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Schneider ER, Gracheva EO, Bagriantsev SN. Evolutionary Specialization of Tactile Perception in Vertebrates. Physiology (Bethesda) 2017; 31:193-200. [PMID: 27053733 DOI: 10.1152/physiol.00036.2015] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Evolution has endowed vertebrates with the remarkable tactile ability to explore the world through the perception of physical force. Yet the sense of touch remains one of the least well understood senses at the cellular and molecular level. Vertebrates specializing in tactile perception can highlight general principles of mechanotransduction. Here, we review cellular and molecular adaptations that underlie the sense of touch in typical and acutely mechanosensitive vertebrates.
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Miller MR, Mannowetz N, Iavarone AT, Safavi R, Gracheva EO, Smith JF, Hill RZ, Bautista DM, Kirichok Y, Lishko PV. Unconventional endocannabinoid signaling governs sperm activation via the sex hormone progesterone. Science 2016; 352:555-9. [PMID: 26989199 DOI: 10.1126/science.aad6887] [Citation(s) in RCA: 158] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Accepted: 03/08/2016] [Indexed: 12/25/2022]
Abstract
Steroids regulate cell proliferation, tissue development, and cell signaling via two pathways: a nuclear receptor mechanism and genome-independent signaling. Sperm activation, egg maturation, and steroid-induced anesthesia are executed via the latter pathway, the key components of which remain unknown. Here, we present characterization of the human sperm progesterone receptor that is conveyed by the orphan enzyme α/β hydrolase domain-containing protein 2 (ABHD2). We show that ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid 2-arachidonoylglycerol (2AG) from plasma membrane. The 2AG inhibits the sperm calcium channel (CatSper), and its removal leads to calcium influx via CatSper and ensures sperm activation. This study reveals that progesterone-activated endocannabinoid depletion by ABHD2 is a general mechanism by which progesterone exerts its genome-independent action and primes sperm for fertilization.
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Hoffstaetter LJ, Tonsfeldt KJ, Matos-Cruz V, Bagriantsev SN, Gracheva EO. Probing the Contribution of Nav1.7 and Nav1.8 to Cold Tolerance in Hibernators. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Bagriantsev SN, Schneider ER, Anderson EO, Matson J, Gracheva EO. Stretch-Gated Ion Channels in Neuronal Mechanoreceptors. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Gracheva EO, Bagriantsev SN. Evolutionary adaptation to thermosensation. Curr Opin Neurobiol 2015; 34:67-73. [PMID: 25698346 DOI: 10.1016/j.conb.2015.01.021] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Revised: 01/28/2015] [Accepted: 01/30/2015] [Indexed: 01/31/2023]
Abstract
Organisms continuously evolve to adapt to changing environmental conditions. Chief among these are daily and seasonal temperature fluctuations. Relatively small in terms of real physical values, temperature fluctuations of just a few degrees can profoundly affect organismal functions. In vertebrates, temperature is detected by primary afferents of somatosensory neurons, which express thermo-gated ion channels. Most of our knowledge about temperature receptors comes from seminal studies in mice and rats. Recent work uncovered thermosensory mechanisms in other vertebrates, shedding light onto the diversity of thermosensory adaptations. Here, we summarize molecular mechanisms of thermosensation in different species and discuss the need to use the standard laboratory rodents and non-standard species side-by-side in order to understand fundamental principles of somatosensation.
