21.Hutter, H. (2019) Formation of longitudinal axon pathways in Caenorhabditis elegans.Semin. Cell Dev. Biol. 85 Formation of longitudinal axon pathways in Caenorhabditis elegans
Axon guidance; Growth cone; Ventral nerve cord; Pioneer; Follower
The small number of neurons and the simple architecture of the Caenorhabditis elegans (C. elegans) nervous system enables researchers to study axonal pathfinding at the level of individually identified axons. Axons in C. elegans extend predominantly along one of the two major body axes, the anterior-posterior axis and the dorso-ventral axis. This review will focus on axon navigation along the anterior-posterior axis, leading to the establishment of the longitudinal axon tracts, with a focus on the largest longitudinal axon tract, the ventral nerve cord (VNC). In the VNC, axons grow out in a stereotypic order, with early outgrowing axons (pioneers) playing an important role in guiding later outgrowing (follower) axons. Genetic screens have identified a number of genes specifically affecting the formation of longitudinal axon tracts. These genes include secreted proteins, putative receptors and adhesion molecules, as well as intracellular proteins regulating the cell's response to guidance cues. In contrast to dorso-ventral navigation, no major general guidance cues required for the establishment of longitudinal pathways have been identified so far. The limited penetrance of defects found in many mutants affecting longitudinal navigation suggests that guidance cues act redundantly in this process. The majority of the axon guidance genes identified in C. elegans are evolutionary conserved, i.e. have homologs in other animals, including vertebrates. For a number of these genes, a role in axon guidance has not been described outside C. elegans. Taken together, studies in C. elegans contribute to a fundamental understanding of the molecular basis of axonal navigation that can be extended to other animals, including vertebrates and probably humans as well. (C) 2017 Elsevier Ltd. All rights reserved. DOI PubMed
20. Taylor, J; Hutter, H. (2019) Multiple Pathways Act Together To Establish Asymmetry of the Ventral Nerve Cord in Caenorhabditis elegans.Genetics 211 Multiple Pathways Act Together To Establish Asymmetry of the Ventral Nerve Cord in Caenorhabditis elegans
asymmetry; central nervous system; ventral nerve cord; axon guidance
The central nervous system of most animals is bilaterally symmetrical. Closer observation often reveals some functional or anatomical left-right asymmetries. In the nematode Caenorhabditis elegans, the most obvious asymmetry in the nervous system is found in the ventral nerve cord (VNC), where most axons are in the right axon tract. The asymmetry is established when axons entering the VNC from the brain switch from the left to the right side at the anterior end of the VNC. In genetic screens we identified several mutations compromising VNC asymmetry. This includes alleles of (encoding a transmembrane collagen), /perlecan and (encoding the actin modulator Enabled/Vasodilator-stimulated phosphoproteins). In addition, we evaluated mutants in known axon guidance pathways for asymmetry defects and used genetic interaction studies to place the genes into genetic pathways. In total we identified four different pathways contributing to the establishment of VNC asymmetry, represented by /netrin, SAX-3/Robo, , and /laminin. The combined inactivation of these pathways in triple and quadruple mutants leads to highly penetrant VNC asymmetry defects, suggesting these pathways are important contributors to the establishment of VNC asymmetry in C. elegans. DOI PubMed
19. Taylor, J; Unsoeld, T; Hutter, H. (2018) The transmembrane collagen COL-99 guides longitudinally extending axons in C-elegans.Mol. Cell. Neurosci. 89 The transmembrane collagen COL-99 guides longitudinally extending axons in C-elegans
