101
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Svoboda KR, Linares AE, Ribera AB. Activity regulates programmed cell death of zebrafish Rohon-Beard neurons. Development 2001; 128:3511-20. [PMID: 11566856 DOI: 10.1242/dev.128.18.3511] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Programmed cell death is a normal aspect of neuronal development. Typically, twice as many neurons are generated than survive. In extreme cases, all neurons within a population disappear during embryogenesis or by early stages of postnatal development. Examples of transient neuronal populations include Cajal-Retzius cells of the cerebral cortex and Rohon-Beard cells of the spinal cord. The novel mechanisms that lead to such massive cell death have not yet been identified.
We provide evidence that electrical activity regulates the cell death program of zebrafish Rohon-Beard cells. Activity was inhibited by reducing Na+ current in Rohon-Beard cells either genetically (the macho mutation) or pharmacologically (tricaine). We examined the effects of activity block on three different reporters of cell death: DNA fragmentation, cytoskeletal rearrangements and cell body loss. Both the mao mutation and pharmacological blockade of Na+ current reduced these signatures of the cell death program. Moreover, the mao mutation and pharmacological blockade of Na+ current produced similar reductions in Rohon-Beard cell death. The results indicate that electrical activity provides signals that are required for the normal elimination of Rohon-Beard cells.
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Affiliation(s)
- K R Svoboda
- Department of Physiology and Biophysics, University of Colorado Health Sciences Center, Denver, CO 80262, USA
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102
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Nass R, Miller DM, Blakely RD. C. elegans: a novel pharmacogenetic model to study Parkinson's disease. Parkinsonism Relat Disord 2001; 7:185-191. [PMID: 11331185 DOI: 10.1016/s1353-8020(00)00056-0] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Although the use of vertebrate and tissue culture systems continue to provide valuable insight into the pathology of the neurodegeneration, the molecular determinants involved in the etiology of the disease remain elusive. Because of the high conservation of genes and metabolic pathways between invertebrates and humans, as well as the availability of genetic strategies to identify novel proteins, protein interactions and drug targets, genetic analysis using invertebrate model systems has enormous potential in deducing the factors involved in neuronal disease. In this article, we discuss the opportunities for the use of the nematode Caenorhabditis elegans (C. elegans) for gaining insight into the molecular mechanisms and pathways involved in PD.
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Affiliation(s)
- R Nass
- Department of Pharmacology, Vanderbilt University School of Medicine, MRBII, Room 419, 37232-6600, Nashville, TN, USA
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103
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Bursch W. The autophagosomal-lysosomal compartment in programmed cell death. Cell Death Differ 2001; 8:569-81. [PMID: 11536007 DOI: 10.1038/sj.cdd.4400852] [Citation(s) in RCA: 488] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2000] [Revised: 01/19/2001] [Accepted: 02/01/2001] [Indexed: 12/14/2022] Open
Abstract
In the last decade a tremendous progress has been achieved in understanding the control of apoptosis by survival and death factors as well as the molecular mechanisms of preparation and execution of the cell's suicide. However, accumulating evidence suggests that programmed cell death (PCD) is not confined to apoptosis but that cells use different pathways for active self-destruction as reflected by different morphology: condensation prominent, type I or apoptosis; autophagy prominent, type II; etc. Autophagic PCD appears to be a phylogenetically old phenomenon, it may occur in physiological and disease states. Recently, distinct biochemical and molecular features have been be assigned to this type of PCD. However, autophagic and apoptotic PCD should not be considered as mutually exclusive phenomena. Rather, they appear to reflect a high degree of flexibility in a cell's response to changes of environmental conditions, both physiological or pathological. Furthermore, recent data suggest that diverse or relatively unspecific signals such as photodamage or lysosomotropic agents may be mediated by lysosomal cysteine proteases (cathepsins) to caspases and thus, apoptosis. The present paper reviews morphological, functional and biochemical/molecular data suggesting the participation of the autophagosomal-lysosomal compartment in programmed cell death.
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Affiliation(s)
- W Bursch
- Institut für Krebsforschung der Universität Wien, Borschkegasse 8a, A-1090 Wien, Austria.
