scholarly journals The C. elegans L1CAM homologue LAD-2 functions as a coreceptor in MAB-20/Sema2–mediated axon guidance

2008 ◽  
Vol 180 (1) ◽  
pp. 233-246 ◽  
Author(s):  
Xuelin Wang ◽  
Wei Zhang ◽  
Thomas Cheever ◽  
Valentin Schwarz ◽  
Karla Opperman ◽  
...  
Keyword(s):  
Axon Guidance ◽  
Cell Adhesion Molecule ◽  
Neuronal Development ◽  
Genetic Data ◽  
Axon Pathfinding ◽  
Spastic Paraplegia ◽  
C Elegans ◽  
Adducted Thumbs ◽  
L1 Cell Adhesion Molecule

The L1 cell adhesion molecule (L1CAM) participates in neuronal development. Mutations in the human L1 gene can cause the neurological disorder CRASH (corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraplegia, and hydrocephalus). This study presents genetic data that shows that L1-like adhesion gene 2 (LAD-2), a Caenorhabditis elegans L1CAM, functions in axon pathfinding. In the SDQL neuron, LAD-2 mediates dorsal axon guidance via the secreted MAB-20/Sema2 and PLX-2 plexin receptor, the functions of which have largely been characterized in epidermal morphogenesis. We use targeted misexpression experiments to provide in vivo evidence that MAB-20/Sema2 acts as a repellent to SDQL. Coimmunoprecipitation assays reveal that MAB-20 weakly interacts with PLX-2; this interaction is increased in the presence of LAD-2, which can interact independently with MAB-20 and PLX-2. These results suggest that LAD-2 functions as a MAB-20 coreceptor to secure MAB-20 coupling to PLX-2. In vertebrates, L1 binds neuropilin1, the obligate receptor to the secreted Sema3A. However, invertebrates lack neuropilins. LAD-2 may thus function in the semaphorin complex by combining the roles of neuropilins and L1CAMs.

scholarly journals Three C. elegans Rac proteins and several alternative Rac regulators control axon guidance, cell migration and apoptotic cell phagocytosis

Development ◽  
2001 ◽  
Vol 128 (22) ◽  
pp. 4475-4488 ◽  
Author(s):  
Erik A. Lundquist ◽  
Peter W. Reddien ◽  
Erika Hartwieg ◽  
H. Robert Horvitz ◽  
Cornelia I. Bargmann
Keyword(s):  
Cell Migration ◽  
Axon Guidance ◽  
Apoptotic Cell ◽  
Regulatory Proteins ◽  
Axon Pathfinding ◽  
C Elegans ◽  
Cell Corpse ◽  
And Function ◽  
Redundant Functions ◽  
Caenorhabditis Elegans Genome

The Caenorhabditis elegans genome contains three rac-like genes, ced-10, mig-2, and rac-2. We report that ced-10, mig-2 and rac-2 act redundantly in axon pathfinding: inactivating one gene had little effect, but inactivating two or more genes perturbed both axon outgrowth and guidance. mig-2 and ced-10 also have redundant functions in some cell migrations. By contrast, ced-10 is uniquely required for cell-corpse phagocytosis, and mig-2 and rac-2 have only subtle roles in this process. Rac activators are also used differentially. The UNC-73 Trio Rac GTP exchange factor affected all Rac pathways in axon pathfinding and cell migration but did not affect cell-corpse phagocytosis. CED-5 DOCK180, which acts with CED-10 Rac in cell-corpse phagocytosis, acted with MIG-2 but not CED-10 in axon pathfinding. Thus, distinct regulatory proteins modulate Rac activation and function in different developmental processes.

scholarly journals Regulation of axon repulsion by MAX-1 SUMOylation and AP-3

2018 ◽  
Vol 115 (35) ◽  
pp. E8236-E8245
Author(s):  
Shih-Yu Chen ◽  
Chun-Ta Ho ◽  
Wei-Wen Liu ◽  
Mark Lucanic ◽  
Hsiu-Ming Shih ◽  
...  
Keyword(s):  
Axon Guidance ◽  
Neural Development ◽  
Biochemical Analysis ◽  
Genetic Interaction ◽  
Motor Axons ◽  
Surface Receptors ◽  
C Elegans ◽  
Guidance Receptors ◽  
Axon Repulsion