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Laursen WJ, Anderson EO, Hoffstaetter LJ, Bagriantsev SN, Gracheva EO. Species-specific temperature sensitivity of TRPA1. Temperature (Austin) 2015; 2:214-26. [PMID: 27227025 PMCID: PMC4843866 DOI: 10.1080/23328940.2014.1000702] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 12/16/2014] [Accepted: 12/16/2014] [Indexed: 11/25/2022] Open
Abstract
Transient receptor potential ankyrin 1 (TRPA1) is a polymodal ion channel sensitive to temperature and chemical stimuli. The importance of temperature and aversive chemical detection for survival has driven the evolutionary diversity of TRPA1 sensitivity. This diversity can be observed in the various roles of TRPA1 in different species, where it is proposed to act as a temperature-insensitive chemosensor, a heat transducer, a noxious cold transducer, or a detector of low-intensity heat for prey localization. Exploring the variation of TRPA1 functions among species provides evolutionary insight into molecular mechanisms that fine-tune thermal and chemical sensitivity, and offers an opportunity to address basic principles of temperature gating in ion channels. A decade of research has yielded a number of hypotheses describing physiological roles of TRPA1, modulators of its activity, and biophysical principles of gating. This review surveys the diversity of TRPA1 adaptations across evolutionary taxa and explores possible mechanisms of TRPA1 activation.
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Bagriantsev SN, Gracheva EO. Molecular mechanisms of temperature adaptation. J Physiol 2015; 593:3483-91. [PMID: 25433072 DOI: 10.1113/jphysiol.2014.280446] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Accepted: 11/21/2014] [Indexed: 11/08/2022] Open
Abstract
Thermal perception is a fundamental physiological process pertaining to the vast majority of organisms. In vertebrates, environmental temperature is detected by the primary afferents of the somatosensory neurons in the skin, which express a 'choir' of ion channels tuned to detect particular temperatures. Nearly two decades of research have revealed a number of receptor ion channels that mediate the perception of several temperature ranges, but most still remain molecularly orphaned. Yet even within this well-researched realm, most of our knowledge largely pertains to two closely related species of rodents, mice and rats. While these are standard biomedical research models, mice and rats provide a limited perspective to elucidate the general principles that drive somatosensory evolution. In recent years, significant advances have been made in understanding the molecular mechanism of temperature adaptation in evolutionarily distant vertebrates and in organisms with acute thermal sensitivity. These studies have revealed the remarkable versatility of the somatosensory system and highlighted adaptations at the molecular level, which often include changes in biophysical properties of ion channels from the transient receptor potential family. Exploiting non-standard animal models has the potential to provide unexpected insights into general principles of thermosensation and thermoregulation, unachievable using the rodent model alone.
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Bagriantsev SN, Gracheva EO, Gallagher PG. Piezo proteins: regulators of mechanosensation and other cellular processes. J Biol Chem 2014; 289:31673-31681. [PMID: 25305018 DOI: 10.1074/jbc.r114.612697] [Citation(s) in RCA: 156] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Piezo proteins have recently been identified as ion channels mediating mechanosensory transduction in mammalian cells. Characterization of these channels has yielded important insights into mechanisms of somatosensation, as well as other mechano-associated biologic processes such as sensing of shear stress, particularly in the vasculature, and regulation of urine flow and bladder distention. Other roles for Piezo proteins have emerged, some unexpected, including participation in cellular development, volume regulation, cellular migration, proliferation, and elongation. Mutations in human Piezo proteins have been associated with a variety of disorders including hereditary xerocytosis and several syndromes with muscular contracture as a prominent feature.
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Laursen WJ, Funk O, Goodman J, Merriman DK, Ingolia NT, Bagriantsev SN, Gracheva EO. Molecular Adaptations to Extreme Thermogenesis in Mammalian Hibernators. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.1931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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Schneider ER, Anderson EO, Gracheva EO, Bagriantsev SN. Temperature sensitivity of two-pore (K2P) potassium channels. CURRENT TOPICS IN MEMBRANES 2014; 74:113-33. [PMID: 25366235 DOI: 10.1016/b978-0-12-800181-3.00005-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
At normal body temperature, the two-pore potassium channels TREK-1 (K2P2.1/KCNK2), TREK-2 (K2P10.1/KCNK10), and TRAAK (K2P4.1/KCNK2) regulate cellular excitability by providing voltage-independent leak of potassium. Heat dramatically potentiates K2P channel activity and further affects excitation. This review focuses on the current understanding of the physiological role of heat-activated K2P current, and discusses the molecular mechanism of temperature gating in TREK-1, TREK-2, and TRAAK.
