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Colak D, Ji SJ, Porse BT, Jaffrey SR. Regulation of axon guidance by compartmentalized nonsense-mediated mRNA decay. Cell 2013; 153:1252-65. [PMID: 23746841 PMCID: PMC3685487 DOI: 10.1016/j.cell.2013.04.056] [Citation(s) in RCA: 147] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2012] [Revised: 03/05/2013] [Accepted: 04/30/2013] [Indexed: 12/13/2022]
Abstract
Growth cones enable axons to navigate toward their targets by responding to extracellular signaling molecules. Growth-cone responses are mediated in part by the local translation of axonal messenger RNAs (mRNAs). However, the mechanisms that regulate local translation are poorly understood. Here we show that Robo3.2, a receptor for the Slit family of guidance cues, is synthesized locally within axons of commissural neurons. Robo3.2 translation is induced by floor-plate-derived signals as axons cross the spinal cord midline. Robo3.2 is also a predicted target of the nonsense-mediated mRNA decay (NMD) pathway. We find that NMD regulates Robo3.2 synthesis by inducing the degradation of Robo3.2 transcripts in axons that encounter the floor plate. Commissural neurons deficient in NMD proteins exhibit aberrant axonal trajectories after crossing the midline, consistent with misregulation of Robo3.2 expression. These data show that local translation is regulated by mRNA stability and that NMD acts locally to influence axonal pathfinding.
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Affiliation(s)
- Dilek Colak
- Department of Pharmacology, Weill Medical College, Cornell University, New York, NY 10065, USA
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52
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Harpaz N, Ordan E, Ocorr K, Bodmer R, Volk T. Multiplexin promotes heart but not aorta morphogenesis by polarized enhancement of slit/robo activity at the heart lumen. PLoS Genet 2013; 9:e1003597. [PMID: 23825967 PMCID: PMC3694841 DOI: 10.1371/journal.pgen.1003597] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 05/16/2013] [Indexed: 11/19/2022] Open
Abstract
The Drosophila heart tube represents a structure that similarly to vertebrates' primary heart tube exhibits a large lumen; the mechanisms promoting heart tube morphology in both Drosophila and vertebrates are poorly understood. We identified Multiplexin (Mp), the Drosophila orthologue of mammalian Collagen-XV/XVIII, and the only structural heart-specific protein described so far in Drosophila, as necessary and sufficient for shaping the heart tube lumen, but not that of the aorta. Mp is expressed specifically at the stage of heart tube closure, in a polarized fashion, uniquely along the cardioblasts luminal membrane, and its absence results in an extremely small heart tube lumen. Importantly, Mp forms a protein complex with Slit, and interacts genetically with both slit and robo in the formation of the heart tube. Overexpression of Mp in cardioblasts promotes a large heart lumen in a Slit-dependent manner. Moreover, Mp alters Slit distribution, and promotes the formation of multiple Slit endocytic vesicles, similarly to the effect of overexpression of Robo in these cells. Our data are consistent with Mp-dependent enhancement of Slit/Robo activity and signaling, presumably by affecting Slit protein stabilization, specifically at the lumen side of the heart tube. This activity results with a Slit-dependent, local reduction of F-actin levels at the heart luminal membrane, necessary for forming the large heart tube lumen. Consequently, lack of Mp results in decreased diastolic capacity, leading to reduced heart contractility, as measured in live fly hearts. In summary, these findings show that the polarized localization of Mp controls the direction, timing, and presumably the extent of Slit/Robo activity and signaling at the luminal membrane of the heart cardioblasts. This regulation is essential for the morphogenetic changes that sculpt the heart tube in Drosophila, and possibly in forming the vertebrates primary heart tube.
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Affiliation(s)
- Nofar Harpaz
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Elly Ordan
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Karen Ocorr
- Development and Aging Program, Sanford-Burnham Medical Research Institute, La Jolla, California, United States of America
| | - Rolf Bodmer
- Development and Aging Program, Sanford-Burnham Medical Research Institute, La Jolla, California, United States of America
| | - Talila Volk
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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Abstract
Commissural circuits are brain and spinal cord connections which interconnect the two sides of the central nervous system (CNS). They play essential roles in brain and spinal cord processing, ensuring left-right coordination and synchronization of information and commands. During the formation of neuronal circuits, all commissural neurons of the central nervous system must accomplish a common task, which is to project their axon onto the other side of the nervous system, across the midline that delineates the two halves of the CNS. How this task is accomplished has been the topic of extensive studies over the last past 20 years and remains one of the best models to investigate axon guidance mechanisms. In the first part of this review, I will introduce the commissural circuits, their general role in the physiology of the nervous system, and their recognized or suspected pathogenic properties in human diseases. In the second part of the review, I will concentrate on two commissural circuits, the spinal commissures and the corpus callosum, to detail the cellular and molecular mechanisms governing their formation, mostly during their navigation at the midline.
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Schweitzer J, Löhr H, Bonkowsky JL, Hübscher K, Driever W. Sim1a and Arnt2 contribute to hypothalamo-spinal axon guidance by regulating Robo2 activity via a Robo3-dependent mechanism. Development 2013; 140:93-106. [PMID: 23222439 DOI: 10.1242/dev.087825] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Precise spatiotemporal control of axon guidance factor expression is a prerequisite for formation of functional neuronal connections. Although Netrin/Dcc- and Robo/Slit-mediated attractive and repulsive guidance of commissural axons have been extensively studied, little is known about mechanisms controlling mediolateral positioning of longitudinal axons in vertebrates. Here, we use a genetic approach in zebrafish embryos to study pathfinding mechanisms of dopaminergic and neuroendocrine longitudinal axons projecting from the hypothalamus into hindbrain and spinal cord. The transcription factors Sim1a and Arnt2 contribute to differentiation of a defined population of dopaminergic and neuroendocrine neurons. We show that both factors also control aspects of axon guidance: Sim1a or Arnt2 depletion results in displacement of hypothalamo-spinal longitudinal axons towards the midline. This phenotype is suppressed in robo3 guidance receptor mutant embryos. In the absence of Sim1a and Arnt2, expression of the robo3 splice isoform robo3a.1 is increased in the hypothalamus, indicating negative control of robo3a.1 transcription by these factors. We further provide evidence that increased Robo3a.1 levels interfere with Robo2-mediated repulsive axon guidance. Finally, we show that the N-terminal domain unique to Robo3a.1 mediates the block of Robo2 repulsive activity. Therefore, Sim1a and Arnt2 contribute to control of lateral positioning of longitudinal hypothalamic-spinal axons by negative regulation of robo3a.1 expression, which in turn attenuates the repulsive activity of Robo2.
