Zhiyuan Lu - Academia.edu (original) (raw)
Papers by Zhiyuan Lu
Stable neural function requires an energy supply that can meet the intense episodic power demands... more Stable neural function requires an energy supply that can meet the intense episodic power demands of neuronal activity. The bioenergetic machinery of glycolysis and oxidative phosphorylation is highly responsive to such demands, but it must occupy a minimum volume if it is to accommodate these demands. We examined the trade-off between presynaptic power demands and the volume available to the bioenergetic machinery. We quantified the energy demands of sixDrosophilamotor nerve terminals through direct measurements of neurotransmitter release and Ca2+entry, and via theoretical estimates of Na+entry and power demands at rest. Electron microscopy revealed that terminals with the highest power demands contained the greatest volume of mitochondria, indicating that mitochondria are allocated according to presynaptic power demands. In addition, terminals with the greatest power demand-to-volume ratio (∼66 nmol·min-1·μL-1) harbor the largest mitochondria packed at the greatest density. If we...
Current Biology, Dec 1, 2011
The Journal of Neuroscience, 2020
The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of... more The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of neurotransmitters and protons from synaptic vesicles, and is supported by direct data from sensory ribbon-type synapses. However, it is unclear whether acidification occurs at non–ribbon-type synapses. Here we used genetically encoded fluorescent pH indicators to examine cleft pH at conventional neuronal synapses. At the neuromuscular junction of femaleDrosophilalarvae, we observed alkaline spikes of over 1 log unit during fictive locomotionin vivo. Ex vivo, single action potentials evoked alkalinizing pH transients of only ∼0.01 log unit, but these transients summated rapidly during burst firing. A chemical pH indicator targeted to the cleft corroborated these findings. Cleft pH transients were dependent on Ca2+movement across the postsynaptic membrane, rather than neurotransmitter release per se, a result consistent with cleft alkalinization being driven by the Ca2+/H+antiporting acti...
Understanding cellular architecture is essential for understanding biology. Electron microscopy (... more Understanding cellular architecture is essential for understanding biology. Electron microscopy (EM) uniquely visualizes cellular structure with nanometer resolution. However, traditional methods, such as thin-section EM or EM tomography, have limitations inasmuch as they only visualize a single slice or a relatively small volume of the cell, respectively. Here, we overcome these limitations by imaging whole cells and tissues with enhanced Focus Ion Beam Scanning Electron Microscopy (FIB-SEM) in high resolution with month-long acquisition duration. We use this approach to generate reference 3D image datasets at 4-nm isotropic voxels for ten different examples, including cultured cells (cancer, macrophages, and T-cells) as well as tissues (mouse pancreatic islets and the Drosophila fan-shaped body). We open access to all datasets in OpenOrganelle, an interactive web platform that allows accessing both the original 3D EM data, and subsequent organelle segmentation. Together, these data will serve as a reference library to explore comprehensive quantification of whole cells and their constituents, thus addressing questions related to cell identities, cell morphologies, cell-cell interactions, as well as intracellular organelle organization and structure. Main Individual cells and organized systems of cells within a tissue can be described with a hierarchy of ultrastructural details, from complex organelle networks down to single protein molecules 1. While transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images from diamond-knife cut thin sections of metal stained samples have profoundly shaped our understanding of organelles 2 , such approaches generate 2D images that can reveal 3D .
The neural circuits responsible for animal behavior remain largely unknown. We summarize new meth... more The neural circuits responsible for animal behavior remain largely unknown. We summarize new methods and present the circuitry of a large fraction of the brain of the fruit fly Drosophila melanogaster. Improved methods include new procedures to prepare, image, align, segment, find synapses in, and proofread such large data sets. We define cell types, refine computational compartments, and provide an exhaustive atlas of cell examples and types, many of them novel. We provide detailed circuits consisting of neurons and their chemical synapses for most of the central brain. We make the data public and simplify access, reducing the effort needed to answer circuit questions, and provide procedures linking the neurons defined by our analysis with genetic reagents. Biologically, we examine distributions of connection strengths, neural motifs on different scales, electrical consequences of compartmentalization, and evidence that maximizing packing density is an important criterion in the ev...
