RESUMEN
During Drosophila metamorphosis, the ddaC dendritic arborisation sensory neurons selectively prune their larval dendrites in response to steroid hormone ecdysone signalling. The Nrf2-Keap1 pathway acts downstream of ecdysone signalling to promote proteasomal degradation and thereby dendrite pruning. However, how the Nrf2-Keap1 pathway is activated remains largely unclear. Here, we demonstrate that the metabolic regulator AMP-activated protein kinase (AMPK) plays a cell-autonomous role in dendrite pruning. Importantly, AMPK is required for Mical and Headcase expression and for activation of the Nrf2-Keap1 pathway. We reveal that AMPK promotes the Nrf2-Keap1 pathway and dendrite pruning partly via inhibition of the insulin pathway. Moreover, the AMPK-insulin pathway is required for ecdysone signalling to activate the Nrf2-Keap1 pathway during dendrite pruning. Overall, this study reveals an important mechanism whereby ecdysone signalling activates the Nrf2-Keap1 pathway via the AMPK-insulin pathway to promote dendrite pruning, and further suggests that during the nonfeeding prepupal stage metabolic alterations lead to activation of the Nrf2-Keap1 pathway and dendrite pruning.
Asunto(s)
Proteínas de Drosophila , Insulinas , Proteínas Quinasas Activadas por AMP/genética , Proteínas Quinasas Activadas por AMP/metabolismo , Animales , Dendritas/metabolismo , Drosophila/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Ecdisona/metabolismo , Regulación del Desarrollo de la Expresión Génica , Insulinas/metabolismo , Proteína 1 Asociada A ECH Tipo Kelch/genética , Proteína 1 Asociada A ECH Tipo Kelch/metabolismo , Factor 2 Relacionado con NF-E2/genética , Factor 2 Relacionado con NF-E2/metabolismo , Plasticidad NeuronalRESUMEN
Pruning that selectively eliminates unnecessary axons/dendrites is crucial for sculpting the nervous system during development. During Drosophila metamorphosis, dendrite arborization neurons, ddaCs, selectively prune their larval dendrites in response to the steroid hormone ecdysone, whereas mushroom body γ neurons specifically eliminate their axon branches within dorsal and medial lobes. However, it is unknown which E3 ligase directs these two modes of pruning. Here, we identified a conserved SCF E3 ubiquitin ligase that plays a critical role in pruning of both ddaC dendrites and mushroom body γ axons. The SCF E3 ligase consists of four core components Cullin1/Roc1a/SkpA/Slimb and promotes ddaC dendrite pruning downstream of EcR-B1 and Sox14, but independently of Mical. Moreover, we demonstrate that the Cullin1-based E3 ligase facilitates ddaC dendrite pruning primarily through inactivation of the InR/PI3K/TOR pathway. We show that the F-box protein Slimb forms a complex with Akt, an activator of the InR/PI3K/TOR pathway, and promotes Akt ubiquitination. Activation of the InR/PI3K/TOR pathway is sufficient to inhibit ddaC dendrite pruning. Thus, our findings provide a novel link between the E3 ligase and the InR/PI3K/TOR pathway during dendrite pruning.
Asunto(s)
Proteínas Cullin/metabolismo , Proteínas de Drosophila/metabolismo , Sistema Nervioso/embriología , Fosfatidilinositol 3-Quinasas/metabolismo , Proteínas Tirosina Quinasas Receptoras/metabolismo , Serina-Treonina Quinasas TOR/metabolismo , Animales , Proteínas de Unión al Calcio , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Proteínas Cullin/genética , Proteínas de Unión al ADN/genética , Dendritas/metabolismo , Drosophila/embriología , Drosophila/genética , Drosophila/metabolismo , Proteínas de Drosophila/genética , Ecdisona/metabolismo , Regulación del Desarrollo de la Expresión Génica , Metamorfosis Biológica , Cuerpos Pedunculados/inervación , Neuronas/metabolismo , Proteínas Nucleares , Proteínas Proto-Oncogénicas c-akt/genética , Proteínas Proto-Oncogénicas c-akt/metabolismo , Interferencia de ARN , ARN Interferente Pequeño , Proteínas Ligasas SKP Cullina F-box/genética , Proteínas Ligasas SKP Cullina F-box/metabolismo , Factores de Transcripción SOXB2/genética , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismo , UbiquitinaciónRESUMEN
Pruning of unnecessary axons and/or dendrites is crucial for maturation of the nervous system. However, little is known about cell adhesion molecules (CAMs) that control neuronal pruning. In Drosophila, dendritic arborization neurons, ddaCs, selectively prune their larval dendrites. Here, we report that Rab5/ESCRT-mediated endocytic pathways are critical for dendrite pruning. Loss of Rab5 or ESCRT function leads to robust accumulation of the L1-type CAM Neuroglian (Nrg) on enlarged endosomes in ddaC neurons. Nrg is localized on endosomes in wild-type ddaC neurons and downregulated prior to dendrite pruning. Overexpression of Nrg alone is sufficient to inhibit dendrite pruning, whereas removal of Nrg causes precocious dendrite pruning. Epistasis experiments indicate that Rab5 and ESCRT restrain the inhibitory role of Nrg during dendrite pruning. Thus, this study demonstrates the cell-surface molecule that controls dendrite pruning and defines an important mechanism whereby sensory neurons, via endolysosomal pathway, downregulate the cell-surface molecule to trigger dendrite pruning.