We have identified the transmembrane collagen, COL-99, in a genetic screen for novel genes involved in axon guidance in the nematode C. deguns. COL-99 is similar to transmembrane collagens type XIII, XXIII and XXV in vertebrates. col-99 mutants exhibit guidance defects in axons extending along the major longitudinal axon tracts, most prominently the left ventral nerve cord (VNC). COL-99 is expressed in the hypodermis during the time of axon outgrowth. We provide evidence that a furin cleavage site in COL-99 is essential for function, suggesting that COL-99 is released from the cells producing it. Vertebrate homologs of COL-99 have been shown to be expressed in mammalian nervous systems and linked to various neurological disease but have not been associated with guidance of extending neurons. col-99 acts genetically with the discoidin domain receptors ddr-1 and ddr-2, which are expressed by neurons affected in col-99 mutants. Discoidin domain receptors are activated by collagens in vertebrates. DDR-1 and DDR-2 may function as receptors for COL-99. Our results establish a novel role for a transmembrane collagen in axonal guidance and asymmetry establishment of the VNC. DOI PubMed
18. Bhat, JM; Hutter, H. (2016) Pioneer Axon Navigation Is Controlled by AEX-3, a Guanine Nucleotide Exchange Factor for RAB-3 in Caenorhabditis elegans.Genetics 203: 1235-1247 Pioneer Axon Navigation Is Controlled by AEX-3, a Guanine Nucleotide Exchange Factor for RAB-3 in Caenorhabditis elegans
nervous system; axon guidance; pioneer; GEF; vesicle trafficking
Precise and accurate axon tract formation is an essential aspect of brain development. This is achieved by the migration of early outgrowing axons (pioneers) allowing later outgrowing axons (followers) to extend toward their targets in the embryo. In Caenorhabditis elegans the AVG neuron pioneers the right axon tract of the ventral nerve cord, the major longitudinal axon tract. AVG is essential for the guidance of follower axons and hence organization of the ventral nerve cord. In an enhancer screen for AVG axon guidance defects in a nid-1/Nidogen mutant background, we isolated an allele of aex-3. aex-3 mutant animals show highly penetrant AVG axon navigation defects. These defects are dependent on a mutation in nid-1/Nidogen, a basement membrane component. Our data suggest that AEX-3 activates RAB-3 in the context of AVG axon navigation. aex-3 genetically acts together with known players of vesicular exocytosis: unc-64/Syntaxin, unc-31/CAPS, and ida-1/IA-2. Furthermore our genetic interaction data suggest that AEX-3 and the UNC-6/Netrin receptor UNC-5 act in the same pathway, suggesting AEX-3 might regulate the trafficking and/or insertion of UNC-5 at the growth cone to mediate the proper guidance of the AVG axon. DOI
17. Chisholm, AD; Hutter, H; Jin, YS; Wadsworth, WG. (2016) The Genetics of Axon Guidance and Axon Regeneration in Caenorhabditis elegans.Genetics 204: 849-882 The Genetics of Axon Guidance and Axon Regeneration in Caenorhabditis elegans
netrin; semaphorin; ephrin; Wnt; Slit; Robo; fasciculation; DLK; growth cone; actin; microtubule; WormBook
The correct wiring of neuronal circuits depends on outgrowth and guidance of neuronal processes during development. In the past two decades, great progress has been made in understanding the molecular basis of axon outgrowth and guidance. Genetic analysis in Caenorhabditis elegans has played a key role in elucidating conserved pathways regulating axon guidance, including Netrin signaling, the slit Slit/Robo pathway, Wnt signaling, and others. Axon guidance factors were first identified by screens for mutations affecting animal behavior, and by direct visual screens for axon guidance defects. Genetic analysis of these pathways has revealed the complex and combinatorial nature of guidance cues, and has delineated how cues guide growth cones via receptor activity and cytoskeletal rearrangement. Several axon guidance pathways also affect directed migrations of non-neuronal cells in C. elegans, with implications for normal and pathological cell migrations in situations such as tumor metastasis. The small number of neurons and highly stereotyped axonal architecture of the C. elegans nervous system allow analysis of axon guidance at the level of single identified axons, and permit in vivo tests of prevailing models of axon guidance. C. elegans axons also have a robust capacity to undergo regenerative regrowth after precise laser injury (axotomy). Although such axon regrowth shares some similarities with developmental axon outgrowth, screens for regrowth mutants have revealed regeneration-specific pathways and factors that were not identified in developmental screens. Several areas remain poorly understood, including how major axon tracts are formed in the embryo, and the function of axon regeneration in the natural environment. DOI
16.Hutter, H; Moerman, D. (2015) Big Data in Caenorhabditis elegans: quo vadis?Molecular Biology of the Cell 26: 3909-3914 Big Data in Caenorhabditis elegans: quo vadis?
