Experiments with themaroon-likemutation ofDrosophila melanogaster

Abstract

SUMMARYCell lineage analysis of themaroon-likemutation ofDrosophila melanogasterrevealed the most extensive degree of non-autonomy reported to date inDrosophila: all 1454 gynandromorphs in whichXchromosome loss uncovered thema-lmutation hadma-l+.eye colour. In contrast, among 331 gynandromorphs in whichXchromosome loss simultaneously uncovered thevermilionandmaroon-likemutations, approximately 16% hadvphenotype but with one possible exception all gynandromorphs again hadma-l+eye colour. These results suggest that very small amounts of thema-l+gene product are necessary for wild-type eye colour development and they are therefore compatible with the one cistron–allelic complementation model that has been proposed for thema-llocus. They also provide the best estimate available to date ofIn(1)wvc-induced internal mosaicism: 7%. A preliminary attempt to detect DNA-induced transformants among 6 DNA-injected preblastodermma-lembryos and at least 80000 of their F1to F4descendants has yielded completely negative results. An investigation of the maternal effect whichma-l+mothers exert on the eye colour of their geneticallyma-loffspring revealed that, in contrast to earlier observations, this effect is not universal: some phenotypicallyma-land intermediatema-lflies were observed in young cultures. The discrepancy between this and earner observations is probably attributable to as yet uncharacterized nutritional deficiencies in the diet of flies used in this experiment. Cytoplasm drawn from blastodermma-l+embryos and injected into the posterior region ofma-lpreblastoderm embryos failed to induce eye-colour alterations in all seven flies which survived the treatment. Injection of the contents of embryos of certain genotypes and developmental stages intoma-lpupae 24–48 h old did alter in some instances the eye colour of treatedma-lflies. Various tests strongly suggest that these alterations are not due to injection of a substance that has been stored in the egg during oogensis or that has been produced by the embryo itself prior to injection and they therefore preclude the possibility that a simplein vivobioassay for thema-l+substance has been achieved. Rather, they indicate that the observed eye-colour alterations are due to transplantation of blastoderm-stage embryos which remain active long enough withinma-lhosts to produce and release a substance into the hosts' haemolymph and that this substance in turn induces phenotypic alterations in the hosts' eye colour. Whenvandma-leye colour changes are simultaneously monitored, it appears that injection of embryonic contents into pupae is equally or more effective in modifying thevphenotype than in modifying thema-lphenotype. Based on these observations, a tentative hypothesis regarding the time of activation of thema-l+gene and the relationship between the immediate product of this gene, the maternal substance stored in the egg and the substance released by tissue transplants is proposed.