Systematic Identification of Genes that Regulate Neuronal Wiring in the Drosophila Visual System (original) (raw)
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Mutations disrupting neuronal connectivity in the Drosophila visual system
Neuron, 1995
The photoreceptor neurons (R cells) of the Drosophila compound eye elaborate a precise array of neuronal connections in the brain. These projections exhibit target specificity and create topographic maps (retinotopy). We have screened histologically for mutations disrupting R cell connectivity in developing tissue. Eighty mutations were isolated from over 6000 ethylmethane sulfonate-mutagenized lines. Characterization of these mutations included genetic mosaic analysis to determine whether the gene is required in the retina or in the optic ganglia. Most mutations were found to affect connectivity indirectly by disrupting development more generally in the eye or brain. Genes were identified as candidates for playing direct roles in R cell connectivity by affecting axonal outgrowth (eddy), target recognition (limbo and nonstop), and retinotopy (limbo).
disconnected: A locus required for neuronal pathway formation in the visual system of drosophila
Cell, 1987
Mutations at the X-linked disconnected locus of D. melanogaster lead to the failure of adult photoreceptor axons to innervate their target cells in the developing optic lobes of the third instar larva, resulting in flies that have rudimentary optic ganglia. The cascade of epigenetic events leading to the adult disconnected phenotype is caused by the misrouting of a larval pioneer nerve, Bolwig's nerve, during embryonic development. In the disconnected mutant this nerve fails to recognize and establish stable connections with its correct synaptic partners. In addition, disconnected affects both the proper aggregation and the movement of the Bolwig neurons to their final location in the embryo. Finally, similar but more subtle defects can be found in a subset of other peripheral neurons in the thoracic and abdominal segments. The different aspects of the phenotype suggest that the disconnected gene plays a role in neuronal cell recognition.
A step-by-step guide to visual circuit assembly in Drosophila
Current Opinion in Neurobiology, 2011
The ability of vertebrates and insects to perceive and process information about the visual world is mediated by neural circuits, which share a strikingly conserved architecture of reiterated columnar and layered synaptic units. Recent genetic approaches conferring single-cell resolution have enabled major advances in our understanding of the cellular and molecular strategies that orchestrate visual circuit assembly in Drosophila. Photoreceptor axon targeting relies on a sequence of interdependent developmental steps to achieve temporal coordination with the formation and maturation of partner neurons. Distinct targeting events depend on anterograde and autocrine signaling, neuron-glia interactions, axon tiling and the timely expression of homophilic cell surface molecules. These mediate local adhesive or repulsive interactions of photoreceptor axons with each other and with target neurons.
Systematic identification of genes regulating synaptic remodeling in the Drosophila visual system
Genes & Genetic Systems, 2020
In many animals, neural activity contributes to the adaptive refinement of synaptic properties, such as firing frequency and the number of synapses, for learning, memorizing and adapting for survival. However, the molecular mechanisms underlying such activity-dependent synaptic remodeling remain largely unknown. In the synapses of Drosophila melanogaster, the presynaptic active zone (AZ) forms a T-shaped presynaptic density comprising AZ proteins, including Bruchpilot (Brp). In a previous study, we found that the signal from a fusion protein molecular marker consisting of Brp and mCherry becomes diffuse under continuous light over three days (LL), reflecting disassembly of the AZ, while remaining punctate under continuous darkness. To identify the molecular players controlling this synaptic remodeling, we used the fusion protein molecular marker and performed RNAi screening against 208 neuron-related transmembrane genes that are highly expressed in the Drosophila visual system. Second analyses using the STaR (synaptic tagging with recombination) technique, which showed a decrease in synapse number under the LL condition, and subsequent mutant and overexpression analysis confirmed that five genes are involved in the activity-dependent AZ disassembly. This work demonstrates the feasibility of identifying genes involved in activity-dependent synaptic remodeling in Drosophila, and also provides unexpected insight into the molecular mechanisms involved in cholesterol metabolism and biosynthesis of the insect molting hormone ecdysone.
