Accelerated disappearance of melanocytes in bcl-2-deficient mice.

Follicular melanocytes in bcl-2(-/-) mice have been reported to turn gray during the second hair cycle. Light microscopic analysis revealed that about half of bcl-2(-/-) mouse hair shafts had no detectable melanin granules after the second hair follicle cycle, but the remaining hair appeared to be pigmented normally. After depilation to induce new anagen hair, more than 97% of the hair shafts did not have visible melanin granules in bcl-2(-/-) mice, whereas 100% of the hair shafts in bcl-2(+/+) mice were pigmented. In bcl-2(+/+) mice, dopa-positive melanocytes appeared on day 4 after depilation, whereas bcl-2(-/-) mice developed few dopa-positive melanocytes after depilation, as assessed by light and electron microscopic observation. bcl-2(-/-) mouse hair in the second hair cycle contained about 60-70% less melanin than normal mouse hair, and newly generated bcl-2(-/-) mouse hair after depilation contained a level of melanin as low as that of albino mouse hair. These observations suggest that the expression of bcl-2 might be essential for melanocyte maintenance after the second hair cycle.