no-bridge and linotte act jointly at the interhemispheric junction to build up the adult central brain of Drosophila melanogaster

The Drosophila transmembrane protein Linotte (Lio) is expressed in a glial transcient interhemispheric fibrous ring (TIFR), which was hypothesised to serve as scaffold for adult brain formation during metamorphosis. We isolated TIFR specific enhancers from the lio locus and showed that only four interhemispheric cells give rise to this complex fibrous structure. We showed that lio controls the TIFR differentiation, and confirmed the major role played by this structure in central brain metamorphosis since its destruction by apoptosis led to a pronounced adult phenotype, which included defects of lio and no-bridge (nob) mutants. lio interhemispheric expression was specifically affected in a nob(1) context, confirming that nob plays a key role in adult brain development via the TIFR.

Genetic elimination of known pheromones reveals the fundamental chemical bases of mating and isolation in Drosophila

Overexpression of the UAS-tra transgene in Drosophila melanogaster females led to the complete elimination of their cuticular pheromones. According to current models of Drosophila behavior, these flies should induce no courtship. In fact, they are still attractive to conspecific males. Three classes of stimuli are shown to induce courtship, with different effects on male behavior: (i) known pheromones produced by control females, (ii) stimuli produced by living control and transgenic flies, and (iii) as-yet-undetermined pheromones present on both control and transgenic flies. Only the latter class of pheromones are required for mating. They appear to represent a layer of ancestral attractive substances present in D. melanogaster and its sibling species; known cuticular pheromones modulate this attractivity positively or negatively. The absence of inhibitory pheromones leads to high levels of interspecific mating, suggesting an important role for these cuticular hydrocarbons in isolation between species.

Genetic feminization of pheromones and its behavioral consequences in Drosophila males

Pheromones are intraspecific chemical signals important for mate attraction and discrimination. In the fruit fly Drosophila melanogaster, hydrocarbons on the cuticular surface of the animal are sexually dimorphic in both their occurrence and their effects: Female-specific molecules stimulate male sexual excitation, whereas the predominant male-specific molecule tends to inhibit male excitation. Complete feminization of the pheromone mixture produced by males was induced by targeted expression of the transformer gene in adult oenocytes (subcuticular abdominal cells) or by ubiquitous expression during early imaginal life. The resulting flies generally exhibited male heterosexual orientation but elicited homosexual courtship from other males.