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Affiliation(s)
- Jörn Schweitzer
- Developmental Biology, Institute Biology 1, Faculty of Biology, University of Freiburg, Hauptstrasse 1, D-79104 Freiburg, Germany.
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55
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Sano H, Kunwar PS, Renault AD, Barbosa V, Clark IBN, Ishihara S, Sugimura K, Lehmann R. The Drosophila actin regulator ENABLED regulates cell shape and orientation during gonad morphogenesis. PLoS One 2012; 7:e52649. [PMID: 23300733 PMCID: PMC3530444 DOI: 10.1371/journal.pone.0052649] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Accepted: 11/16/2012] [Indexed: 12/27/2022] Open
Abstract
Organs develop distinctive morphologies to fulfill their unique functions. We used Drosophila embryonic gonads as a model to study how two different cell lineages, primordial germ cells (PGCs) and somatic gonadal precursors (SGPs), combine to form one organ. We developed a membrane GFP marker to image SGP behaviors live. These studies show that a combination of SGP cell shape changes and inward movement of anterior and posterior SGPs leads to the compaction of the spherical gonad. This process is disrupted in mutants of the actin regulator, enabled (ena). We show that Ena coordinates these cell shape changes and the inward movement of the SGPs, and Ena affects the intracellular localization of DE-cadherin (DE-cad). Mathematical simulation based on these observations suggests that changes in DE-cad localization can generate the forces needed to compact an elongated structure into a sphere. We propose that Ena regulates force balance in the SGPs by sequestering DE-cad, leading to the morphogenetic movement required for gonad compaction.
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Affiliation(s)
- Hiroko Sano
- HHMI and Developmental Genetics Program, Skirball Institute of Biomolecular Medicine, Department of Cell Biology, New York University Medical Center, New York, New York, United States of America.
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56
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St Johnston D. Using mutants, knockdowns, and transgenesis to investigate gene function in Drosophila. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2012; 2:587-613. [PMID: 24014449 DOI: 10.1002/wdev.101] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The sophisticated genetic techniques available in Drosophila are largely responsible for its success as a model organism. One of the most important of these is the ability to disrupt gene function in vivo and observe the resulting phenotypes. This review considers the ever-increasing repertoire of approaches for perturbing the functions of specific genes in flies, ranging from classical and transposon-mediated mutageneses to newer techniques, such as homologous recombination and RNA interference. Since most genes are used over and over again in different contexts during development, many important advances have depended on being able to interfere with gene function at specific times or places in the developing animal, and a variety of approaches are now available to do this. Most of these techniques rely on being able to create genetically modified strains of Drosophila and the different methods for generating lines carrying single copy transgenic constructs will be described, along with the advantages and disadvantages of each approach.
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Affiliation(s)
- Daniel St Johnston
- The Gurdon Institute and the Department of Genetics, University of Cambridge, Cambridge CB2 1QN, UK.
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57
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Long-range targeted manipulation of the Drosophila genome by site-specific integration and recombinational resolution. Genetics 2012; 193:411-9. [PMID: 23150601 DOI: 10.1534/genetics.112.145631] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Significant advances in genomics underscore the importance of targeted mutagenesis for gene function analysis. Here we have developed a scheme for long-range targeted manipulation of genes in the Drosophila genome. Utilizing an attP attachment site for the phiC31 integrase previously targeted to the nbs gene, we integrated an 80-kb genomic fragment at its endogenous locus to generate a tandem duplication of the region. We achieved reduction to a single copy by inducing recombination via a site-specific DNA break. We report that, despite the large size of the DNA fragment, both plasmid integration and duplication reduction can be accomplished efficiently. Importantly, the integrating genomic fragment can serve as a venue for introducing targeted modifications to the entire region. We successfully introduced a new attachment site 70 kb from the existing attP using this two-step scheme, making a new region susceptible to targeted mutagenesis. By experimenting with different placements of the future DNA break site in the integrating vector, we established a vector configuration that facilitates the recovery of desired modifications. We also show that reduction events can occur efficiently through unequal meiotic crossing over between the large duplications. Based on our results, we suggest that a collection of 1200 lines with attachment sites inserted every 140 kb throughout the genome would render all Drosophila genes amenable to targeted mutagenesis. Excitingly, all of the components involved are likely functional in other eukaryotes, making our scheme for long-range targeted manipulation readily applicable to other systems.
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58
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Sakai N, Kaprielian Z. Guidance of longitudinally projecting axons in the developing central nervous system. Front Mol Neurosci 2012; 5:59. [PMID: 22586366 PMCID: PMC3343325 DOI: 10.3389/fnmol.2012.00059] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 04/14/2012] [Indexed: 12/26/2022] Open
Abstract
The directed and stereotypical growth of axons to their synaptic targets is a crucial phase of neural circuit formation. Many axons in the developing vertebrate and invertebrate central nervous systems (CNSs), including those that remain on their own (ipsilateral), and those that cross over to the opposite (commissural), side of the midline project over long distances along the anterior-posterior (A-P) body axis within precisely positioned longitudinally oriented tracts to facilitate the transmission of information between CNS regions. Despite the widespread distribution and functional importance of these longitudinal tracts, the mechanisms that regulate their formation and projection to poorly characterized synaptic targets remain largely unknown. Nevertheless, recent studies carried out in a variety of invertebrate and vertebrate model systems have begun to elucidate the molecular logic that controls longitudinal axon guidance.
