The patchwork mouse phenotype: Implication for melanocyte replacement in the hair follicle

Mice homozygous for the recessive patchwork (pwk) mutation are characterize d by a variegated pigment pattern with a mixture of unpigmented and normall y pigmented hairs. The pigmented hair bulbs contain functional melanocytes, By contrast, the unpigmented hair bulbs contain no melanocytes. This lack results from the death of melanoblasts in the hair follicle at the end of e mbryogenesis. Here, we report that melanoblasts and melanocytes are found i n the epidermis of pwk/pwk mice. Furthermore, these epidermal pigment cells are able to colonize new hair follicles after skin wounding. Despite the p resence of epidermal pigment cells with a colonization potential, a follicl e that had produced an unpigmented hair produces a new unpigmented hair dur ing the successive hair growth cycles. This hair color continuity is also t rue for the pigmented hair follicles, Thus, in normal conditions, the hair acts as an independent functional unit as regards its pigment cells populat ion.