scholarly journals Conserved and divergent aspects of Robo receptor signaling and regulation between Drosophila Robo1 and C. elegans SAX-3

Genetics ◽  
2021 ◽  
Vol 217 (3) ◽  
Author(s):  
Trent Daiber ◽  
Christine J VanderZwan-Butler ◽  
Greg J Bashaw ◽  
Timothy A Evans
Keyword(s):  
Fruit Fly ◽  
Negative Regulator ◽  
Genetic Rescue ◽  
Signaling Mechanism ◽  
Endosomal Sorting ◽  
C Elegans ◽  
Midline Crossing ◽  
Robo Receptors ◽  
Guidance Receptors

Abstract The evolutionarily conserved Roundabout (Robo) family of axon guidance receptors control midline crossing of axons in response to the midline repellant ligand Slit in bilaterian animals including insects, nematodes, and vertebrates. Despite this strong evolutionary conservation, it is unclear whether the signaling mechanism(s) downstream of Robo receptors are similarly conserved. To directly compare midline repulsive signaling in Robo family members from different species, here we use a transgenic approach to express the Robo family receptor SAX-3 from the nematode Caenorhabditis elegans in neurons of the fruit fly, Drosophila melanogaster. We examine SAX-3’s ability to repel Drosophila axons from the Slit-expressing midline in gain of function assays, and test SAX-3’s ability to substitute for Drosophila Robo1 during fly embryonic development in genetic rescue experiments. We show that C. elegans SAX-3 is properly translated and localized to neuronal axons when expressed in the Drosophila embryonic CNS, and that SAX-3 can signal midline repulsion in Drosophila embryonic neurons, although not as efficiently as Drosophila Robo1. Using a series of Robo1/SAX-3 chimeras, we show that the SAX-3 cytoplasmic domain can signal midline repulsion to the same extent as Robo1 when combined with the Robo1 ectodomain. We show that SAX-3 is not subject to endosomal sorting by the negative regulator Commissureless (Comm) in Drosophila neurons in vivo, and that peri-membrane and ectodomain sequences are both required for Comm sorting of Drosophila Robo1.

scholarly journals Conserved and divergent aspects of Robo receptor signaling and regulation between Drosophila Robo1 and C. elegans SAX-3

2020 ◽  
Author(s):  
Trent Daiber ◽  
Christine J. VanderZwan-Butler ◽  
Greg J. Bashaw ◽  
Timothy A. Evans
Keyword(s):  
Fruit Fly ◽  
Negative Regulator ◽  
Genetic Rescue ◽  
Signaling Mechanism ◽  
Endosomal Sorting ◽  
C Elegans ◽  
Midline Crossing ◽  
Robo Receptors ◽  
Guidance Receptors

AbstractThe evolutionarily conserved Roundabout (Robo) family of axon guidance receptors control midline crossing of axons in response to the midline repellant ligand Slit in bilaterian animals including insects, nematodes, and vertebrates. Despite this strong evolutionary conservation, it is unclear whether the signaling mechanism(s) downstream of Robo receptors are similarly conserved. To directly compare midline repulsive signaling in Robo family members from different species, here we use a transgenic approach to express the Robo family receptor SAX-3 from the nematode Caenorhabditis elegans in neurons of the fruit fly, Drosophila melanogaster. We examine SAX-3’s ability to repel Drosophila axons from the Slit-expressing midline in gain of function assays, and test SAX-3’s ability to substitute for Drosophila Robo1 during fly embryonic development in genetic rescue experiments. We show that C. elegans SAX-3 is properly translated and localized to neuronal axons when expressed in the Drosophila embryonic CNS, and that SAX-3 can signal midline repulsion in Drosophila embryonic neurons, although not as efficiently as Drosophila Robo1. Using a series of Robo1/SAX-3 chimeras, we show that the SAX-3 cytoplasmic domain can signal midline repulsion to the same extent as Robo1 when combined with the Robo1 ectodomain. We show that SAX-3 is not subject to endosomal sorting by the negative regulator Commissureless (Comm) in Drosophila neurons in vivo, and that peri-membrane and ectodomain sequences are both required for Comm sorting of Drosophila Robo1.