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Affiliation(s)
- Nozomi Sakai
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx NY, USA
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59
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Evans TA, Bashaw GJ. Slit/Robo-mediated axon guidance in Tribolium and Drosophila: divergent genetic programs build insect nervous systems. Dev Biol 2012; 363:266-78. [PMID: 22245052 PMCID: PMC4128232 DOI: 10.1016/j.ydbio.2011.12.046] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2011] [Revised: 12/21/2011] [Accepted: 12/28/2011] [Indexed: 12/23/2022]
Abstract
As the complexity of animal nervous systems has increased during evolution, developmental control of neuronal connectivity has become increasingly refined. How has functional diversification within related axon guidance molecules contributed to the evolution of nervous systems? To address this question, we explore the evolution of functional diversity within the Roundabout (Robo) family of axon guidance receptors. In Drosophila, Robo and Robo2 promote midline repulsion, while Robo2 and Robo3 specify the position of longitudinal axon pathways. The Robo family has expanded by gene duplication in insects; robo2 and robo3 exist as distinct genes only within dipterans, while other insects, like the flour beetle Tribolium castaneum, retain an ancestral robo2/3 gene. Both Robos from Tribolium can mediate midline repulsion in Drosophila, but unlike the fly Robos cannot be down-regulated by Commissureless. The overall architecture and arrangement of longitudinal pathways are remarkably conserved in Tribolium, despite it having only two Robos. Loss of TcSlit causes midline collapse of axons in the beetle, a phenotype recapitulated by simultaneous knockdown of both Robos. Single gene knockdowns reveal that beetle Robos have specialized axon guidance functions: TcRobo is dedicated to midline repulsion, while TcRobo2/3 also regulates longitudinal pathway formation. TcRobo2/3 knockdown reproduces aspects of both Drosophila robo2 and robo3 mutants, suggesting that TcRobo2/3 has two functions that in Drosophila are divided between Robo2 and Robo3. The ability of Tribolium to organize longitudinal axons into three discrete medial-lateral zones with only two Robo receptors demonstrates that beetle and fly achieve equivalent developmental outcomes using divergent genetic programs.
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Affiliation(s)
- Timothy A Evans
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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60
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Abstract
The Slit family of secreted proteins and their transmembrane receptor, Robo, were originally identified in the nervous system where they function as axon guidance cues and branching factors during development. Since their discovery, a great number of additional roles have been attributed to Slit/Robo signaling, including regulating the critical processes of cell proliferation and cell motility in a variety of cell and tissue types. These processes are often deregulated during cancer progression, allowing tumor cells to bypass safeguarding mechanisms in the cell and the environment in order to grow and escape to new tissues. In the past decade, it has been shown that the expression of Slit and Robo is altered in a wide variety of cancer types, identifying them as potential therapeutic targets. Further, studies have demonstrated dual roles for Slits and Robos in cancer, acting as both oncogenes and tumor suppressors. This bifunctionality is also observed in their roles as axon guidance cues in the developing nervous system, where they both attract and repel neuronal migration. The fact that this signaling axis can have opposite functions depending on the cellular circumstance make its actions challenging to define. Here, we summarize our current understanding of the dual roles that Slit/Robo signaling play in development, epithelial tumor progression, and tumor angiogenesis.
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Affiliation(s)
- Mimmi S. Ballard
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz CA 95064
| | - Lindsay Hinck
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz CA 95064
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61
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Morphological characterization of the entire interneuron population reveals principles of neuromere organization in the ventral nerve cord of Drosophila. J Neurosci 2011; 31:15870-83. [PMID: 22049430 DOI: 10.1523/jneurosci.4009-11.2011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Decisive contributions to our understanding of the mechanisms underlying the development of the nervous system have been made by studies performed at the level of single, identified cells in the fruit fly Drosophila. While all the motor neurons and glial cells in thoracic and abdominal segments of the Drosophila embryo have been individually identified, few of the interneurons, which comprise the vast majority of cells in the CNS, have been characterized at this level. We have applied a single cell labeling technique to carry out a detailed morphological characterization of the entire population of interneurons in abdominal segments A1-A7. Based on the definition of a set of spatial parameters specifying axonal projection patterns and cell body positions, we have identified 270 individual cell types as the complete hemisegmental set of interneurons and placed these in an interactive database. As well as facilitating analyses of developmental processes, this comprehensive set of data sheds light on the principles underlying the formation and organization of an entire segmental unit of the CNS.
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62
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Crossing the border: molecular control of motor axon exit. Int J Mol Sci 2011; 12:8539-61. [PMID: 22272090 PMCID: PMC3257087 DOI: 10.3390/ijms12128539] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2011] [Revised: 11/05/2011] [Accepted: 11/08/2011] [Indexed: 11/23/2022] Open
Abstract
Living organisms heavily rely on the function of motor circuits for their survival and for adapting to ever-changing environments. Unique among central nervous system (CNS) neurons, motor neurons (MNs) project their axons out of the CNS. Once in the periphery, motor axons navigate along highly stereotyped trajectories, often at considerable distances from their cell bodies, to innervate appropriate muscle targets. A key decision made by pathfinding motor axons is whether to exit the CNS through dorsal or ventral motor exit points (MEPs). In contrast to the major advances made in understanding the mechanisms that regulate the specification of MN subtypes and the innervation of limb muscles, remarkably little is known about how MN axons project out of the CNS. Nevertheless, a limited number of studies, mainly in Drosophila, have identified transcription factors, and in some cases candidate downstream effector molecules, that are required for motor axons to exit the spinal cord. Notably, specialized neural crest cell derivatives, referred to as Boundary Cap (BC) cells, pre-figure and demarcate MEPs in vertebrates. Surprisingly, however, BC cells are not required for MN axon exit, but rather restrict MN cell bodies from ectopically migrating along their axons out of the CNS. Here, we describe the small set of studies that have addressed motor axon exit in Drosophila and vertebrates, and discuss our fragmentary knowledge of the mechanisms, which guide motor axons out of the CNS.
