A HIGH-RESOLUTION LINKAGE MAP OF THE LETHAL SPOTTING LOCUS - A MOUSE MODEL FOR HIRSCHSPRUNG DISEASE

Mice homozygous for the lethal spotting (ls) mutation exhibit aganglio nic megacolon and a white spotted coat owing to a lack of neural crest -derived enteric ganglia and melanocytes. The ls mutation disrupts the migration, differentiation, or survival of these neural crest lineage s during mammalian development. A human congenital disorder, Hirschspr ung disease (HSCR), is also characterized by aganglionic megacolon of the distal bowel and can be accompanied by hypopigmentation of the ski n. HSCR has been attributed to multiple loci acting independently or i n combination. The ls mouse serves as one animal model for HSCR, and t he ls gene may represent one of the loci responsible for some cases of HSCR in humans. This study uses 753 N-2 progeny from a combination of three intersubspecific backcrosses to define the molecular genetic li nkage map of the Es region and to provide resources necessary for posi tional cloning. Similar to some cases of HSCR, the ls mutation acts se midominantly, its phenotypic effects dependent upon the presence of mo difier genes segregating in the crosses. We have now localized the ls mutation to a 0.8-cM region between the D2Mit113 and D2Mit73/D2Mit174 loci. Three genes, endothelin-3 (Edn3), guanine nucleotide-binding pro tein ex-stimulating polypeptide 1 (Gnas), and phosphoenolpyruvate carb oxykinase (Pck1) were assessed as candidates for the ls mutation. Only Edn3 and Gnas did not recombine with the ls mutation. Mutational anal ysis of the Edn3 and Gnas genes will determine whether either gene is responsible for the neural crest deficiencies observed in ls/ls mice.