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Andrini O, Ben Soussia I, Tardy P, Walker DS, Peña-Varas C, Ramírez D, Gendrel M, Mercier M, El Mouridi S, Leclercq-Blondel A, González W, Schafer WR, Jospin M, Boulin T. Constitutive sodium permeability in a C. elegans two-pore domain potassium channel. Proc Natl Acad Sci U S A 2024; 121:e2400650121. [PMID: 39405352 PMCID: PMC11513965 DOI: 10.1073/pnas.2400650121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Accepted: 09/11/2024] [Indexed: 10/30/2024] Open
Abstract
Two-pore domain potassium (K2P) channels play a central role in modulating cellular excitability and neuronal function. The unique structure of the selectivity filter in K2P and other potassium channels determines their ability to allow the selective passage of potassium ions across cell membranes. The nematode C. elegans has one of the largest K2P families, with 47 subunit-coding genes. This remarkable expansion has been accompanied by the evolution of atypical selectivity filter sequences that diverge from the canonical TxGYG motif. Whether and how this sequence variation may impact the function of K2P channels has not been investigated so far. Here, we show that the UNC-58 K2P channel is constitutively permeable to sodium ions and that a cysteine residue in its selectivity filter is responsible for this atypical behavior. Indeed, by performing in vivo electrophysiological recordings and Ca2+ imaging experiments, we demonstrate that UNC-58 has a depolarizing effect in muscles and sensory neurons. Consistently, unc-58 gain-of-function mutants are hypercontracted, unlike the relaxed phenotype observed in hyperactive mutants of many neuromuscular K2P channels. Finally, by combining molecular dynamics simulations with functional studies in Xenopus laevis oocytes, we show that the atypical cysteine residue plays a key role in the unconventional sodium permeability of UNC-58. As predicting the consequences of selectivity filter sequence variations in silico remains a major challenge, our study illustrates how functional experiments are essential to determine the contribution of such unusual potassium channels to the electrical profile of excitable cells.
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Yue Z, Li Y, Yu B, Xu Y, Chen L, Chitturi J, Meng J, Wang Y, Tian Y, Mouridi SE, Zhang C, Zhen M, Boulin T, Gao S. A leak K + channel TWK-40 sustains the rhythmic motor program. PNAS NEXUS 2024; 3:pgae234. [PMID: 38957449 PMCID: PMC11217676 DOI: 10.1093/pnasnexus/pgae234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Accepted: 06/05/2024] [Indexed: 07/04/2024]
Abstract
Leak potassium (K+) currents, conducted by two-pore domain K+ (K2P) channels, are critical for the stabilization of the membrane potential. The effect of K2P channels on motor rhythm remains enigmatic. We show here that the K2P TWK-40 contributes to the rhythmic defecation motor program (DMP) in Caenorhabditis elegans. Disrupting TWK-40 suppresses the expulsion defects of nlp-40 and aex-2 mutants. By contrast, a gain-of-function (gf) mutant of twk-40 significantly reduces the expulsion frequency per DMP cycle. In situ whole-cell patch clamping demonstrates that TWK-40 forms an outward current that hyperpolarize the resting membrane potential of dorsorectal ganglion ventral process B (DVB), an excitatory GABAergic motor neuron that activates expulsion muscle contraction. In addition, TWK-40 substantially contributes to the rhythmic activity of DVB. Specifically, DVB Ca2+ oscillations exhibit obvious defects in loss-of-function (lf) mutant of twk-40. Expression of TWK-40(gf) in DVB recapitulates the expulsion deficiency of the twk-40(gf) mutant, and inhibits DVB Ca2+ oscillations in both wild-type and twk-40(lf) animals. Moreover, DVB innervated enteric muscles also exhibit rhythmic Ca2+ defects in twk-40 mutants. In summary, these findings establish TWK-40 as a crucial neuronal stabilizer of DMP, linking leak K2P channels with rhythmic motor activity.