eLife, 2019
Understanding the circuit mechanisms behind motion detection is a long-standing question in visua... more Understanding the circuit mechanisms behind motion detection is a long-standing question in visual neuroscience. In Drosophila melanogaster, recently discovered synapse-level connectomes in the optic lobe, particularly in ON-pathway (T4) receptive-field circuits, in concert with physiological studies, suggest a motion model that is increasingly intricate when compared with the ubiquitous Hassenstein-Reichardt model. By contrast, our knowledge of OFF-pathway (T5) has been incomplete. Here, we present a conclusive and comprehensive connectome that, for the first time, integrates detailed connectivity information for inputs to both the T4 and T5 pathways in a single EM dataset covering the entire optic lobe. With novel reconstruction methods using automated synapse prediction suited to such a large connectome, we successfully corroborate previous findings in the T4 pathway and comprehensively identify inputs and receptive fields for T5. Although the two pathways are probably evolutiona...
Microscopy and Microanalysis, 2018
Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) is used to volume image heavy metalstaine... more Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) is used to volume image heavy metalstained, plastic-embedded biological samples with resolutions below 10 x 10 x 10nm, an ability that is especially important in connectomics [1]. FIB-SEM samples are typically restricted to be <50µm in the direction of the FIB beam because glancing angle milling results in artifacts over longer distances [1]. Removal rate is also restricted due to a current/spot size tradeoff. These limitations are especially problematic when one contemplates combining FIB with the increased speed offered by multibeam SEMs like the 91 beam Zeiss MultiSEM [2]. The MultiSEM's minimum field of view is ~180µm, and its imaging rate is approximately two orders of magnitude faster than FIB's milling rate. These considerations appear to preclude the integration of traditional FIB milling with MultiSEM imaging.
The neural circuits responsible for behavior remain largely unknown. Previous efforts have recons... more The neural circuits responsible for behavior remain largely unknown. Previous efforts have reconstructed the complete circuits of small animals, with hundreds of neurons, and selected circuits for larger animals. Here we (the FlyEM project at Janelia and collaborators at Google) summarize new methods and present the complete circuitry of a large fraction of the brain of a much more complex animal, the fruit fly Drosophila melanogaster. Improved methods include new procedures to prepare, image, align, segment, find synapses, and proofread such large data sets; new methods that define cell types based on connectivity in addition to morphology; and new methods to simplify access to a large and evolving data set. From the resulting data we derive a better definition of computational compartments and their connections; an exhaustive atlas of cell examples and types, many of them novel; detailed circuits for most of the central brain; and exploration of the statistics and structure of dif...
Deriving the detailed synaptic connections of the entire nervous system has been a long term but ... more Deriving the detailed synaptic connections of the entire nervous system has been a long term but unrealized goal of the nascent field of connectomics. For Drosophila, in particular, three sample preparation problems must be solved before the requisite imaging and analysis can even begin. The first is dissecting the brain, connectives, and ventral nerve cord (roughly comparable to the brain, neck, and spinal cord of vertebrates) as a single contiguous unit. Second is fixing and staining the resulting specimen, too large for previous techniques such as flash freezing, so as to permit the necessary automated segmentation of neuron membranes. Finally the contrast must be sufficient to support synapse detection at imaging speeds that enable the entire connectome to be collected. To address these issues, we report three major novel methods to dissect, fix, dehydrate and stain this tiny but complex nervous system in its entirety; together they enable us to uncover a Focused Ion-Beam Scanni...
