Biomedical subjects

Yishi Jin

Publications and source records attributed to Yishi Jin.

At least 19 recordsLinked to original sources

PubMed2006

SYD-2 Liprin-alpha organizes presynaptic active zone formation through ELKS.

A central event in synapse development is formation of the presynaptic active zone in response to positional cues. Three active zone proteins, RIM, ELKS (also known as ERC or CAST) and Liprin-alpha, bind each other and are implicated in linking active zone formation to synaptic vesicle release. Loss of function in Caenorhabditis elegans syd-2 Liprin-alpha alters the size of presynaptic specializations and disrupts synaptic vesicle accumulation. Here we report that a missense mutation in the coiled-coil domain of SYD-2 causes a gain of function. In HSN synapses, the syd-2(gf) mutation promotes synapse formation in the absence of syd-1, which is essential for HSN synapse formation. syd-2(gf) also partially suppresses the synaptogenesis defects in syg-1 and syg-2 mutants. The activity of syd-2(gf) requires elks-1, an ELKS homolog; but not unc-10, a RIM homolog. The mutant SYD-2 shows increased association with ELKS. These results establish a functional dependency for assembly of the presynaptic active zone in which SYD-2 plays a key role.

Animals↗

PubMed2006

The C2H2 zinc-finger protein SYD-9 is a putative posttranscriptional regulator for synaptic transmission.

Communication between neurons is largely achieved through chemical synapses, where neurotransmitters are released from synaptic vesicles at presynaptic terminals to activate postsynaptic cells. Exo- and endocytosis are coordinated to replenish the synaptic vesicle pool for sustained neuronal activity. We identified syd-9 (syd, synapse defective), a gene that encodes multiple C2H2 zinc-finger domain-containing proteins specifically required for synaptic function in Caenorhabditis elegans. syd-9 loss-of-function mutants exhibit locomotory defects, a diffuse distribution of synaptic proteins, and decreased synaptic transmission with unaffected neurodevelopment. syd-9 mutants share phenotypic and ultrastructural characteristics with mutants that lack synaptic proteins that are required for endocytosis. syd-9 mutants also display genetic interactions with these endocytotic mutants, suggesting that SYD-9 regulates endocytosis. SYD-9 proteins are enriched in the nuclei of both neuron and muscle cells, but their neuronal expression plays a major role in locomotion. SYD-9 isoforms display a speckle-like expression pattern that is typical of RNA-binding proteins that regulate premRNA splicing. Furthermore, syd-9 functions in parallel with unc-75 (unc, uncoordinated), the C. elegans homologue of the CELF/BrunoL family protein that regulates mRNA alternative splicing and processing, and is also required specifically for synaptic transmission. We propose that neuronal SYD-9 proteins are previously uncharacterized and specific posttranscriptional regulators of synaptic vesicle endocytosis.

Animals↗

PubMed2006

The short coiled-coil domain-containing protein UNC-69 cooperates with UNC-76 to regulate axonal outgrowth and normal presynaptic organization in Caenorhabditis elegans.

BACKGROUND: The nematode Caenorhabditis elegans has been used extensively to identify the genetic requirements for proper nervous system development and function. Key to this process is the direction of vesicles to the growing axons and dendrites, which is required for growth-cone extension and synapse formation in the developing neurons. The contribution and mechanism of membrane traffic in neuronal development are not fully understood, however. RESULTS: We show that the C. elegans gene unc-69 is required for axon outgrowth, guidance, fasciculation and normal presynaptic organization. We identify UNC-69 as an evolutionarily conserved 108-amino-acid protein with a short coiled-coil domain. UNC-69 interacts physically with UNC-76, mutations in which produce similar defects to loss of unc-69 function. In addition, a weak reduction-of-function allele, unc-69(ju69), preferentially causes mislocalization of the synaptic vesicle marker synaptobrevin. UNC-69 and UNC-76 colocalize as puncta in neuronal processes and cooperate to regulate axon extension and synapse formation. The chicken UNC-69 homolog is highly expressed in the developing central nervous system, and its inactivation by RNA interference leads to axon guidance defects. CONCLUSION: We have identified a novel protein complex, composed of UNC-69 and UNC-76, which promotes axonal growth and normal presynaptic organization in C. elegans. As both proteins are conserved through evolution, we suggest that the mammalian homologs of UNC-69 and UNC-76 (SCOCO and FEZ, respectively) may function similarly.