During neural development, growing axons express specific surface receptors in response to various environmental guidance cues. These axon guidance receptors are regulated through intracellular trafficking and degradation to enable navigating axons to reach their targets. In Caenorhabditis elegans, the UNC-5 receptor is necessary for dorsal migration of developing motor axons. We previously found that MAX-1 is required for UNC-5–mediated axon repulsion, but its mechanism of action remained unclear. Here, we demonstrate that UNC-5–mediated axon repulsion in C. elegans motor axons requires both max-1 SUMOylation and the AP-3 complex β subunit gene, apb-3. Genetic interaction studies show that max-1 is SUMOylated by gei-17/PIAS1 and acts upstream of apb-3. Biochemical analysis suggests that constitutive interaction of MAX-1 and UNC-5 receptor is weakened by MAX-1 SUMOylation and by the presence of APB-3, a competitive interactor with UNC-5. Overexpression of APB-3 reroutes the trafficking of UNC-5 receptor into the lysosome for protein degradation. In vivo fluorescence recovery after photobleaching experiments shows that MAX-1 SUMOylation and APB-3 are required for proper trafficking of UNC-5 receptor in the axon. Our results demonstrate that SUMOylation of MAX-1 plays an important role in regulating AP-3–mediated trafficking and degradation of UNC-5 receptors during axon guidance.

scholarly journals Microtubule-dependent ribosome localization in C. elegans neurons

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Kentaro Noma ◽  
Alexandr Goncharov ◽  
Mark H Ellisman ◽  
Yishi Jin
Keyword(s):  
Cell Biology ◽  
Neuronal Development ◽  
Ultrastructural Level ◽  
Synthesis Methods ◽  
Tissue Specific ◽  
C Elegans ◽  
Multicellular Organisms ◽  
Axonal Trafficking ◽  
Insight Into

Subcellular localization of ribosomes defines the location and capacity for protein synthesis. Methods for in vivo visualizing ribosomes in multicellular organisms are desirable in mechanistic investigations of the cell biology of ribosome dynamics. Here, we developed an approach using split GFP for tissue-specific visualization of ribosomes in Caenorhabditis elegans. Labeled ribosomes are detected as fluorescent puncta in the axons and synaptic terminals of specific neuron types, correlating with ribosome distribution at the ultrastructural level. We found that axonal ribosomes change localization during neuronal development and after axonal injury. By examining mutants affecting axonal trafficking and performing a forward genetic screen, we showed that the microtubule cytoskeleton and the JIP3 protein UNC-16 exert distinct effects on localization of axonal and somatic ribosomes. Our data demonstrate the utility of tissue-specific visualization of ribosomes in vivo, and provide insight into the mechanisms of active regulation of ribosome localization in neurons.

scholarly journals C. elegans PVD Neurons: A Platform for Functionally Validating and Characterizing Neuropsychiatric Risk Genes

2016 ◽  
Author(s):  
Cristina Aguirre-Chen ◽  
Nuri Kim ◽  
Olivia Mendivil Ramos ◽  
Melissa Kramer ◽  
W. Richard McCombie ◽  
...  
Keyword(s):  
Protein Function ◽  
Molecular Mechanisms ◽  
Neuronal Development ◽  
De Novo ◽  
Genetic Interaction ◽  
Cost Effective ◽  
Chromatin Remodelers ◽  
C Elegans ◽  
Effective Manner

AbstractOne of the primary challenges in the field of psychiatric genetics is the lack of an in vivo model system in which to functionally validate candidate neuropsychiatric risk genes (NRGs) in a rapid and cost-effective manner1−3. To overcome this obstacle, we performed a candidate-based RNAi screen in which C. elegans orthologs of human NRGs were assayed for dendritic arborization and cell specification defects using C. elegans PVD neurons. Of 66 NRGs, identified via exome sequencing of autism (ASD)4 or schizophrenia (SCZ)5−9 probands and whose mutations are de novo and predicted to result in a complete or partial loss of protein function, the C. elegans orthologs of 7 NRGs were found to be required for proper neuronal development and represent a variety of functional classes, including transcriptional regulators and chromatin remodelers, molecular chaperones, and cytoskeleton-related proteins. Notably, the positive hit rate, when selectively assaying C. elegans orthologs of ASD and SCZ NRGs, is enriched >14-fold as compared to unbiased RNAi screening10. Furthermore, we find that RNAi phenotypes associated with the depletion of NRG orthologs is recapitulated in genetic mutant animals, and, via genetic interaction studies, we show that the NRG ortholog of ANK2, unc-44, is required for SAX-7/MNR-1/DMA-1 signaling. Collectively, our studies demonstrate that C. elegans PVD neurons are a tractable model in which to discover and dissect the fundamental molecular mechanisms underlying neuropsychiatric disease pathogenesis.