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 Minimal structural elements required for midline repulsive signaling and regulation of Drosophila Robo1

2020 ◽  
Author(s):  
Haley E. Brown ◽  
Timothy A. Evans
Keyword(s):  
Axon Guidance ◽  
Biochemical Properties ◽  
Structural Elements ◽  
Wild Type ◽  
Domain Interaction ◽  
Robo Receptors ◽  
Guidance Receptors ◽  
Repulsive Signaling

AbstractThe Roundabout (Robo) family of axon guidance receptors has a conserved ectodomain arrangement of five immunoglobulin-like (Ig) domains plus three fibronectin (Fn) repeats. Based on the strong evolutionary conservation of this domain structure among Robo receptors, as well as in vitro structural and domain-domain interaction studies of Robo family members, this ectodomain arrangement is predicted to be important for Robo receptor signaling in response to Slit ligands. Here, we define the minimal ectodomain structure required for Slit binding and midline repulsive signaling in vivo by Drosophila Robo1. We find that the majority of the Robo1 ectodomain is dispensable for both Slit binding and repulsive signaling. We show that a significant level of midline repulsive signaling activity is retained when all Robo1 ectodomain elements apart from Ig1 are deleted, and that the combination of Ig1 plus one additional ectodomain element (Ig2, Ig5, or Fn3) is sufficient to restore midline repulsion to wild type levels. Further, we find that deleting four out of five Robo1 Ig domains (ΔIg2-5) does not affect negative regulation of Robo1 by Commissureless (Comm) or Robo2, while variants lacking all three fibronectin repeats (ΔFn1-3 and ΔIg2-Fn3) are insensitive to regulation by both Comm and Robo2, signifying a novel regulatory role for Robo1’s Fn repeats. Our results provide an in vivo perspective on the importance of the conserved 5+3 ectodomain structure of Robo receptors, and suggest that specific biochemical properties and/or ectodomain structural conformations observed in vitro for domains other than Ig1 may have limited significance for in vivo signaling in the context of midline repulsion.

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 Molecular Evolution of a Sex Determination Protein: FEM-2 (PP2C) in Caenorhabditis

Genetics ◽  
1998 ◽  
Vol 149 (3) ◽  
pp. 1353-1362 ◽  
Author(s):  
Dave Hansen ◽  
Dave Pilgrim
Keyword(s):  
Sex Determination ◽  
Phosphatase Activity ◽  
Catalytic Domain ◽  
Sequence Similarity ◽  
Signal Transduction Pathway ◽  
Negative Regulator ◽  
Amino Terminus ◽  
C Elegans

Abstract Somatic sex determination in Caenorhabditis elegans involves a signal transduction pathway linking a membrane receptor to a transcription factor. The fem-2 gene is central to this pathway, producing a protein phosphatase (FEM-2) of the type 2C (PP2C). FEM-2 contains a long amino terminus that is absent in canonical PP2C enzymes. The function of this domain is difficult to predict, since it shows no sequence similarity to any other known proteins or motifs. Here we report the cloning of the fem-2 homologue from Caenorhabditis briggsae (Cb-fem-2). The sequence identity is much higher than that observed for other C. briggsae homologues of C. elegans sex determination proteins. However, this level is not uniform across the entire lengths of the proteins; it is much lower in the amino termini. Thus, the two domains of the same protein are evolving at different rates, suggesting that they have different functional constraints. Consistent with this, Cb-FEM-2 is able to replace some, but not all, of the Ce-FEM-2 in vivo function. We show that removal of the amino terminus from Ce-FEM-2 has no effect on its in vitro phosphatase activity, or its ability to replace the in vivo function of a yeast PP2C enzyme, but that it is necessary for proper FEM-2 function in worms. This demonstrates that the amino terminus is not an extended catalytic domain or a direct negative regulator of phosphatase activity.

scholarly journals SNX-1 and RME-8 oppose the assembly of HGRS-1/ESCRT-0 degradative microdomains on endosomes

2017 ◽  
Vol 114 (3) ◽  
pp. E307-E316 ◽  
Author(s):  
Anne Norris ◽  
Prasad Tammineni ◽  
Simon Wang ◽  
Julianne Gerdes ◽  
Alexandra Murr ◽  
...  
Keyword(s):  
Kinase Substrate ◽  
Endosomal Sorting ◽  
Sorting Nexin ◽  
Binding Partner ◽  
Regulatory Interactions ◽  
C Elegans ◽  
J Domain ◽  
Vacuolar Protein ◽  
Hepatocyte Growth