A clear definition of what constitutes "Big Data" is difficult to identify, but we find it most useful to define Big Data as a data collection that is complete. By this criterion, researchers on Caenorhabditis elegans have a long history of collecting Big Data, since the organism was selected with the idea of obtaining a complete biological description and understanding of development. The complete wiring diagram of the nervous system, the complete cell lineage, and the complete genome sequence provide a framework to phrase and test hypotheses. Given this history, it might be surprising that the number of "complete" data sets for this organism is actually rather small-not because of lack of effort, but because most types of biological experiments are not currently amenable to complete large-scale data collection. Many are also not inherently limited, so that it becomes difficult to even define completeness. At present, we only have partial data on mutated genes and their phenotypes, gene expression, and protein-protein interaction-important data for many biological questions. Big Data can point toward unexpected correlations, and these unexpected correlations can lead to novel investigations; however, Big Data cannot establish causation. As a result, there is much excitement about Big Data, but there is also a discussion on just what Big Data contributes to solving a biological problem. Because of its relative simplicity, C. elegans is an ideal test bed to explore this issue and at the same time determine what is necessary to build a multicellular organism from a single cell. DOI
15. Magner, DB; Wollam, J; Shen, YD; Hoppe, C; Li, DL; Latza, C; Rottiers, V; Hutter, H; Antebi, A. (2013) The NHR-8 Nuclear Receptor Regulates Cholesterol and Bile Acid Homeostasis in C. elegans.Cell Metabolism 18: 212-224 The NHR-8 Nuclear Receptor Regulates Cholesterol and Bile Acid Homeostasis in C. elegans
CAENORHABDITIS-ELEGANS; LIFE-SPAN; DAUER FORMATION; SERUM-CHOLESTEROL; SIGNALING PATHWAY; METABOLISM; DISEASE; MECHANISMS; LONGEVITY; OXYGENASE
Hormone-gated nuclear receptors (NRs) are conserved transcriptional regulators of metabolism, reproduction, and homeostasis. Here we show that C. elegans NHR-8 NR, a homolog of vertebrate liver X and vitamin D receptors, regulates nematode cholesterol balance, fatty acid desaturation, apolipoprotein production, and bile acid metabolism. Loss of nhr-8 results in a deficiency in bile acid-like steroids, called the dafachronic acids, which regulate the related DAF-12/NR, thus controlling entry into the long-lived dauer stage through cholesterol availability. Cholesterol supplementation rescues various nhr-8 phenotypes, including developmental arrest, unsaturated fatty acid deficiency, reduced fertility, and shortened life span. Notably, nhr-8 also interacts with daf-16/FOXO to regulate steady-state cholesterol levels and is synthetically lethal in combination with insulin signaling mutants that promote unregulated growth. Our studies provide important insights into nuclear receptor control of cholesterol balance and metabolism and their impact on development, reproduction, and aging in the context of larger endocrine networks. DOI
14. Steimel, A; Suh, J; Hussainkhel, A; Deheshi, S; Grants, JM; Zapf, R; Moerman, DG; Taubert, S; Hutter, H. (2013) The C. elegans CDK8 Mediator module regulates axon guidance decisions in the ventral nerve cord and during dorsal axon navigation.Developmental Biology 377: 385-398 The C. elegans CDK8 Mediator module regulates axon guidance decisions in the ventral nerve cord and during dorsal axon navigation
RNA-POLYMERASE-II; CHROMOSOME DOSAGE COMPENSATION; LIM HOMEOBOX GENE; CAENORHABDITIS-ELEGANS; TRANSCRIPTIONAL ACTIVATION; NEURONAL DIFFERENTIATION; PHARYNX DEVELOPMENT; COMBINATORIAL CODE; COLORECTAL-CANCER; ROBO RECEPTORS
Receptors expressed on the growth cone of outgrowing axons detect cues required for proper navigation. The pathway choices available to an axon are in part defined by the set of guidance receptors present on the growth cone. Regulated expression of receptors and genes controlling the localization and activity of receptors ensures that axons respond only to guidance cues relevant for reaching their targets. In genetic screens for axon guidance mutants, we isolated an allele of let-19/mdt-13, a component of the Mediator, a large similar to 30 subunit protein complex essential for gene transcription by RNA polymerase II. LET-19/MDT-13 is part of the CDK8 module of the Mediator. By testing other Mediator components, we found that all subunits of the CDK8 module as well as some other Mediator components are required for specific axon navigation decisions in a subset of neurons. Expression profiling demonstrated that let-19/mdt-13 regulates the expression of a large number of genes in interneurons. A mutation in the sax-3 gene, encoding a receptor for the repulsive guidance cue SLT-1, suppresses the commissure navigation defects found in cdk-8 mutants. This suggests that the CDK8 module specifically represses the SAX-3/ROBO pathway to ensure proper commissure navigation. (C) 2013 Elsevier Inc. All rights reserved. DOI
