Experimental evidence for autonomous action of the periodic albinism (ap) gene within developing retinal pigment cells and melanophores of Xenopus laevis.

Genes which affect pigment elaboration may do so by autonomous action within the developing pigment cells or by way of tissue interactions leading to pigment cell differentiation. The site of action of the periodic albinism (ap) gene was investigated by substituting presumptive neural ectoderm of gastrulae of one genotype with uncommitted ectoderm of different genotype. Retinal pigment cells and melanophores arising from such grafts were found to differentiate according to their own genotype in spite of having spent their entire developmental history in tissues of different genotype. This finding demonstrates autonomous action of the ap gene within pigment cell derivatives and does not support recent proposals that the ap gene is involved in inductive interactions leading to melanogenesis. Experiments in which portions of presumptive dorsal mesoderm, implanted in gastrulae of different genotype, induced secondary pigment cells of host phenotype further support the proposal that the ap effect on pigment cells is not mediated by inductive interactions.