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Laursen WJ, Bagriantsev SN, Gracheva EO. TRPA1 channels: chemical and temperature sensitivity. CURRENT TOPICS IN MEMBRANES 2014; 74:89-112. [PMID: 25366234 DOI: 10.1016/b978-0-12-800181-3.00004-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Transient receptor potential ankyrin 1 (TRPA1) is a polymodal excitatory ion channel found in sensory neurons of different organisms, ranging from worms to humans. Since its discovery as an uncharacterized transmembrane protein in human fibroblasts, TRPA1 has become one of the most intensively studied ion channels. Its function has been linked to regulation of heat and cold perception, mechanosensitivity, hearing, inflammation, pain, circadian rhythms, chemoreception, and other processes. Some of these proposed functions remain controversial, while others have gathered considerable experimental support. A truly polymodal ion channel, TRPA1 is activated by various stimuli, including electrophilic chemicals, oxygen, temperature, and mechanical force, yet the molecular mechanism of TRPA1 gating remains obscure. In this review, we discuss recent advances in the understanding of TRPA1 physiology, pharmacology, and molecular function.
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Giordano F, Saheki Y, Idevall-Hagren O, Colombo SF, Pirruccello M, Milosevic I, Gracheva EO, Bagriantsev SN, Borgese N, De Camilli P. PI(4,5)P(2)-dependent and Ca(2+)-regulated ER-PM interactions mediated by the extended synaptotagmins. Cell 2013; 153:1494-509. [PMID: 23791178 DOI: 10.1016/j.cell.2013.05.026] [Citation(s) in RCA: 416] [Impact Index Per Article: 37.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Revised: 04/24/2013] [Accepted: 05/10/2013] [Indexed: 12/28/2022]
Abstract
Most available information on endoplasmic reticulum (ER)-plasma membrane (PM) contacts in cells of higher eukaryotes concerns proteins implicated in the regulation of Ca(2+) entry. However, growing evidence suggests that such contacts play more general roles in cell physiology, pointing to the existence of additionally ubiquitously expressed ER-PM tethers. Here, we show that the three extended synaptotagmins (E-Syts) are ER proteins that participate in such tethering function via C2 domain-dependent interactions with the PM that require PI(4,5)P2 in the case of E-Syt2 and E-Syt3 and also elevation of cytosolic Ca(2+) in the case of E-Syt1. As they form heteromeric complexes, the E-Syts confer cytosolic Ca(2+) regulation to ER-PM contact formation. E-Syts-dependent contacts, however, are not required for store-operated Ca(2+) entry. Thus, the ER-PM tethering function of the E-Syts (tricalbins in yeast) mediates the formation of ER-PM contacts sites, which are functionally distinct from those mediated by STIM1 and Orai1.
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Yu SC, Klosterman SM, Martin AA, Gracheva EO, Richmond JE. Differential roles for snapin and synaptotagmin in the synaptic vesicle cycle. PLoS One 2013; 8:e57842. [PMID: 23469084 PMCID: PMC3585204 DOI: 10.1371/journal.pone.0057842] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 01/29/2013] [Indexed: 11/19/2022] Open
Abstract
Evoked synaptic transmission is dependent on interactions between the calcium sensor Synaptotagmin I and the SNARE complex, comprised of Syntaxin, SNAP-25, and Synaptobrevin. Recent evidence suggests that Snapin may be an important intermediate in this process, through simultaneous interactions of Snapin dimers with SNAP-25 and Synaptotagmin. In support of this model, cultured neurons derived from embryonically lethal Snapin null mutant mice exhibit desynchronized release and a reduced readily releasable vesicle pool. Based on evidence that a dimerization-defective Snapin mutation specifically disrupts priming, Snapin is hypothesized to stabilize primed vesicles by structurally coupling Synaptotagmin and SNAP-25. To explore this model in vivo we examined synaptic transmission in viable, adult C. elegans Snapin (snpn-1) mutants. The kinetics of synaptic transmission were unaffected at snpn-1 mutant neuromuscular junctions (NMJs), but the number of docked, fusion competent vesicles was significantly reduced. However, analyses of snt-1 and snt-1;snpn-1 double mutants suggest that the docking role of SNPN-1 is independent of Synaptotagmin. Based on these results we propose that the primary role of Snapin in C. elegans is to promote vesicle priming, consistent with the stabilization of SNARE complex formation through established interactions with SNAP-25 upstream of the actions of Synaptotagmin in calcium-sensing and endocytosis.