scholarly journals Flavin Monooxygenases Regulate C. elegans Axon Guidance and Growth Cone Protrusion with UNC-6/Netrin signaling and Rac GTPases

2017 ◽  
Author(s):  
Mahekta Gujar ◽  
Aubrie M. Stricker ◽  
Erik A. Lundquist
Keyword(s):  
Axon Guidance ◽  
Growth Cone ◽  
Molecular Mechanisms ◽  
Direct Oxidation ◽  
Rac Gtpase ◽  
C Elegans ◽  
Growth Cone Collapse ◽  
Rac Gtpases ◽  
Inhibition Of Growth

AbstractThe guidance cue UNC-6/Netrin regulates both attractive and repulsive axon guidance. Our previous work showed that in C. elegans, the attractive UNC-6/Netrin receptor UNC-40/DCC stimulates growth cone protrusion, and that the repulsive receptor, an UNC-5/UNC-40 heterodimer, inhibits growth cone protrusion. We have also shown that inhibition of growth cone protrusion downstream of the UNC-5/UNC-40 repulsive receptor involves Rac GTPases, the Rac GTP exchange factor UNC-73/Trio, and the cytoskeletal regulator UNC-33/CRMP, which mediates Semaphorin-induced growth cone collapse in other systems. The multidomain flavoprotein monooxygenase (FMO) MICAL also mediates growth cone collapse in response to Semaphorin by directly oxidizing F-actin, resulting in depolymerization. The C. elegans genome does not encode a multidomain MICAL-like molecule, but does encode five flavin monooxygenases (FMO-1, -2, -3, -4, and 5) and another molecule, EHBP-1, similar to the non-FMO portion of MICAL.Here we show that FMO-1, FMO-4, FMO-5, and EHBP-1 may play a role in UNC-6/Netrin directed repulsive guidance mediated through UNC-40 and UNC-5 receptors. Mutations in fmo-1, fmo-4, fmo-5, and ehbp-1 showed VD/DD axon guidance and branching defects, and variably enhanced unc-40 and unc-5 VD/DD guidance defects. Developing growth cones in vivo of fmo-1, fmo-4, fmo-5, and ehbp-1 mutants displayed excessive filopodial protrusion, and transgenic expression of FMO-5 inhibited growth cone protrusion. Mutations suppressed growth cone inhibition caused by activated UNC-40 and UNC-5 signaling, and activated Rac GTPase CED-10 and MIG-2, suggesting that these molecules are required downstream of UNC-6/Netrin receptors and Rac GTPases. From these studies, we conclude that FMO-1, FMO-4, FMO-5, and EHBP-1 represent new players downstream of UNC-6/Netrin receptors and Rac GTPases that inhibit growth cone filopodial protrusion in repulsive axon guidance.Author SummaryMolecular mechanisms of axon repulsion mediated by UNC-6/Netrin are not well understood. Inhibition of growth cone lamellipodial and filopodial protrusion is critical to repulsive axon guidance. Previous work identified a novel pathway involving Rac GTPases and the cytoskeletal interacting molecule UNC-33/CRMP required for UNC-6/Netrin-mediated inhibition of growth cone protrusion. In other systems, CRMP mediates growth cone collapse in response to semaphorin. Here we demonstrate a novel role of flavoprotein monooxygenases (FMOs) in repulsive axon guidance and inhibition of growth cone protrusion downstream of UNC-6/Netrin signaling and Rac GTPases. In Drosophila and vertebrates, the multidomain MICAL FMO mediates semaphorin-dependent growth cone collapse by direct oxidation and depolymerization of F-actin. The C. elegans genome does not encode a multidomain MICAL-like molecule, and we speculate that the C. elegans FMOs might have an equivalent role downstream of UNC-6/Netrin signaling. Indeed, we show that EHBP-1, similar to the non-FMO portion of MICAL, also controls repulsive axon guidance and growth cone inhibition, suggesting that in C. elegans, the functions of the multidomain MICAL molecule might be distributed across different molecules. In sum, we show conservation of function of molecules involved in semaphorin growth cone collapse with inhibition of growth cone protrusion downstream of UNC-6/Netrin signaling.