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63
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Venken KJ, Simpson JH, Bellen HJ. Genetic manipulation of genes and cells in the nervous system of the fruit fly. Neuron 2011; 72:202-30. [PMID: 22017985 PMCID: PMC3232021 DOI: 10.1016/j.neuron.2011.09.021] [Citation(s) in RCA: 301] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/26/2011] [Indexed: 12/26/2022]
Abstract
Research in the fruit fly Drosophila melanogaster has led to insights in neural development, axon guidance, ion channel function, synaptic transmission, learning and memory, diurnal rhythmicity, and neural disease that have had broad implications for neuroscience. Drosophila is currently the eukaryotic model organism that permits the most sophisticated in vivo manipulations to address the function of neurons and neuronally expressed genes. Here, we summarize many of the techniques that help assess the role of specific neurons by labeling, removing, or altering their activity. We also survey genetic manipulations to identify and characterize neural genes by mutation, overexpression, and protein labeling. Here, we attempt to acquaint the reader with available options and contexts to apply these methods.
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Affiliation(s)
- Koen J.T. Venken
- Department of Molecular and Human Genetics, Neurological Research Institute, Baylor College of Medicine, Houston, Texas, 77030
| | - Julie H. Simpson
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, 20147
| | - Hugo J. Bellen
- Department of Molecular and Human Genetics, Neurological Research Institute, Baylor College of Medicine, Houston, Texas, 77030
- Program in Developmental Biology, Department of Neuroscience, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, 77030
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64
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Kim M, Roesener AP, Mendonca PRF, Mastick GS. Robo1 and Robo2 have distinct roles in pioneer longitudinal axon guidance. Dev Biol 2011; 358:181-8. [PMID: 21820427 PMCID: PMC3171630 DOI: 10.1016/j.ydbio.2011.07.025] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2011] [Revised: 07/16/2011] [Accepted: 07/16/2011] [Indexed: 11/16/2022]
Abstract
Pioneer longitudinal axons grow long distances parallel to the floor plate and precisely maintain their positions using guidance molecules released from the floor plate. Two receptors, Robo1 and Robo2, are critical for longitudinal axon guidance by the Slit family of chemorepellents. Previous studies showed that Robo1(-/-);2(-/-) double mutant mouse embryos have disruptions in both ventral and dorsal longitudinal tracts. However, the role of each Robo isoform remained unclear, because Robo1 or 2 single mutants have mild or no errors. Here we utilized a more sensitive genetic strategy to reduce Robo levels for determining any separate functions of the Robo1 and 2 isoforms. We found that Robo1 is the predominant receptor for guiding axons in ventral tracts and prevents midline crossing. In contrast, Robo2 is the main receptor for directing axons within dorsal tracts. Robo2 also has a distinct function in repelling neuron cell bodies from the floor plate. Therefore, while Robo1 and 2 have some genetic overlap to cooperate in guiding longitudinal axons, each isoform has distinct functions in specific longitudinal axon populations.
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Affiliation(s)
- Minkyung Kim
- Department of Biology, University of Nevada, Reno, USA
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65
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Xiao T, Staub W, Robles E, Gosse NJ, Cole GJ, Baier H. Assembly of lamina-specific neuronal connections by slit bound to type IV collagen. Cell 2011; 146:164-76. [PMID: 21729787 DOI: 10.1016/j.cell.2011.06.016] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2010] [Revised: 04/10/2011] [Accepted: 06/09/2011] [Indexed: 01/08/2023]
Abstract
The mechanisms that generate specific neuronal connections in the brain are under intense investigation. In zebrafish, retinal ganglion cells project their axons into at least six layers within the neuropil of the midbrain tectum. Each axon elaborates a single, planar arbor in one of the target layers and forms synapses onto the dendrites of tectal neurons. We show that the laminar specificity of retinotectal connections does not depend on self-sorting interactions among RGC axons. Rather, tectum-derived Slit1, signaling through axonal Robo2, guides neurites to their target layer. Genetic and biochemical studies indicate that Slit binds to Dragnet (Col4a5), a type IV Collagen, which forms the basement membrane on the surface of the tectum. We further show that radial glial endfeet are required for the basement-membrane anchoring of Slit. We propose that Slit1 signaling, perhaps in the form of a superficial-to-deep gradient, presents laminar positional cues to ingrowing retinal axons.
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Affiliation(s)
- Tong Xiao
- Programs in Neuroscience, Department of Physiology, University of California, San Francisco, 1550 Fourth Street, San Francisco, CA 94158-2722, USA
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66
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Nawabi H, Castellani V. Axonal commissures in the central nervous system: how to cross the midline? Cell Mol Life Sci 2011; 68:2539-53. [PMID: 21538161 PMCID: PMC11114790 DOI: 10.1007/s00018-011-0691-9] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Revised: 04/08/2011] [Accepted: 04/14/2011] [Indexed: 01/02/2023]
Abstract
Organisms with bilateral symmetry elaborate patterns of neuronal projections connecting both sides of the central nervous system at all levels of the neuraxis. During development, these so-called commissural projections navigate across the midline to innervate their contralateral targets. Commissural axon pathfinding has been extensively studied over the past years and turns out to be a highly complex process, implicating modulation of axon responsiveness to the various guidance cues that instruct axon trajectories towards, within and away from the midline. Understanding the molecular mechanisms allowing these switches of response to take place at the appropriate time and place is a major challenge for current research. Recent work characterized several instructive processes controlling the spatial and temporal fine-tuning of the guidance molecular machinery. These findings illustrate the molecular strategies by which commissural axons modulate their sensitivity to guidance cues during midline crossing and show that regulation at both transcriptional and post-transcriptional levels are crucial for commissural axon guidance.