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104
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Gumienny TL, Hengartner MO. How the worm removes corpses: the nematode C. elegans as a model system to study engulfment. Cell Death Differ 2001; 8:564-8. [PMID: 11536006 DOI: 10.1038/sj.cdd.4400850] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2000] [Revised: 01/02/2001] [Accepted: 01/09/2001] [Indexed: 12/31/2022] Open
Abstract
Apoptotic cell death in the nematode C. elegans culminates with the removal of the dying cells from the organism. This removal is brought forth through a rapid and specific engulfment of the doomed cell by one of its neighbors. Over half a dozen genes have been identified that function in this process in the worm. Many of these engulfment genes have functional homologs in Drosophila and higher vertebrates. Indeed, there is growing evidence supporting the hypothesis that the pathways that mediate the removal of apoptotic cells might be, at least in part, conserved through evolution.
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Affiliation(s)
- T L Gumienny
- Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA
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105
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Affiliation(s)
- A H Wyllie
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom
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106
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Chung S, Gumienny TL, Hengartner MO, Driscoll M. A common set of engulfment genes mediates removal of both apoptotic and necrotic cell corpses in C. elegans. Nat Cell Biol 2000; 2:931-7. [PMID: 11146658 DOI: 10.1038/35046585] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Similar to mammalian excitotoxic cell death, necrotic-like cell death (NCD) in Caenorhabditis elegans can be initiated by hyperactive ion channels. Here we investigate the requirements for genes that execute and regulate programmed cell death (PCD) in necrotic-like neuronal death caused by a toxic MEC-4 channel. Neither the kinetics of necrosis onset nor the total number of necrotic corpses generated is altered by any C. elegans mutation known to block PCD, which provides genetic evidence that the activating mechanisms for NCD and apoptotic cell death are distinct. In contrast, all previously reported ced genes required for phagocytotic removal of apoptotic corpses, as well as ced-12, a new engulfment gene we have identified, are required for efficient elimination of corpses generated by distinct necrosis-inducing stimuli. Our results show that a common set of genes acts to eliminate cell corpses irrespective of the mode of cell death, and provide the first identification of the C. elegans genes that are required for orderly removal of necrotic cells. As phagocytotic mechanisms seem to be conserved from nematodes to humans, our findings indicate that injured necrotic cells in higher organisms might also be eliminated before lysis through a controlled process of corpse removal, a hypothesis that has significant therapeutic implications.
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Affiliation(s)
- S Chung
- Department of Molecular Biology and Biochemistry, Nelson Biological Laboratories, Rutgers University, 604 Allison Road, Piscataway, New Jersey 08854, USA
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107
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Affiliation(s)
- L A Herndon
- Department of Molecular Biology and Biochemistry, Nelson Biological Laboratories, Rutgers University, Piscataway, NJ 08854, USA
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108
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Hong K, Mano I, Driscoll M. In vivo structure-function analyses of Caenorhabditis elegans MEC-4, a candidate mechanosensory ion channel subunit. J Neurosci 2000; 20:2575-88. [PMID: 10729338 PMCID: PMC6772260] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/1999] [Revised: 01/19/2000] [Accepted: 01/26/2000] [Indexed: 02/15/2023] Open
Abstract
Mechanosensory signaling mediated by mechanically gated ion channels constitutes the basis for the senses of touch and hearing and contributes fundamentally to the development and homeostasis of all organisms. Despite this profound importance in biology, little is known of the molecular identities or functional requirements of mechanically gated ion channels. We report a genetically based structure-function analysis of the candidate mechanotransducing channel subunit MEC-4, a core component of a touch-sensing complex in Caenorhabditis elegans and a member of the DEG/ENaC superfamily. We identify molecular lesions in 40 EMS-induced mec-4 alleles and further probe residue and domain function using site-directed approaches. Our analysis highlights residues and subdomains critical for MEC-4 activity and suggests possible roles of these in channel assembly and/or function. We describe a class of substitutions that disrupt normal channel activity in touch transduction but remain permissive for neurotoxic channel hyperactivation, and we show that expression of an N-terminal MEC-4 fragment interferes with in vivo channel function. These data advance working models for the MEC-4 mechanotransducing channel and identify residues, unique to MEC-4 or the MEC-4 degenerin subfamily, that might be specifically required for mechanotransducing function. Because many other substitutions identified by our study affect residues conserved within the DEG/ENaC channel superfamily, this work also provides a broad view of structure-function relations in the superfamily as a whole. Because the C. elegans genome encodes representatives of a large number of eukaryotic channel classes, we suggest that similar genetic-based structure-activity studies might be generally applied to generate insight into the in vivo function of diverse channel types.
