SUMMARYThe effect of dietary supplements of individual l-amino acids on the expression of the eyegone and eyelessK mutants of Drosophila melanogaster are compared. In both mutants, eye size is reduced by excess levels of tryptophan, phenylalanine and methionine, and in each case the effects are independent of metabolic competition for pyridoxal phosphate. A dietary interaction involving methionine and UNA can be demonstrated in the eyK strain, but the mechanism of action of this amino acid is obscure. Tryptophan metabolism is examined in detail. Although both tryptamine and serotonin have significant effects, the action of tryptophan on eye development is largely independent of its metabolic products. Conversely, the effect of dietary supplements of certain catecholamines is consistent with the action of phenylalanine. The action of certain metabolic inhibitors provides additional support for the suggestion that the catecholamines have an important effect on morphogenesis in the eye imaginai disks. Eye development is also affected by increasing concentrations of γ-amino-butyric acid, and this, taken together with the effect of the catecholamines and indolalkylamines, suggests that physiological control of the action of the mutant genes on eye development involves a group of compounds characteristically associated with nervous tissue. Eye development in the eyK strain may be influenced by the availability of acetyl CoA, which would be expected to affect acetylcholine biosynthesis. Possible mechanisms of action of the effective dietary treatments are discussed, together with a tentative hypothesis regarding the mode of action of the mutant genes on eye development.
The physiological control of gene action in the eyeless and eyegone mutants of Drosophila melanogaster