Melanocyte developmental genetics: biphasic control of dopa oxidase activity by the E locus of the fowl

Aliquots of developing feather papillae isolates were measured for oxygen consumption before and after incubation in the substrate, L‐dopa. Net oxidation (dopa minus basal) indicated the amount of L‐dopa oxidized by melanocytes. The albino‐like mutant ey/ey c/c showed minimal net oxidation when compared to its counterpart ey/ey +C/+C. This shows that the c mutation severely restricts dopa oxidase activity. The eumelanic genotype (E/E) had high net oxidation at stage 34 which regressed to a low value by stage 38. The pheomelanic‐producing genotype (ey/ey) had a low net oxidation at stage 34 which progressed to a high value by stage 38. Dopa oxidase activity in the eumelanin and pheomelanin producing genotype (standard; +E/ +E) was biphasic. Cells from these embryos had high net oxidation at both stages 34 and 38 and a low value at stage 36. High net oxidation at stage 34 in E/E and +E/+E seem associated with eumelanogenesis, while the high net oxidation at stage 38 in +E/+E and ey/ey is thought to be related to pheomelanogenesis. L‐dopa substrate utilization values were also completed for the heterozygote E/ey to determine if differences were detectable between this genotype and its respective homozygotes. The heterozygote net oxidation resembled E/E in pattern but at about one‐half the E/E values. The data are discussed in terms of the E locus as a possible control gene locus which determines whether eumelanin or pheomelanin is synthesized.