Background: Gastric cancer (GC) is a highly prevalent disease, being the fourth most common cancer and the second leading cause of cancer-associated deaths worldwide. Although many genes have been implicated in its development, many cases remain genetically unexplained. Hence, there is an urgent need to find new disease-related genes. Methods: A transgenic Drosophila model was used to screen for novel genes putatively involved in GC. The authors evaluated the expression of the most interesting candidates in GC cell lines and primary tumours by semi-quantitative reverse transcription PCR, dissected the molecular mechanisms responsible for the deregulation of the most relevant one, and analysed its functional role in vitro and in a chicken embryo model. Results: Six candidate genes were identified, of which cytoplasmic polyadenylation element binding protein 1 ( CPEB1 ) was downregulated in all GC cell lines and in 11 of 12 primary GC tumours. The pivotal CPEB1 promoter CpG site was determined, and it was found that methylation at this 79th CpG site was associated with CPEB1 silencing in GC cell lines and primary tumours. It was also discovered that methylation of this site was significantly more prevalent in diffuse type GC (p=0.007) and in cases with lymph node metastases (p=0.042). In vitro, CPEB1 impaired invasion. Its antiangiogenic role was also discovered, which was associated with downregulation of MMP14 and VEGFA . Conclusions: The first evidence of CPEB1 involvement in GC is presented, along with the molecular mechanism underlying the regulation of its expression and its potential role in invasion and angiogenesis.

The nucleolus is a subnuclear factory, the activity of which is required beyond ribosome biogenesis for the regulation of cell growth, death and proliferation. In both Drosophila and mammalian cells, the activity of the nucleolus is regulated by the protooncogene Myc. Myc induces the transcription of genes required for ribosome biogenesis and the synthesis of rRNA by RNA polymerase I, a nucleolar event that is rate limiting for cell growth. Here, we show that the fruit fly Nol12 homologue Viriato is a key determinant of nucleolar architecture that is required for tissue growth and cell survival during Drosophila development. We further show that viriato expression is controlled by Drosophila Myc (dMyc), and that the ability of dMyc to stimulate nucleolar and cellular growth depends on viriato expression. Therefore, viriato acts downstream of dMyc to ensure a coordinated nucleolar response to dMyc-induced growth and, thereby, normal organ development.

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.

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 cis‐regulatory 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.