13. Thompson, O; Edgley, M; Strasbourger, P; Flibotte, S; Ewing, B; Adair, R; Au, V; Chaudhry, I; Fernando, L; Hutter, H; Kieffer, A; Lau, J; Lee, N; Miller, A; Raymant, G; Shen, B; Shendure, J; Taylor, J; Turner, EH; Hillier, LW; Moerman, DG; Waterston, RH. (2013) The million mutation project: A new approach to genetics in Caenorhabditis elegans.Genome Research 23: 1749-1762 The million mutation project: A new approach to genetics in Caenorhabditis elegans
SACCHAROMYCES-CEREVISIAE GENOME; C-ELEGANS; FUNCTIONAL GENOMICS; RNA INTERFERENCE; LINKED SITES; GENES; YEAST; IDENTIFICATION; DROSOPHILA; DELETION
We have created a library of 2007 mutagenized Caenorhabditis elegans strains, each sequenced to a target depth of 15-fold coverage, to provide the research community with mutant alleles for each of the worm's more than 20,000 genes. The library contains over 800,000 unique single nucleotide variants (SNVs) with an average of eight nonsynonymous changes per gene and more than 16,000 insertion/deletion (indel) and copy number changes, providing an unprecedented genetic resource for this multicellular organism. To supplement this collection, we also sequenced 40 wild isolates, identifying more than 630,000 unique SNVs and 220,000 indels. Comparison of the two sets demonstrates that the mutant collection has a much richer array of both nonsense and missense mutations than the wild isolate set. We also find a wide range of rDNA and telomere repeat copy number in both sets. Scanning the mutant collection for molecular phenotypes reveals a nonsense suppressor as well as strains with higher levels of indels that harbor mutations in DNA repair genes and strains with abundant males associated with him mutations. All the strains are available through the Caenorhabditis Genetics Center and all the sequence changes have been deposited in WormBase and are available through an interactive website. DOI
12. Unsoeld, T; Park, JO; Hutter, H. (2013) Discoidin domain receptors guide axons along longitudinal tracts in C. elegans.Developmental Biology 374: 142-152 Discoidin domain receptors guide axons along longitudinal tracts in C. elegans
TYROSINE KINASE FAMILY; BASEMENT-MEMBRANE COLLAGEN; CAENORHABDITIS-ELEGANS; IV COLLAGEN; MATRIX METALLOPROTEINASE-2; EXTRACELLULAR-MATRIX; PROTEIN-KINASES; GENE-EXPRESSION; CELL-MIGRATION; XIII COLLAGEN
Discoidin domain receptors are a family of receptor tyrosine kinases activated by collagens. Here we characterize the role of the two discoidin domain receptors, ddr-1 and ddr-2, of the nematode C. elegans during nervous system development. ddr-2 mutant animals exhibit axon guidance defects in major longitudinal tracts most prominently in the ventral nerve cord. ddr-1 mutants show no significant phenotype on their own but significantly enhance guidance defects of ddr-2 in double mutants. ddr-1 and ddr-2 GFP-reporter constructs are expressed in neurons with axons in all affected nerve tracts. DDR-1 and DDR-2 GFP fusion proteins localize to axons. DDR-2 is required cell-autonomously in the PVPR neuron for the guidance of the PVPR pioneer axon, which establishes the left ventral nerve cord tract and serves as substrate for later outgrowing follower axons. Our results provide the first insight on discoidin domain receptor function in invertebrates and establish a novel role for discoidin domain receptors in axon navigation and axon tract formation. (c) 2012 Elsevier Inc. All rights reserved.Website DOI
11. Suh, J; Hutter, H. (2012) A survey of putative secreted and transmembrane proteins encoded in the C-elegans genome.BMC Genomics 13 A survey of putative secreted and transmembrane proteins encoded in the C-elegans genome
NEMATODE CAENORHABDITIS-ELEGANS; GENE FAMILY; SUBCELLULAR-LOCALIZATION; EXPRESSION ANALYSIS; AXON FASCICULATION; CELL-ADHESION; DATABASE; PREDICTION; RNAI; CLASSIFICATION