Animals↗

PubMed2005

Neuronal differentiation in C. elegans.

The small size and defined connectivity of the C. elegans nervous system and the amenability of this species to systematic functional screens have continued to yield new insights into neuronal differentiation. Many aspects of C. elegans neuronal development resemble those of other more complex neurons. The basic cellular machinery of synaptic transmission is highly conserved. Recent work has begun to unveil the roles of proteoglycans in axon guidance and branching, and of the extracellular matrix in neuronal process maintenance. The importance of ubiquitin-mediated protein turnover in neuronal differentiation is revealed by the identification of new and conserved pathways that promote the organization and function of the synapse.

Animals↗

PubMed2005

The two isoforms of the Caenorhabditis elegans leukocyte-common antigen related receptor tyrosine phosphatase PTP-3 function independently in axon guidance and synapse formation.

Leukocyte-common antigen related (LAR)-like phosphatase receptors are conserved cell adhesion molecules that function in multiple developmental processes. The Caenorhabditis elegans ptp-3 gene encodes two LAR family isoforms that differ in the extracellular domain. We show here that the long isoform, PTP-3A, localizes specifically at synapses and that the short isoform, PTP-3B, is extrasynaptic. Mutations in ptp-3 cause defects in axon guidance that can be rescued by PTP-3B but not by PTP-3A. Mutations that specifically affect ptp-3A do not affect axon guidance but instead cause alterations in synapse morphology. Genetic double-mutant analysis is consistent with ptp-3A acting with the extracellular matrix component nidogen, nid-1, and the intracellular adaptor alpha-liprin, syd-2. nid-1 and syd-2 are required for the recruitment and stability of PTP-3A at synapses, and mutations in ptp-3 or nid-1 result in aberrant localization of SYD-2. Overexpression of PTP-3A is able to bypass the requirement for nid-1 for the localization of SYD-2 and RIM. We propose that PTP-3A acts as a molecular link between the extracellular matrix and alpha-liprin during synaptogenesis.

Animals↗

PubMed2005

Expression profiling of GABAergic motor neurons in Caenorhabditis elegans.

Neurons constitute the most diverse cell types and acquire their identity by the activity of particular genetic programs . The GABAergic nervous system in C. elegans consists of 26 neurons that fall into six classes . Animals that are defective in GABAergic neuron function and development display "shrinker" movement , abnormal foraging and defecation . Among the known shrinker genes, unc-25 and unc-47 encode the GABA biosynthetic enzyme glutamic acid decarboxylase and vesicular transporter, respectively . unc-30 encodes a homeodomain protein of the Pitx family and regulates the differentiation of the D-type GABAergic neurons . unc-46 probably functions in presynaptic GABA release , but its identity has not been reported. By cell-based microarray analysis, we identified over 250 genes with enriched expression in GABAergic neurons. The highly enriched gene set included all known genes. In vivo expression study with computational predictions further identified six new genes that are potential transcriptional targets of UNC-30. Behavioral studies of a deletion mutant implicate a function of a nicotinic receptor subunit in D-type neurons. Our analysis demonstrates the utility of neuron-specific genomics in identifying cell-specific genes and regulatory networks.

Animals↗

PubMed2005

Regulation of a DLK-1 and p38 MAP kinase pathway by the ubiquitin ligase RPM-1 is required for presynaptic development.

