Expression of an activated ras gene causes developmental abnormalities in transgenic Drosophila melanogaster

We describe the developmental effects of the expression of a normal and mutated Drosophila ras gene ras2 in transgenic Drosophila. A Gly14----Val14 mutant (Gly14 in ras2 is equivalent to Gly12 in mammalian ras proteins) was constructed in ras2 by site-directed mutagenesis. Inducible constructs of ras2 and ras2Val14 were made by coupling the hsp70 promoter to each of the genes. In addition, the endogenous ras2 promoter was placed upstream of the mutated ras2Val14. These constructs were introduced into the germ line of Drosophila to yield transgenic lines by P-element-mediated transformation. A wide variety of developmental disorders were displayed in flies carrying the mutated ras2 gene driven by either the endogenous or the hsp70 promoter. The basal level of transcription of mutated ras from the uninduced hsp70 promoter was sufficient to produce disturbances in the development of several tissue types. In contrast, phenotypic disturbances were not seen with the normal ras2 gene driven by the hsp70 promoter even when induced by heat shock to very high levels of transcription over normal ras2 levels. A subset of the tissues expressing ras2 during development was particularly sensitive to the expression of ras2Val14. The compound eye was found to develop a dorsal-to-ventral 'scar' correlated with the wave of differentiation occurring in the eye imaginal disc at the time of a single brief induction of the hsp70 promoted ras2Val14 construct.