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Gracheva EO, Cordero-Morales JF, González-Carcacóa JA, Ingolia NT, Manno M, Aranguren CI, Weissman JS, Julius D. Ganglion-Specific Splicing of TRPV1 Underlies Infrared Sensation in Vampire Bats. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022] Open
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Cordero-Morales JF, Gracheva EO, Julius D. Cytoplasmic Ankyrin Repeats of Transient Receptor Potential A1 (TRPA1) Dictate Sensitivity to Thermal and Chemical Stimuli. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.151] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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Gracheva EO, Cordero-Morales JF, González-Carcacía JA, Ingolia NT, Manno C, Aranguren CI, Weissman JS, Julius D. Ganglion-specific splicing of TRPV1 underlies infrared sensation in vampire bats. Nature 2011; 476:88-91. [PMID: 21814281 PMCID: PMC3535012 DOI: 10.1038/nature10245] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Accepted: 06/03/2011] [Indexed: 01/06/2023]
Abstract
Vampire bats (Desmodus rotundus) are obligate blood feeders that have evolved specialized systems to suit their unique sanguinary lifestyle 1–3. Chief among such adaptations is the ability to detect infrared radiation as a means of locating hot spots on warm-blooded prey. Among vertebrates, only vampire bats, boas, pythons, and pit vipers are capable of detecting infrared radiation 1,4. In each case, infrared heat is detected by trigeminal nerve fibers that innervate specialized pit organs on the animal’s face 5–10. Thus, vampire bats and snakes have taken thermosensation to the extreme by developing specialized systems for detecting infrared radiation. As such, these creatures provide a window into the molecular and genetic mechanisms underlying evolutionary tuning of thermoreceptors in a species or cell type specific manner. Previously, we have shown that snakes co-opt a non-heat sensitive channel (vertebrate TRPA1) to produce an infrared detector 6. Here we show that vampire bats tune an already heat sensitive channel (TRPV1) by lowering its thermal activation threshold to ~30°C. This is achieved through alternative splicing of TRPV1 transcripts to produce a channel with a truncated C-terminal cytoplasmic domain. Remarkably, these splicing events occur exclusively in trigeminal ganglia (TG), and not dorsal root ganglia (DRG), thereby maintaining a role for TRPV1 as a detector of noxious heat in somatic afferents. This reflects a unique organization of the bat TRPV1 gene that we show to be characteristic of Laurasiatheria mammals (cows, dogs, and moles), supporting a close phylogenetic relationship with bats. These findings reveal a unique molecular mechanism for physiological tuning of thermosensory nerve fibers.