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Peysson A, Zariohi N, Gendrel M, Chambert-Loir A, Frébault N, Cheynet E, Andrini O, Boulin T. Wnt-Ror-Dvl signalling and the dystrophin complex organize planar-polarized membrane compartments in C. elegans muscles. Nat Commun 2024; 15:4935. [PMID: 38858388 PMCID: PMC11164867 DOI: 10.1038/s41467-024-49154-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 05/24/2024] [Indexed: 06/12/2024] Open
Abstract
Cell polarity mechanisms allow the formation of specialized membrane domains with unique protein compositions, signalling properties, and functional characteristics. By analyzing the localization of potassium channels and proteins belonging to the dystrophin-associated protein complex, we reveal the existence of distinct planar-polarized membrane compartments at the surface of C. elegans muscle cells. We find that muscle polarity is controlled by a non-canonical Wnt signalling cascade involving the ligand EGL-20/Wnt, the receptor CAM-1/Ror, and the intracellular effector DSH-1/Dishevelled. Interestingly, classical planar cell polarity proteins are not required for this process. Using time-resolved protein degradation, we demonstrate that -while it is essentially in place by the end of embryogenesis- muscle polarity is a dynamic state, requiring continued presence of DSH-1 throughout post-embryonic life. Our results reveal the unsuspected complexity of the C. elegans muscle membrane and establish a genetically tractable model system to study cellular polarity and membrane compartmentalization in vivo.
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Meng J, Ahamed T, Yu B, Hung W, EI Mouridi S, Wang Z, Zhang Y, Wen Q, Boulin T, Gao S, Zhen M. A tonically active master neuron modulates mutually exclusive motor states at two timescales. SCIENCE ADVANCES 2024; 10:eadk0002. [PMID: 38598630 PMCID: PMC11006214 DOI: 10.1126/sciadv.adk0002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 03/07/2024] [Indexed: 04/12/2024]
Abstract
Continuity of behaviors requires animals to make smooth transitions between mutually exclusive behavioral states. Neural principles that govern these transitions are not well understood. Caenorhabditis elegans spontaneously switch between two opposite motor states, forward and backward movement, a phenomenon thought to reflect the reciprocal inhibition between interneurons AVB and AVA. Here, we report that spontaneous locomotion and their corresponding motor circuits are not separately controlled. AVA and AVB are neither functionally equivalent nor strictly reciprocally inhibitory. AVA, but not AVB, maintains a depolarized membrane potential. While AVA phasically inhibits the forward promoting interneuron AVB at a fast timescale, it maintains a tonic, extrasynaptic excitation on AVB over the longer timescale. We propose that AVA, with tonic and phasic activity of opposite polarities on different timescales, acts as a master neuron to break the symmetry between the underlying forward and backward motor circuits. This master neuron model offers a parsimonious solution for sustained locomotion consisted of mutually exclusive motor states.
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Mignerot L, Gimond C, Bolelli L, Bouleau C, Sandjak A, Boulin T, Braendle C. Natural variation in the Caenorhabditis elegans egg-laying circuit modulates an intergenerational fitness trade-off. eLife 2024; 12:RP88253. [PMID: 38564369 PMCID: PMC10987095 DOI: 10.7554/elife.88253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024] Open
Abstract
Evolutionary transitions from egg laying (oviparity) to live birth (viviparity) are common across various taxa. Many species also exhibit genetic variation in egg-laying mode or display an intermediate mode with laid eggs containing embryos at various stages of development. Understanding the mechanistic basis and fitness consequences of such variation remains experimentally challenging. Here, we report highly variable intra-uterine egg retention across 316 Caenorhabditis elegans wild strains, some exhibiting strong retention, followed by internal hatching. We identify multiple evolutionary origins of such phenotypic extremes and pinpoint underlying candidate loci. Behavioral analysis and genetic manipulation indicates that this variation arises from genetic differences in the neuromodulatory architecture of the egg-laying circuitry. We provide experimental evidence that while strong egg retention can decrease maternal fitness due to in utero hatching, it may enhance offspring protection and confer a competitive advantage. Therefore, natural variation in C. elegans egg-laying behaviour can alter an apparent trade-off between different fitness components across generations. Our findings highlight underappreciated diversity in C. elegans egg-laying behavior and shed light on its fitness consequences. This behavioral variation offers a promising model to elucidate the molecular changes in a simple neural circuit underlying evolutionary shifts between alternative egg-laying modes in invertebrates.
