Meng L et al. (2020) Dev Cell "NLR-1/CASPR Anchors F-Actin to Promote Gap Junction Formation."

Yan D, Meng L

[Dev Cell, 2020]

Gap junctions are present in most tissues and play essential roles in various biological processes. However, we know surprisingly little about the molecular mechanisms underlying gap junction formation. Here, we uncover the essential role of a conserved EGF- and laminin-G-domain-containing protein nlr-1/CASPR in the regulation of gap junction formation in multiple tissues across different developmental stages in C.elegans. NLR-1 is located in the gap junction perinexus, a region adjacent to but not overlapping with gap junctions, and forms puncta before the clusters of gap junction channels appear on the membrane. We show that NLR-1 can directly bind to actin to recruit F-actin networks at the gap junction formation plaque, and the formation of F-actin patches plays a critical role in the assembly of gap junction channels. Our findings demonstrate that nlr-1/CASPR acts as an early stage signal for gap junction formation through anchoring of F-actin networks.

Meng L et al. (2013) J Genet Genomics "Roles of microRNAs in the Caenorhabditis elegans nervous system."

Chen L, Li Z, Wu ZX, Meng L, Shan G

[J Genet Genomics, 2013]

The first microRNA was discovered in Caenorhabditis elegans in 1993, and since then, thousands of microRNAs have been identified from almost all eukaryotic organisms examined. MicroRNAs function in many biological events such as cell fate determination, metabolism, apoptosis, and carcinogenesis. So far, more than 250 microRNAs have been identified in C. elegans; however, functions for most of these microRNAs are still unknown. A small number of C. elegans microRNAs are associated with known physiological roles such as developmental timing, cell differentiation, stress response, and longevity. In this review, we summarize known roles of microRNAs in neuronal differentiation and function of C. elegans, and discuss interesting perspectives for future studies.

Meng L et al. (2016) Elife "Regulation of Neuronal Axon Specification by Glia-Neuron Gap Junctions in C. elegans."

Meng L, Jin Y, Zhang A, Yan D

[Elife, 2016]

Axon specification is a critical step in neuronal development, and the function of glial cells in this process is not fully understood. Here we show that C. elegans GLR glial cells regulate axon specification of their nearby GABAergic RME neurons through GLR-RME gap junctions. Disruption of GLR-RME gap junctions causes misaccumulation of axonal markers in non-axonal neurites of RME neurons and converts microtubules in those neurites to form an axon-like assembly. We further uncover that GLR-RME gap junctions regulate RME axon specification through activation of the CDK-5 pathway in a calcium-dependent manner, involving a calpain clp-4. Therefore, our study reveals the function of glia-neuron gap junctions in neuronal axon specification and shows that calcium originated from glial cells can regulate neuronal intracellular pathways through gap junctions.

Meng, L. et al. (2015) International Worm Meeting "Glial cells instruct neuronal polarity through gap junctions."

Yan, D., Jin, Y., Wan, A., Meng, L.

[International Worm Meeting, 2015]

Glial cells function in diverse aspects of neuronal development and plasticity. Gap junctions also play multiple roles in the nervous system. However the functions of neuron-glia gap junctions in neuronal polarity have not been explored. Here we showed that gap junctions between C. elegans GLR glial cells and RME neurons were required for establishment of RME neuronal polarity. In a genetic screen for RME neuronal circuit formation, we found that loss-of-function in a gap junction regulator, unc-1, induce strong polarity defects. Gap junctions in C. elegans are composed by innexins, two of which unc-7 and unc-9 are expressed in RME neurons. We found that unc-7 unc-9 double mutants displayed similar phenotype as unc-1, suggesting that gap junctions were required for the establishment of RME neuronal polarity. Furthermore, our rescue experiments showed that unc-1 and unc-7 were required in both RME neurons and GLR glial cells, indicating the RME-GLR gap junctions were important for RME polarity. Since microtubule polarity plays a fundamental role in neuronal polarity, we further examined the role of RME-GLR gap junctions in regulation of microtubules using EBP-2::GFP reporter. We found that microtubules orientations were almost evenly mixed in RME dendrites in control animals, but the majority of microtubules were plus-end out cell body in RME dendrites in gap junction mutants. Consistent with this finding, loss-of-function in the minus-end to plus-end motor protein unc-104 was able to suppress the polarity defects in gap junction mutants. In C. elegans, several signal pathways have been reported to regulate microtubule polarity, including the P35-CDK-5 pathway. We found that loss-of-function in each members of the P35-CDK-5 pathway induced similar polarity defects in RME neurons. Double mutants of cdk-5 and unc-7 neither enhanced nor suppressed single mutant phenotypes, suggesting the CDK-5 pathway might function in the gap junction pathway. Previous study showed that the cleavage of P35 was essential for the activation of the P35-CDK-5 pathway. If gap junctions function through the P35-CDK-5 pathway, disruption of gap junctions should affect the cleavage of P35. Indeed, we found the cleavage of P35 was nearly undetectable in gap junction mutants. Furthermore, overexpression of the active version of P35, P25, was able to suppress unc-1 phenotypes. These data suggested that RME-GLR gap junctions functioned through P35-CDK-5 pathway to regulate microtubule polarity. In summary, our study described the role of neuron-glia gap junctions in vivo, and provided a novel mechanism for neuronal polarity, that glial cells directly form gap junctions with neurons to regulate neuronal intracellular pathways.

