RESUMO
The Drosophila Mitogen Activated Protein Kinase (MAPK) Rolled is a key regulator of developmental signaling, relaying information from the cytoplasm into the nucleus. Cytoplasmic MEK phosphorylates MAPK (pMAPK), which then dimerizes and translocates to the nucleus where it regulates transcription factors. In cell culture, MAPK nuclear translocation directly follows phosphorylation, but in developing tissues pMAPK can be held in the cytoplasm for extended periods (hours). Here, we show that Moleskin antigen (Drosophila Importin 7/Msk), a MAPK transport factor, is sequestered apically at a time when lateral inhibition is required for patterning in the developing eye. We suggest that this apical restriction of Msk limits MAPK nuclear translocation and blocks Ras pathway nuclear signaling. Ectopic expression of Msk overcomes this block and disrupts patterning. Additionally, the MAPK cytoplasmic hold is genetically dependent on the presence of Decapentaplegic (Dpp) and Hedgehog receptors.
Assuntos
Proteínas de Drosophila/fisiologia , Drosophila/crescimento & desenvolvimento , Olho/crescimento & desenvolvimento , Carioferinas/fisiologia , Sistema de Sinalização das MAP Quinases/fisiologia , Proteínas Serina-Treonina Quinases/fisiologia , Receptores de Superfície Celular/fisiologia , Receptores Acoplados a Proteínas G/fisiologia , Animais , Drosophila/enzimologia , Proteínas de Drosophila/genética , Olho/enzimologia , Larva/enzimologia , Larva/crescimento & desenvolvimento , Sistema de Sinalização das MAP Quinases/genética , Proteínas Quinases Ativadas por Mitógeno/fisiologia , Proteínas Serina-Treonina Quinases/genética , Receptores de Superfície Celular/genética , Receptores Acoplados a Proteínas G/genética , Receptor SmoothenedRESUMO
The Hedgehog and Decapentaplegic pathways have several well-characterized functions in the developing Drosophila compound eye, including initiation and progression of the morphogenetic furrow. Other functions involve control of cell cycle and cell survival as well as cell type specification. Here we have used the mosaic clone analysis of null mutations of the smoothened and thickveins genes (which encode the receptors for these two signals) both alone and in combination, to study cell cycle and cell fate in the developing eye. We conclude that both pathways have several, but differing roles in furrow induction and cell fate and survival, but that neither directly affects cell type specification.
Assuntos
Ciclo Celular/genética , Proteínas de Drosophila/genética , Drosophila/crescimento & desenvolvimento , Olho/crescimento & desenvolvimento , Morfogênese/genética , Proteínas Serina-Treonina Quinases/genética , Receptores de Superfície Celular/genética , Receptores Acoplados a Proteínas G/genética , Animais , Drosophila/genética , Drosophila/metabolismo , Proteínas de Drosophila/metabolismo , Proteínas de Drosophila/fisiologia , Olho/citologia , Regulação da Expressão Gênica no Desenvolvimento , Proteínas Hedgehog , Mosaicismo , Mutação , Proteínas Serina-Treonina Quinases/metabolismo , Receptores de Superfície Celular/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Transdução de Sinais/genética , Receptor SmoothenedRESUMO
Mitogen-activated protein kinases (MAPKs) phosphorylate target proteins in both the cytoplasm and nucleus, and a strong correlation exists between the subcellular localization of MAPK and resulting cellular responses. It was thought that MAPK phosphorylation was always followed by rapid nuclear translocation. However, we and others have found that MAPK phosphorylation is not always sufficient for nuclear translocation in vivo. In the developing Drosophila wing, MAPK-mediated signaling is required both for patterning and for cell proliferation, although the mechanism of this differential control is not fully understood. Here, we show that phosphorylated MAPK (pMAPK) is held in the cytoplasm in differentiating larval and pupal wing vein cells, and we show that this cytoplasmic hold is required for vein cell fate. At the same time, we show that MAPK does move into the nucleus of other wing cells where it promotes cell proliferation. We propose a novel Ras pathway bifurcation in Drosophila and our results suggest a mechanism by which MAPK phosphorylation can signal two different cellular outcomes (differentiation versus proliferation) based on the subcellular localization of MAPK.