Microscopy and Microanalysis, 2018
Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) generates 3D datasets optimally suited fo... more Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) generates 3D datasets optimally suited for segmentation of cell ultrastructure and automated connectome tracing but is limited to small fields of view and is therefore incompatible with the new generation of ultrafast multibeam SEMs. In contrast, section-based techniques are multibeam-compatible but are limited in z-resolution making automatic segmentation of cellular ultrastructure difficult. Here we demonstrate a novel 3D electron microscopy technique, Gas Cluster Ion Beam SEM (GCIB-SEM), in which top-down, wide-area ion milling is performed on a series of thick sections, acquiring < 10 nm isotropic datasets of each which are then stitched together to span the full sectioned volume. Based on our results, incorporating GCIB-SEM into existing single beam and multibeam SEM workflows should be straightforward and should dramatically increase reliability while simultaneously improving z-resolution by a factor of 3 or more.
Proceedings of the National Academy of Sciences, 2015
Significance Circuit diagrams of brains are generally reported only as absolute or consensus netw... more Significance Circuit diagrams of brains are generally reported only as absolute or consensus networks; these diagrams fail to identify the accuracy of connections, however, for which multiple circuits of the same neurons must be documented. For this reason, the modular composition of the Drosophila visual system, with many identified neuron classes, is ideal. Using EM, we identified synaptic connections in the fly’s second visual relay neuropil, or medulla, in the 20 neuron classes in a so-called “core connectome,” those neurons present in seven neighboring columns. These connections identify circuits for motion. Their error rates for wiring reveal that <1% of contacts overall are not part of a consensus circuit but incorporate errors of either omission or commission. Autapses are occasionally seen.
Journal of Neurogenetics, 2009
The shape of a neuron, its morphological signature, dictates the neuron's function by establishin... more The shape of a neuron, its morphological signature, dictates the neuron's function by establishing its synaptic partnerships. Here, we review various anatomical methods used to reveal neuron shape and the contributions these have made to our current understanding of neural function in the Drosophila brain, especially the optic lobe. These methods, including Golgi impregnation, genetic reporters, and electron microscopy (EM), necessarily incorporate biases of various sorts that are easy to overlook, but that filter the morphological signatures we see. Nonetheless, the application of these methods to the optic lobe has led to reassuringly congruent findings on the number and shapes of neurons and their connection patterns, indicating that morphological classes are actually genetic classes. Genetic methods using, especially, GAL4 drivers and associated reporters have largely superceded classical Golgi methods for cellular analyses and, moreover, allow the manipulation of neuronal activity, thus enabling us to establish a bridge between morphological studies and functional ones. While serial-EM reconstruction remains the only reliable, albeit labor-intensive, method to determine actual synaptic connections, genetic approaches in combination with EM or high-resolution light microscopic techniques are promising methods for the rapid determination of synaptic circuit function.
Journal of Neurogenetics, 2014
Each neuropil module, or cartridge, in the fly&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;am... more Each neuropil module, or cartridge, in the fly&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s lamina has a fixed complement of cells. Of five types of monopolar cell interneurons, only L4 has collaterals that invade neighboring cartridges. In the proximal lamina, these collaterals form reciprocal synapses with both the L2 of their own cartridge and the L4 collateral branches from two other neighboring cartridges. During synaptogenesis, L4 collaterals strongly express the cell adhesion protein Kirre, a member of the irre cell recognition module (IRM) group of proteins ( Fischbach et al., 2009 , J Neurogenet, 23, 48-67). The authors show by mutant analysis and gene knockdown techniques that L4 neurons develop their lamina collaterals in the absence of this cell adhesion protein. Using electron microscopy (EM), the authors demonstrate, however, that without Kirre protein these L4 collaterals selectively form fewer synapses. The collaterals of L4 neurons of various genotypes reconstructed from serial-section EM revealed that the number of postsynaptic sites was dramatically reduced in the absence of Kirre, almost eliminating any synaptic input to L4 neurons. A significant reduction of presynaptic sites was also detected in kirre(0) mutants and gene knockdown flies using RNA interference. L4 neuron reciprocal synapses are thus almost eliminated. A presynaptic marker, Brp-short(GFP) confirmed these data using confocal microscopy. This study reveals that removing Kirre protein specifically disrupts the functional L4 synaptic network in the Drosophila lamina.