scholarly journals The Atypical Rho GTPase CHW-1 Works With SAX-3/Robo to Mediate Axon Guidance in Caenorhabditis elegans

2018 ◽  
Author(s):  
Jamie K. Alan ◽  
Sara Robinson ◽  
Katie Magsig ◽  
Rafael S. Demarco ◽  
Erik A. Lundquist
Keyword(s):  
Caenorhabditis Elegans ◽  
Axon Guidance ◽  
Motor Neurons ◽  
Rho Gtpases ◽  
Rho Gtpase ◽  
Genetic Interaction ◽  
Small Gtpases ◽  
Axon Pathfinding ◽  
Rho Proteins ◽  
C Elegans

AbstractDuring development, neuronal cells extend an axon towards their target destination in response to a cue to form a properly functioning nervous system. Rho proteins, Ras-related small GTPases that regulate cytoskeletal organization and dynamics, cell adhesion, and motility, are known to regulate axon guidance. Despite extensive knowledge about canonical Rho proteins (RhoA/Rac1/Cdc42), little is known about the Caenorhabditis elegans (C. elegans) atypical Cdc42-like family members CHW-1 and CRP-1 in regards to axon pathfinding and neuronal migration. chw-1(Chp/Wrch) encodes a protein that resembles human Chp (Wrch-2/RhoV) and Wrch-1 (RhoU), and crp-1 encodes for a protein that resembles TC10 and TCL. Here, we show that chw-1 works redundantly with crp-1 and cdc-42 in axon guidance. Furthermore, proper levels of chw-1 expression and activity are required for proper axon guidance. When examining CHW-1 GTPase mutants, we found that the native CHW-1 protein is likely partially activated, and mutations at a conserved residue (position 12 using Ras numbering, position 18 in CHW-1) alter axon guidance and neural migration. Additionally, we showed that chw-1 genetically interacts with the guidance receptor sax-3 in PDE neurons. Finally, in VD/DD motor neurons, chw-1 works downstream of sax-3 to control axon guidance. In summary, this is the first study implicating the atypical Rho GTPases chw-1 and crp-1 in axon guidance. Furthermore, this is the first evidence of genetic interaction between chw-1 and the guidance receptor sax-3. These data suggest that chw-1 is likely acting downstream and/or in parallel to sax-3 in axon guidance.

scholarly journals RHO-1 and the Rho GEF RHGF-1 interact with UNC-6/Netrin signaling to regulate growth cone protrusion and microtubule organization in C. elegans

2019 ◽  
Author(s):  
Mahekta R. Gujar ◽  
Aubrie M. Stricker ◽  
Erik A. Lundquist
Keyword(s):  
Axon Guidance ◽  
Growth Cone ◽  
Neural Circuit ◽  
Growth Cones ◽  
Negative Regulator ◽  
Microtubule Organization ◽  
C Elegans ◽  
Guidance Cue ◽  
Rho Gef