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Affiliation(s)
- K Hong
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA
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109
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Koike T, Tanaka S, Oda1 T, Ninomiya T. Sodium overload through voltage-dependent Na(+) channels induces necrosis and apoptosis of rat superior cervical ganglion cells in vitro. Brain Res Bull 2000; 51:345-55. [PMID: 10704786 DOI: 10.1016/s0361-9230(99)00246-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Using the failure to exclude trypan blue as a criterion for cell death, we found that veratridine, the voltage-dependent Na(+) channel activator, exerted its toxicity to cultured sympathetic neurons in a dose-dependent manner (half-maximal toxicity occurred at 2 microM). The co-presence of tetrodotoxin completely reversed the toxicity only at concentrations of veratridine < 20 microM. Veratridine neurotoxicity was due to the influx of Na(+); a medium low in Na(+) (36 mM) completely abolished its neurotoxicity, whereas a Ca(2+)-free medium did not attenuate its neurotoxicity. Furthermore, the buffering action of 1, 2-Bis-(2-aminophenoxy)ethane-N,N,N',N',-tetraacetate (BAPTA) on veratridine-induced increase in intracellular Ca(2+) levels neither blocked veratridine neurotoxicity in normal medium, nor attenuated the low Na(+) effect. Elevated K(+) effectively blocked veratridine neurotoxicity in a Ca(2+)-dependent manner. Cytoplasmic pH measurements using a fluorescent pH indicator demonstrated that cellular acidification (from pH 7.0 to pH 6.5) occurred upon treatment with veratridine. Both veratridine-induced acidification and cell death were ameliorated by 5-(N-ethyl-N-isopropyl)amiloride, the specific inhibitor of the Na(+)/H(+) exchanger (IC(50) = 0.5 microM). Finally, necrosis occurred predominantly in veratridine neurotoxicity, but both staining with bis-benzimide and TUNEL analysis showed nuclear features of apoptosis in sympathetic neurons undergoing cell death.
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Affiliation(s)
- T Koike
- Molecular Neurobiology Laboratory, Graduate School of Science, Hokkaido University, Sapporo, Japan.
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110
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Sakai H, Lingueglia E, Champigny G, Mattei MG, Lazdunski M. Cloning and functional expression of a novel degenerin-like Na+ channel gene in mammals. J Physiol 1999; 519 Pt 2:323-33. [PMID: 10457052 PMCID: PMC2269506 DOI: 10.1111/j.1469-7793.1999.0323m.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. A degenerate polymerase chain reaction (PCR) homology screening procedure was applied to rat brain cDNA in order to identify novel genes belonging to the amiloride-sensitive Na+ channel and degenerin (NaC/DEG) family of ion channels. A single gene was identified that encodes a protein related to but clearly different from the already cloned members of the family (18-30 % amino acid sequence identity). Phylogenetic analysis linked this protein to the group of ligand-gated channels that includes the mammalian acid-sensing ion channels and the Phe-Met-Arg-Phe-amide (FMRFamide)-activated Na+ channel. 2. Expression of gain-of-function mutants after cRNA injection into Xenopus laevis oocytes or transient transfection of COS cells induced large constitutive currents. The activated channel was amiloride sensitive (IC50, 1.31 microM) and displayed a low conductance (9-10 pS) and a high selectivity for Na+ over K+ (ratio of the respective permeabilities, PNa+/PK+ >= 10), all of which are characteristic of NaC/DEG channel behaviour. 3. Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed a predominant expression of its mRNA in the small intestine, the liver (including hepatocytes) and the brain. This channel has been called the brain-liver-intestine amiloride-sensitive Na+ channel (BLINaC). 4. Corresponding gain-of-function mutations in Caenorhabditis elegans degenerins are responsible for inherited neurodegeneration in the nematode. Besides the BLINaC physiological function that remains to be established, mutations in this novel mammalian degenerin-like channel might be of pathophysiological importance in inherited neurodegeneration and liver or intestinal pathologies.