Current Biology, 2006
Many types of synapses have highly characteristic shapes and tightly regulated distributions of a... more Many types of synapses have highly characteristic shapes and tightly regulated distributions of active zones, parameters that are important to the function of neuronal circuits. The development of terminal arborizations must therefore include mechanisms to regulate the spacing of terminals, the frequency of branching, and the distribution and density of release sites. At present, however, the mechanisms that control these features remain obscure. Here, we report the development of supernumerary or ''satellite'' boutons in a variety of endocytic mutants at the Drosophila neuromuscular junction. Mutants in endophilin, synaptojanin, dynamin, AP180, and synaptotagmin all show increases in supernumerary bouton structures. These satellite boutons contain releasable vesicles and normal complements of synaptic proteins that are correctly localized within terminals. Interestingly, however, synaptojanin terminals have more active zones per unit of surface area and more dense bodies (T-bars) within these active zones, which may in part compensate for reduced transmission per active zone. The altered structural development of the synapse is selectively encountered in endocytosis mutants and is not observed when synaptic transmission is reduced by mutations in glutamate receptors or when synaptic transmission is blocked by tetanus toxin. We propose that endocytosis plays a critical role in sculpting the structure of synapses, perhaps through the endocytosis of unknown regulatory signals that organize morphogenesis at synaptic terminals. Results and Discussion
This is data generated by the FlyEM project at Janelia and our collaborators at Google. It contai... more This is data generated by the FlyEM project at Janelia and our collaborators at Google. It contains the connectome (neurons and their connections) of a large fractionof the brain of the fruit fly <i>Drosophila melanogaster,</i> and the means to access this connectome.<br>This data is associated with the paper, BIORXIV/2020/911859, "A Connectome of the Adult Drosophila Central Brain" by C. Shan Xu, et al. published 22 January 2020. This is version 1.0 of the data; improved versions are expected to become available as research continues. <br><i><br></i>The data can be found at:<br>https://www.janelia.org/project-team/flyem/hemibrain
Arthropod Structure & Development
Stable neural function requires an energy supply that can meet the intense episodic power demands... more Stable neural function requires an energy supply that can meet the intense episodic power demands of neuronal activity. The bioenergetic machinery of glycolysis and oxidative phosphorylation is highly responsive to such demands, but it must occupy a minimum volume if it is to accommodate these demands. We examined the trade-off between presynaptic power demands and the volume available to the bioenergetic machinery. We quantified the energy demands of sixDrosophilamotor nerve terminals through direct measurements of neurotransmitter release and Ca2+entry, and via theoretical estimates of Na+entry and power demands at rest. Electron microscopy revealed that terminals with the highest power demands contained the greatest volume of mitochondria, indicating that mitochondria are allocated according to presynaptic power demands. In addition, terminals with the greatest power demand-to-volume ratio (∼66 nmol·min-1·μL-1) harbor the largest mitochondria packed at the greatest density. If we...
Current Biology, Dec 1, 2011
The Journal of Neuroscience, 2020
The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of... more The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of neurotransmitters and protons from synaptic vesicles, and is supported by direct data from sensory ribbon-type synapses. However, it is unclear whether acidification occurs at non–ribbon-type synapses. Here we used genetically encoded fluorescent pH indicators to examine cleft pH at conventional neuronal synapses. At the neuromuscular junction of femaleDrosophilalarvae, we observed alkaline spikes of over 1 log unit during fictive locomotionin vivo. Ex vivo, single action potentials evoked alkalinizing pH transients of only ∼0.01 log unit, but these transients summated rapidly during burst firing. A chemical pH indicator targeted to the cleft corroborated these findings. Cleft pH transients were dependent on Ca2+movement across the postsynaptic membrane, rather than neurotransmitter release per se, a result consistent with cleft alkalinization being driven by the Ca2+/H+antiporting acti...