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Affiliation(s)
- Homaira Nawabi
- F.M. Kirby Neurobiology Center, Children's Hospital and Department of Neurology, Harvard Medical School, Boston, MA 02115, USA.
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67
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de Wit J, Hong W, Luo L, Ghosh A. Role of leucine-rich repeat proteins in the development and function of neural circuits. Annu Rev Cell Dev Biol 2011; 27:697-729. [PMID: 21740233 DOI: 10.1146/annurev-cellbio-092910-154111] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The nervous system consists of an ensemble of billions of neurons interconnected in a highly specific pattern that allows proper propagation and integration of neural activities. The organization of these specific connections emerges from sequential developmental events including axon guidance, target selection, and synapse formation. These events critically rely on cell-cell recognition and communication mediated by cell-surface ligands and receptors. Recent studies have uncovered central roles for leucine-rich repeat (LRR) domain-containing proteins, not only in organizing neural connectivity from axon guidance to target selection to synapse formation, but also in various nervous system disorders. Their versatile LRR domains, in particular, serve as key sites for interactions with a wide diversity of binding partners. Here, we focus on a few exquisite examples of secreted or membrane-associated LRR proteins in Drosophila and mammals and review the mechanisms by which they regulate diverse aspects of nervous system development and function.
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Affiliation(s)
- Joris de Wit
- Neurobiology Section, Division of Biology, University of California, San Diego, La Jolla, California 92093-0366, USA
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68
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Smart AD, Course MM, Rawson J, Selleck S, Van Vactor D, Johnson KG. Heparan sulfate proteoglycan specificity during axon pathway formation in the Drosophila embryo. Dev Neurobiol 2011; 71:608-18. [PMID: 21500363 PMCID: PMC3115403 DOI: 10.1002/dneu.20854] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Axon guidance is influenced by the presence of heparan sulfate (HS) proteoglycans (HSPGs) on the surface of axons and growth cones (Hu, [2001]: Nat Neurosci 4:695-701; Irie et al. [2002]: Development 129:61-70; Inatani et al. [2003]: Science 302:1044-1046; Johnson et al. [2004]: Curr Biol 14:499-504; Steigemann et al. [2004]: Curr Biol 14:225-230). Multiple HSPGs, including Syndecans, Glypicans and Perlecans, carry the same carbohydrate polymer backbones, raising the question of how these molecules display functional specificity during nervous system development. Here we use the Drosophila central nervous system (CNS) as a model to compare the impact of eliminating Syndecan (Sdc) and/or the Glypican Dally-like (Dlp). We show that Dlp and Sdc share a role in promoting accurate patterns of axon fasciculation in the lateral longitudinal neuropil; however, unlike mutations in sdc, which disrupt the ability of the secreted repellent Slit to prevent inappropriate passage of axons across the midline, mutations in dlp show neither midline defects nor genetic interactions with Slit and its Roundabout (Robo) receptors at the midline. Dlp mutants do show genetic interactions with Slit and Robo in lateral fascicle formation. In addition, simultaneous loss of Dlp and Sdc demonstrates an important role for Dlp in midline repulsion, reminiscent of the functional overlap between Robo receptors. A comparison of HSPG distribution reveals a pattern that leaves midline proximal axons with relatively little Dlp. Finally, the loss of Dlp alters Slit distribution distal but not proximal to the midline, suggesting that distinct yet overlapping pattern of HSPG expression provides a spatial system that regulates axon guidance decisions.
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Affiliation(s)
- Ashley D. Smart
- Department of Biology and Program in Neuroscience, 175 West 6 Street, Pomona College, Claremont, CA 91711
| | - Meredith M. Course
- Department of Biology and Program in Neuroscience, 175 West 6 Street, Pomona College, Claremont, CA 91711
| | | | | | - David Van Vactor
- Department of Cell Biology and Program in Neuroscience, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115
| | - Karl G. Johnson
- Department of Biology and Program in Neuroscience, 175 West 6 Street, Pomona College, Claremont, CA 91711
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69
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Wu Z, Sweeney LB, Ayoob JC, Chak K, Andreone BJ, Ohyama T, Kerr R, Luo L, Zlatic M, Kolodkin AL. A combinatorial semaphorin code instructs the initial steps of sensory circuit assembly in the Drosophila CNS. Neuron 2011; 70:281-98. [PMID: 21521614 DOI: 10.1016/j.neuron.2011.02.050] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/09/2011] [Indexed: 01/19/2023]
Abstract
Longitudinal axon fascicles within the Drosophila embryonic CNS provide connections between body segments and are required for coordinated neural signaling along the anterior-posterior axis. We show here that establishment of select CNS longitudinal tracts and formation of precise mechanosensory afferent innervation to the same CNS region are coordinately regulated by the secreted semaphorins Sema-2a and Sema-2b. Both Sema-2a and Sema-2b utilize the same neuronal receptor, plexin B (PlexB), but serve distinct guidance functions. Localized Sema-2b attraction promotes the initial assembly of a subset of CNS longitudinal projections and subsequent targeting of chordotonal sensory afferent axons to these same longitudinal connectives, whereas broader Sema-2a repulsion serves to prevent aberrant innervation. In the absence of Sema-2b or PlexB, chordotonal afferent connectivity within the CNS is severely disrupted, resulting in specific larval behavioral deficits. These results reveal that distinct semaphorin-mediated guidance functions converge at PlexB and are critical for functional neural circuit assembly.