Synapses display a stereotyped ultrastructural organization, commonly containing a single electron-dense presynaptic density surrounded by a cluster of synaptic vesicles. The mechanism controlling subsynaptic proportion is not understood. Loss of function in the C. elegans rpm-1 gene, a putative RING finger/E3 ubiquitin ligase, causes disorganized presynaptic cytoarchitecture. RPM-1 is localized to the presynaptic periactive zone. We report that RPM-1 negatively regulates a p38 MAP kinase pathway composed of the dual leucine zipper-bearing MAPKKK DLK-1, the MAPKK MKK-4, and the p38 MAP kinase PMK-3. Inactivation of this pathway suppresses rpm-1 loss of function phenotypes, whereas overexpression or constitutive activation of this pathway causes synaptic defects resembling rpm-1(lf) mutants. DLK-1, like RPM-1, is localized to the periactive zone. DLK-1 protein levels are elevated in rpm-1 mutants. The RPM-1 RING finger can stimulate ubiquitination of DLK-1. Our data reveal a presynaptic role of a previously unknown p38 MAP kinase cascade.

Animals↗

PubMed2004

Neurosurgery: functional regeneration after laser axotomy.

Understanding how nerves regenerate is an important step towards developing treatments for human neurological disease, but investigation has so far been limited to complex organisms (mouse and zebrafish) in the absence of precision techniques for severing axons (axotomy). Here we use femtosecond laser surgery for axotomy in the roundworm Caenorhabditis elegans and show that these axons functionally regenerate after the operation. Application of this precise surgical technique should enable nerve regeneration to be studied in vivo in its most evolutionarily simple form.

Animals↗

PubMed2004

The Caenorhabditis elegans UNC-14 RUN domain protein binds to the kinesin-1 and UNC-16 complex and regulates synaptic vesicle localization.

Kinesin-1 is a heterotetramer composed of kinesin heavy chain (KHC) and kinesin light chain (KLC). The Caenorhabditis elegans genome has a single KHC, encoded by the unc-116 gene, and two KLCs, encoded by the klc-1 and klc-2 genes. We show here that UNC-116/KHC and KLC-2 form a complex orthologous to conventional kinesin-1. KLC-2 also binds UNC-16, the C. elegans JIP3/JSAP1 JNK-signaling scaffold protein, and the UNC-14 RUN domain protein. The localization of UNC-16 and UNC-14 depends on kinesin-1 (UNC-116 and KLC-2). Furthermore, mutations in unc-16, klc-2, unc-116, and unc-14 all alter the localization of cargos containing synaptic vesicle markers. Double mutant analysis is consistent with these four genes functioning in the same pathway. Our data support a model whereby UNC-16 and UNC-14 function together as kinesin-1 cargos and regulators for the transport or localization of synaptic vesicle components.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Intermediate filaments are required for C. elegans epidermal elongation.

Cytoplasmic intermediate filaments (cIFs) are thought to provide mechanical strength to vertebrate cells; however, their function in invertebrates has been largely unexplored. The Caenorhabditis elegans genome encodes multiple cIFs. The C. elegans ifb-1 locus encodes two cIF isoforms, IFB-1A and IFB-1B, that differ in their head domains. We show that both IFB-1 isoforms are expressed in epidermal cells, within which they are localized to muscle-epidermal attachment structures. Reduction in IFB-1A function by mutation or RNA interference (RNAi) causes epidermal fragility, abnormal epidermal morphogenesis, and muscle detachment, consistent with IFB-1A providing mechanical strength to epidermal attachment structures. Reduction in IFB-1B function causes morphogenetic defects and defective outgrowth of the excretory cell. Reduction in function of both IFB-1 isoforms results in embryonic arrest due to muscle detachment and failure in epidermal cell elongation at the 2-fold stage. Two other cIFs, IFA-2 and IFA-3, are expressed in epidermal cells. We show that loss of function in IFA-3 results in defects in morphogenesis indistinguishable from those of embryos lacking ifb-1. In contrast, IFA-2 is not required for embryonic morphogenesis. Our data indicate that IFB-1 and IFA-3 are likely the major cIF isoforms in embryonic epidermal attachment structures.