Meng L et al. (2016) PLoS Genet "Regulation of Gap Junction Dynamics by UNC-44/ankyrin and UNC-33/CRMP through VAB-8 in C. elegans Neurons."

Chen CH, Meng L, Yan D

[PLoS Genet, 2016]

Gap junctions are present in both vertebrates and invertebrates from nematodes to mammals. Although the importance of gap junctions has been documented in many biological processes, the molecular mechanisms underlying gap junction dynamics remain unclear. Here, using the C. elegans PLM neurons as a model, we show that UNC-44/ankyrin acts upstream of UNC-33/CRMP in regulation of a potential kinesin VAB-8 to control gap junction dynamics, and loss-of-function in the UNC-44/UNC-33/VAB-8 pathway suppresses the turnover of gap junction channels. Therefore, we first show a signal pathway including ankyrin, CRMP, and kinesin in regulating gap junctions.

Meng L et al. (2015) Cell Rep "The Cell Death Pathway Regulates Synapse Elimination through Cleavage of Gelsolin in Caenorhabditis elegans Neurons."

Cook SJ, Yan D, Meng L, Mulcahy B, Neubauer M, Wan A, Jin Y

[Cell Rep, 2015]

Synapse elimination occurs in development, plasticity, and disease. Although the importance of synapse elimination has been documented in many studies, the molecular mechanisms underlying this process are unclear. Here, using the development of C. elegans RME neurons as a model, we have uncovered a function for the apoptosis pathway in synapse elimination. We find that the conserved apoptotic cell death (CED) pathway and axonal mitochondria are required for the elimination of transiently formed clusters of presynaptic components in RME neurons. This function of the CED pathway involves the activation of the actin-filament-severing protein, GSNL-1. Furthermore, we show that caspase CED-3 cleaves GSNL-1 at a conserved C-terminal region and that the cleaved active form of GSNL-1 promotes its actin-severing ability. Our data suggest that activation of the CED pathway contributes to selective elimination of synapses through disassembly of the actin filament network.

Hunter CP et al. (1991) International C. elegans Meeting "NON-AUTONOMY OF HER-1 FUNCTION IMPLICATES CELL INTERACTIONS IN C. ELEGANS SEX DETERMINATION."

Hunter CP, Wood WB

[International C. elegans Meeting, 1991]

Activity of the her-l gene is required for normal male development in C. elegans. Loss-of-function her-l mutations cause feminization of XO animals (normally male) to produce fertile hermaphrodites, while gain-of-function her-l mutations cause masculinization of XX animals ( normally hermaphrodite) to produce pseudo-males. Genetic analysis indicated that her-l functions early in the hierarchy of regulatory interactions among the major sex determination genes (1). We have analyzed her-l genetic mosaics to determine which cells must express her-l for wild-type male development. If her-l functions cell- autonomously, then in XO animals her-l (+) cells will follow male fates, and her-1(-) cells will follow hermaphrodite fates. If her-l or a her-l regulated activity functions non-autonomously, then the her-l genotype of a cell may not determine its sexual phenotype. The phenotypes of XO her-l genetic mosaics are variable, but clearly show that both her-1(-) and her-l (+) cells can follow either hermaphrodite or male fates. We conclude that her-l is neither necessary nor sufficient to cell-autonomously determine male sexual phenotypes and, therefore, that her-l or a her-l regulated activity must be able to function non-autonomously. The observed patterns of non-autonomous effects suggest that many or all cells express and respond to her-l activity. These findings implicate cell interactions in C. elegans sex determination. Earlier genetic analysis indicated that her-l might directly control tra-2 activity (1). Molecular characterization of the gene products of her-l and tra-2 (see abstracts by M. Perry et al. and P. Kuwabara et al) is consistent with a model in which a secreted ligand encoded by her-l interacts with a cell-surface receptor encoded by tra-2. We will discuss the possible role of such an interaction in coordinating the sex determination decision.

Forrester S et al. (2007) Foodborne Pathog Dis "Evaluation of the pathogenicity of Listeria spp. in Caenorhabditis elegans."