AbstractUNC-6/Netrin is a conserved axon guidance cue that directs growth cone migrations in the dorsal-ventral axis of C. elegans and in the vertebrate spinal cord. UNC-6/Netrin is expressed in ventral cells, and growth cones migrate ventrally toward or dorsally away from UNC-6/Netrin. Recent studies of growth cone behavior during outgrowth in vivo in C. elegans have led to a polarity/protrusion model in directed growth cone migration away from UNC-6/Netrin. In this model, UNC-6/Netrin first polarizes the growth cone via the UNC-5 receptor, leading to dorsally biased protrusion and F-actin accumulation. UNC-6/Netrin then regulates protrusion based on this polarity. The receptor UNC-40/DCC drives protrusion dorsally, away from the UNC-6/Netrin source, and the UNC-5 receptor inhibits protrusion ventrally, near the UNC-6/Netrin source, resulting in dorsal migration. UNC-5 inhibits protrusion in part by excluding microtubules from the growth cone, which are pro-protrusive. Here we report that the RHO-1/RhoA GTPase and its activator GEF RHGF-1 inhibit growth cone protrusion and MT accumulation in growth cones, similar to UNC-5. However, growth cone polarity of protrusion and F-actin were unaffected by RHO-1 and RHGF-1. Thus, RHO-1 signaling acts specifically as a negative regulator of protrusion and MT accumulation, and not polarity. Genetic interactions suggest that RHO-1 and RHGF-1 act with UNC-5, as well as with a parallel pathway, to regulate protrusion. The cytoskeletal interacting molecule UNC-33/CRMP was required for RHO-1 activity to inhibit MT accumulation, suggesting that UNC-33/CRMP might act downstream of RHO-1. In sum, these studies describe a new role of RHO-1 and RHGF-1 in regulation of growth cone protrusion by UNC-6/Netrin.Author SummaryNeural circuits are formed by precise connections between axons. During axon formation, the growth cone leads the axon to its proper target in a process called axon guidance. Growth cone outgrowth involves asymmetric protrusion driven by extracellular cues that stimulate and inhibit protrusion. How guidance cues regulate growth cone protrusion in neural circuit formation is incompletely understood. This work shows that the signaling molecule RHO-1 acts downstream of the UNC-6/Netrin guidance cue to inhibit growth cone protrusion in part by excluding microtubules from the growth cone, which are structural elements that drive protrusion.

scholarly journals The Amyloid Precursor-like Protein APL-1 Regulates Axon Regeneration

2018 ◽  
Author(s):  
Lewie Zeng ◽  
Rachid El Bejjani ◽  
Marc Hammarlund
Keyword(s):  
Motor Neurons ◽  
Neuronal Development ◽  
Axon Regeneration ◽  
Neuronal Response ◽  
Small Gtpase ◽  
C Elegans ◽  
Protein Levels ◽  
Mature Neurons ◽  
And Function

AbstractMembers of the Amyloid Precursor Protein (APP) family have important functions during neuronal development. However, their physiological functions in the mature nervous system are not fully understood. Here we use the C. elegans GABAergic motor neurons to study the post-developmental function of the APP-like protein APL-1 in vivo. We find that apl-1 has minimum roles in the maintenance of gross neuron morphology and function. However, we show that apl-1 is an inhibitor of axon regeneration, acting on mature neurons to limit regrowth in response to injury. The small GTPase Rab6/RAB-6.2 also inhibits regeneration, and does so in part by maintaining protein levels of APL-1. To inhibit regeneration, APL-1 functions via the E2 domain of its ectodomain; the cytoplasmic tail, transmembrane anchoring, and the E1 domain are not required for this function. Our data defines a novel role for APL-1 in modulating the neuronal response to injury.

scholarly journals L1CAM in the Early Enteric and Urogenital System

2016 ◽  
Vol 65 (1) ◽  
pp. 21-32 ◽  
Author(s):  
Elisabeth Judith Pechriggl ◽  
Nicole Concin ◽  
Michael J. Blumer ◽  
Mario Bitsche ◽  
Marit Zwierzina ◽  
...  
Keyword(s):  
Cell Adhesion Molecule ◽  
Neuronal Development ◽  
Axonal Guidance ◽  
Urogenital System ◽  
Fetal Period ◽  
L1 Protein ◽  
Early Human ◽  
L1 Cell Adhesion Molecule ◽  
L1cam Expression

L1 cell adhesion molecule (L1CAM) is a transmembrane molecule belonging to the L1 protein family. It has shown to be a key player in axonal guidance in the course of neuronal development. Furthermore, L1CAM is also crucial for the establishment of the enteric and urogenital organs and is aberrantly expressed in cancer originating in these organs. Carcinogenesis and embryogenesis follow a lot of similar molecular pathways, but unfortunately, comprehensive data on L1CAM expression and localization in human developing organs are lacking so far. In the present study we, therefore, examined the spatiotemporal distribution of L1CAM in the early human fetal period (weeks 8–12 of gestation) by means of immunohistochemistry and in situ hybridization (ISH). In the epithelia of the gastrointestinal organs, L1CAM localization cannot be observed in the examined stages most likely due to their advanced polarization and differentiation. Despite these results, our ISH data indicate weak L1CAM expression, but only in few epithelial cells. The genital tracts, however, are distinctly L1CAM positive throughout the entire fetal period. We, therefore, conclude that in embryogenesis L1CAM is crucial for further differentiation of epithelia.

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