The EMBO Journal, 1992
Mutations in the Drosophila gene giant lens (gi) affect ommatidial development, photoreceptor axon guidance and optic lobe development. We have cloned the gene using an enhancer trap line. Molecular analysis of gil suggests that it encodes a secreted protein with an epidermal-growth-factor-like motif. We have generated mutations at the gil locus by imprecise excision of the enhancer trap P-element. In the absence ofgil, additional photoreceptors develop at the expense of pigment cells, suggesting an involvement of gil in cell determination during eye development. In addition, gil mutants show drastic effects on photoreceptor axon guidance and optic lobe development. In wildtype flies, photoreceptor axons grow from the eye disc through the optic stalk into the larval brain hemisphere, where retinal innervation is required for the normal development of the lamina and distal medulla. The projection pattern of these axons in the developing lamina and medulla is highly regular and reproducible. In gil, photoreceptor axons enter the larval brain but fail to establish proper connections in the lamina or medulla. We propose that gil encodes a new type of signaflng molecule involved in the process of axon pathfimding and cell determination in the visual system of Drosophila.
Genetics, 2007
To identify novel regulators of nervous system development, we used the GAL4-UAS misexpression system in Drosophila to screen for genes that influence axon guidance in developing embryos. We mobilized the Gene Search (GS) P element and identified 42 lines with insertions in unique loci, including leak/roundabout2, which encodes an axon guidance receptor and confirms the utility of our screen. The genes we identified encode proteins of diverse classes, some acting near the cell surface and others in the cytoplasm or nucleus. We found that one GS line drove misexpression of the NF-kB transcription factor Dorsal, causing motor axons to bypass their correct termination sites. In the developing visual system, Dorsal misexpression also caused photoreceptor axons to reach incorrect positions within the optic lobe. This mistargeting occurred without observable changes of cell fate and correlated with localization of ectopic Dorsal in distal axons. We found that Dorsal and its inhibitor Cactus are expressed in photoreceptors, though neither was required for axon targeting. However, mutation analyses of genes known to act upstream of Dorsal revealed a requirement for the interleukin receptor-associated kinase family kinase Pelle for layerspecific targeting of photoreceptor axons, validating our screen as a means to identify new molecular determinants of nervous system development in vivo.
Visual circuit development in Drosophila
Current Opinion in Neurobiology, 2007
Fly visual circuits are organized into lattice-like arrays and layers. Recent genetic studies have provided insights into how these reiterated structures are assembled through stepwise processes and how precise connections are established during development. Afferent-derived morphogens, such as Hedgehog, play a key role in organizing the overall structure by inducing and recruiting target neurons and glia. In turn, the target-derived ligand DWnt4 guides Frizzled2-expressing photoreceptor afferents to their proper destination. Photoreceptor afferents select specific synaptic targets by forming adhesive interactions and regulating actin cytoskeleton in growth cones. Target specificity is probably achieved by restricting the expression of adhesive molecules, such as Capricious, to appropriate presynaptic and postsynaptic partners, and by differentially regulating the function of broadly expressed adhesive molecules such as N-cadherin.
Journal of cell science, 2002
Gap junctions (GJs) are composed of proteins from two distinct families. In vertebrates, GJs are composed of connexins; a connexin hexamer on one cell lines up with a hexamer on an apposing cell to form the intercellular channel. In invertebrates, GJs are composed of an unrelated protein family, the innexins. Different connexins have distinct properties that make them largely non-interchangeable in the animal. Innexins are also a large family with high sequence homology, and some functional differences have been reported. The biological implication of innexin differences, such as their ability to substitute for one another in the animal, has not been explored. Recently, we showed that GJ proteins are necessary for the development of normal neural transmission in the Drosophila visual system. Mutations in either of two Drosophila GJ genes (innexins), shakB and ogre, lead to a loss of transients in the electroretinogram (ERG), which is indicative of a failure of the lamina to respond ...
Cell, 2006
Alternative splicing of Dscam generates an enormous molecular diversity with maximally 38,016 different receptors. Whether this large diversity is required in vivo is currently unclear. We examined the role of Dscam in neuron-target recognition of single mechanosensory neurons, which connect with different target cells through multiple axonal branches. Analysis of Dscam null neurons demonstrated an essential role of Dscam for growth and directed extension of axon branches. Expression of randomly chosen single isoforms could not rescue connectivity but did restore basic axonal extension and rudimentary branching. Moreover, two Dscam alleles were generated that each reduced the maximally possible Dscam diversity to 22,176 isoforms. Reduction of Dscam diversity resulted in specific connectivity defects of mechanosensory neurons. Furthermore, the observed allelespecific phenotypes suggest functional differences among isoforms. Our findings provide evidence that a very large number of structurally unique receptor isoforms is required to ensure fidelity and precision of neuronal connectivity.