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Delinière A, Jaupart L, Janin A, Millat G, Boulin T, Andrini O, Chevalier P. Functional and clinical characterization of a novel homozygous KCNH2 missense variant in the pore region of Kv11.1 leading to a viable but severe long-QT syndrome. Gene 2024; 897:148076. [PMID: 38086455 DOI: 10.1016/j.gene.2023.148076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Revised: 11/22/2023] [Accepted: 12/08/2023] [Indexed: 12/24/2023]
Abstract
BACKGROUND Among KCNH2 missense loss of function (LOF) variants, homozygosity -at any position in the Kv11.1/hERG channel - is very rare and generally leads to intrauterine death, while heterozygous variants in the pore are responsible for severe Type 2 long-QT syndrome (LQTS). We report a novel homozygous p.Gly603Ser missense variant in the pore of Kv11.1/hERG (KCNH2 c.1807G > A) discovered in the context of a severe LQTS. METHODS We carried out a phenotypic family study combined with a functional analysis of mutated and wild-type (WT) Kv11.1 by two-electrode voltage-clamp using the Xenopus laevis oocyte heterologous expression system. RESULTS The variant resulted in a severe LQTS phenotype (very prolonged corrected QT interval, T-wave alternans, multiple Torsades de pointes) with a delayed clinical expression in later childhood in the homozygous state, and in a Type 2 LQTS phenotype in the heterozygous state. Expression of KCNH2 p.Gly603Ser cRNA alone elicited detectable current in Xenopus oocytes. Inactivation kinetics and voltage dependence of activation were not significantly affected by the variant. The macroscopic slope conductance of the variant was three-fold less compared to the WT (18.5 ± 9.01 vs 54.7 ± 17.2 μS, p < 0.001). CONCLUSIONS We characterized the novel p.Gly603Ser KCNH2 missense LOF variant in the pore region of Kv11.1/hERG leading to a severe but viable LQTS in the homozygous state and an attenuated Type 2 LQTS in heterozygous carriers. To our knowledge we provide the first description of a homozygous variant in the pore-forming region of Kv11.1 with a functional impact but a delayed clinical expression.
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Rawsthorne-Manning H, Calahorro F, G. Izquierdo P, Tardy P, Boulin T, Holden-Dye L, O’Connor V, Dillon J. Confounds of using the unc-58 selection marker highlights the importance of genotyping co-CRISPR genes. PLoS One 2022; 17:e0253351. [PMID: 35041685 PMCID: PMC8765651 DOI: 10.1371/journal.pone.0253351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 10/29/2021] [Indexed: 11/19/2022] Open
Abstract
Multiple advances have been made to increase the efficiency of CRISPR/Cas9 editing using the model genetic organism Caenorhabditis elegans (C. elegans). Here we report on the use of co-CRISPR 'marker' genes: worms in which co-CRISPR events have occurred have overt, visible phenotypes which facilitates the selection of worms that harbour CRISPR events in the target gene. Mutation in the co-CRISPR gene is then removed by outcrossing to wild type but this can be challenging if the CRISPR and co-CRISPR gene are hard to segregate. However, segregating away the co-CRISPR modified gene can be less challenging if the worms selected appear wild type and are selected from a jackpot brood. These are broods in which a high proportion of the progeny of a single injected worm display the co-CRISPR phenotype suggesting high CRISPR efficiency. This can deliver worms that harbour the desired mutation in the target gene locus without the co-CRISPR mutation. We have successfully generated a discrete mutation in the C. elegans nlg-1 gene using this method. However, in the process of sequencing to authenticate editing in the nlg-1 gene we discovered genomic rearrangements that arise at the co-CRISPR gene unc-58 that by visual observation were phenotypically silent but nonetheless resulted in a significant reduction in motility scored by thrashing behaviour. This highlights that careful consideration of the hidden consequences of co-CRISPR mediated genetic changes should be taken before downstream analysis of gene function. Given this, we suggest sequencing of co-CRISPR genes following CRISPR procedures that utilise phenotypic selection as part of the pipeline.