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Gracheva EO, Maryon EB, Berthelot-Grosjean M, Richmond JE. Differential Regulation of Synaptic Vesicle Tethering and Docking by UNC-18 and TOM-1. Front Synaptic Neurosci 2010; 2:141. [PMID: 21423527 PMCID: PMC3059690 DOI: 10.3389/fnsyn.2010.00141] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Accepted: 08/13/2010] [Indexed: 02/02/2023] Open
Abstract
The assembly of SNARE complexes between syntaxin, SNAP-25 and synaptobrevin is required to prime synaptic vesicles for fusion. Since Munc18 and tomosyn compete for syntaxin interactions, the interplay between these proteins is predicted to be important in regulating synaptic transmission. We explored this possibility, by examining genetic interactions between C. elegans unc-18(Munc18), unc-64(syntaxin) and tom-1(tomosyn). We have previously demonstrated that unc-18 mutants have reduced synaptic transmission, whereas tom-1 mutants exhibit enhanced release. Here we show that the unc-18 mutant release defect is associated with loss of two morphologically distinct vesicle pools; those tethered within 25 nm of the plasma membrane and those docked with the plasma membrane. In contrast, priming defective unc-13 mutants accumulate tethered vesicles, while docked vesicles are greatly reduced, indicating tethering is UNC-18-dependent and occurs in the absence of priming. C. elegans unc-64 mutants phenocopy unc-18 mutants, losing both tethered and docked vesicles, whereas overexpression of open syntaxin preferentially increases vesicle docking, suggesting UNC-18/closed syntaxin interactions are responsible for vesicle tethering. Given the competition between vertebrate tomosyn and Munc18, for syntaxin binding, we hypothesized that C. elegans TOM-1 may inhibit both UNC-18-dependent vesicle targeting steps. Consistent with this hypothesis, tom-1 mutants exhibit enhanced UNC-18 plasma membrane localization and a concomitant increase in both tethered and docked synaptic vesicles. Furthermore, in tom-1;unc-18 double mutants the docked, primed vesicle pool is preferentially rescued relative to unc-18 single mutants. Together these data provide evidence for the differential regulation of two vesicle targeting steps by UNC-18 and TOM-1 through competitive interactions with syntaxin.
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Gracheva EO, Hadwiger G, Nonet ML, Richmond JE. Direct interactions between C. elegans RAB-3 and Rim provide a mechanism to target vesicles to the presynaptic density. Neurosci Lett 2008; 444:137-42. [PMID: 18721860 DOI: 10.1016/j.neulet.2008.08.026] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2008] [Revised: 07/19/2008] [Accepted: 08/08/2008] [Indexed: 01/19/2023]
Abstract
Rim is a multi-domain, active zone protein that regulates exocytosis and is implicated in vesicle priming and presynaptic plasticity. We recently demonstrated that synaptic defects associated with loss of Caenorhabditis elegans Rim (termed UNC-10) are accompanied by a reduction in docked vesicles adjacent to the presynaptic density. Since Rim is known to interact with the vesicle-associated GTPase Rab3A, here we asked whether UNC-10-dependent recruitment of synaptic vesicles to the presynaptic density was through an UNC-10/Rab-3 interaction. We first established that C. elegans Rab3 (termed RAB-3) in its GTP but not GDP-bound state interacts with UNC-10. We then demonstrated by EM analysis that rab-3 mutant synapses exhibit the same vesicle-targeting defect as unc-10 mutants. Furthermore, unc-10;rab-3 double mutants phenocopy the targeting defects of the single mutants, suggesting UNC-10 and RAB-3 act in the same pathway to target vesicles at the presynaptic density. Endogenous release of unc-10;rab-3 double mutants was similar to that of unc-10 single mutants, but more severe than rab-3 mutants, suggesting the common targeting defects are reflected by the milder rab-3 release defect. Rim has recently been shown to positively regulate calcium influx through direct interactions with calcium channels. Consistent with this notion we found UNC-10 colocalized with the calcium channel, UNC-2 at C. elegans presynaptic densities and synaptic release in unc-10 and rab-3 mutants exhibit reduced calcium-sensitivity. Together these results suggest that vesicles targeted to the presynaptic density by RAB-3/UNC-10 interactions are ideally positioned for efficient calcium-dependent release.