Background: Almost half of the Caenorhabditis elegans genome encodes proteins with either a signal peptide or a transmembrane domain. Therefore a substantial fraction of the proteins are localized to membranes, reside in the secretory pathway or are secreted. While these proteins are of interest to a variety of different researchers ranging from developmental biologists to immunologists, most of secreted proteins have not been functionally characterized so far. Results: We grouped proteins containing a signal peptide or a transmembrane domain using various criteria including evolutionary origin, common domain organization and functional categories. We found that putative secreted proteins are enriched for small proteins and nematode-specific proteins. Many secreted proteins are predominantly expressed in specific life stages or in one of the two sexes suggesting stage- or sex-specific functions. More than a third of the putative secreted proteins are upregulated upon exposure to pathogens, indicating that a substantial fraction may have a role in immune response. Slightly more than half of the transmembrane proteins can be grouped into broad functional categories based on sequence similarity to proteins with known function. By far the largest groups are channels and transporters, various classes of enzymes and putative receptors with signaling function. Conclusion: Our analysis provides an overview of all putative secreted and transmembrane proteins in C. elegans. This can serve as a basis for selecting groups of proteins for large-scale functional analysis using reverse genetic approaches. DOI
10. Ash, PEA; Zhang, YJ; Roberts, CM; Saldi, T; Hutter, H; Buratti, E; Petrucelli, L; Link, CD. (2010) Neurotoxic effects of TDP-43 overexpression in C-elegans.Human Molecular Genetics 19: 3206-3218 Neurotoxic effects of TDP-43 overexpression in C-elegans
RNA-binding protein TDP-43 has been associated with multiple neurodegenerative diseases, including amyotrophic lateral sclerosis and frontotemporal lobar dementia. We have engineered pan-neuronal expression of human TDP-43 protein in Caenorhabditis elegans, with the goal of generating a convenient in vivo model of TDP-43 function and neurotoxicity. Transgenic worms with the neuronal expression of human TDP-43 exhibit an 'uncoordinated' phenotype and have abnormal motorneuron synapses. Caenorhabditis elegans contains a single putative ortholog of TDP-43, designated TDP-1, which we show can support alternative splicing of CFTR in a cell-based assay. Neuronal overexpression of TDP-1 also results in an uncoordinated phenotype, while genetic deletion of the tdp-1 gene does not affect movement or alter motorneuron synapses. By using the uncoordinated phenotype as a read-out of TDP-43 overexpression neurotoxicty, we have investigated the contribution of specific TDP-43 domains and subcellular localization to toxicity. Full-length (wild-type) human TDP-43 expressed in C. elegans is localized to the nucleus. Deletion of either RNA recognition domain (RRM1 or RRM2) completely blocks neurotoxicity, as does deletion of the C-terminal region. These deleted TDP-43 variants still accumulate in the nucleus, although their subnuclear distribution is altered. Interestingly, fusion of TDP-1 C-terminal sequences to TDP-43 missing its C-terminal domain restores normal subnuclear localization and toxicity in C. elegans and CFTR splicing in cell-based assays. Overexpression of wild-type, full-length TDP-43 in mammalian cells (differentiated M17 cells) can also result in cell toxicity. Our results demonstrate that in vivo TDP-43 neurotoxicity can result from nuclear activity of overexpressed full-length protein. DOI
9. Schlotterer, A; Hamann, A; Kukudov, G; Ibrahim, Y; Heckmann, B; Bozorgmehr, F; Pfeiffer, M; Hutter, H; Stern, D; Du, XL; Brownlee, M; Bierhaus, A; Nawroth, P; Morcos, M. (2010) Apurinic/apyrimidinic endonuclease 1, p53, and thioredoxin are linked in control of aging in C-elegans.Aging Cell 9: 420-432 Apurinic/apyrimidinic endonuclease 1, p53, and thioredoxin are linked in control of aging in C-elegans
Aging; C; elegans; DNA repair; mitochondrial DNA; reactive oxygen species; p53
P>Deletions in mitochondrial DNA (mtDNA) accumulate during aging. Expression of the Caenorhabditis elegans apurinic/apyrimidinic endonuclease 1 (APE1) ortholog exo-3, involved in DNA repair, is reduced by 45% (P < 0.05) during aging of C. elegans. Suppression of exo-3 by treatment with RNAi resulted in a threefold increase in mtDNA deletions (P < 0.05), twofold enhanced generation of reactive oxygen species (ROS) (P < 0.01), distortion of the structural integrity of the nervous system, reduction of head motility by 43% (P < 0.01) and whole animal motility by 38% (P < 0.05). Suppression of exo-3 significantly reduced life span: mean life span decreased from 18.5 +/- 0.4 to 15.4 +/- 0.1 days (P < 0.001) and maximum life span from 25.9 +/- 0.4 to 23.2 +/- 0.1 days (P = 0.001). Additional treatment of exo-3-suppressed animals with a mitochondrial uncoupler decreased ROS levels, reduced neuronal damage, and increased motility and life span. Additional suppression of the C. elegans p53 ortholog cep-1 in exo-3 RNAi-treated animals similarly decreased ROS levels, preserved neuronal integrity, and increased motility and life span. In wild-type animals, suppression of cep-1, involved in downregulation of exo-3, increased expression of exo-3 without a significant effect on ROS levels, preserved neuronal integrity, and increased motility and life span. Suppression of the C. elegans thioredoxin orthologs trx-1 and trx-2, involved in the redox chaperone activity of exo-3, overrides the protective effect of cep-1 RNAi treatment on neuronal integrity, neuronal function, mean and maximum life span. These results show that APE1/EXO-3, p53/CEP-1, and thioredoxin affect each other and that these interactions determine aging as well as neuronal structure and function. DOI