Schwab U, Wiedmann M, Hoose WA, Milillo SR, Forrester S

[Foodborne Pathog Dis, 2007]

Caenorhabditis has proven to be a useful model for studying host-pathogen interactions as well as the ability of nematodes to serve as vectors for the dispersal of foodborne pathogens. In this study, we evaluated whether C. elegans can serve as a host for Listeria spp. While there was an effect of growth media on C. elegans killing, C. elegans exposed to L. monocytogenes and L. innocua pregrown in Luria-Bertani medium showed reduced survival when compared to nonpathogenic E. coli OP50, while L. seeligeri showed survival similar to E. coli OP50. In a preference assay, C. elegans preferred E. coli over L. monocytogenes and L. innocua, but showed no preference between L. monocytogenes and L. innocua. A gentamicin assay indicated that L. monocytogenes did not persist within the C. elegans intestinal tract. Our findings that L. monocytogenes and L. innocua strains tested have equally deleterious effects on C. elegans and that L. monocytogenes did not establish intestinal infection conflict with other recently published results, which found intestinal infection and killing of C. elegans by L. monocytogenes. Further studies are thus needed to clarify the interactions between L. monocytogenes and C. elegans, including effects of environmental conditions and strain differences on killing and intestinal infection.

Kenyon CJ et al. (1994) Worm Breeder's Gazette "A polyray Suppressor"

Kenyon CJ, Maloof JN

[Worm Breeder's Gazette, 1994]

A polyray-l suppressor Julin Maloof and Cynthia Kenyon, Dept of Biochemistry, U.C.S.F, San Francisco, CA 94143 The polyray-l (pry-l) gene is required to keep homeotic selector (HOM-C) genes repressed where their expression has not been initiated (see accompanying abstract and WBG 12(5):39). pry-l mutant worms have numerous homeotic transformations and are very sick, so we were intrigued by a plate of pry-l mutant worms which appeared much healthier than normal. I outcrossed the strain and found F2s with the full pry-l mutant phenotype, suggesting that the "healthy" strain contained both pry-l and an extragenic suppressor. Does the suppressor have a phenotype on its own? Since pry-l causes homeotic transformations due to ectopic HOM-C expression, it seemed possible that the suppressor would cause transformations in the opposite direction, similar to those seen in HOM-C loss of function mutants. Indeed some F2s from the outcross had descendants of the QL neuroblast in the anterior of the worms, a phenotype also caused by loss-of function mutations in the HOM-C gene mab-5. We are calling this newly identified gene spy-l for suppressor of polyray-l. spy-l seems to suppress all of the pry-l mutant-phenotypes: pry-l; spy-l double mutant worms do not have extra rays, are no longer Muv, are not Unc, and have anteriorly placed QR descendants. spy-l could suppress pry-l either by preventing ectopic HOM-C expression, or by preventing ectopically expressed HOM-C genes from having any effect. mab-5-lacZ expression was examined and found to be normal in the p1y-l; spy-l double, so wild-type spy-l is required for the ectopic HOM-C expression seen in pry-l mutant animals. The fact that there is a QL migration defect in worms mutant for spy-l alone suggests that spy-l may normally be required to turn on mab-5 in QL. We compared expression of mab-5-lacZ in wild- type and spy-l mutant worms at 3.5-5 hours and at 8-10 hours after hatching. At 3.5-5 hours 100% (n=20) of the mutant and 95% (n=20) of the wild-type worms had expression in QL. At 8- 10 hours 0% (n=30) of the mutant worms has expression of mab- 5 in the descendants of QL, but 87% (n=30) of the wild-type worms showed expression. It appears that spy-l is not required to initiate mab-5 expression in QL, but that it is required to maintain expression once it is initiated. It is possible that spy-l is required to maintain the ON state of a number of HOM-C genes, in a manner analogous to the brahma and trithorax genes of Drosophila. spy-l is located on X, in a region well covered by cosmids. Hopefully a molecular analysis of spy-l along with the isolation and study of more spy-l alleles will enable us to determine how similar the C. elegans and Drosophila maintenance systems are, and how spy-l and other maintenance genes are used to maintain and specify pattern.

Ellis RE et al. (1991) International C. elegans Meeting "PROGRESS IN CLONING fog- 1"

Kimble JE, Ellis RE

[International C. elegans Meeting, 1991]

The fog-l gene plays an important role in the decision of germ cells to differentiate as either spermatocytes or oocytes (Doniach 1986, Barton and Kimble 1990). In fog-l mutants, all germ cells develop into oocytes. This is true for both males and hermaphrodites. However, these fog-l mutations do not appear to affect other aspects of sexual development. Furthermore, the fog-l mutant phenotype is not suppressed by mutations in any of the other genes known to control sex- determination. Thus fog-l might function to initiate spermatogenesis in response to other genes that regulate general sexdetermination. There are 42 fog-l mutations. These mutations arise at a frequency typical for knockout mutations in other C. elegans genes, and four of these fog-l alleles were isolated from a screen capable of recovering deletions. Thus it is likely that these mutations cause a loss of fog- l function. In order to study the mechanisms by which fog-l functions, and to determine how fog-l expression is regulated by the genes that control sex-determination, we are now cloning this gene. The fog-l gene is located on the left arm of LGI, between sup-ll and unc-ll, a region spanned by a large contig of about one megabase in size. By mapping DNA polymorphisms with respect to fog-l, we have narrowed down the region in which fog-l must be located, and are now injecting YAC DNA that covers this region in an attempt to rescue fog-l mutants.