Sato, H. et al. (2017) International Worm Meeting "A gustatory neural circuit for experience-dependent behavioral plasticity."

Sato, H., Kunitomo, H., Hashimoto, K., Iino, Y., Fei, X.

[International Worm Meeting, 2017]

Most animals show experience-dependent behavioral plasticity in response to taste cues. C. elegans is known to memorize the particular concentraion of salt (sodium chloride) at which it is cultivated and keeps approaching the memorized concentration. In this study, we searched for the neural circuit required for the memory of salt concentration. We investigated the relationship between the neural response and locomotion of worms. We used a tracking-imaging system with microfluidic arena that allowed worms to crawl in a controlled liquid environment, and simultaneously recorded neural responses and locomotion of worms. First, we focused on the salt-sensing chemosensory neuron ASER and its downstream neurons AIB and RIM. Worms showed reversal behavior only when the salt concentration changed away from the cultivation concentration. On the other hand, the responses of ASER always correlated with the sensory input, and the responses of AIB and RIM neurons correlated with the behavioral output. Therefore, it seems that the modulation of experience-dependent salt chemotaxis occurs, at least in part, in the neural circuit ASER-AIB-RIM, and the sensory information is processed and converted to the behavioral output between the sensory neuron and the interneurons. Next, to determine whether the input from ASER neuron is sufficient for the observed response of AIB and its changes, we used cell-specific rescue of sensory functions. In these experiments, we used the dyf-11 mutants. DYF-11 is required for formation and maintenance of ciliary segments in sensory neurons and thus dyf-11 mutants show defects in salt perception. We simultaneously monitored the velocity of worms and the calcium response of AIB in dyf-11 mutant in which ASER was solely rescued. Upon both increase and decrease of salt concenration, these worms showed almost the same response as the wild type. These results indicate that inputs from ASER generate and modulate AIB response and the behavior of worms in an experience-dependent manner.

Sato, H. et al. (2013) International Worm Meeting "A gustatory neural circuit for salt concentration memory in Caenorhabditis elegans."

Kunitomo, H., Sato, H., Oda, S., Iino, Y.

[International Worm Meeting, 2013]

Caenorhabditis elegans is able to memorize a salt concentration. However, little is known about how worms form memory and how they modulate their behaviors on the basis of the memory. To answer the question, we first monitored the activity of the salt-sensing chemosensory neuron ASER by calcium imaging. We found that ASER changed the magnitude of its responses depending on previously exposed salt concentrations. We then investigated the response of ASER in two mutants, which are defective in the release of either synaptic vesicles or dense-core vesicles. In both mutants, the changes of the amplitude of ASER responses were similar to the wild type. The results suggested that the plasticity of ASER response is independent of inputs from other neurons. Next, we investigated the activity of three interneurons; AIA, AIB, and AIY. These neurons are postsynaptic neurons of ASER. We found that AIB and AIY changed their responses depending on the salt concentration at which the worms had been cultivated. On the other hand, the response of AIA did not significantly change depending on the past experience. To determine whether the sensory input to ASER is sufficient for the change of AIB responses, we used cell-specific rescue of sensory functions, and the results indicated that ASER can in fact drive the change of AIB responses. Furthermore, to assess the contribution of the three interneurons to the behavior, we investigated behavioral responses of worms whose interneurons were genetically ablated individually. Although the worms showed normal salt chemotaxis, their reversal frequency was different from that of the wild type. Therefore, each of these interneurons contributes to the regulation of reversal behavior, but there are redundancies in the neural circuit for salt responses. These results provide deeper understandings into the mechanisms for making the salt concentration memory and modulating the animal's behavior.

Sato, H. et al. (2019) International Worm Meeting "Neural dynamics for bidirectional regulation of experience-dependent gustatory behavior."

Fei, X., Iino, Y., Sato, H., Kunitomo, H., Hashimoto, K.

[International Worm Meeting, 2019]