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Affiliation(s)
- Zhuhao Wu
- The Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Howard Hughes Medical Institute, Baltimore, MD 21205, USA
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70
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Kolodkin AL, Tessier-Lavigne M. Mechanisms and molecules of neuronal wiring: a primer. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a001727. [PMID: 21123392 DOI: 10.1101/cshperspect.a001727] [Citation(s) in RCA: 430] [Impact Index Per Article: 33.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The complex patterns of neuronal wiring in the adult nervous system depend on a series of guidance events during neural development that establish a framework on which functional circuits can be built. In this subject collection, the cellular and molecular mechanisms that underlie neuronal guidance are considered from several perspectives, ranging from how cytoskeletal dynamics within extending neuronal growth cones steer axons, to how guidance cues influence synaptogenesis. We introduce here some basic topics to frame the more detailed reviews in following articles, including the cellular strategies that define basic themes governing neuronal wiring throughout life, an enumeration of the molecular cues and receptors known to play key guidance roles during neural development, and an overview of the signaling mechanisms that transduce guidance information into growth-cone steering.
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Affiliation(s)
- Alex L Kolodkin
- Solomon H. Snyder Department of Neuroscience at the Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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71
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Bacon C, Endris V, Andermatt I, Niederkofler V, Waltereit R, Bartsch D, Stoeckli ET, Rappold G. Evidence for a role of srGAP3 in the positioning of commissural axons within the ventrolateral funiculus of the mouse spinal cord. PLoS One 2011; 6:e19887. [PMID: 21655271 PMCID: PMC3104994 DOI: 10.1371/journal.pone.0019887] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Accepted: 04/09/2011] [Indexed: 01/20/2023] Open
Abstract
Slit-Robo signaling guides commissural axons away from the floor-plate of the spinal cord and into the longitudinal axis after crossing the midline. In this study we have evaluated the role of the Slit-Robo GTPase activating protein 3 (srGAP3) in commissural axon guidance using a knockout (KO) mouse model. Co-immunoprecipitation experiments confirmed that srGAP3 interacts with the Slit receptors Robo1 and Robo2 and immunohistochemistry studies showed that srGAP3 co-localises with Robo1 in the ventral and lateral funiculus and with Robo2 in the lateral funiculus. Stalling axons have been reported in the floor-plate of Slit and Robo mutant spinal cords but our axon tracing experiments revealed no dorsal commissural axon stalling in the floor plate of the srGAP3 KO mouse. Interestingly we observed a significant thickening of the ventral funiculus and a thinning of the lateral funiculus in the srGAP3 KO spinal cord, which has also recently been reported in the Robo2 KO. However, axons in the enlarged ventral funiculus of the srGAP3 KO are Robo1 positive but do not express Robo2, indicating that the thickening of the ventral funiculus in the srGAP3 KO is not a Robo2 mediated effect. We suggest a role for srGAP3 in the lateral positioning of post crossing axons within the ventrolateral funiculus.
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Affiliation(s)
- Claire Bacon
- Department of Human Molecular Genetics, University of Heidelberg, Heidelberg, Germany.
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72
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Robo-3--mediated repulsive interactions guide R8 axons during Drosophila visual system development. Proc Natl Acad Sci U S A 2011; 108:7571-6. [PMID: 21490297 DOI: 10.1073/pnas.1103419108] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The formation of neuronal connections requires the precise guidance of developing axons toward their targets. In the Drosophila visual system, photoreceptor neurons (R cells) project from the eye into the brain. These cells are grouped into some 750 clusters comprised of eight photoreceptors or R cells each. R cells fall into three classes: R1 to R6, R7, and R8. Posterior R8 cells are the first to project axons into the brain. How these axons select a specific pathway is not known. Here, we used a microarray-based approach to identify genes expressed in R8 neurons as they extend into the brain. We found that Roundabout-3 (Robo3), an axon-guidance receptor, is expressed specifically and transiently in R8 growth cones. In wild-type animals, posterior-most R8 axons extend along a border of glial cells demarcated by the expression of Slit, the secreted ligand of Robo3. In contrast, robo3 mutant R8 axons extend across this border and fasciculate inappropriately with other axon tracts. We demonstrate that either Robo1 or Robo2 rescues the robo3 mutant phenotype when each is knocked into the endogenous robo3 locus separately, indicating that R8 does not require a function unique to the Robo3 paralog. However, persistent expression of Robo3 in R8 disrupts the layer-specific targeting of R8 growth cones. Thus, the transient cell-specific expression of Robo3 plays a crucial role in establishing neural circuits in the Drosophila visual system by selectively regulating pathway choice for posterior-most R8 growth cones.
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73
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Geutskens SB, Hordijk PL, van Hennik PB. The chemorepellent Slit3 promotes monocyte migration. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2010; 185:7691-8. [PMID: 21078908 DOI: 10.4049/jimmunol.0903898] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Directional migration is an essential step for monocytes to infiltrate sites of inflammation, a process primarily regulated by chemoattractants. Slits are large matrix proteins that are secreted by endothelial cells; they were reported to inhibit the chemoattractant-induced migration of different cell types, including leukocytes. The aim of this study was to determine the effect of Slit3 on primary monocyte migration and to address the underlying mechanisms. We show that Roundabout (Robo)1, one of the Robo receptors that recognize Slit3, is the only Robo homolog expressed by CD14(+) monocytes. Interestingly, we found that stimulation with Slit3 increased the spontaneous and chemoattractant-induced migration of primary monocytes in vitro and increased the myeloid cell recruitment during peritoneal inflammation in vivo. In addition, Slit3 did not seem to act as a chemoattractant itself; it promoted directed migration triggered by chemoattractants, such as CXCL12, by inducing a chemokinetic effect. We further show that Slit3 prevented monocyte spreading and induced rounding of spread monocytes without affecting monocyte adhesion. Stimulation with Slit3 was not associated with changes in the levels of phosphorylated p38, p42/p44, or Src, known regulators of monocyte migration, but it directly acts on molecular pathways involved in basal leukocyte migration by activating RhoA. These findings show an unexpected response of monocytes to Slit3 and add insights into the possible role of Slit proteins during inflammatory cell recruitment.