8. Steimel, A; Wong, LN; Najarro, EH; Ackley, BD; Garriga, G; Hutter, H. (2010) The Flamingo ortholog FMI-1 controls pioneer-dependent navigation of follower axons in C. elegans.Development 137: 3663-3673 The Flamingo ortholog FMI-1 controls pioneer-dependent navigation of follower axons in C. elegans
Axon guidance; flamingo; C. elegans; Pioneer; Follower; Nervous system; Cadherin; Adhesion; GPCR
Development of a functional neuronal network during embryogenesis begins with pioneer axons creating a scaffold along which later-outgrowing axons extend. The molecular mechanism used by these follower axons to navigate along pre-existing axons remains poorly understood. We isolated loss-of-function alleles of fmi-1, which caused strong axon navigation defects of pioneer and follower axons in the ventral nerve cord (VNC) of C. elegans. Notably follower axons, which exclusively depend on pioneer axons for correct navigation, frequently separated from the pioneer. fmi-1 is the sole C. elegans ortholog of Drosophila flamingo and vertebrate Celsr genes, and this phenotype defines a new role for this important molecule in follower axon navigation. FMI-1 has a unique and strikingly conserved structure with cadherin and C-terminal G-protein coupled receptor domains and could mediate cell-cell adhesion and signaling functions. We found that follower axon navigation depended on the extracellular but not on the intracellular domain, suggesting that FMI-1 mediates primarily adhesion between pioneer and follower axons. By contrast, pioneer axon navigation required the intracellular domain, suggesting that FMI-1 acts as receptor transducing a signal in this case. Our findings indicate that FMI-1 is a cell-type dependent axon guidance factor with different domain requirements for its different functions in pioneers and followers. DOI
7. Almedom, RB; Liewald, JF; Hernando, G; Schultheis, C; Rayes, D; Pan, J; Schedletzky, T; Hutter, H; Bouzat, C; Gottschalk, A. (2009) An ER-resident membrane protein complex regulates nicotinic acetylcholine receptor subunit composition at the synapse.EMBO Journal 28: 2636-2649 An ER-resident membrane protein complex regulates nicotinic acetylcholine receptor subunit composition at the synapse
ELEGANS NEUROMUSCULAR-JUNCTION; NEMATODE CAENORHABDITIS-ELEGANS; ALPHA-SUBUNIT; TGF-BETA; GENE ENCODES; C. ELEGANS; MUSCLE; IDENTIFICATION; VISUALIZATION; TRAFFICKING
Nicotinic acetylcholine receptors (nAChRs) are homo- or heteropentameric ligand-gated ion channels mediating excitatory neurotransmission and muscle activation. Regulation of nAChR subunit assembly and transfer of correctly assembled pentamers to the cell surface is only partially understood. Here, we characterize an ER transmembrane (TM) protein complex that influences nAChR cell-surface expression and functional properties in Caenorhabditis elegans muscle. Loss of either type I TM protein, NRA-2 or NRA-4 (nicotinic receptor associated), affects two different types of muscle nAChRs and causes in vivo resistance to cholinergic agonists. Sensitivity to subtype-specific agonists of these nAChRs is altered differently, as demonstrated by whole-cell voltage-clamp of dissected adult muscle, when applying exogenous agonists or after photo-evoked, channelrhodopsin-2 (ChR2) mediated acetylcholine (ACh) release, as well as in single-channel recordings in cultured embryonic muscle. These data suggest that nAChRs desensitize faster in nra-2 mutants. Cell-surface expression of different subunits of the 'levamisole-sensitive' nAChR (L-AChR) is differentially affected in the absence of NRA-2 or NRA-4, suggesting that they control nAChR subunit composition or allow only certain receptor assemblies to leave the ER. The EMBO Journal (2009) 28, 2636-2649. doi: 10.1038/emboj.2009.204; Published online 16 July 2009 Subject Categories: membranes & transport; neuroscience DOI