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Boulin T, Itani O, El Mouridi S, Leclercq-Blondel A, Gendrel M, Macnamara E, Soldatos A, Murphy JL, Gorman MP, Lindsey A, Shimada S, Turner D, Silverman GA, Baldridge D, Malicdan MC, Schedl T, Pak SC. Functional analysis of a de novo variant in the neurodevelopment and generalized epilepsy disease gene NBEA. Mol Genet Metab 2021; 134:195-202. [PMID: 34412939 PMCID: PMC10626981 DOI: 10.1016/j.ymgme.2021.07.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 06/21/2021] [Accepted: 07/30/2021] [Indexed: 01/09/2023]
Abstract
Neurobeachin (NBEA) was initially identified as a candidate gene for autism. Recently, variants in NBEA have been associated with neurodevelopmental delay and childhood epilepsy. Here, we report on a novel NBEA missense variant (c.5899G > A, p.Gly1967Arg) in the Domain of Unknown Function 1088 (DUF1088) identified in a child enrolled in the Undiagnosed Diseases Network (UDN), who presented with neurodevelopmental delay and seizures. Modeling of this variant in the Caenorhabditis elegans NBEA ortholog, sel-2, indicated that the variant was damaging to in vivo function as evidenced by altered cell fate determination and trafficking of potassium channels in neurons. The variant effect was indistinguishable from that of the reference null mutation suggesting that the variant is a strong hypomorph or a complete loss-of-function. Our experimental data provide strong support for the molecular diagnosis and pathogenicity of the NBEA p.Gly1967Arg variant and the importance of the DUF1088 for NBEA function.
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Vigne P, Gimond C, Ferrari C, Vielle A, Hallin J, Pino-Querido A, El Mouridi S, Mignerot L, Frøkjær-Jensen C, Boulin T, Teotónio H, Braendle C. A single-nucleotide change underlies the genetic assimilation of a plastic trait. SCIENCE ADVANCES 2021; 7:7/6/eabd9941. [PMID: 33536214 PMCID: PMC7857674 DOI: 10.1126/sciadv.abd9941] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 12/15/2020] [Indexed: 05/09/2023]
Abstract
Genetic assimilation-the evolutionary process by which an environmentally induced phenotype is made constitutive-represents a fundamental concept in evolutionary biology. Thought to reflect adaptive phenotypic plasticity, matricidal hatching in nematodes is triggered by maternal nutrient deprivation to allow for protection or resource provisioning of offspring. Here, we report natural Caenorhabditis elegans populations harboring genetic variants expressing a derived state of near-constitutive matricidal hatching. These variants exhibit a single amino acid change (V530L) in KCNL-1, a small-conductance calcium-activated potassium channel subunit. This gain-of-function mutation causes matricidal hatching by strongly reducing the sensitivity to environmental stimuli triggering egg-laying. We show that reestablishing the canonical KCNL-1 protein in matricidal isolates is sufficient to restore canonical egg-laying. While highly deleterious in constant food environments, KCNL-1 V530L is maintained under fluctuating resource availability. A single point mutation can therefore underlie the genetic assimilation-by either genetic drift or selection-of an ancestrally plastic trait.
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Ben Soussia I, El Mouridi S, Kang D, Leclercq-Blondel A, Khoubza L, Tardy P, Zariohi N, Gendrel M, Lesage F, Kim EJ, Bichet D, Andrini O, Boulin T. Mutation of a single residue promotes gating of vertebrate and invertebrate two-pore domain potassium channels. Nat Commun 2019; 10:787. [PMID: 30770809 PMCID: PMC6377628 DOI: 10.1038/s41467-019-08710-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 01/23/2019] [Indexed: 01/28/2023] Open
Abstract
Mutations that modulate the activity of ion channels are essential tools to understand the biophysical determinants that control their gating. Here, we reveal the conserved role played by a single amino acid position (TM2.6) located in the second transmembrane domain of two-pore domain potassium (K2P) channels. Mutations of TM2.6 to aspartate or asparagine increase channel activity for all vertebrate K2P channels. Using two-electrode voltage-clamp and single-channel recording techniques, we find that mutation of TM2.6 promotes channel gating via the selectivity filter gate and increases single channel open probability. Furthermore, channel gating can be progressively tuned by using different amino acid substitutions. Finally, we show that the role of TM2.6 was conserved during evolution by rationally designing gain-of-function mutations in four Caenorhabditis elegans K2P channels using CRISPR/Cas9 gene editing. This study thus describes a simple and powerful strategy to systematically manipulate the activity of an entire family of potassium channels. Mutations that modulate the activity of ion channels are essential tools to understand the biophysical determinants that control their gating. Here authors reveal the role played by a single residue in the second transmembrane domain of vertebrate and invertebrate two-pore domain potassium channels.