Animals↗

PubMed2004

Presynaptic terminal differentiation: transport and assembly.

The formation of chemical synapses involves reciprocal induction and independent assembly of pre- and postsynaptic structures. The major events in presynaptic terminal differentiation are the formation of the active zone and the clustering of synaptic vesicles. A number of proteins that are present in the presynaptic active zone have been identified. Recent studies of various mutants have clarified the in vivo functions of some of the main players. Time-lapse imaging studies have captured dynamic and transient events in the transport of synaptic components, and therefore provided insight into the early stages of synaptogenesis.

Animals↗

PubMed2004

Genetic analysis of synaptic target recognition and assembly.

Formation of synapses by neurons onto specific targets is essential to the function of a nervous system. The isolation and analysis of Caenorhabditis elegans and Drosophila mutants with synaptogenesis defects has provided insight into the functions of evolutionarily conserved molecules at single-synapse resolution. Importantly, such studies have uncovered novel molecules and signaling mechanisms. Here, recent progress on synaptic target recognition and synaptic assembly are reviewed.

Animals↗

PubMed2004

The AHR-1 aryl hydrocarbon receptor and its co-factor the AHA-1 aryl hydrocarbon receptor nuclear translocator specify GABAergic neuron cell fate in C. elegans.

The aryl hydrocarbon receptors (AHR) are bHLH-PAS domain containing transcription factors. In mammals, they mediate responses to environmental toxins such as 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). Such functions of AHRs require a cofactor, the aryl hydrocarbon receptor nuclear translocator (ARNT), and the cytoplasmic chaperonins HSP90 and XAP2. AHR homologs have been identified throughout the animal kingdom. We report here that the C. elegans orthologs of AHR and ARNT, ahr-1 and aha-1, regulate GABAergic motor neuron fate specification. Four C. elegans neurons known as RMED, RMEV, RMEL and RMER express the neurotransmitter GABA and control head muscle movements. ahr-1 is expressed in RMEL and RMER neurons. Loss of function in ahr-1 causes RMEL and RMER neurons to adopt a RMED/RMEV-like fate, whereas the ectopic expression of ahr-1 in RMED and RMEV neurons can transform them into RMEL/RMER-like neurons. This function of ahr-1 requires aha-1, but not daf-21/hsp90. Our results demonstrate that C. elegans ahr-1 functions as a cell-type specific determinant. This study further supports the notion that the ancestral role of the AHR proteins is in regulating cellular differentiation in animal development.

Animals↗

PubMed2003

C. elegans ankyrin repeat protein VAB-19 is a component of epidermal attachment structures and is essential for epidermal morphogenesis.

Elongation of the epidermis of the nematode Caenorhabditis elegans involves both actomyosin-mediated changes in lateral epidermal cell shape and body muscle attachment to dorsal and ventral epidermal cells via intermediate-filament/hemidesmosome structures. vab-19 mutants are defective in epidermal elongation and muscle attachment to the epidermis. VAB-19 is a member of a conserved family of ankyrin repeat-containing proteins that includes the human tumor suppressor Kank. In epidermal cells, VAB-19::GFP localizes with components of epidermal attachment structures. In vab-19 mutants, epidermal attachment structures form normally but do not remain localized to muscle-adjacent regions of the epidermis. VAB-19 localization requires function of the transmembrane attachment structure component Myotactin. vab-19 mutants also display aberrant actin organization in the epidermis. Loss of function in the spectrin SMA-1 partly bypasses the requirement for VAB-19 in elongation, suggesting that VAB-19 and SMA-1/spectrin might play antagonistic roles in regulation of the actin cytoskeleton.

Actins↗

PubMed2003

The basement membrane components nidogen and type XVIII collagen regulate organization of neuromuscular junctions in Caenorhabditis elegans.

