The two genes vestigial (vg) and scalloped (sd) are required for wing development in Drosophila melanogaster. They present similar patterns of expression in second and third instar wing discs and similar wing mutant phenotypes. vg encodes a nuclear protein without any recognized nucleic acid-binding motif. Sd is a transcription factor homologous to the human TEF-1 factor whose promoter activity depends on cell-specific cofactors. We postulate that Vg could be a cofactor of Sd in the wing morphogenetic process and that, together, they could constitute a functional transcription complex. We investigated genetic interactions between the two genes. We show here that vg and sd co-operate in vivo in a manner dependent on the structure of the Vg protein. We ectopically expressed vg in the patch (ptc) domains. We show evidence that wing-like outgrowths induced by ectopic expression of vg are severely reduced in vg or sd mutant backgrounds. Accordingly, we demonstrate that ptc-GAL4-driven expression of vg induces both expressions of the endogenous vg and sd genes and that the two Vg and Sd proteins have to be produced together to promote wing proliferation. Furthermore, we show an interaction between the two proteins by double hybrid experiments in yeast. Our results therefore support the hypothesis that Sd and Vg directly interact in vivo to form a complex regulating the proliferation of wing tissue.

The vestigial (vg) gene of Drosophila melanogaster encodes a novel nuclear protein which is required for wing formation but its function is not restricted to this developmental process. In this report, we have examined the possible role of vestigial in the formation of the peripheral nervous system. We found that most vestigial mutants display ectopic or missing macrochaetae. We also show that vestigial interacts in a dose dependant manner with different alleles of the scute gene and with the extramacrochaetae gene and that mis-expression of the vestigial gene in the wing disc increases the domain of scute expression and allows the formation of supernumerary ectopic bristles. From these results, we conclude that vestigial affects scute expression and plays a role in the differentiation of the peripheral nervous system.

The supernatant of Bacillus thuringiensis cultures contains a thermostable toxin: the beta exotoxin or thuringiensin, which in vivo acts as a preferential inhibitor of ribosomal RNA synthesis. Added to Drosophila melanogaster culture medium, it induces, during the flies' development, a lethal effect that is, in our Oregon R strain, greater for females than for males. The authors have previously shown that a diminution of the ribosomal DNA amount increases the sensitivity to the lethal effect of the supernatant. From a stock subjected for several generations to a 28 degrees C temperature and more, they have spontaneously obtained a variant population where males and females have similar resistance. It is shown here that this difference between the two populations is expressed in the X/X female genotypes, and that there is a correlation between the sensitivity to the lethal effect of the Berliner Bacillus thuringiensis supernatant and the sensitivity to the effect of the 28 degrees C developmental temperature; genotypes resistant to the lethal effect of the temperature were positively selected when the temperature of development was increased. The better resistance of these genotypes could be related to more active ribosomal units on the X chromosome.

We report here the genetical and X chromosome rDNA molecular study of two Drosophila melanogaster Oregon R lines. These lines differ extensively in the degree of resistance of the females both to the lethal effect of an increased temperature and to that of Bacillus thuringiensis beta-exotoxin, which is an inhibitor of the nucleolar RNA polymerase. The 3B line, whose females are resistant, came from an Oregon R population subjected over several generations to increased temperature, 28°C or over, while the other line is derived from the initial stock. Twofold variation was observed in the total number of ribosomal genes between the two lines. This variation applied to most ribosomal units, including the active ones. Variations among X chromosome rDNA content in a wild type population have thus been revealed using tests of resistance to the Bacillus thuringiensis beta-exotoxin. Additive variations in specific unit types between the two lines indicate that modifications to the rDNA content are not rare events.