After endocytosis, transmembrane cargo reaches endosomes, where it encounters complexes dedicated to opposing functions: recycling and degradation. Microdomains containing endosomal sorting complexes required for transport (ESCRT)-0 component Hrs [hepatocyte growth factor-regulated tyrosine kinase substrate (HGRS-1) in Caenorhabditis elegans] mediate cargo degradation, concentrating ubiquitinated cargo and organizing the activities of ESCRT. At the same time, retromer associated sorting nexin one (SNX-1) and its binding partner, J-domain protein RME-8, sort cargo away from degradation, promoting cargo recycling to the Golgi. Thus, we hypothesized that there could be important regulatory interactions between retromer and ESCRT that balance degradative and recycling functions. Taking advantage of the naturally large endosomes of the C. elegans coelomocyte, we visualized complementary ESCRT-0 and RME-8/SNX-1 microdomains in vivo and assayed the ability of retromer and ESCRT microdomains to regulate one another. We found in snx-1(0) and rme-8(ts) mutants increased endosomal coverage and intensity of HGRS-1–labeled microdomains, as well as increased total levels of HGRS-1 bound to membranes. These effects are specific to SNX-1 and RME-8, as loss of other retromer components SNX-3 and vacuolar protein sorting-associated protein 35 (VPS-35) did not affect HGRS-1 microdomains. Additionally, knockdown of hgrs-1 had little to no effect on SNX-1 and RME-8 microdomains, suggesting directionality to the interaction. Separation of the functionally distinct ESCRT-0 and SNX-1/RME-8 microdomains was also compromised in the absence of RME-8 and SNX-1, a phenomenon we observed to be conserved, as depletion of Snx1 and Snx2 in HeLa cells also led to greater overlap of Rme-8 and Hrs on endosomes.

scholarly journals Comprehensive identification and characterization of conserved small ORFs in animals

2015 ◽  
Author(s):  
Sebastian D Mackowiak ◽  
Henrik Zauber ◽  
Chris Bielow ◽  
Denise Thiel ◽  
Kamila Kutz ◽  
...  
Keyword(s):  
Purifying Selection ◽  
Fruit Fly ◽  
Ribosome Profiling ◽  
Open Reading Frames ◽  
Mass Spectrometry Data ◽  
C Elegans ◽  
Small Orfs ◽  
Identification And Characterization

There is increasing evidence that non-annotated short open reading frames (sORFs) can encode functional micropeptides, but computational identification remains challenging. We expand our published method and predict conserved sORFs in human, mouse, zebrafish, fruit fly and the nematode C. elegans. Isolating specific conservation signatures indicative of purifying selection on encoded amino acid sequence, we identify about 2000 novel sORFs in the untranslated regions of canonical mRNAs or on transcripts annotated as non-coding. Predicted sORFs show stronger conservation signatures than those identified in previous studies and are sometimes conserved over large evolutionary distances. Encoded peptides have little homology to known proteins and are enriched in disordered regions and short interaction motifs. Published ribosome profiling data indicate translation for more than 100 of novel sORFs, and mass spectrometry data gives peptidomic evidence for more than 70 novel candidates. We thus provide a catalog of conserved micropeptides for functional validation in vivo.

scholarly journals Rap2 and TNIK control Plexin-dependent tiled synaptic innervation in C. elegans

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Xi Chen ◽  
Akihiro CE Shibata ◽  
Ardalan Hendi ◽  
Mizuki Kurashina ◽  
Ethan Fortes ◽  
...  
Keyword(s):  
Synapse Formation ◽  
Small Gtpase ◽  
Negative Regulator ◽  
Gtpase Activity ◽  
C Elegans ◽  
Receptor Interactions ◽  
Presynaptic Assembly ◽  
Intracellular Mechanisms

During development, neurons form synapses with their fate-determined targets. While we begin to elucidate the mechanisms by which extracellular ligand-receptor interactions enhance synapse specificity by inhibiting synaptogenesis, our knowledge about their intracellular mechanisms remains limited. Here we show that Rap2 GTPase (rap-2) and its effector, TNIK (mig-15), act genetically downstream of Plexin (plx-1) to restrict presynaptic assembly and to form tiled synaptic innervation in C. elegans. Both constitutively GTP- and GDP-forms of rap-2 mutants exhibit synaptic tiling defects as plx-1 mutants, suggesting that cycling of the RAP-2 nucleotide state is critical for synapse inhibition. Consistently, PLX-1 suppresses local RAP-2 activity. Excessive ectopic synapse formation in mig-15 mutants causes a severe synaptic tiling defect. Conversely, overexpression of mig-15 strongly inhibited synapse formation, suggesting that mig-15 is a negative regulator of synapse formation. These results reveal that subcellular regulation of small GTPase activity by Plexin shapes proper synapse patterning in vivo.

