. Clones verified to contain the homologous canine gene coding sequences are screened for "gene-associated" simple sequence repeat polymorphisms (SSRPs). The unique sequences flanking the repeats are used to design PCR primers to amplify the repeat and gene-associated SSR length differences that are informative for linkage analysis used in canine pedigrees to study linkage between loci or with diseases. The same canine clones are employed as probes in fluorescence in situ hybridization (FISH) studies to physically map the loci to specific sites on dog chromosomes. This approach creates a combined gene and gene-associated microsatellite anchor locus framework map. In this article we review our recent use of this approach to map a series of genes found on human chromosome 17 (HSA17) to two dog chromosomes. Canine chromosome 9 (CFA9) contains 11 loci found on HSA17q, while two genes from HSA17p map to CFA5, demonstrating disruption of HSA17 synteny at the centromere. The order of 11 HSA17q genes on CFA9 was conserved in the dog, but the entire group is inverted with respect to the centromere when compared to human and mouse. Maps created by this approach can be used to advantage for integrating anonymous microsatellites with gene maps, including microsatellites found in genome scans to be linked to canine diseases. This makes it possible to identify the homologous chromosomal region in the human or mouse genome and to make use of this information in formulating hypotheses regarding candidate genes, as has recently been illustrated by other investigators.