Vertebrate neuromuscular junctions (NMJs) contain specialized basal laminas enriched for proteins not found at high concentrations extrasynaptically. Alterations in NMJ basement membrane components can result in loss of NMJ structural integrity and lead to muscular dystrophies. We demonstrate here that the conserved Caenorhabditis elegans basement membrane-associated molecules nidogen/entactin (NID-1) and type XVIII collagen (CLE-1) are associated with axons and particularly enriched near synaptic contacts. NID-1 is concentrated laterally, between the nerve cord and muscles, whereas CLE-1 is concentrated dorsal to the ventral nerve cord and ventral to the dorsal nerve cord, above the regions where synapses form. Mutations in these molecules cause specific and distinct defects in the organization of neuromuscular junctions. The mutant animals exhibit mild movement defects and altered responses to an inhibitor of acetylcholinesterase and a cholinergic agonist, indicating altered synaptic function. Our results provide the first demonstration that basement membrane molecules are important for NMJ formation and/or maintenance in C. elegans and that collagen XVIII and nidogen can have important roles in synapse organization.

Alleles↗

PubMed2003

UNC-71, a disintegrin and metalloprotease (ADAM) protein, regulates motor axon guidance and sex myoblast migration in C. elegans.

The migration of cells and growth cones is a process that is guided by extracellular cues and requires the controlled remodeling of the extracellular matrix along the migratory path. The ADAM proteins are important regulators of cellular adhesion and recognition because they can combine regulated proteolysis with modulation of cell adhesion. We report that the C. elegans gene unc-71 encodes a unique ADAM with an inactive metalloprotease domain. Loss-of-function mutations in unc-71 cause distinct defects in motor axon guidance and sex myoblast migration. Many unc-71 mutations affect the disintegrin and the cysteine-rich domains, supporting a major function of unc-71 in cell adhesion. UNC-71 appears to be expressed in a selected set of cells. Genetic mosaic analysis and tissue-specific expression studies indicate that unc-71 acts in a cell non-autonomous manner for both motor axon guidance and sex myoblast migration. Finally, double mutant analysis of unc-71 with other axon guidance signaling molecules suggests that UNC-71 probably functions in a combinatorial manner with integrins and UNC-6/netrin to provide distinct axon guidance cues at specific choice points for motoneurons.

Alleles↗

PubMed2002

MAX-1, a novel PH/MyTH4/FERM domain cytoplasmic protein implicated in netrin-mediated axon repulsion.

The netrin UNC-6 repels motor axons by activating the UNC-5 receptor alone or in combination with the UNC-40/DCC receptor. In a genetic screen for C. elegans mutants exhibiting partial defects in motor axon projections, we isolated the max-1 gene (required for motor neuron axon guidance). max-1 loss-of-function mutations cause fully penetrant but variable axon guidance defects. Mutations in unc-5 and unc-6, but not in unc-40, dominantly enhance the mutant phenotypes of max-1, whereas overexpression of unc-5 or unc-6, but not of unc-40, bypasses the requirement for max-1. MAX-1 proteins contain PH, MyTH4, and FERM domains and appear to be localized to neuronal processes. Human MAX-1 and UNC5H2 colocalize in discrete subcellular regions of transfected cells. Our results suggest a possible role for MAX-1 in netrin-induced axon repulsion by modulating the UNC-5 receptor signaling pathway.

Amino Acid Sequence↗

PubMed2002

Getting a GRIP on liprins.

Two papers in this issue of Neuron add a new dimension to our understanding of liprin and LAR RPTP function during synapse formation. present evidence that Dliprin-alpha interacts with Dlar to regulate presynaptic morphogenesis of the Drosophila neuromuscular junction. demonstrate that mammalian liprin-alpha1 forms a complex with the PDZ protein GRIP and LAR in both pre- and postsynaptic compartments of hippocampal neurons and is required for the clustering of the GluR2 glutamate receptor in dendritic spines.

Animals↗