The gene dominant spotting in the mouse affects coat colour. The heterozygotes for the viable allele (Wv) have one or two white spots and a general greying of the coat. The homozygotes are entirely white. There is evidence that the gene causes abnormalities of pigmentation by affecting the neural crest.
The inner ears of 33 Wv/Wv, 23 Wv/+ and Wv/+ mice were examined. Marked abnormalities were found in the cochlea of all Wv/Wv mice and in the saccule of many. They also occurred, though in a restricted form, in a small part of the cochlea of a few old Wv/+ mice. The +/+ animals were all normal.
These findings may be interpreted as follows. The neural crest contributes to the formation of the acoustic ganglion, and as it is abnormal in Wv/Wv mice in its undifferentiated state, both the melanoblasts and the ganglionic primordia are affected. The abnormality of the primordium of the acoustic ganglion manifests itself as pathological changes in the inner ear.
This interpretation is supported by the results of an earlier study on the mutant piebald-lethal (sl). But as there is considerable evidence that the otic placode also contributes to the formation of this ganglion, it probably has a dual origin. Since the vestibular part of the inner ear in both Wv/Wv and sl/sl mice appears to be unaffected, it may be assumed that the placodal moiety innervates this region, and the neural crest moiety the cochlea and the saccule.
The mode of formation of the acoustic ganglion suggested here should also be applicable to man, the dog, the cat, the mink and the deer mouse, if not to all mammals. In the species named above inner ear abnormalities have either been observed or been inferred from the behaviour, and when examined they have been found to be extraordinarily similar to those discovered in the mouse mutants.
A gene triplet in the mouse