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Bagriantsev SN, Gracheva EO, Richmond JE, Liebman SW. Variant-specific [PSI+] infection is transmitted by Sup35 polymers within [PSI+] aggregates with heterogeneous protein composition. Mol Biol Cell 2008; 19:2433-43. [PMID: 18353968 DOI: 10.1091/mbc.e08-01-0078] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The [PSI(+)] prion is the aggregated self-propagating form of the Sup35 protein from the yeast Saccharomyces cerevisiae. Aggregates of Sup35 in [PSI(+)] cells exist in different heritable conformations, called "variants," and they are composed of detergent-resistant Sup35 polymers, which may be closely associated with themselves, other proteins, or both. Here, we report that disassembly of the aggregates into individual Sup35 polymers and non-Sup35 components increases their infectivity while retaining their variant specificity, showing that variant-specific [PSI(+)] infection can be transmitted by Sup35 polymers alone. Morphological analysis revealed that Sup35 isolated from [PSI(+)] yeast has the appearance of short barrels, and bundles, which seem to be composed of barrels. We show that the major components of two different variants of [PSI(+)] are interacting infectious Sup35 polymers and Ssa1/2. Using a candidate approach, we detected Hsp104, Ssb1/2, Sis1, Sse1, Ydj1, and Sla2 among minor components of the aggregates. We demonstrate that Ssa1/2 efficiently binds to the prion domain of Sup35 in [PSI(+)] cells, but that it interacts poorly with the nonaggregated Sup35 found in [psi(-)] cells. Hsp104, Sis1, and Sse1 interact preferentially with the prion versus nonprion form of Sup35, whereas Sla2 and Ssb1/2 interact with both forms of Sup35 with similar efficiency.
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Wang W, Bouhours M, Gracheva EO, Liao EH, Xu K, Sengar AS, Xin X, Roder J, Boone C, Richmond JE, Zhen M, Egan SE. ITSN-1 controls vesicle recycling at the neuromuscular junction and functions in parallel with DAB-1. Traffic 2008; 9:742-54. [PMID: 18298590 DOI: 10.1111/j.1600-0854.2008.00712.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intersectins (Itsn) are conserved EH and SH3 domain containing adaptor proteins. In Drosophila melanogaster, ITSN is required to regulate synaptic morphology, to facilitate efficient synaptic vesicle recycling and for viability. Here, we report our genetic analysis of Caenorhabditis elegans intersectin. In contrast to Drosophila, C. elegans itsn-1 protein null mutants are viable and display grossly normal locomotion and development. However, motor neurons in these mutants show a dramatic increase in large irregular vesicles and accumulate membrane-associated vesicles at putative endocytic hotspots, approximately 300 nm from the presynaptic density. This defect occurs precisely where endogenous ITSN-1 protein localizes in wild-type animals and is associated with a significant reduction in synaptic vesicle number and reduced frequency of endogenous synaptic events at neuromuscular junctions (NMJs). ITSN-1 forms a stable complex with EHS-1 (Eps15) and is expressed at reduced levels in ehs-1 mutants. Thus, ITSN-1 together with EHS-1, coordinate vesicle recycling at C. elegans NMJs. We also found that both itsn-1 and ehs-1 mutants show poor viability and growth in a Disabled (dab-1) null mutant background. These results show for the first time that intersectin and Eps15 proteins function in the same genetic pathway, and appear to function synergistically with the clathrin-coat-associated sorting protein, Disabled, for viability.
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Gracheva EO, Burdina AO, Touroutine D, Berthelot-Grosjean M, Parekh H, Richmond JE. Tomosyn negatively regulates CAPS-dependent peptide release at Caenorhabditis elegans synapses. J Neurosci 2007; 27:10176-84. [PMID: 17881523 PMCID: PMC3874420 DOI: 10.1523/jneurosci.2339-07.2007] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The syntaxin-interacting protein tomosyn is thought to be a key regulator of exocytosis, although its precise mechanism of action has yet to be elucidated. Here we examined the role of tomosyn in peptide secretion in Caenorhabditis elegans tomosyn (tom-1) mutants. Ultrastructural analysis of tom-1 mutants revealed a 50% reduction in presynaptic dense-core vesicles (DCVs) corresponding to enhanced neuropeptide release. Conversely, overexpression of TOM-1 led to an accumulation of DCVs. Together, these data provide the first in vivo evidence that TOM-1 negatively regulates DCV exocytosis. In C. elegans, neuropeptide release is promoted by the calcium-dependent activator protein for secretion (CAPS) homolog UNC-31. To test for a genetic interaction between tomosyn and CAPS, we generated tom-1;unc-31 double mutants. Loss of TOM-1 suppressed the behavioral, electrophysiological, and DCV ultrastructural phenotypes of unc-31 mutants, indicating that TOM-1 antagonizes UNC-31-dependent DCV release. Because unc-31 mutants exhibit synaptic transmission defects, we postulated that loss of DCV release in these mutants and the subsequent suppression by tom-1 mutants could simply reflect alterations in synaptic activity, rather than direct regulation of DCV release. To distinguish between these two possibilities, we analyzed C. elegans Rim mutants (unc-10), which have a comparable reduction in synaptic transmission to unc-31 mutants, specifically attributed to defects in synaptic vesicle (SV) exocytosis. Based on this analysis, we conclude that the changes in DCV release in tom-1 and unc-31 mutants reflect direct effects of TOM-1 and UNC-31 on DCV exocytosis, rather than altered SV release.