Understanding cellular architecture is essential for understanding biology. Electron microscopy (... more Understanding cellular architecture is essential for understanding biology. Electron microscopy (EM) uniquely visualizes cellular structure with nanometer resolution. However, traditional methods, such as thin-section EM or EM tomography, have limitations inasmuch as they only visualize a single slice or a relatively small volume of the cell, respectively. Here, we overcome these limitations by imaging whole cells and tissues with enhanced Focus Ion Beam Scanning Electron Microscopy (FIB-SEM) in high resolution with month-long acquisition duration. We use this approach to generate reference 3D image datasets at 4-nm isotropic voxels for ten different examples, including cultured cells (cancer, macrophages, and T-cells) as well as tissues (mouse pancreatic islets and the Drosophila fan-shaped body). We open access to all datasets in OpenOrganelle, an interactive web platform that allows accessing both the original 3D EM data, and subsequent organelle segmentation. Together, these data will serve as a reference library to explore comprehensive quantification of whole cells and their constituents, thus addressing questions related to cell identities, cell morphologies, cell-cell interactions, as well as intracellular organelle organization and structure. Main Individual cells and organized systems of cells within a tissue can be described with a hierarchy of ultrastructural details, from complex organelle networks down to single protein molecules 1. While transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images from diamond-knife cut thin sections of metal stained samples have profoundly shaped our understanding of organelles 2 , such approaches generate 2D images that can reveal 3D .
The neural circuits responsible for animal behavior remain largely unknown. We summarize new meth... more The neural circuits responsible for animal behavior remain largely unknown. We summarize new methods and present the circuitry of a large fraction of the brain of the fruit fly Drosophila melanogaster. Improved methods include new procedures to prepare, image, align, segment, find synapses in, and proofread such large data sets. We define cell types, refine computational compartments, and provide an exhaustive atlas of cell examples and types, many of them novel. We provide detailed circuits consisting of neurons and their chemical synapses for most of the central brain. We make the data public and simplify access, reducing the effort needed to answer circuit questions, and provide procedures linking the neurons defined by our analysis with genetic reagents. Biologically, we examine distributions of connection strengths, neural motifs on different scales, electrical consequences of compartmentalization, and evidence that maximizing packing density is an important criterion in the ev...
eLife, 2019
Understanding the circuit mechanisms behind motion detection is a long-standing question in visua... more Understanding the circuit mechanisms behind motion detection is a long-standing question in visual neuroscience. In Drosophila melanogaster, recently discovered synapse-level connectomes in the optic lobe, particularly in ON-pathway (T4) receptive-field circuits, in concert with physiological studies, suggest a motion model that is increasingly intricate when compared with the ubiquitous Hassenstein-Reichardt model. By contrast, our knowledge of OFF-pathway (T5) has been incomplete. Here, we present a conclusive and comprehensive connectome that, for the first time, integrates detailed connectivity information for inputs to both the T4 and T5 pathways in a single EM dataset covering the entire optic lobe. With novel reconstruction methods using automated synapse prediction suited to such a large connectome, we successfully corroborate previous findings in the T4 pathway and comprehensively identify inputs and receptive fields for T5. Although the two pathways are probably evolutiona...
Microscopy and Microanalysis, 2018
Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) is used to volume image heavy metalstaine... more Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) is used to volume image heavy metalstained, plastic-embedded biological samples with resolutions below 10 x 10 x 10nm, an ability that is especially important in connectomics [1]. FIB-SEM samples are typically restricted to be <50µm in the direction of the FIB beam because glancing angle milling results in artifacts over longer distances [1]. Removal rate is also restricted due to a current/spot size tradeoff. These limitations are especially problematic when one contemplates combining FIB with the increased speed offered by multibeam SEMs like the 91 beam Zeiss MultiSEM [2]. The MultiSEM's minimum field of view is ~180µm, and its imaging rate is approximately two orders of magnitude faster than FIB's milling rate. These considerations appear to preclude the integration of traditional FIB milling with MultiSEM imaging.