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D'Alessandro M, Richard M, Stigloher C, Gache V, Boulin T, Richmond JE, Bessereau JL. CRELD1 is an evolutionarily-conserved maturational enhancer of ionotropic acetylcholine receptors. eLife 2018; 7:39649. [PMID: 30407909 PMCID: PMC6245729 DOI: 10.7554/elife.39649] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 11/05/2018] [Indexed: 12/22/2022] Open
Abstract
The assembly of neurotransmitter receptors in the endoplasmic reticulum limits the number of receptors delivered to the plasma membrane, ultimately controlling neurotransmitter sensitivity and synaptic transfer function. In a forward genetic screen conducted in the nematode C. elegans, we identified crld-1 as a gene required for the synaptic expression of ionotropic acetylcholine receptors (AChR). We demonstrated that the CRLD-1A isoform is a membrane-associated ER-resident protein disulfide isomerase (PDI). It physically interacts with AChRs and promotes the assembly of AChR subunits in the ER. Mutations of Creld1, the human ortholog of crld-1a, are responsible for developmental cardiac defects. We showed that Creld1 knockdown in mouse muscle cells decreased surface expression of AChRs and that expression of mouse Creld1 in C. elegans rescued crld-1a mutant phenotypes. Altogether these results identify a novel and evolutionarily-conserved maturational enhancer of AChR biogenesis, which controls the abundance of functional receptors at the cell surface.
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El Mouridi S, Lecroisey C, Tardy P, Mercier M, Leclercq-Blondel A, Zariohi N, Boulin T. Reliable CRISPR/Cas9 Genome Engineering in Caenorhabditis elegans Using a Single Efficient sgRNA and an Easily Recognizable Phenotype. G3 (BETHESDA, MD.) 2017; 7:1429-1437. [PMID: 28280211 PMCID: PMC5427500 DOI: 10.1534/g3.117.040824] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 03/02/2017] [Indexed: 12/26/2022]
Abstract
CRISPR/Cas9 genome engineering strategies allow the directed modification of the Caenorhabditis elegans genome to introduce point mutations, generate knock-out mutants, and insert coding sequences for epitope or fluorescent tags. Three practical aspects, however, complicate such experiments. First, the efficiency and specificity of single-guide RNAs (sgRNA) cannot be reliably predicted. Second, the detection of animals carrying genome edits can be challenging in the absence of clearly visible or selectable phenotypes. Third, the sgRNA target site must be inactivated after editing to avoid further double-strand break events. We describe here a strategy that addresses these complications by transplanting the protospacer of a highly efficient sgRNA into a gene of interest to render it amenable to genome engineering. This sgRNA targeting the dpy-10 gene generates genome edits at comparatively high frequency. We demonstrate that the transplanted protospacer is cleaved at the same time as the dpy-10 gene. Our strategy generates scarless genome edits because it no longer requires the introduction of mutations in endogenous sgRNA target sites. Modified progeny can be easily identified in the F1 generation, which drastically reduces the number of animals to be tested by PCR or phenotypic analysis. Using this strategy, we reliably generated precise deletion mutants, transcriptional reporters, and translational fusions with epitope tags and fluorescent reporter genes. In particular, we report here the first use of the new red fluorescent protein mScarlet in a multicellular organism. wrmScarlet, a C. elegans-optimized version, dramatically surpassed TagRFP-T by showing an eightfold increase in fluorescence in a direct comparison.
