The precise regulation of wingless (wg) expression in the Drosophila eye disc is key to control the anteroposterior and dorsoventral patterning of this disc. Here, we identify an eye disc-specific wg cisregulatory element that functions as a regulatory rheostat. Pannier (Pnr), a transcription factor previously proposed to act as an upstream activator of wg, is sufficient to activate the eye disc enhancer but required for wg expression only in the peripodial epithelium of the disc. We propose that this regulation of wg by Pnr appeared associated to the development of the peripodial epithelium in higher dipterans and was added to an existing mechanism regulating the deployment of wingless in the dorsal region of the eye primordium. In addition, our analysis identifies a separate ventral disc enhancer that lies adjacent to the eye-specific one, and thus altogether, they define a 1-kb genomic region where disc-specific enhancers of the wg gene are located. Developmental Dynamics 235:225-234, 2006.

Germline mutations in the human E-cadherin (hEcad) gene, CDH1, are initiating events in cases of human hereditary diffuse gastric cancer (HDGC) indicating that hEcad is a tumor suppressor. Among the hEcad mutations identified so far, some are missense, but the pathological relevance of these missense mutants is still unclear. In vitro assays show that missense mutations result in full-length hEcad molecules that retain some distinct biological activity, but in vivo functional studies in animal models are still lacking. Here we verify the potential of a Drosophila model to in vivo characterize the functional consequences of HDGC-associated germline missense mutations and to identify signaling pathways affected by these mutations. To this end, we have generated transgenic fly strains expressing the wild-type hEcad gene or its missense mutations. Similar to the fly Ecad, expression of wild-type hEcad and missense forms in fly epithelia resulted in their localization to the subapical region. In addition, we verify a genotype-phenotype correlation associated to the specific domain affected by the mutations, because cells expressing normal or missense mutant hEcad display different migratory and invasive behaviors in fly epithelia. We show that some of these effects might be mediated through hEcad interacting with the endogenous fly ss-catenin, Armadillo, thus interfering with the Wnt signaling pathway. Therefore, the use of this simple in vivo system will contribute to characterize the effects that missense hEcad have on cell behavior in a tissue environment, and might help to understand their significance in gastric cancer onset.

To understand the function and evolution of genes with complex patterns of expression, such as the Drosophila wingless gene, it is essential to know how their transcription is regulated. However, extracting the relevant regulatory information from a genome is still a complex task. We used a combination of comparative genomics and functional approaches to identify putative regulatory sequences in two introns (1 and 3) of the wingless gene and to infer their evolution. Comparison of the sequences obtained from several Drosophila species revealed colinear and well-conserved sequence blocks in both introns. Drosophila willistoni showed a rate of evolution, in both introns, faster than expected from its phylogenetic position. Intron 3 appeared to be composed of two separate modules, one of them lost in the willistoni group. We tested whether sequence conservation in noncoding regions is a reliable indicator of regulatory function and, if this function is conserved, by analyzing D. melanogaster transgenic reporter lines harboring intron 3 sequences from D. melanogaster (Sophophora subgenus) and the species from the Drosophila subgenus presenting the most divergent sequence, D. americana. The analysis indicated that intron 3 contains pupal enhancers conserved during the evolution of the genus, despite the fact that only 30% of the D. melanogaster intron 3 sequences lie in conserved blocks. Additional analysis of D. melanogaster transgenic reporter lines harboring intron 3 sequences from D. willistoni revealed the absence of an abdomen-specific expression pattern, probably due to the above-mentioned loss of a regulatory module in this species.