The neural circuits responsible for behavior remain largely unknown. Previous efforts have recons... more The neural circuits responsible for behavior remain largely unknown. Previous efforts have reconstructed the complete circuits of small animals, with hundreds of neurons, and selected circuits for larger animals. Here we (the FlyEM project at Janelia and collaborators at Google) summarize new methods and present the complete circuitry of a large fraction of the brain of a much more complex animal, the fruit fly Drosophila melanogaster. Improved methods include new procedures to prepare, image, align, segment, find synapses, and proofread such large data sets; new methods that define cell types based on connectivity in addition to morphology; and new methods to simplify access to a large and evolving data set. From the resulting data we derive a better definition of computational compartments and their connections; an exhaustive atlas of cell examples and types, many of them novel; detailed circuits for most of the central brain; and exploration of the statistics and structure of dif...
Deriving the detailed synaptic connections of the entire nervous system has been a long term but ... more Deriving the detailed synaptic connections of the entire nervous system has been a long term but unrealized goal of the nascent field of connectomics. For Drosophila, in particular, three sample preparation problems must be solved before the requisite imaging and analysis can even begin. The first is dissecting the brain, connectives, and ventral nerve cord (roughly comparable to the brain, neck, and spinal cord of vertebrates) as a single contiguous unit. Second is fixing and staining the resulting specimen, too large for previous techniques such as flash freezing, so as to permit the necessary automated segmentation of neuron membranes. Finally the contrast must be sufficient to support synapse detection at imaging speeds that enable the entire connectome to be collected. To address these issues, we report three major novel methods to dissect, fix, dehydrate and stain this tiny but complex nervous system in its entirety; together they enable us to uncover a Focused Ion-Beam Scanni...
Microscopy and Microanalysis, 2018
Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) generates 3D datasets optimally suited fo... more Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) generates 3D datasets optimally suited for segmentation of cell ultrastructure and automated connectome tracing but is limited to small fields of view and is therefore incompatible with the new generation of ultrafast multibeam SEMs. In contrast, section-based techniques are multibeam-compatible but are limited in z-resolution making automatic segmentation of cellular ultrastructure difficult. Here we demonstrate a novel 3D electron microscopy technique, Gas Cluster Ion Beam SEM (GCIB-SEM), in which top-down, wide-area ion milling is performed on a series of thick sections, acquiring < 10 nm isotropic datasets of each which are then stitched together to span the full sectioned volume. Based on our results, incorporating GCIB-SEM into existing single beam and multibeam SEM workflows should be straightforward and should dramatically increase reliability while simultaneously improving z-resolution by a factor of 3 or more.
Proceedings of the National Academy of Sciences, 2015
Significance Circuit diagrams of brains are generally reported only as absolute or consensus netw... more Significance Circuit diagrams of brains are generally reported only as absolute or consensus networks; these diagrams fail to identify the accuracy of connections, however, for which multiple circuits of the same neurons must be documented. For this reason, the modular composition of the Drosophila visual system, with many identified neuron classes, is ideal. Using EM, we identified synaptic connections in the fly’s second visual relay neuropil, or medulla, in the 20 neuron classes in a so-called “core connectome,” those neurons present in seven neighboring columns. These connections identify circuits for motion. Their error rates for wiring reveal that <1% of contacts overall are not part of a consensus circuit but incorporate errors of either omission or commission. Autapses are occasionally seen.
Journal of Neurogenetics, 2009
The shape of a neuron, its morphological signature, dictates the neuron's function by establishin... more The shape of a neuron, its morphological signature, dictates the neuron's function by establishing its synaptic partnerships. Here, we review various anatomical methods used to reveal neuron shape and the contributions these have made to our current understanding of neural function in the Drosophila brain, especially the optic lobe. These methods, including Golgi impregnation, genetic reporters, and electron microscopy (EM), necessarily incorporate biases of various sorts that are easy to overlook, but that filter the morphological signatures we see. Nonetheless, the application of these methods to the optic lobe has led to reassuringly congruent findings on the number and shapes of neurons and their connection patterns, indicating that morphological classes are actually genetic classes. Genetic methods using, especially, GAL4 drivers and associated reporters have largely superceded classical Golgi methods for cellular analyses and, moreover, allow the manipulation of neuronal activity, thus enabling us to establish a bridge between morphological studies and functional ones. While serial-EM reconstruction remains the only reliable, albeit labor-intensive, method to determine actual synaptic connections, genetic approaches in combination with EM or high-resolution light microscopic techniques are promising methods for the rapid determination of synaptic circuit function.
