The Drosophila genes spalt major (salm) and spalt-related (salr) encode Zn-finger transcription factors regulated by the Decapentaplegic (Dpp) signalling pathway in the wing imaginal disc. The function of these genes is required for cell survival and proliferation in the central region of the wing disc, and also for vein patterning in the lateral regions. The identification of direct Salm and Salr target genes, and the analysis of their functions, are critical steps towards understanding the genetic control of growth and patterning of the Drosophila wing imaginal disc by the Dpp pathway. To identify candidate Salm/Salr target genes, we have compared the expression profile of salm/salr knockdown wing discs with control discs in microarray experiments. We studied by in situ hybridization the expression pattern of the genes whose mRNA levels varied significantly, and uncovered a complex transcription landscape regulated by the Spalt proteins in the wing disc. Interestingly, candidate Salm/Salr targets include genes which expression is turned off and genes which expression is positively regulated by Salm/Salr. Furthermore, loss-of-function phenotypic analysis of these genes indicates, for a fraction of them, a requirement for wing growth and patterning. The identification and analysis of candidate Salm/Salr target genes opens a new avenue to reconstruct the genetic structure of the wing, linking the activity of the Dpp pathway to the development of this epithelial tissue.

Transforming Growth Factor b (TGFb) signaling has a complex influence on cell proliferation, acting to stop cell division in differentiating cells, but also promoting cell division in immature cells. The activity of the pathway in Drosophila is mostly required to stimulate the proliferation of neural and epithelial tissues. Most interestingly, this function is not absolutely required for cell division, but it is needed for these tissues to reach their correct size. It is not known how TGFb signaling promotes cell division in imaginal discs, or what the interactions between TGFb activity and other signaling pathways regulating cell proliferation are. In this work, we have explored the disc autonomous function of TGFb that promotes wing imaginal disc growth. We have studied the genetic interactions between TGFb signaling and other pathways regulating wing disc growth, such as the Insulin and Hippo/Salvador/Warts pathways, as well as cell cycle regulators. We have also identified a collection of TGFb candidate target genes affecting imaginal growth using expression profiles. These candidates correspond to genes participating in the regulation of a variety of biochemical processes, including different aspects of cell metabolism, suggesting that TGFb could affect cell proliferation by regulating the metabolic fitness of imaginal cells.

The Drosophila genome contains approximately 14.000 protein coding genes encoding all the necessary information to sustain cellular physiology, tissue organization, organism development and behavior. In this manuscript we describe in some detail the phenotypes in the adult fly wing generated after knockdown of approximately 80% of Drosophila genes. We combined this phenotypic description with a comprehensive molecular classification of the Drosophila proteins into classes that summarize the main expected or known biochemical/functional aspect of each protein. This information, combined with mRNA expression levels and in situ expression patterns, provides a simplified atlas of the Drosophila genome, from housekeeping proteins to the components of the signaling pathways directing wing development, that might help to further understand the contribution of each gene group to wing formation.