RESUMO
Development of the segmented central nerve cords of vertebrates and invertebrates requires connecting successive neuromeres. Here, we show both how a pathway is constructed to guide pioneer axons between segments of the Drosophila CNS, and how motility of the pioneers along that pathway is promoted. First, canonical Notch signaling in specialized glial cells causes nearby differentiating neurons to extrude a mesh of fine projections, and shapes that mesh into a continuous carpet that bridges from segment to segment, hugging the glial surface. This is the direct substratum that pioneer axons follow as they grow. Simultaneously, Notch uses an alternate, non-canonical signaling pathway in the pioneer growth cones themselves, promoting their motility by suppressing Abl signaling to stimulate filopodial growth while presumably reducing substratum adhesion. This propels the axons as they establish the connection between successive segments.
Assuntos
Axônios/fisiologia , Comunicação Celular/genética , Sistema Nervoso Central/embriologia , Proteínas de Drosophila/fisiologia , Drosophila melanogaster/embriologia , Receptores Notch/fisiologia , Animais , Animais Geneticamente Modificados , Axônios/metabolismo , Comunicação Celular/fisiologia , Diferenciação Celular/genética , Diferenciação Celular/fisiologia , Processos de Crescimento Celular/genética , Processos de Crescimento Celular/fisiologia , Sistema Nervoso Central/citologia , Sistema Nervoso Central/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Drosophila melanogaster/fisiologia , Embrião não Mamífero , Cones de Crescimento/metabolismo , Cones de Crescimento/fisiologia , Modelos Biológicos , Fatores de Crescimento Neural/metabolismo , Receptores de Netrina , Netrina-1 , Neuroglia/metabolismo , Neuroglia/fisiologia , Pseudópodes/genética , Pseudópodes/metabolismo , Pseudópodes/fisiologia , Receptores de Superfície Celular/metabolismo , Receptores Notch/genética , Receptores Notch/metabolismo , Sinapses/genética , Sinapses/metabolismo , Sinapses/fisiologia , Proteínas Supressoras de Tumor/metabolismoRESUMO
The receptor Notch interacts with the Abl tyrosine kinase signaling pathway to control axon growth and guidance in Drosophila motor neurons. In part, this is mediated by binding to Trio, a guanine nucleotide exchange factor (GEF) for Rho GTPases. We show here that one of the two GEF domains of Trio, the Rac-specific GEF1, is essential for Trio-dependent motor axon guidance and for the genetic suppression of Notch function in motor axon patterning, but the Rho-specific GEF2 domain is not. Consistent with this, we show that Rac, and not Rho1 or Cdc42, interacts genetically with Notch in a manner indistinguishable from that of bona fide Abl signaling components. We infer, therefore, that Rac is a key component of Abl signaling in Drosophila motor axons, and specifically that it is the crucial Rho GTPase in "noncanonical" Notch/Abl signaling.
Assuntos
Axônios/fisiologia , Movimento Celular/fisiologia , Proteínas de Drosophila/metabolismo , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Neurônios Motores/fisiologia , Fosfoproteínas/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Receptores Notch/metabolismo , Proteínas rac de Ligação ao GTP/metabolismo , Animais , Axônios/ultraestrutura , Proteínas de Drosophila/genética , Drosophila melanogaster/fisiologia , Fatores de Troca do Nucleotídeo Guanina/genética , Neurônios Motores/citologia , Fosfoproteínas/genética , Proteínas Serina-Treonina Quinases/genética , Receptores Notch/genética , Transdução de Sinais/fisiologia , Proteínas rac de Ligação ao GTP/genéticaRESUMO
Abl is an essential regulator of cell migration and morphogenesis in both vertebrates and invertebrates. It has long been speculated that the adaptor protein Disabled (Dab), which is a key regulator of neuronal migration in the vertebrate brain, might be a component of this signaling pathway, but this idea has been controversial. We now demonstrate that null mutations of Drosophila Dab result in phenotypes that mimic Abl mutant phenotypes, both in axon guidance and epithelial morphogenesis. The Dab mutant interacts genetically with mutations in Abl, and with mutations in the Abl accessory factors trio and enabled (ena). Genetic epistasis tests show that Dab functions upstream of Abl and ena, and, consistent with this, we show that Dab is required for the subcellular localization of these two proteins. We therefore infer that Dab is a bona fide component of the core Abl signaling pathway in Drosophila.
Assuntos
Proteínas de Drosophila/genética , Proteínas de Drosophila/fisiologia , Drosophila/embriologia , Drosophila/genética , Proteínas do Tecido Nervoso/fisiologia , Proteínas Tirosina Quinases/genética , Animais , Animais Geneticamente Modificados , Movimento Celular/genética , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Drosophila/fisiologia , Proteínas de Drosophila/metabolismo , Embrião não Mamífero , Epistasia Genética , Feminino , Redes Reguladoras de Genes/genética , Redes Reguladoras de Genes/fisiologia , Modelos Biológicos , Neurônios Motores/metabolismo , Neurônios Motores/fisiologia , Mutação/fisiologia , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Proteínas Tirosina Quinases/metabolismo , Proteínas Tirosina Quinases/fisiologia , Transdução de Sinais/genética , Transdução de Sinais/fisiologiaRESUMO
During Drosophila embryogenesis, both the cytoplasmic Abelson tyrosine kinase (Abl) and the membrane bound tyrosine phosphatase PTP69D are required for proper guidance of CNS and motor axons. We provide evidence that PTP69D modulates signaling by Abl and its antagonist, Ena. An Abl loss-of function mutation dominantly suppresses most Ptp69D mutant phenotypes including larval/pupal lethality and CNS and motor axon defects, while increased Abl and decreased Ena expression dramatically increase the expressivity of Ptp69D axonal defects. In contrast, Ptp69D mutations do not affect Abl mutant phenotypes. These results support the hypothesis that PTP69D antagonizes the Abl/Ena genetic pathway, perhaps as an upstream regulator. We also find that mutation of the gene encoding the cytoplasmic Src64B tyrosine kinase exacerbates Ptp69D phenotypes, suggesting that two different cytoplasmic tyrosine kinases, Abl and Src64B, modify PTP69D-mediated axon patterning in quite different ways.