The Genetics of Dopa Decarboxylase and a-Methyl Dopa Sensitivity inDrosophila melanogaster

Abstract

Dopa decarboxylase (DDC) in the Diptera is an enzyme involved in sclerotinization of the cuticle in the epidermis and the production of neurogenic amines in the central nervous system. Its appearance in the epidermis at pupariation is induced by the molting hormone ecdysone. The dietary administration of the analog inhibitor α-methyl dopa (a MD) was used to isolate resistant and hypersensitive mutants. Two of three dominant resistant strains isolated increase DDC activity 35-70%. For both the increase is due to mutations between rdo (53) and pr (54.5) on the left arm of the 2nd chromosome (2L). The very highly resistant strain which does not affect DDC in any way is located at 54.0 on 2L. Twelve dominant, l(2) amdH —α MD hypersensitive alleles located immediately to the right of hk (53.9) on 2L have been recovered. All are recessive lethals and exhibit some intracistronic complementation, and none of them, not even heteroallelic heterozygotes, affect DDC in any way. The.recovery and analysis of 16 overlapping deficiencies permitted the localization of a DDC dosage effect to bands 37B10-C7 on 2L; a region which includes the l(2) amd locus. Subsequently eight DDC deficient lethal alleles were recovered in this eleven band region which as heterozygotes reduce activities to 28–53 % of controls. Some heteroallelic heterozygotes exhibit intracistronic complementation; most with viabilities 5% and with a mutant phenotype probably derived from inadequately sclerotinized cuticle. These Ddc alleles are within 0.004 Map Units to the right of l(2) amd . None as Ddc/CyO heterozygotes are sensitive to α-MD, and complementation occurs between the Ddc alleles and the l(2)amd alleles both on the basis of viability and DDC activity. Although the protein product mutated by the l(2) amd alleles has not yet been identified, it seems likely that the two groups of mutants are functionally related. Finally, the Ddc structural mutants reduce DDC activity in the central nervous system as well as the epidermis.