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Gomes JE, Tavernier N, Richaudeau B, Formstecher E, Boulin T, Mains PE, Dumont J, Pintard L. Microtubule severing by the katanin complex is activated by PPFR-1-dependent MEI-1 dephosphorylation. ACTA ACUST UNITED AC 2013; 202:431-9. [PMID: 23918937 PMCID: PMC3734088 DOI: 10.1083/jcb.201304174] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dephosphorylation of MEI-1 activates katanin during meiosis, whereas ubiquitin-mediated degradation of both MEI-1 and its activator PPFR-1 ensure efficient katanin inactivation during mitosis. Katanin is an evolutionarily conserved microtubule (MT)-severing complex implicated in multiple aspects of MT dynamics. In Caenorhabditis elegans, the katanin homologue MEI-1 is required for meiosis, but must be inactivated before mitosis. Here we show that PPFR-1, a regulatory subunit of a trimeric protein phosphatase 4 complex, enhanced katanin MT-severing activity during C. elegans meiosis. Loss of ppfr-1, similarly to the inactivation of MT severing, caused a specific defect in meiosis II spindle disassembly. We show that a fraction of PPFR-1 was degraded after meiosis, contributing to katanin inactivation. PPFR-1 interacted with MEL-26, the substrate recognition subunit of the CUL-3 RING E3 ligase (CRL3MEL-26), which also targeted MEI-1 for post-meiotic degradation. Reversible protein phosphorylation of MEI-1 may ensure temporal activation of the katanin complex during meiosis, whereas CRL3MEL-26-mediated degradation of both MEI-1 and its activator PPFR-1 ensure efficient katanin inactivation in the transition to mitosis.
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Boulin T, Fauvin A, Charvet CL, Cortet J, Cabaret J, Bessereau JL, Neveu C. Functional reconstitution of Haemonchus contortus acetylcholine receptors in Xenopus oocytes provides mechanistic insights into levamisole resistance. Br J Pharmacol 2012; 164:1421-32. [PMID: 21486278 DOI: 10.1111/j.1476-5381.2011.01420.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND AND PURPOSE The cholinergic agonist levamisole is widely used to treat parasitic nematode infestations. This anthelmintic drug paralyses worms by activating a class of levamisole-sensitive acetylcholine receptors (L-AChRs) expressed in nematode muscle cells. However, levamisole efficacy has been compromised by the emergence of drug-resistant parasites, especially in gastrointestinal nematodes such as Haemonchus contortus. We report here the first functional reconstitution and pharmacological characterization of H. contortus L-AChRs in a heterologous expression system. EXPERIMENTAL APPROACH In the free-living nematode Caenorhabditis elegans, five AChR subunit and three ancillary protein genes are necessary in vivo and in vitro to synthesize L-AChRs. We have cloned the H. contortus orthologues of these genes and expressed them in Xenopus oocytes. We reconstituted two types of H. contortus L-AChRs with distinct pharmacologies by combining different receptor subunits. KEY RESULTS The Hco-ACR-8 subunit plays a pivotal role in selective sensitivity to levamisole. As observed with C. elegans L-AChRs, expression of H. contortus receptors requires the ancillary proteins Hco-RIC-3, Hco-UNC-50 and Hco-UNC-74. Using this experimental system, we demonstrated that a truncated Hco-UNC-63 L-AChR subunit, which was specifically detected in a levamisole-resistant H. contortus isolate, but not in levamisole-sensitive strains, hampers the normal function of L-AChRs, when co-expressed with its full-length counterpart. CONCLUSIONS AND IMPLICATIONS We provide the first functional evidence for a putative molecular mechanism involved in levamisole resistance in any parasitic nematode. This expression system will provide a means to analyse molecular polymorphisms associated with drug resistance at the electrophysiological level.