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Gracheva EO, Burdina AO, Touroutine D, Berthelot-Grosjean M, Parekh H, Richmond JE. Tomosyn negatively regulates both synaptic transmitter and neuropeptide release at the C. elegans neuromuscular junction. J Physiol 2007; 585:705-9. [PMID: 17627987 PMCID: PMC2375516 DOI: 10.1113/jphysiol.2007.138321] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The SNARE proteins, syntaxin, SNAP-25 and synaptobrevin form a tertiary complex essential for vesicle fusion. Proteins that influence SNARE complex assembly are therefore likely to be important regulators of fusion events. In this study we have focused on tomosyn, a highly conserved, neuronally enriched, syntaxin-binding protein that has been implicated in the regulation of vesicle exocytosis. To directly test the role of tomosyn in neurosecretion we analysed loss-of-function mutants in the single Caenorhabditis elegans tomosyn gene, tom-1. These mutants exhibit enhanced synaptic transmission based on electrophysiological analysis of neuromuscular junction activity. This phenotype is the result of increased synaptic vesicle priming. In addition, we present evidence that tom-1 mutants also exhibit enhanced peptide release from dense core vesicles. These results indicate that tomosyn negatively regulates secretion for both vesicle types, possibly through a common mechanism, interfering with SNARE complex formation, thereby inhibiting vesicle fusion.
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Gracheva EO, Burdina AO, Holgado AM, Berthelot-Grosjean M, Ackley BD, Hadwiger G, Nonet ML, Weimer RM, Richmond JE. Tomosyn inhibits synaptic vesicle priming in Caenorhabditis elegans. PLoS Biol 2006; 4:e261. [PMID: 16895441 PMCID: PMC1514790 DOI: 10.1371/journal.pbio.0040261] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2006] [Accepted: 06/06/2006] [Indexed: 11/19/2022] Open
Abstract
Caenorhabditis elegans TOM-1 is orthologous to vertebrate tomosyn, a cytosolic syntaxin-binding protein implicated in the modulation of both constitutive and regulated exocytosis. To investigate how TOM-1 regulates exocytosis of synaptic vesicles in vivo, we analyzed
C. elegans tom-1 mutants. Our electrophysiological analysis indicates that evoked postsynaptic responses at
tom-1 mutant synapses are prolonged leading to a two-fold increase in total charge transfer. The enhanced response in
tom-1 mutants is not associated with any detectable changes in postsynaptic response kinetics, neuronal outgrowth, or synaptogenesis. However, at the ultrastructural level, we observe a concomitant increase in the number of plasma membrane-contacting vesicles in
tom-1 mutant synapses, a phenotype reversed by neuronal expression of TOM-1. Priming defective
unc-13 mutants show a dramatic reduction in plasma membrane-contacting vesicles, suggesting these vesicles largely represent the primed vesicle pool at the
C. elegans neuromuscular junction. Consistent with this conclusion, hyperosmotic responses in
tom-1 mutants are enhanced, indicating the primed vesicle pool is enhanced. Furthermore, the synaptic defects of
unc-13 mutants are partially suppressed in
tom-1 unc-13 double mutants. These data indicate that in the intact nervous system, TOM-1 negatively regulates synaptic vesicle priming.
