Fig. 4. Regeneration melanocytes acquire kit-independence as they mature during late stages of regeneration. Melanocyte survival rates (y-axis) from kitj1e99 (black) and wild-type regenerates (red) shifted from 25°C to 33°C at the stages of regeneration indicated (x-axis), or kitj1e99 held constitutively at 25°C (blue) are shown. To document the acquisition of kit-independence by regeneration melanocytes, melanocytes in the presumptive central stripe of caudal fins regenerating at 25°C were counted at the stages of regeneration indicated. The fish were then moved into PTU to inhibit the appearance of new melanocytes, and either shifted to 33°C or maintained at 25°C for six subsequent stages. The final number of melanocytes in the presumptive stripe from an individual regenerate after six stages was assessed and then divided by the initial number of melanocytes to determine the percent survival rate. The persistent melanocytes in kitj1e99 regenerates following upshift at stage 7 (black; 38%) consist largely of cells which were pigmented prior to amputation and subsequently migrated into the proximal regenerate (not shown). Error bars show 95% confidence intervals. (See Materials and Methods for further details.)