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Affiliation(s)
- H Sakai
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UPR 411, 660 route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
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111
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Kim S, Ren XC, Fox E, Wadsworth WG. SDQR migrations in Caenorhabditis elegans are controlled by multiple guidance cues and changing responses to netrin UNC-6. Development 1999; 126:3881-90. [PMID: 10433916 DOI: 10.1242/dev.126.17.3881] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The netrin guidance cue, UNC-6, and the netrin receptors, UNC-5 and UNC-40, guide SDQR cell and axon migrations in C. elegans. In wild-type larvae, SDQR migrations are away from ventral UNC-6-expressing cells, suggesting that UNC-6 repels SDQR. In unc-6 null larvae, SDQR migrations are towards the ventral midline, indicating a response to other guidance cues that directs the migrations ventrally. Although ectopic UNC-6 expression dorsal to the SDQR cell body would be predicted to cause ventral SDQR migrations in unc-6 null larvae, in fact, more migrations are directed dorsally, suggesting that SDQR is not always repelled from the dorsal source of UNC-6. UNC-5 is required for dorsal SDQR migrations, but not for the ventral migrations in unc-6 null larvae. UNC-40 appears to moderate both the response to UNC-6 and to the other cues. Our results show that SDQR responds to multiple guidance cues and they suggest that, besides UNC-6, other factors influence whether an UNC-6 responsive cell migrates toward or away from an UNC-6 source in vivo. We propose that multiple signals elicited by the guidance cues are integrated and interpreted by SDQR and that the response to UNC-6 can change depending on the combination of cues encountered during migration. These responses determine the final dorsoventral position of the SDQR cell and axon.
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Affiliation(s)
- S Kim
- Department of Pathology, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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112
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113
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Abstract
To the surprise of many, studies of molecular mechanisms of touch transduction and analyses of epithelial Na+ transport have converged to define a new class of ion channel subunits. Based on the names of the first two identified subfamilies, the Caenorhabditis elegans degenerins and the vertebrate epithelial amiloride-sensitive Na+ channel, this ion channel class is called the DEG/ENaC superfamily. Members of the DEG/ENaC superfamily have been found in nematodes, flies, snails, and vertebrates. Family members share common topology, such that they span the membrane twice and have intracellular N- and C-termini; a large extracellular loop includes a conserved cysteine-rich region. DEG/ENaC channels have been implicated a broad spectrum of cellular functions, including mechanosensation, proprioception, pain sensation, gametogenesis, and epithelial Na+ transport. These channels exhibit diverse gating properties, ranging from near constitutive opening to rapid inactivation. We discuss working understanding of DEG/ENaC functions, channel properties, structure/activity correlations and possible evolutionary relationship to other channel classes.
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Affiliation(s)
- I Mano
- Department of Molecular Biology and Biochemistry, Rutgers, State University of New Jersey, Piscataway 08854, USA
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114
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Abstract
The brain Na+ channel-1 (BNC1, also known as MDEG1 or ASIC2) is a member of the DEG/ENaC cation channel family. Mutation of a specific residue (Gly430) that lies N-terminal to the second membrane-spanning domain activates BNC1 and converts it from a Na+-selective channel to one permeable to both Na+ and K+. Because all K+ channels are blocked by tetraethylammonium (TEA), we asked if TEA would inhibit BNC1 with a mutation at residue 430. External TEA blocked BNC1 when residue 430 was a Val or a Thr. Block was steeply voltage-dependent and was reduced when current was outward, suggesting multi-ion block within the channel pore. Block was dependent on the size of the quaternary ammonium; the smaller tetramethylammonium blocked with similar properties, whereas the larger tetrapropylammonium had little effect. When residue 430 was Phe, the effects of tetramethylammonium and tetrapropylammonium were not altered. In contrast, block by TEA was much less voltage-dependent, suggesting that the Phe mutation introduced a new TEA binding site located approximately 30% of the way across the electric field. These results provide insight into the structure and function of BNC1 and suggest that TEA may be a useful tool to probe function of this channel family.
