RXRA and HSPA5 map to the telomeric end of dog chromosome 9

Previous results showed that loci from human chromosome 17q (HSA17q) map to the centromeric two-thirds of dog chromosome 9 (CFA9). In these studies fluorescence in situ hybridization (FISH) using a human total chromosome 17 painting probe, indicated that the telomeric one-third of CFA9 must have homology to one or more human chromosomes other than HSA17. Here we report that this distal part of CFA9 contains a segment syntenic to the telomeric end of HSA9q and mouse chromosome 2 (MMU2). The gene loci encoding retinoid X receptor, alpha (RXRA) and heat shock protein 5 (HSPA5 or GRP78), which are found on HSA9q34 and MMU2, occupy a region on CFA9 distal to NF1 and CRYBA1. FISH of a canine specific genomic cosmid clone for RXRA demonstrated the more telomeric localization of this locus to NF1 on CFA9. A linkage map developed for the distal region of CFA9 included: NF1-(2.7 CM)-CRYBA1-(6.5 CM)-RXRA-(22CM)-HSPA5. The next best order, RXRA-NF1-CRYBA1-HSPA5 with a difference in the log odds of 1.43 does not correspond to our findings with FISH. The most probable map order places HSPA5 distal to RXRA on CFA9 whereas in humans it lies centromeric of RXRA on HSA9q34.