ACCELERATED DISAPPEARANCE OF MELANOCYTES IN BCL-2-DEFICIENT MICE

Follicular melanocytes in bcl-2(-/-) mice were examined. bcl-2(-/-) mi ce have been reported to turn gray during the second hair cycle, Light microscopic analysis revealed that about half of bcl-2(-/-) mouse hai r shafts had no detectable melanin granules after the second hair foll icle 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, where as 100% of the hair shafts in bcl-2(+/+) mice were pigmented, In bcl-2 (+/+) mice, dopa-positive melanocytes appeared on day 4 after depilati on, whereas bcl-2(-/-) mice developed few dopa-positive melanocytes af ter depilation, as assessed hy light and electron microscopic observat ion, 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 express ion of bcl-2 might be essential for melanocyte maintenance after the s econd hair cycle.