Effects of microphthalmic white (Miwh) on the number and function of cutaneous melanocytes.

Microphthalmic white (Miwh), when heterozygous, causes dilution of black fur to a uniform gray color. Miwh/+ also reduces the coloration of ear and tail skin. The present study, a quantitative assessment of the effects of Miwh/+ on cutaneous melanocytes, demonstrates that the primary effect of Miwh/+ on cutaneous pigmentation is to reduce the number of epidermal melanocytes. There is also indirect evidence that Miwh/+ reduces the rate of melanosome production within follicular melanocytes. These actions of Miwh/+ cause both lightened coloration of ear and tail skin and the deposition of fewer numbers of smaller melanosomes within the hair.