Journal of Neurogenetics, 2014
Each neuropil module, or cartridge, in the fly&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;am... more Each neuropil module, or cartridge, in the fly&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s lamina has a fixed complement of cells. Of five types of monopolar cell interneurons, only L4 has collaterals that invade neighboring cartridges. In the proximal lamina, these collaterals form reciprocal synapses with both the L2 of their own cartridge and the L4 collateral branches from two other neighboring cartridges. During synaptogenesis, L4 collaterals strongly express the cell adhesion protein Kirre, a member of the irre cell recognition module (IRM) group of proteins ( Fischbach et al., 2009 , J Neurogenet, 23, 48-67). The authors show by mutant analysis and gene knockdown techniques that L4 neurons develop their lamina collaterals in the absence of this cell adhesion protein. Using electron microscopy (EM), the authors demonstrate, however, that without Kirre protein these L4 collaterals selectively form fewer synapses. The collaterals of L4 neurons of various genotypes reconstructed from serial-section EM revealed that the number of postsynaptic sites was dramatically reduced in the absence of Kirre, almost eliminating any synaptic input to L4 neurons. A significant reduction of presynaptic sites was also detected in kirre(0) mutants and gene knockdown flies using RNA interference. L4 neuron reciprocal synapses are thus almost eliminated. A presynaptic marker, Brp-short(GFP) confirmed these data using confocal microscopy. This study reveals that removing Kirre protein specifically disrupts the functional L4 synaptic network in the Drosophila lamina.
Current Biology, 2006
Many types of synapses have highly characteristic shapes and tightly regulated distributions of a... more Many types of synapses have highly characteristic shapes and tightly regulated distributions of active zones, parameters that are important to the function of neuronal circuits. The development of terminal arborizations must therefore include mechanisms to regulate the spacing of terminals, the frequency of branching, and the distribution and density of release sites. At present, however, the mechanisms that control these features remain obscure. Here, we report the development of supernumerary or ''satellite'' boutons in a variety of endocytic mutants at the Drosophila neuromuscular junction. Mutants in endophilin, synaptojanin, dynamin, AP180, and synaptotagmin all show increases in supernumerary bouton structures. These satellite boutons contain releasable vesicles and normal complements of synaptic proteins that are correctly localized within terminals. Interestingly, however, synaptojanin terminals have more active zones per unit of surface area and more dense bodies (T-bars) within these active zones, which may in part compensate for reduced transmission per active zone. The altered structural development of the synapse is selectively encountered in endocytosis mutants and is not observed when synaptic transmission is reduced by mutations in glutamate receptors or when synaptic transmission is blocked by tetanus toxin. We propose that endocytosis plays a critical role in sculpting the structure of synapses, perhaps through the endocytosis of unknown regulatory signals that organize morphogenesis at synaptic terminals. Results and Discussion
This is data generated by the FlyEM project at Janelia and our collaborators at Google. It contai... more This is data generated by the FlyEM project at Janelia and our collaborators at Google. It contains the connectome (neurons and their connections) of a large fractionof the brain of the fruit fly <i>Drosophila melanogaster,</i> and the means to access this connectome.<br>This data is associated with the paper, BIORXIV/2020/911859, "A Connectome of the Adult Drosophila Central Brain" by C. Shan Xu, et al. published 22 January 2020. This is version 1.0 of the data; improved versions are expected to become available as research continues. <br><i><br></i>The data can be found at:<br>https://www.janelia.org/project-team/flyem/hemibrain
Arthropod Structure & Development