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Boulin T, Hobert O. From genes to function: the C. elegans genetic toolbox. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2011; 1:114-37. [PMID: 23801671 DOI: 10.1002/wdev.1] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
This review aims to provide an overview of the technologies which make the nematode Caenorhabditis elegans an attractive genetic model system. We describe transgenesis techniques and forward and reverse genetic approaches to isolate mutants and clone genes. In addition, we discuss the new possibilities offered by genome engineering strategies and next-generation genome analysis tools.
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Abstract
We describe a protocol for mutating genes in the nematode Caenorhabditis elegans using the Mos1 transposon of Drosophila mauritiana. Mutated genes containing a Mos1 insertion are molecularly tagged by this heterologous transposable element. Mos1 insertions can therefore be identified in as little as 3 weeks using only basic molecular biology techniques. Mutagenic efficiency of Mos1 is tenfold lower than classical chemical mutagens. However, the ease and speed with which mutagenic insertions can be mapped compares favorably with the vast amount of work involved in classical genetic mapping. Therefore, Mos1 could be the tool of choice when screening procedures are efficient. In addition, Mos1 mutagenesis can greatly simplify the mapping of mutations that exhibit low penetrance, subtle or synthetic phenotypes. The recent development of targeted engineering of C. elegans loci carrying Mos1 insertions further increases the attractiveness of Mos1-mediated mutagenesis.
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Boulin T, Pocock R, Hobert O. A novel Eph receptor-interacting IgSF protein provides C. elegans motoneurons with midline guidepost function. Curr Biol 2006; 16:1871-83. [PMID: 17027485 DOI: 10.1016/j.cub.2006.08.056] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2006] [Revised: 08/07/2006] [Accepted: 08/09/2006] [Indexed: 01/23/2023]
Abstract
BACKGROUND The ventral midline is a prominent structure in vertebrate and invertebrate nervous systems that provides crucial topological information for guiding axons to their appropriate target destinations. Rather than being composed of specialized midline glia cells as in many other species, the embryonic midline of the nematode Caenorhabditis elegans is physically defined by motoneuron cell bodies that separate the left from the right ventral cord fascicles. Their function during development, if any, is not known. RESULTS We show here that besides being components of the postembryonic locomotory circuit, these embryonic motoneurons (eMNs) actively provide midline guidance information for a specific subset of ventral midline axons. This information is provided in the form of a novel, cell-surface-anchored immunoglobulin superfamily (IgSF) member, WRK-1. WRK-1 acts in eMNs to prevent follower axons from inappropriately crossing the ventral midline. We describe the function of the Eph receptor vab-1 and multiple ephrin ligands at the midline, and we show by double mutant analysis and physical interaction tests that WRK-1 functionally interacts with the Eph receptor system. This interaction appears to occur exclusively in the context of axon guidance at the ventral midline but not in other cellular contexts, thereby suggesting that Eph receptor signaling is mechanistically distinct in different tissue types. CONCLUSIONS Our studies reveal cellular and molecular components of axon midline patterning and suggest that Ephrin signaling relies on previously unknown accessory components.
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Faumont S, Boulin T, Hobert O, Lockery SR. Developmental regulation of whole cell capacitance and membrane current in identified interneurons in C. elegans. J Neurophysiol 2006; 95:3665-73. [PMID: 16554520 DOI: 10.1152/jn.00052.2006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Postembryonic developmental changes in electrophysiological properties of the AIY interneuron class were investigated using whole cell voltage clamp. AIY interneurons displayed an increase in cell capacitance during larval development, whereas steady-state current amplitude did not increase. The time course of the outward membrane current, carried at least in part by K+ ions, matured, from a slowly activating, sustained current to a rapidly activating, decaying current. We also investigated how the development of capacitance and outward current was altered by loss-of-function mutations in genes expressed in AIY. One such gene, the LIM homeobox gene ttx-3, is known to be involved in the specification of the AIY neuronal subtype. In ttx-3 mutants, capacitance and outward current matured precociously. In mutants of the gene wrk-1, an immunoglobulin superfamily (IgSF) member whose expression is regulated by ttx-3, capacitance matured normally, whereas outward current matured precociously. We conclude that AIY interneurons contain distinct pathways for regulating capacitance and membrane current.