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Affiliation(s)
- C M Adams
- Howard Hughes Medical Institute and Departments of Internal Medicine and Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242 USA
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115
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Affiliation(s)
- D L Vaux
- The Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital Victoria, Australia.
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116
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García-Añoveros J, García JA, Liu JD, Corey DP. The nematode degenerin UNC-105 forms ion channels that are activated by degeneration- or hypercontraction-causing mutations. Neuron 1998; 20:1231-41. [PMID: 9655510 DOI: 10.1016/s0896-6273(00)80503-6] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Nematode degenerins have been implicated in touch sensitivity and other forms of mechanosensation. Certain mutations in several degenerin genes cause the swelling, vacuolation, and death of neurons, and other mutations in the muscle degenerin gene unc-105 cause hypercontraction. Here, we confirm that unc-105 encodes an ion channel and show that it is constitutively active when mutated. These mutations disrupt different regions of the channel and have different effects on its gating. The UNC-105 channels are permeable to small monovalent cations but show voltage-dependent block by Ca2+ and Mg2+. Amiloride also produces voltage-dependent block, consistent with a single binding site 65% into the electric field. Mammalian cells expressing the mutant channels accumulate membranous whorls and multicompartment vacuoles, hallmarks of degenerin-induced cell death across species.
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Affiliation(s)
- J García-Añoveros
- Howard Hughes Medical Institute, Department of Neurobiology, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA
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117
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Affiliation(s)
- B Pettmann
- INSERM U.382, Developmental Biology Institute of Marseille (IBDM), CNRS-INSERM-Université Mediterrané-AP Marseille Campus de Luminy, France
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118
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Garvin C, Holdeman R, Strome S. The phenotype of mes-2, mes-3, mes-4 and mes-6, maternal-effect genes required for survival of the germline in Caenorhabditis elegans, is sensitive to chromosome dosage. Genetics 1998; 148:167-85. [PMID: 9475730 PMCID: PMC1459798 DOI: 10.1093/genetics/148.1.167] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Mutations in mes-2, mes-3, mes-4, and mes-6 result in maternal-effect sterility: hermaphrodite offspring of mes/mes mothers are sterile because of underproliferation and death of the germ cells, as well as an absence of gametes. Mutant germ cells do not undergo programmed cell death, but instead undergo a necrotic-type death, and their general poor health apparently prevents surviving germ cells from forming gametes. Male offspring of mes mothers display a significantly less severe germline phenotype than their hermaphrodite siblings, and males are often fertile. This differential response of hermaphrodite and male offspring to the absence of mes+ product is a result of their different X chromosome compositions; regardless of their sexual phenotype, XX worms display a more severe germline phenotype than XO worms, and XXX worms display the most severe phenotype. The sensitivity of the mutant phenotype to chromosome dosage, along with the similarity of two MES proteins to chromatin-associated regulators of gene expression in Drosophila, suggest that the essential role of the mes genes is in control of gene expression in the germline. An additional, nonessential role of the mes genes in the soma is suggested by the surprising finding that mutations in the mes genes, like mutations in dosage compensation genes, feminize animals whose male sexual identity is somewhat ambiguous. We hypothesize that the mes genes encode maternally supplied regulators of chromatin structure and gene expression in the germline and perhaps in somatic cells of the early embryo, and that at least some of their targets are on the X chromosomes.