6. Brandt, R; Gergou, A; Wacker, I; Fath, T; Hutter, H. (2009) A Caenorhabditis elegans model of tau hyperphosphorylation: Induction of developmental defects by transgenic overexpression of Alzheimer's disease-like modified tau.Neurobiology of Aging 30: 22-33 A Caenorhabditis elegans model of tau hyperphosphorylation: Induction of developmental defects by transgenic overexpression of Alzheimer's disease-like modified tau
Tauopathy; Neurodegenerative disease; Animal model; Cytoskeleton; Phosphorylation; Aggregation
The microtubule-associated tau proteins become functionally and structurally altered in Alzheimer's disease (AD). To analyze tau modification and its role in a non-vertebrate animal model, we produced transgenic Caenorhabditis elegans strains with a panneuronal expression of human tau and a pseudohyperphosphorylated (PHP) tau construct that mimics AD-relevant tau modification. We show that human tau in C. elegans becomes highly phosphorylated and exhibits conformational changes similar to PHP tau and human PHF tau. Both, wt tau and PHP tau induced a progressive age-dependent development of a phenotype of uncoordinated locomotion (unc) in the absence of neuronal degeneration. However, only PHP tau induced a defective pattern of motor neuron development as indicated by the presence of gaps in the dorsal cord. commissures on the wrong side and local broadening of axons. The data indicate that C. elgans is capable of highly phosphorylating human tau to an AD-like state whereas only stable disease-like tau modification induce developmental defects suggesting a specific interference of pathologic tau with intracellular mechanisms of axonal out-growth and pathfinding. (C) 2007 Elsevier Inc. All rights reserved. DOI
5. Schlotterer, A; Kukudov, G; Bozorgmehr, F; Hutter, H; Du, XL; Oikonomou, D; Ibrahim, Y; Pfisterer, F; Rabbani, N; Thornalley, P; Sayed, A; Fleming, T; Humpert, P; Schwenger, V; Zeier, M; Hamann, A; Stern, D; Brownlee, M; Bierhaus, A; Nawroth, P; Morcos, M. (2009) C-elegans as Model for the Study of High Glucose-Mediated Life Span Reduction.Diabetes 58: 2450-2456 C-elegans as Model for the Study of High Glucose-Mediated Life Span Reduction
CAENORHABDITIS-ELEGANS; GLYOXALASE SYSTEM; DAF-16; METHYLGLYOXAL; GENES
OBJECTIVE-Establishing Caenorhabditis elegans as a model for glucose toxicity-mediated life span reduction. RESEARCH DESIGN AND METHODS-C. elegans were maintained to achieve glucose concentrations resembling the hyperglycemic conditions in diabetic patients. The effects of high glucose on life span, glyoxalase-1 activity, advanced glycation end products (AGEs), and reactive oxygen species (ROS) formation and on mitochondrial function were studied. RESULTS-High glucose conditions reduced mean life span from 18.5 +/- 0.4 to 16.5 +/- 0.6 days and maximum life span from 25.9 +/- 0.4 to 23.2 +/- 0.4 days, independent of glucose effects on cuticle or bacterial metabolization of glucose. The formation of methylglyoxal-modified mitochondrial proteins and ROS was significantly increased by high glucose conditions and reduced by mitochondrial uncoupling and complex IIIQo inhibition. Overexpression of the methylglyoxal-detoxifying enzyme glyoxalase-1 attenuated the life-shortening effect of glucose by reducing AGE accumulation (by 65%) and ROS formation (by 50%) and restored mean (16.5 +/- 0.6 to 20.6 +/- 0.4 days) and maximum life span (23.2 +/- 0.4 to 27.7 +/- 2.3 days). In contrast, inhibition of glyoxalase-1 by RNAi further reduced mean (16.5 +/- 0.6 to 13.9 +/- 0.7 days) and maximum life span (23.2 +/- 0.4 to 20.3 +/- 1.1 days). The life span reduction by glyoxalase-1 inhibition was independent from the insulin signaling pathway because high glucose conditions also affected daf-2 knockdown animals in a similar manner. CONCLUSIONS-C. elegans is a suitable model organism to study glucose toxicity, in which high glucose conditions limit the life span by increasing ROS formation and AGE modification of mitochondrial proteins in a daf-2 independent manner. Most importantly, glucose toxicity can be prevented by improving glyoxalase-l-dependent methylglyoxal detoxification or preventing mitochondrial dysfunction. Diabetes 58:2450-2456, 2009 DOI
4. Ikeda, DD; Duan, Y; Matsuki, M; Kunitomo, H; Hutter, H; Hedgecock, EM; Iino, Y. (2008) CASY-1, an ortholog of calsyntenins/alcadeins, is essential for learning in Caenorhabditis elegans.Proceedings of the National Academy of Sciences of the United States of America 105: 5260-5265 CASY-1, an ortholog of calsyntenins/alcadeins, is essential for learning in Caenorhabditis elegans
ectodomain shedding; learning and memory