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Affiliation(s)
- Sacha B Geutskens
- Department of Molecular Cell Biology, Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
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74
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Williamson WR, Yang T, Terman JR, Hiesinger PR. Guidance receptor degradation is required for neuronal connectivity in the Drosophila nervous system. PLoS Biol 2010; 8:e1000553. [PMID: 21151882 PMCID: PMC2998435 DOI: 10.1371/journal.pbio.1000553] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2010] [Accepted: 10/21/2010] [Indexed: 12/23/2022] Open
Abstract
Axon pathfinding and synapse formation rely on precise spatiotemporal localization of guidance receptors. However, little is known about the neuron-specific intracellular trafficking mechanisms that underlie the sorting and activity of these receptors. Here we show that loss of the neuron-specific v-ATPase subunit a1 leads to progressive endosomal guidance receptor accumulations after neuronal differentiation. In the embryo and in adult photoreceptors, these accumulations occur after axon pathfinding and synapse formation is complete. In contrast, receptor missorting occurs sufficiently early in neurons of the adult central nervous system to cause connectivity defects. An increase of guidance receptors, but not of membrane proteins without signaling function, causes specific gain-of-function phenotypes. A point mutant that promotes sorting but prevents degradation reveals spatiotemporally specific guidance receptor turnover and accelerates developmental defects in photoreceptors and embryonic motor neurons. Our findings indicate that a neuron-specific endolysosomal degradation mechanism is part of the cell biological machinery that regulates guidance receptor turnover and signaling.
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Affiliation(s)
- W. Ryan Williamson
- Department of Physiology and Green Center for Systems Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Taehong Yang
- Departments of Neuroscience and Pharmacology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Jonathan R. Terman
- Departments of Neuroscience and Pharmacology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - P. Robin Hiesinger
- Department of Physiology and Green Center for Systems Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- * E-mail:
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75
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Fabre CCG, Casal J, Lawrence PA. Mechanosensilla in the adult abdomen of Drosophila: engrailed and slit help to corral the peripheral sensory axons into segmental bundles. Development 2010; 137:2885-94. [PMID: 20667917 PMCID: PMC2938919 DOI: 10.1242/dev.044552] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/14/2010] [Indexed: 11/20/2022]
Abstract
The abdomen of adult Drosophila bears mechanosensory bristles with axons that connect directly to the CNS, each hemisegment contributing a separate nerve bundle. Here, we alter the amount of Engrailed protein and manipulate the Hedgehog signalling pathway in clones of cells to study their effects on nerve pathfinding within the peripheral nervous system. We find that high levels of Engrailed make the epidermal cells inhospitable to bristle neurons; sensory axons that are too near these cells are either deflected or fail to extend properly or at all. We then searched for the engrailed-dependent agent responsible for these repellent properties. We found slit to be expressed in the P compartment and, using genetic mosaics, present evidence that Slit is the responsible molecule. Blocking the activity of the three Robo genes (putative receptors for Slit) with RNAi supported this hypothesis. We conclude that, during normal development, gradients of Slit protein repel axons away from compartment boundaries - in consequence, the bristles from each segment send their nerves to the CNS in separated sets.
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MESH Headings
- Abdomen/physiology
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/physiology
- Animals
- Animals, Genetically Modified
- Axons/physiology
- Drosophila/genetics
- Drosophila/growth & development
- Drosophila/physiology
- Drosophila Proteins/genetics
- Drosophila Proteins/physiology
- Gene Expression Regulation, Developmental
- Genes, Insect
- Hedgehog Proteins/genetics
- Hedgehog Proteins/physiology
- Homeodomain Proteins/genetics
- Homeodomain Proteins/physiology
- Mechanoreceptors/physiology
- Models, Neurological
- Nerve Tissue Proteins/antagonists & inhibitors
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/physiology
- Neurogenesis/genetics
- Neurogenesis/physiology
- RNA Interference
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/physiology
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/physiology
- Receptors, Immunologic/antagonists & inhibitors
- Receptors, Immunologic/genetics
- Receptors, Immunologic/physiology
- Smoothened Receptor
- Transcription Factors/genetics
- Transcription Factors/physiology
- Roundabout Proteins
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76
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Further tales of the midline. Curr Opin Neurobiol 2010; 21:68-75. [PMID: 20724139 DOI: 10.1016/j.conb.2010.07.008] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Revised: 07/22/2010] [Accepted: 07/22/2010] [Indexed: 11/24/2022]
Abstract
In the vertebrate central nervous system (CNS), specialized glial and neuronal cells positioned at the dorsal and ventral midline act as intermediate targets for commissural axons by secreting a variety of attractants and repellents. Despite the diversity of commissural projections, recent findings suggest that the same basic set of molecules controls midline crossing at all level of the CNS. Midline crossing is associated with an important switch of the combinatorial expression of several axon guidance receptors on the growth cone of commissural axons. I will review here novel studies that reveal how the expression of these receptors and the activity of their ligands are modulated by transcriptional, translational, and post-translational modifications. This also uncovers extensive cross talks between axon guidance pathways.
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77
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Jaworski A, Long H, Tessier-Lavigne M. Collaborative and specialized functions of Robo1 and Robo2 in spinal commissural axon guidance. J Neurosci 2010; 30:9445-53. [PMID: 20631173 PMCID: PMC6632452 DOI: 10.1523/jneurosci.6290-09.2010] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2009] [Revised: 06/01/2010] [Accepted: 06/03/2010] [Indexed: 11/21/2022] Open
Abstract
Commissural neurons project axons across the floor plate at the spinal cord ventral midline. After crossing, commissural axons turn rostrally, sort into distinct positions within the ventrolateral funiculus, and never reenter the floor plate. Robo1 and Robo2 are receptors for the midline repellents Slit1-Slit3, and upregulation of Robos in post-crossing axons allows expulsion from the floor plate and prevents recrossing. Before crossing, Robo-mediated repulsion is attenuated by the divergent family member Robo3/Rig-1. To define the relative contributions of Robo family members to commissural axon guidance in mice, we studied commissural axon trajectories in combination mutants between Robo1, Robo2, and Robo3. Our results suggest the existence of another receptor contributing to Slit repulsion because the failure of midline crossing in Robo3 mutants is rescued largely but not entirely by loss of both Robo1 and Robo2 and because axon guidance defects in mice lacking both Robo1 and Robo2 are less severe than in mice lacking all Slits. Analysis of post-crossing axon trajectories indicates that Robo1 and Robo2 collaborate to prevent axons from reentering the gray matter and projecting dorsally alongside contralateral pre-crossing axons. We also discovered a previously unappreciated division of labor between Robo1 and Robo2 in post-crossing axons. Robo2 is required for axons to project away from the floor plate into the lateral funiculus. In contrast, Robo1 prevents axonal stalling after crossing. Our results reveal specialized and complementary actions of Robo1 and Robo2 in commissural axon guidance and suggest the existence of an as yet unidentified Slit receptor.