Asunto(s)
Moléculas de Adhesión Celular Neuronal/metabolismo , Dendritas/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila/metabolismo , Endosomas/metabolismo , Animales , Moléculas de Adhesión Celular Neuronal/genética , Regulación hacia Abajo , Drosophila/embriología , Proteínas de Drosophila/genética , Endocitosis , Complejos de Clasificación Endosomal Requeridos para el Transporte/genética , Complejos de Clasificación Endosomal Requeridos para el Transporte/metabolismo , Epistasis Genética , Proteínas de Unión al GTP rab5/genética , Proteínas de Unión al GTP rab5/metabolismoRESUMEN
The control of self-renewal and differentiation of neural stem and progenitor cells is a crucial issue in stem cell and cancer biology. Drosophila type II neuroblast lineages are prone to developing impaired neuroblast homeostasis if the limited self-renewing potential of intermediate neural progenitors (INPs) is unrestrained. Here, we demonstrate that Drosophila SWI/SNF chromatin remodeling Brahma (Brm) complex functions cooperatively with another chromatin remodeling factor, Histone deacetylase 3 (HDAC3) to suppress the formation of ectopic type II neuroblasts. We show that multiple components of the Brm complex and HDAC3 physically associate with Earmuff (Erm), a type II-specific transcription factor that prevents dedifferentiation of INPs into neuroblasts. Consistently, the predicted Erm-binding motif is present in most of known binding loci of Brm. Furthermore, brm and hdac3 genetically interact with erm to prevent type II neuroblast overgrowth. Thus, the Brm-HDAC3-Erm repressor complex suppresses dedifferentiation of INPs back into type II neuroblasts. DOI: http://dx.doi.org/10.7554/eLife.01906.001.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Desdiferenciación Celular , Linaje de la Célula , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Histona Desacetilasas/metabolismo , Células-Madre Neurales/metabolismo , Transactivadores/metabolismo , Factores de Transcripción/metabolismo , Animales , Animales Modificados Genéticamente , Sitios de Unión , Proteínas de Ciclo Celular/genética , Línea Celular , Proteínas de Drosophila/genética , Drosophila melanogaster/citología , Drosophila melanogaster/genética , Regulación de la Expresión Génica , Histona Desacetilasas/genética , Complejos Multiproteicos , Unión Proteica , Interferencia de ARN , Transducción de Señal , Transactivadores/genética , Factores de Transcripción/genética , TransfecciónRESUMEN
Pruning that selectively removes unnecessary axons/dendrites is crucial for sculpting neural circuits during development. During Drosophila metamorphosis, dendritic arborization sensory neurons, ddaCs, selectively prune their larval dendrites in response to the steroid hormone ecdysone. However, it is unknown whether epigenetic factors are involved in dendrite pruning. Here, we analyzed 81 epigenetic factors, from which a Brahma (Brm)-containing chromatin remodeler and a histone acetyltransferase CREB-binding protein (CBP) were identified for their critical roles in initiating dendrite pruning. Brm and CBP specifically activate a key ecdysone response gene, sox14, but not EcR-B1. Furthermore, the HAT activity of CBP is important for sox14 expression and dendrite pruning. EcR-B1 associates with CBP in the presence of ecdysone, which is facilitated by Brm, resulting in local enrichment of an active chromatin mark H3K27Ac at the sox14 locus. Thus, specific intrinsic epigenetic factors cooperate with steroid hormones to activate selective transcriptional programs, thereby initiating neuronal remodeling.