Drosophila larval crawling is a simple behavior that allows us to dissect the functions of specific neurons in the intact animal and explore the roles of genes in the specification of those neurons. By inhibiting subsets of neurons in the PNS, we have found that two classes of multidendritic neurons play a major role in larval crawling. The bipolar dendrites and class I mds send a feedback signal to the CNS that keeps the contraction wave progressing quickly, allowing smooth forward movement. Genetic manipulation of the sensory neurons suggests that this feedback depends on proper dendritic morphology and axon pathfinding to appropriate synaptic target areas in the CNS. Our data suggest that coordination of muscle activity in larval crawling requires feedback from neurons acting as proprioceptors, sending a "mission accomplished" signal in response to segment contraction, and resulting in rapid relaxation of the segment and propagation of the wave.

In nervous systems with bilateral symmetry, many neurons project axons across the midline to the opposite side. In each segment of the Drosophila embryonic nervous system, axons that display this projection pattern choose one of two distinct tracts: the anterior or posterior commissure. Commissure choice is controlled by Derailed, an atypical receptor tyrosine kinase expressed on axons projecting in the anterior commissure. Here we show that Derailed keeps these axons out of the posterior commissure by acting as a receptor for Wnt5, a member of the Wnt family of secreted signalling molecules. Our results reveal an unexpected role in axon guidance for a Wnt family member, and show that the Derailed receptor is an essential component of Wnt signalling in these guidance events.

Gliomas, the most common malignant tumors of the nervous system, frequently harbor mutations that activate the epidermal growth factor receptor (EGFR) and phosphatidylinositol-3 kinase (PI3K) signaling pathways. To investigate the genetic basis of this disease, we developed a glioma model in Drosophila. We found that constitutive coactivation of EGFR-Ras and PI3K pathways in Drosophila glia and glial precursors gives rise to neoplastic, invasive glial cells that create transplantable tumor-like growths, mimicking human glioma. Our model represents a robust organotypic and cell-type-specific Drosophila cancer model in which malignant cells are created by mutations in signature genes and pathways thought to be driving forces in a homologous human cancer. Genetic analyses demonstrated that EGFR and PI3K initiate malignant neoplastic transformation via a combinatorial genetic network composed primarily of other pathways commonly mutated or activated in human glioma, including the Tor, Myc, G1 Cyclins-Cdks, and Rb-E2F pathways. This network acts synergistically to coordinately stimulate cell cycle entry and progression, protein translation, and inappropriate cellular growth and migration. In particular, we found that the fly orthologs of CyclinE, Cdc25, and Myc are key rate-limiting genes required for glial neoplasia. Moreover, orthologs of Sin1, Rictor, and Cdk4 are genes required only for abnormal neoplastic glial proliferation but not for glial development. These and other genes within this network may represent important therapeutic targets in human glioma.

SUMMARY Under fasting conditions, metazoans maintain energy balance by shifting from glucose to fat burning. In the fasted state, SIRT1 promotes catabolic gene expression by deacetylating the forkhead factor FOXO in response to stress and nutrient deprivation. The mechanisms by which hormonal signals regulate FOXO deacetylation remain unclear, however. We identified a hormone-dependent module, consisting of the Ser/Thr kinase SIK3 and the class IIa deacetylase HDAC4, which regulates FOXO activity in Drosophila. During feeding, HDAC4 is phosphorylated and sequestered in the cytoplasm by SIK3, whose activity is upregulated in response to insulin. SIK3 is inactivated during fasting, leading to the de-phosphorylation and nuclear translocation of HDAC4, and to FOXO deacetylation. SIK3 mutant flies are starvation-sensitive, reflecting FOXO-dependent increases in lipolysis that deplete triglyceride stores; reducing HDAC4 expression restored lipid accumulation. Our results reveal a hormone-regulated pathway that functions in parallel with the nutrient-sensing SIRT1 pathway to maintain energy balance.

We have isolated the Drosophila homolog of the vertebrate islet-1 and islet-2 genes, two members of the LIM homeodomain family implicated in the transcriptional control of motor neuronal differentiation. Similar to vertebrates, Drosophila islet is expressed in a discrete subset of embryonic motor neurons and interneurons that includes the dopaminergic and serotonergic cells of the ventral nerve cord. In contrast to mouse where mutation of islet-1 leads to loss of neurons due to programmed cell death, Drosophila islet is not required for neuron survival. Instead, loss of islet function causes defects in axon pathfinding and targeting plus loss of dopamine and serotonin synthesis. Ectopic expression of islet induces both specific alterations in pathfinding and changes in neurotransmitter identity. These findings indicate that islet coordinately controls two distinct aspects of neuronal identity.