Galanin receptor 1 gene (Galnr1) is tightly linked to the myelin basic protein gene on chromosome 18 in mouse

Galanin receptor (GALNR1) is a G-protein coupled receptor linked to voltage gated calcium channels. The GALNR1 ligand is galanin, a 29-amino acid neuropeptide widely distributed in the central and peripheral nervous systems of numerous species. Galanin controls endocrine and exocrine pancreatic secretions, regulates intestinal motility, modulates behavioural, cognitive, and sensory functions, and may modulate growth hormone secretion. Despite strong evidence of extensive homology between mouse and human Chr 18, only seven human chromosome 18q loci have been comparatively mapped in these two species. To localize the mouse Galnr1 gene, we analyzed the segregation of an RFLP in DNAs derived from the offspring of The Jackson Lab BSS and BSB backcross panels. Figure 1A shows a TaqI RFLP detected with a rat galanin receptor cDNA probe, consisting of 6.5-kb and 2.5-kb M. spretus genomic DNA fragments and 7.1-kb and 2.8-kb C57BL/6J genomic fragments. Haplotype analysis of the backcross panel data showed no recombinants between Mbp and Galnr1, indicating complete linkage between these two genes. Tight linkage between MBP and GALNR1 is also observed on human Chr 18q based on co-location of these two genes on YAC clones 809_B_4 and 776_F_5. The region around MBP has been implicated as a region involved in the growth hormone insufficiency phenotype of patients with Chr 18q-syndrome. By correlating genotype with phenotype in affected children, it should be possible to determine whether GALNR1 or MBP is responsible for specific 18q-syndrome phenotypic features. (DBO)