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Affiliation(s)
- C Garvin
- Department of Biology, Indiana University, Bloomington 47405, USA
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119
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Harbinder S, Tavernarakis N, Herndon LA, Kinnell M, Xu SQ, Fire A, Driscoll M. Genetically targeted cell disruption in Caenorhabditis elegans. Proc Natl Acad Sci U S A 1997; 94:13128-33. [PMID: 9371811 PMCID: PMC24274 DOI: 10.1073/pnas.94.24.13128] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/1997] [Accepted: 09/11/1997] [Indexed: 02/05/2023] Open
Abstract
The elimination of identified cells is a powerful tool for investigating development and system function. Here we report on genetically mediated cell disruption effected by the toxic Caenorhabditis elegans mec-4(d) allele. We found that ectopic expression of mec-4(d) in the nematode causes dysfunction of a wide range of nerve, muscle, and hypodermal cells. mec-4(d)-mediated toxicity is dependent on the activity of a second gene, mec-6, rendering cell disruption conditionally dependent on genetic background. We describe a set of mec-4(d) vectors that facilitate construction of cell-specific disruption reagents and note that genetic cell disruption can be used for functional analyses of specific neurons or neuronal classes, for confirmation of neuronal circuitry, for generation of nematode populations lacking defined classes of functional cells, and for genetic screens. We suggest that mec-4(d) and/or related genes may be effective general tools for cell inactivation that could be used toward similar purposes in higher organisms.
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Affiliation(s)
- S Harbinder
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Center for Advanced Biotechnology and Medicine, Piscataway 08855, USA
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120
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Lingueglia E, de Weille JR, Bassilana F, Heurteaux C, Sakai H, Waldmann R, Lazdunski M. A modulatory subunit of acid sensing ion channels in brain and dorsal root ganglion cells. J Biol Chem 1997; 272:29778-83. [PMID: 9368048 DOI: 10.1074/jbc.272.47.29778] [Citation(s) in RCA: 398] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
MDEG1 is a cation channel expressed in brain that belongs to the degenerin/epithelial Na+ channel superfamily. It is activated by the same mutations which cause neurodegeneration in Caenorhabditis elegans if present in the degenerins DEG-1, MEC-4, and MEC-10. MDEG1 shares 67% sequence identity with the recently cloned proton-gated cation channel ASIC (acid sensing ion channel), a new member of the family which is present in brain and in sensory neurons. We have now identified MDEG1 as a proton-gated channel with properties different from those of ASIC. MDEG1 requires more acidic pH values for activation and has slower inactivation kinetics. In addition, we have cloned from mouse and rat brain a splice variant form of the MDEG1 channel which differs in the first 236 amino acids, including the first transmembrane region. This new membrane protein, which has been called MDEG2, is expressed in both brain and sensory neurons. MDEG2 is activated neither by mutations that bring neurodegeneration once introduced in C. elegans degenerins nor by low pH. However, it can associate both with MDEG1 and another recently cloned H+-activated channel DRASIC to form heteropolymers which display different kinetics, pH dependences, and ion selectivities. Of particular interest is the subunit combination specific for sensory neurons, MDEG2/DRASIC. In response to a drop in pH, it gives rise to a biphasic current with a sustained current which discriminates poorly between Na+ and K+, like the native H+-gated current recorded in dorsal root ganglion cells. This sustained current is thought to be required for the tonic sensation of pain caused by acids.
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Affiliation(s)
- E Lingueglia
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UPR 411, 660 route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
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121
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Tavernarakis N, Shreffler W, Wang S, Driscoll M. unc-8, a DEG/ENaC family member, encodes a subunit of a candidate mechanically gated channel that modulates C. elegans locomotion. Neuron 1997; 18:107-19. [PMID: 9010209 DOI: 10.1016/s0896-6273(01)80050-7] [Citation(s) in RCA: 152] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Mechanically gated ion channels are important modulators of coordinated movement, yet little is known of their molecular properties. We report that C. elegans unc-8, originally identified by gain-of-function mutations that induce neuronal swelling and severe uncoordination, encodes a DEG/ENaC family member homologous to subunits of a candidate mechanically gated ion channel. unc-8 is expressed in several sensory neurons, interneurons, and motor neurons. unc-8 null mutants exhibit previously unrecognized but striking defects in the amplitude and wavelength of sinusoidal tracks inscribed as they move through an E. coli lawn. We hypothesize that UNC-8 channels could modulate coordinated movement in response to body stretch. del-1, a second DEG/ENaC family member coexpressed with unc-8 in a subset of motor neurons, might also participate in a channel that contributes to nematode proprioception.
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Affiliation(s)
- N Tavernarakis
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway 08855, USA
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