THE GENE ACTION AND FUNCTION OF TWO DOPA OXIDASE POSITIVE MELANOCYTE MUTANTS OF THE FOWL

Ultrastructural and autoradiographic analysis revealed the developmental genetic differences between the dopa oxidase positive pk and I mutations of the fowl. The differences were revealed by the results of five measurements involving homozygous mutant melanocytes, heterozygous melanocytes, and standard melanocytes at each of the loci. The measurements were: ultrastructural comparisons of melanosomes in pigmented epithelial (PE) and neural crest derived (NC) melanocytes, the number of 3H-dopa and 3H-leucine grains/µ2 of melanosome, the 3H-dopa/3H-leucine ratio, and the percentage of cytoplasmic 3H-leucine grains that were melanosomal. The pk mutation altered both PE and NC melanosomes. +/pk melanocytes were characterized by suppressed 3H-dopa/µ2 and 3H-dopa/3H-leucine values. +/pk cells, however, had the same percentage of melanosomal 3H-leucine grains as the "pk" standard. The I mutation altered only NC melanosomes. +/I melanocytes were characterized by 3H-dopa/µ2 and 3H-dopa/3H-leucine values similar to the "I" standard. +/I cells had a lower percentage of melanosomal 3H-leucine grains than the "I" standard, however. These data suggest that pk is a structural mutation affecting melanin binding to the premelanosome, while I seems to be a control gene mutation partially suppressing the production of premelanosomal components in NC melanocytes.