scholarly journals The RhoGAP SPV-1 regulates calcium signaling to control the contractility of theC. elegansspermatheca during embryo transits

2018 ◽  
Author(s):  
Jeff Bouffard ◽  
Alyssa D. Cecchetelli ◽  
Coleman Clifford ◽  
Kriti Sethi ◽  
Ronen Zaidel-Bar ◽  
...  
Keyword(s):  
Calcium Signaling ◽  
Signaling Pathways ◽  
Calcium Release ◽  
Small Gtpase ◽  
Negative Regulator ◽  
Calcium Signal ◽  
C Elegans ◽  
Spatial Regulation ◽  
Calcium Indicator

AbstractContractility of the non-muscle and smooth muscle cells that comprise biological tubing is regulated by the Rho-ROCK and calcium signaling pathways. Although many molecular details about these signaling pathways are known, less is known about how they are coordinated spatiotemporally in biological tubes. The spermatheca of theC. elegansreproductive system enables study of the signaling pathways regulating actomyosin contractility in live adult animals. The RhoGAP SPV-1 was previously identified as a negative regulator of RHO-1/Rho and spermathecal contractility. Here, we uncover a role for SPV-1 as a key regulator of calcium signaling.spv-1mutants expressing the calcium indicator GCaMP in the spermatheca exhibit premature calcium release, elevated calcium levels, and disrupted spatial regulation of calcium signaling during spermathecal contraction. Although RHO-1 is required for spermathecal contractility, RHO-1 does not play a significant role in regulating calcium. In contrast, activation of CDC-42 recapitulates many aspects ofspv-1mutant calcium signaling. Depletion ofcdc-42by RNAi does not suppress the premature or elevated calcium signal seen inspv-1mutants, suggesting other targets remain to be identified. Our results suggest SPV-1 works through both the Rho-ROCK and calcium signaling pathways to coordinate cellular contractility.Highlight SummaryThroughin vivoimaging of the calcium sensor GCaMP, we show that the RhoGAP SPV-1 is a key regulator of calcium signaling in theC. elegansspermatheca. Our data suggests SPV-1 acts at least partially through the small GTPase CDC-42 to modulate calcium signaling, while also acting on RHO-1 to modulate Rho-ROCK signaling. This places SPV-1 as a central regulator of cellular contractility.

scholarly journals Rap2 and TNIK control Plexin-dependent synaptic tiling in C. elegans

2017 ◽  
Author(s):  
Xi Chen ◽  
Akihiro C.E. Shibata ◽  
Ardalan Hendi ◽  
Mizuki Kurashina ◽  
Ethan Fortes ◽  
...  
Keyword(s):  
Synapse Formation ◽  
Small Gtpase ◽  
Negative Regulator ◽  
Gtpase Activity ◽  
C Elegans ◽  
Receptor Interactions ◽  
Presynaptic Assembly ◽  
Intracellular Mechanisms

AbstractDuring development, neurons form synapses with their fate-determined targets. While we begin to elucidate the mechanisms by which extracellular ligand-receptor interactions enhance synapse specificity by inhibiting synaptogenesis, our knowledge about their intracellular mechanisms remains limited. Here we show that Rap2 GTPase (rap-2) and its effector, TNIK (mig-15), act downstream of Plexin (plx-1) to restrict presynaptic assembly and to form tiled synaptic innervation in C. elegans. Both constitutively GTP- and GDP-forms of rap-2 mutants exhibit synaptic tiling defects as plx-1 mutants, suggesting that cycling of the RAP-2 nucleotide state is critical for synapse inhibition. Consistently, RAP-2 activity is locally suppressed by PLX-1. Excessive ectopic synapse formation in mig-15 mutants causes a severe synaptic tiling defect. Conversely, overexpression of mig-15 strongly inhibited synapse formation, suggesting that mig-15 is a negative regulator of synapse formation. These results reveal that subcellular regulation of small GTPase activity by Plexin shapes proper synapse patterning in vivo.

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