RESUMO
Recent studies in Drosophila melanogaster of the protocadherins Dachsous and Fat suggest that they act as ligand and receptor, respectively, for an intercellular signaling pathway that influences tissue polarity, growth and gene expression, but the basis for signaling downstream of Fat has remained unclear. Here, we characterize functional relationships among D. melanogaster tumor suppressors and identify the kinases Discs overgrown and Warts as components of a Fat signaling pathway. fat, discs overgrown and warts regulate a common set of downstream genes in multiple tissues. Genetic experiments position the action of discs overgrown upstream of the Fat pathway component dachs, whereas warts acts downstream of dachs. Warts protein coprecipitates with Dachs, and Warts protein levels are influenced by fat, dachs and discs overgrown in vivo, consistent with its placement as a downstream component of the pathway. The tumor suppressors Merlin, expanded, hippo, salvador and mob as tumor suppressor also share multiple Fat pathway phenotypes but regulate Warts activity independently. Our results functionally link what had been four disparate groups of D. melanogaster tumor suppressors, establish a basic framework for Fat signaling from receptor to transcription factor and implicate Warts as an integrator of multiple growth control signals.
Assuntos
Moléculas de Adesão Celular/metabolismo , Proteínas de Drosophila/metabolismo , Genes Supressores de Tumor , Transdução de Sinais , Animais , Moléculas de Adesão Celular/genética , Proteínas de Ciclo Celular/genética , Proteínas de Drosophila/genética , Drosophila melanogaster , Regulação da Expressão Gênica , Peptídeos e Proteínas de Sinalização Intracelular , Proteínas de Membrana/genética , Miosinas/genética , Miosinas/metabolismo , Neurofibromina 2/genética , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Proteínas Serina-Treonina Quinases/genética , Transativadores/genética , Transativadores/metabolismo , Proteínas de Sinalização YAPRESUMO
The precise coordination of signals that control proliferation is a key feature of growth regulation in developing tissues . While much has been learned about the basic components of signal transduction pathways, less is known about how receptor localization, compartmentalization, and trafficking affect signaling in developing tissues. Here we examine the mechanism by which the Drosophila Neurofibromatosis 2 (NF2) tumor suppressor ortholog Merlin (Mer) and the related tumor suppressor expanded (ex) regulate proliferation and differentiation in imaginal epithelia. Merlin and Expanded are members of the FERM (Four-point one, Ezrin, Radixin, Moesin) domain superfamily, which consists of membrane-associated cytoplasmic proteins that interact with transmembrane proteins and may function as adapters that link to protein complexes and/or the cytoskeleton . We demonstrate that Merlin and Expanded function to regulate the steady-state levels of signaling and adhesion receptors and that loss of these proteins can cause hyperactivation of associated signaling pathways. In addition, pulse-chase labeling of Notch in living tissues indicates that receptor levels are upregulated at the plasma membrane in Mer; ex double mutant cells due to a defect in receptor clearance from the cell surface. We propose that these proteins control proliferation by regulating the abundance, localization, and turnover of cell-surface receptors and that misregulation of these processes may be a key component of tumorigenesis.
Assuntos
Proteínas de Drosophila/fisiologia , Drosophila/metabolismo , Endocitose/fisiologia , Proteínas de Membrana/fisiologia , Neurofibromina 2/fisiologia , Receptores de Superfície Celular/metabolismo , Transdução de Sinais , Animais , Membrana Celular/metabolismo , Proliferação de Células , Drosophila/anatomia & histologia , Drosophila/genética , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Glicoproteínas de Membrana , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Mutação , Neurofibromina 2/genética , Complexo Glicoproteico GPIb-IX de Plaquetas , Transporte Proteico/fisiologia , Receptores de Superfície Celular/genética , Receptores Notch/metabolismo , Regulação para Cima , Asas de Animais/anatomia & histologia , Asas de Animais/metabolismoRESUMO
The mechanisms that control energy homeostasis and tissue growth during development are closely linked through the insulin signal transduction pathway. Changes in the level of insulin and other hormones reflect the nutritional status of the animal to control circulating sugar levels and fat metabolism. Systemic defects in insulin responsiveness can lead to elevated circulating glucose levels and fat accumulation. Here we present evidence that the microRNA miR-278 plays a role in the control of energy homeostasis in Drosophila. miR-278 mutants have elevated insulin production and are correspondingly lean. Despite the elevated insulin levels, miR-278 mutants have elevated circulating sugar, mobilized from adipose-tissue glycogen stores. We provide evidence that miR-278 mutants are insulin resistant and that miR-278 acts through regulation of the expanded transcript.
Assuntos
Drosophila/genética , Metabolismo Energético/fisiologia , Homeostase/fisiologia , Resistência à Insulina/genética , Insulina/metabolismo , MicroRNAs/genética , Transdução de Sinais/genética , Animais , Pareamento de Bases , Sequência de Bases , Glicemia , Northern Blotting , Metabolismo Energético/genética , Componentes do Gene , Homeostase/genética , Insulina/sangue , Dados de Sequência Molecular , Mutação/genética , Oligonucleotídeos , Reação em Cadeia da Polimerase , Transdução de Sinais/fisiologiaRESUMO
In Drosophila, the insecticide resistant 91-R strain is an overproducer and susceptible 91-C and ry(506) strains are the underproducers of CYP6A8 mRNA encoded by a cytochrome P450 gene, Cyp6a8. Low expression of Cyp6a8 in the underproducer strains is due to a downregulatory effect of a putative repressor locus, which is thought to be mutant in the overproducer strain. In the present investigation, organization of Cyp6a8 and promoter activity of its upstream DNA were analyzed. Cyp6a8 has two introns of which intron II is similar to the introns of other insect CYP genes with respect to its length and position. Intron I is only 36 bp long and lacks consensus splice sites. It is also in-frame with the CYP6A8 open reading frame. Therefore, inefficient splicing of intron I may produce two isoforms of CYP6A8. Analysis of Cyp6a8 upstream DNA of the overproducer 91-R strain showed that DNA sequences between -199 and -761 bp are required for the highest constitutive and barbital-induced expression of Cyp6a8. This region has six barbie boxes and binding sites for various transcription factors. Promoter activity of the -11/-761 DNA of the overproducer 91-R strain was found to be 4-fold lower in the genome of underproducer ry(506) strain, which is wild type for the putative repressor gene, than in the genome of F1 hybrids of 91-R and ry(506) strains. These results suggest that -11/-761 Cyp6a8 DNA of the 91-R strain can respond to the active repressor present in the hybrid genome and further support our previous findings that overexpression of Cyp6a8 is a result of mutation of a repressor gene rather than mutation of the cis-regulatory sequences.