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Williams DC, Boulin T, Ruaud AF, Jorgensen EM, Bessereau JL. Characterization of Mos1-mediated mutagenesis in Caenorhabditis elegans: a method for the rapid identification of mutated genes. Genetics 2005; 169:1779-85. [PMID: 15654093 PMCID: PMC1449563 DOI: 10.1534/genetics.104.038265] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Insertional mutagenesis with a heterologous transposon provides a method to rapidly determine the molecular identity of mutated genes. The Drosophila transposon Mos1 can be mobilized to cause mutations in Caenorhabditis elegans (Bessereau et al. 2001); however, the mutagenic rate was initially too low for use in most forward genetic screens. To increase the effectiveness of Mos1-mediated mutagenesis we examined the conditions influencing Mos1 transposition. First, optimal transposition occurs 24 hr after expression of the transposase and is unlikely to occur in differentiated sperm or oocytes. Second, transposition is limited to germ-cell nuclei that contain donor elements, but the transposase enzyme can diffuse throughout the gonad syncytium. Third, silencing of transposition is caused by changes in the donor array that occur over time. Finally, multiple transposition events occur in individual germ cells. By using screening techniques based on these results, Mos1 mutagenicity was increased to within an order of magnitude of chemical mutagens.
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Bülow HE, Boulin T, Hobert O. Differential functions of the C. elegans FGF receptor in axon outgrowth and maintenance of axon position. Neuron 2004; 42:367-74. [PMID: 15134634 DOI: 10.1016/s0896-6273(04)00246-6] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2004] [Revised: 03/03/2004] [Accepted: 03/23/2004] [Indexed: 12/20/2022]
Abstract
Wiring of the nervous system requires that axons navigate to their targets and maintain their correct positions in axon fascicles after termination of axon outgrowth. We show here that the C. elegans fibroblast growth factor receptor (FGFR), EGL-15, affects both processes in fundamentally distinct manners. FGF-dependent activation of the EGL-15 tyrosine kinase and subsequently the GTPase LET-60/ras is required within epidermal cells, the substratum for most outgrowing axon, for appropriate outgrowth of specific axon classes to their target area. In contrast, genetic elimination of the FGFR isoform EGL-15(5A), defined by the inclusion of an alternative extracellular interimmunoglobulin domain, has no consequence for axon outgrowth but leads to a failure to postembryonically maintain axon position within defined axon fascicles. An engineered, secreted form of EGL-15(5A) containing only its ectodomain is sufficient for maintenance of axon position, thus providing novel insights into receptor tyrosine kinase function and the process of maintaining axon position.
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Aurelio O, Boulin T, Hobert O. Identification of spatial and temporal cues that regulate postembryonic expression of axon maintenance factors in the C. elegans ventral nerve cord. Development 2003; 130:599-610. [PMID: 12490565 DOI: 10.1242/dev.00277] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Patterns of gene expression are under precise spatial and temporal control. A particularly striking example is represented by several members of the zig gene family, which code for secreted immunoglobulin domain proteins required for maintaining ventral nerve cord organization in Caenorhabditis elegans. These genes are coordinately expressed in a single interneuron in the ventral nerve cord, known as PVT. Their expression is initiated at a precise postembryonic stage, long after PVT has been generated in mid-embryogenesis. We define spatial and temporal cues that are required for the precise regulation of zig gene expression. We find that two LIM homeobox genes, the Lhx3-class gene ceh-14 and the Lmx-class gene lim-6 are coordinately required for zig gene expression in PVT. Temporal control of zig gene expression is conferred by the heterochronic gene lin-14, a nuclear factor previously implicated in developmental timing in various contexts. Loss of the lim-6 and ceh-14 transcription factors and the developmental timer lin-14 cause not only a loss of zig gene expression but also lead to defects in the maintenance of ventral nerve cord architecture. Overriding the normal spatiotemporal control of zig gene expression through expression of one of the zig genes under control of heterologous promoters also causes axon patterning defects in the ventral nerve cord. Our findings illustrate the importance of spatial and temporal control of gene expression in the nervous system and, furthermore, implicate heterochronic genes in postmitotic neural patterning events.
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