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Affiliation(s)
- Alexander Jaworski
- Division of Research, Genentech Inc., South San Francisco, California 94080
| | - Hua Long
- Division of Research, Genentech Inc., South San Francisco, California 94080
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78
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Ypsilanti AR, Zagar Y, Chédotal A. Moving away from the midline: new developments for Slit and Robo. Development 2010; 137:1939-52. [DOI: 10.1242/dev.044511] [Citation(s) in RCA: 185] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In most tissues, the precise control of cell migration and cell-cell interaction is of paramount importance to the development of a functional structure. Several families of secreted molecules have been implicated in regulating these aspects of development, including the Slits and their Robo receptors. These proteins have well described roles in axon guidance but by influencing cell polarity and adhesion, they participate in many developmental processes in diverse cell types. We review recent progress in understanding both the molecular mechanisms that modulate Slit/Robo expression and their functions in neural and non-neural tissue.
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Affiliation(s)
- Athena R. Ypsilanti
- INSERM, U968, Paris F-75012, France
- UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, 17 rue Moreau, Paris F-75012, France
- CNRS, UMR_7210, Paris F-75012, France
| | - Yvrick Zagar
- INSERM, U968, Paris F-75012, France
- UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, 17 rue Moreau, Paris F-75012, France
- CNRS, UMR_7210, Paris F-75012, France
| | - Alain Chédotal
- INSERM, U968, Paris F-75012, France
- UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, 17 rue Moreau, Paris F-75012, France
- CNRS, UMR_7210, Paris F-75012, France
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79
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Dickson BJ, Zou Y. Navigating intermediate targets: the nervous system midline. Cold Spring Harb Perspect Biol 2010; 2:a002055. [PMID: 20534708 DOI: 10.1101/cshperspect.a002055] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In a bilaterally symmetric animal, the midline plays a key role in directing axon growth during wiring of the nervous system. Midline cells provide a variety of guidance cues for growing axons, to which different types of axons respond in different ways and at different times. For some axons, the midline is an intermediate target. They first seek it out, but then move on towards their final targets on the opposite side. For others, the midline is a repulsive barrier that keeps them on their own side of the midline. And for many of these axons the midline provides signals that guide them along specific lateral pathways or up and down the longitudinal axis.
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Affiliation(s)
- Barry J Dickson
- Research Institute of Molecular Pathology, Dr. Bohrgasse 7, A-1030 Vienna, Austria.
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80
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Abstract
The secreted signal Slit and its three receptors, Robo1-3, regulate axon guidance in the Drosophila nervous system. Differences in expression and structure of Robo paralogs contribute to diversifying growth cone responses to a common ligand.
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Affiliation(s)
- Kartik S Pappu
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
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81
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Banerjee S, Blauth K, Peters K, Rogers SL, Fanning AS, Bhat MA. Drosophila neurexin IV interacts with Roundabout and is required for repulsive midline axon guidance. J Neurosci 2010; 30:5653-67. [PMID: 20410118 PMCID: PMC2869042 DOI: 10.1523/jneurosci.6187-09.2010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2009] [Revised: 02/26/2010] [Accepted: 03/14/2010] [Indexed: 11/21/2022] Open
Abstract
Slit/Roundabout (Robo) signaling controls midline repulsive axon guidance. However, proteins that interact with Slit/Robo at the cell surface remain largely uncharacterized. Here, we report that the Drosophila transmembrane septate junction-specific protein Neurexin IV (Nrx IV) functions in midline repulsive axon guidance. Nrx IV is expressed in the neurons of the developing ventral nerve cord, and nrx IV mutants show crossing and circling of ipsilateral axons and fused commissures. Interestingly, the axon guidance defects observed in nrx IV mutants seem independent of its other binding partners, such as Contactin and Neuroglian and the midline glia protein Wrapper, which interacts in trans with Nrx IV. nrx IV mutants show diffuse Robo localization, and dose-dependent genetic interactions between nrx IV/robo and nrx IV/slit indicate that they function in a common pathway. In vivo biochemical studies reveal that Nrx IV associates with Robo, Slit, and Syndecan, and interactions between Robo and Slit, or Nrx IV and Slit, are affected in nrx IV and robo mutants, respectively. Coexpression of Nrx IV and Robo in mammalian cells confirms that these proteins retain the ability to interact in a heterologous system. Furthermore, we demonstrate that the extracellular region of Nrx IV is sufficient to rescue Robo localization and axon guidance phenotypes in nrx IV mutants. Together, our studies establish that Nrx IV is essential for proper Robo localization and identify Nrx IV as a novel interacting partner of the Slit/Robo signaling pathway.
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Affiliation(s)
| | | | - Kimberly Peters
- Department of Biology, Carolina Center for Genome Sciences, Lineberger Cancer Center
| | - Stephen L. Rogers
- Department of Biology, Carolina Center for Genome Sciences, Lineberger Cancer Center
| | | | - Manzoor A. Bhat
- Department of Cell and Molecular Physiology
- Curriculum in Neurobiology
- University of North Carolina Neuroscience Center, and
- Neurodevelopmental Disorders Research Center, University of North Carolina School of Medicine Chapel Hill, Chapel Hill, North Carolina 27599-7545
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