This paper examines the in vivo role of the syntaxin binding protein tomosyn in synaptic transmission at the
C. elegans neuromuscular junction. Tomosyn inhibits vesicle priming by regulating the size of the readily releasable vesicle pool.
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Vitrenko YA, Gracheva EO, Richmond JE, Liebman SW. Visualization of aggregation of the Rnq1 prion domain and cross-seeding interactions with Sup35NM. J Biol Chem 2006; 282:1779-87. [PMID: 17121829 DOI: 10.1074/jbc.m609269200] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Factors triggering the de novo appearance of prions are still poorly understood. In yeast, the appearance of one prion, [PSI(+)], is enhanced by the presence of another prion, [PIN(+)]. The [PSI(+)] and [PIN(+)] prion-forming proteins are, respectively, the translational termination factor Sup35 and the yet poorly characterized Rnq1 protein that is rich in glutamines and asparagines. The prion domain of Rnq1 (RnqPD) polymerizes more readily in vitro than the full-length protein. As is typical for amyloidogenic proteins, the reaction begins with a lag phase, followed by exponential growth. Seeding with pre-formed aggregates significantly shortens the lag. A generic antibody against pre-amyloid oligomer inhibits the unseeded but not the self-seeded reaction. As revealed by electron microscopy, RnqPD polymerizes predominantly into spherical species that eventually agglomerate. We observed infrequent fiber-like structures in samples taken at 4 h of polymerization, but in overnight samples SDS treatment was required to reveal fibers among agglomerates. Polymerization reactions in which RnqPD and the prion domain of Sup35 (Sup35NM) cross-seed each other proceeded with a shortened lag that only depends weakly on the protein concentration. Cross-seeded Sup35NM fibers appear to sprout from globular RnqPD aggregates as seen by electron microscopy. RnqPD spherical aggregates appear to associate with and, later occlude, Sup35NM seed fibers. Our kinetic and morphological analyses suggest that, upon cross-seeding, the aggregate provides the surface on which oligomers of the heterologous protein nucleate their subsequent amyloid formation.
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Weimer RM, Gracheva EO, Meyrignac O, Miller KG, Richmond JE, Bessereau JL. UNC-13 and UNC-10/rim localize synaptic vesicles to specific membrane domains. J Neurosci 2006; 26:8040-7. [PMID: 16885217 PMCID: PMC3874421 DOI: 10.1523/jneurosci.2350-06.2006] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptic vesicles undergo a maturation step, termed priming, in which they become competent to fuse with the plasma membrane. To morphologically define the site of vesicle priming and identify fusion-competent synaptic vesicles, we combined a rapid physical-fixation technique with immunogold staining and high-resolution morphometric analysis at Caenorhabditis elegans neuromuscular junctions. In these presynaptic terminals, a subset of synaptic vesicles contact the plasma membrane within approximately 100 nm of a presynaptic dense projection. UNC-13, a protein required for vesicle priming, localizes to this same region of the plasma membrane. In an unc-13 null mutant, few synaptic vesicles contact the plasma membrane, suggesting that membrane-contacting synaptic vesicles represent the morphological correlates of primed vesicles. Interestingly, a subpopulation of membrane-contacting vesicles, located within 30 nm of a dense projection, are unperturbed in unc-13 mutants. We show that UNC-10/Rim, a protein implicated in presynaptic plasticity, localizes to dense projections and that loss of UNC-10/Rim causes an UNC-13-independent reduction in membrane-contacting synaptic vesicles within 30 nm of the dense projections. Our data together identify a discrete domain for vesicle priming within 100 nm of dense projections and further suggest that UNC-10/Rim and UNC-13 separately contribute to the membrane localization of synaptic vesicles within this domain.
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