The murine dilute suppressor gene dsu suppresses the coat-color phenotype of three pigment mutations that alter melanocyte morphology, d, ash and ln.

The murine dilute suppressor gene, dsu, was identified because of its ability to suppress the dilute coat color of mice homozygous for the retrovirally induced allele (dv) of the dilute locus (d). dsu is unlinked to the d locus and has recently been shown to be semidominantly inherited. The dilute phenotype of d/d mice is the consequence of abnormal melanocyte morphology. While wild-type melanocytes are dendritic, d/d melanocytes are adendritic. dsu apparently suppresses the dilute phenotype by restoring normal melanocyte morphology. In addition to d, two other loci, ashen (ash) and leaden (ln), have been identified that produce a diluted coat color associated with adendritic melanocytes. Interestingly, d and ash are closely linked on chromosome 9 while dsu and ln are located on chromosome 1. In experiments described here, we present genetic mapping data between ash and d indicating that, despite their identical phenotypes, they are separate genes and are not intragenic complementing alleles of the same locus. We also show that dsu is only loosely linked to ln (approximately 9 cM proximal) and that dsu can suppress, at least partially, the coat color of ln/ln mice and ash/ash mice. The partial suppression of ln and ash coat colors is associated with the partial restoration of normal melanocyte morphology. These studies provide new insights into the mechanism of action of dsu and into the interrelationships between members of a family of pigment genes.