Calsyntenins/alcadeins are type I transmembrane proteins with two extracellular cadherin domains highly expressed in mammalian brain. They form a tripartite complex with X11/X11L and APP (amyloid precursor protein) and are proteolytically processed in a similar fashion to APP. Although a genetic association of calsyntenin-2 with human memory performance has recently been reported, physiological roles and molecular functions of the protein in the nervous system are poorly understood. Here, we show that CASY-1, the Caenorhabditis elegans ortholog of calsyntenins/alcadeins, is essential for multiple types of learning. Through a genetic screen, we found that casy-1 mutants show defects in salt chemotaxis learning. casy-1 mutants also show defects in temperature learning, olfactory adaptation, and integration of two sensory signals. casy-1 is widely expressed in the nervous system. Expression of casy-1 in a single sensory neuron and at the post-developmental stage is sufficient for its function in salt chemotaxis learning. The fluorescent protein-tagged ectodomain of CASY-1 is released from neurons. Moreover, functional domain analyses revealed that both cytoplasmic and transmembrane domains of this protein are dispensable, whereas the ectodomain, which contains the LG/LNS-like domain, is critically required for learning. These results suggest that learning is modulated by the released ectodomain of CASY-1. DOI
3. Morcos, M; Du, XL; Pfisterer, F; Hutter, H; Sayed, AAR; Thornalley, P; Ahmed, N; Baynes, J; Thorpe, S; Kukudov, G; Schlotterer, A; Bozorgmehr, F; El Baki, RA; Stern, D; Moehrlen, F; Ibrahim, Y; Oikonomou, D; Hamann, A; Becker, C; Zeier, M; Schwenger, V; Miftari, N; Humpert, P; Hammes, HP; Buechler, M; Bierhaus, A; Brownlee, M; Nawroth, PP. (2008) Glyoxalase-1 prevents mitochondrial protein modification and enhances lifespan in Caenorhabditis elegans.Aging Cell 7: 260-269 Glyoxalase-1 prevents mitochondrial protein modification and enhances lifespan in Caenorhabditis elegans
aging; lifespan; C; elegans; Advanced Glycation Endproducts; mitochondria; metabolic rate; reactive oxygen species; glyoxalase-1
Studies of mutations affecting lifespan in Caenorhabditis elegans show that mitochondrial generation of reactive oxygen species (ROS) plays a major causative role in organismal aging. Here, we describe a novel mechanism for regulating mitochondrial ROS production and lifespan in C. elegans: progressive mitochondrial protein modification by the glycolysis-derived dicarbonyl metabolite methylglyoxal (MG). We demonstrate that the activity of glyoxalase-1, an enzyme detoxifying MG, is markedly reduced with age despite unchanged levels of glyoxalase-1 mRNA. The decrease in enzymatic activity promotes accumulation of MG-derived adducts and oxidative stress markers, which cause further inhibition of glyoxalase-1 expression. Over-expression of the C. elegans glyoxalase-1 orthologue CeGly decreases MG modifications of mitochondrial proteins and mitochondrial ROS production, and prolongs C. elegans lifespan. In contrast, knock-down of CeGly increases MG modifications of mitochondrial proteins and mitochondrial ROS production, and decreases C. elegans lifespan. DOI
2. Wang, XL; Zhang, W; Cheever, T; Schwarz, V; Opperman, K; Hutter, H; Koepp, D; Chen, L. (2008) The C-elegans L1CAM homologue LAD-2 functions as a coreceptor in MAB-20/Sema2-mediated axon guidance.Journal of Cell Biology 180: 233-246 The C-elegans L1CAM homologue LAD-2 functions as a coreceptor in MAB-20/Sema2-mediated axon guidance
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. DOI
1. Fielenbach, N; Guardavaccaro, D; Neubert, K; Chan, T; Li, DL; Feng, Q; Hutter, H; Pagano, M; Antebi, A. (2007) DRE-1: An evolutionarily conserved F box protein that regulates C-elegans developmental age.Developmental Cell 12: 443-455 DRE-1: An evolutionarily conserved F box protein that regulates C-elegans developmental age
During metazoan development, cells acquire both positional and temporal identities. The Caenorhabditis elegans heterochronic loci are global regulators of larval temporal fates. Most encode conserved transcriptional and translational factors, which affect stage-appropriate programs in various tissues. Here, we describe dre-1, a heterochronic gene, whose mutant phenotypes include precocious terminal differentiation of epidermal stem cells and altered temporal patterning of gonadal outgrowth. Genetic interactions with other heterochronic loci place dre-1 in the larval-to-adult switch. dre-1 encodes a highly conserved F box protein, suggesting a role in an SCF ubiquitin ligase complex. Accordingly, RNAi knockdown of the C. elegans SKP1-like homolog SKR-1, the cullin CUL-1, and ring finger RBX homologs yielded similar heterochronic phenotypes. DRE-1 and SKR-1 form a complex, as do the human orthologs, hFBX011 and SKP1, revealing a phyletically ancient interaction. The identification of core components involved in SCF-mediated modification and/or proteolysis suggests an important level of regulation in the heterochronic hierarchy. DOI