Most animals memorize environmental cues and change their behavior based on the memory. C. elegans shows this sort of response to NaCl by memorizing and moving towards particular salt concentrations at which they were cultivated. In this study, we identified a specific neural circuit and its dynamics required for salt concentration memory. We investigated the relationship between the locomotory behavior and the response of salt-sensing neural circuit. Animals responded to salt stimuli by changing their turning frequency depending on the difference of salt concentrations between current stimulus and previous cultivation: salt-concentration decrease induced turning after cultivation at a salt concentration higher than the stimulus, whereas salt-concentration increase induced turning after cultivation at a salt concentration lower than the stimulus. With regard to the neural response, we focused on the salt chemosensory neuron ASER and its downstream neurons, AIB, RIM, and AVA. The response of ASER always correlated with sensory input: it was activated by salt concentration decrease irrespective of cultivation conditions. On the other hand, the responses of downstream neurons correlated well with the behavioral output. These results indicate that the neural circuit ASER-AIB-RIM-AVA modulates experience-dependent salt chemotaxis, and the sensory information is processed and converted to a behavioral decision at the level between the sensory neuron and the interneurons. Cell-specific rescue of sensory function demonstrated that input from ASER generates the bidirectional AIB response as well as the behavior of worms. Furthermore, we revealed that glutamate signaling from ASER to AIB is necessary for generating responses to both increase and decrease in ambient salt concentration. There are several sets of interneurons other than AIB that act downstream of ASER. These neurons may play modulatory roles in the transmission from ASER to AIB. Therefore, we genetically ablated AIA and AIY, and monitored the responses of AIB as well as the behavior of the worms. These worms showed attenuated response to salt concentration decrease, but showed almost no response to salt concentration increase, indicating that AIA and AIY are involved in the responsivity of AIB.

Dana L. Miller et al. (2007) International Worm Meeting "Adaptation to hydrogen sulfide increases thermotolerance and lifespan."

Mark B. Roth, Dana L. Miller

[International Worm Meeting, 2007]

Hydrogen sulfide (H₂S), which is naturally produced in animal cells, has been shown to effect physiological changes that improve the capacity of mammals to survive environmental changes. We have investigated the physiological response of C. elegans to H₂S to begin to elucidate the molecular mechanisms of H₂S action. We show that nematodes exposed to H₂S are apparently healthy and do not exhibit phenotypes consistent with metabolic inhibition. However, we observed that animals exposed to H₂S had increased thermotolerance and lifespan and survived subsequent exposure to otherwise lethal concentrations of H₂S. Increased thermotolerance and lifespan is not observed in the sir-2.1(ok434) deletion mutant exposed to H₂S. However, mutants in the insulin signaling pathway (both daf-2 and daf-16), animals with mitochondrial dysfunction (isp-1 and clk-1) and a genetic model of caloric restriction (eat-2) all exhibit H₂S-induced increased thermotolerance. These data suggest that H₂S activates a pathway including SIR-2.1 that is separate from dietary restriction and insulin signaling that results in increased lifespan. Moreover, these studies suggest that SIR-2.1 activity may translate environmental change into physiological alterations that improve survival. It is interesting to consider the possibility that the mechanisms by which H₂S increases thermotolerance and lifespan in nematodes are conserved, and that studies using C. elegans may help explain beneficial effects observed in mammals exposed to H₂S.

Abergel, Z. et al. (2017) International Worm Meeting "Adaptation of the nematode C. elegans to hypoxia and reoxygenation stress reveals an unexpected function of the neuroglobin GLB-5 in innate immunity."

Zuckerman, B., Zelmanovich, V., Abergel, Z., Abergel, R., Gross, E., Smith, Y., Romero, L., Livshits, L.

[International Worm Meeting, 2017]

Deprivation of oxygen (hypoxia) followed by reoxygenation (H/R stress) is a major component in several pathological conditions such as vascular inflammation, myocardial ischemia, and stroke. However how animals adapt and recover from H/R stress remains an open question. Previous studies showed that the neuroglobin GLB-5(Haw) is essential for the fast recovery of the nematode Caenorhabditis elegans (C. elegans) from H/R stress. Here, we characterize the changes in neuronal gene expression during the adaptation of worms to hypoxia and recovery from H/R stress. Our analysis shows that innate immunity genes are differentially expressed during both adaptation to hypoxia and recovery from reoxygenation stress. Moreover, we reveal that the prolyl hydroxylase EGL-9, a known regulator of both adaptation to hypoxia and the innate immune response, inhibits the fast recovery from H/R stress through its activity in the O2-sensing neurons AQR, PQR, and URX. Finally, we show that GLB-5(Haw) acts in AQR, PQR, and URX to increase the tolerance of worms to bacterial pathogenesis. Together, our studies suggest that innate immunity and recovery from H/R stress are regulated by overlapping signaling pathways.

Rasika Kalamegham et al. (2004) East Coast Worm Meeting "EGL-26 belongs to the NlpC/P60 superfamily of putative enzymes and is closely related to a mammalian acyl transferase"

Wendy Hanna-Rose, Rasika Kalamegham

[East Coast Worm Meeting, 2004]

egl-26 was identified in a genetic screen to uncover mutants with vulval morphology defects. In egl-26 mutants the morphology of a single vulval toroid (vulF) is abnormal and a proper connection to the uterus is not made leading to the egg-laying defect. EGL-26 is a member of the NlpC/P60 superfamily of enzymes, which is characterized by a Histidine containing domain and a Cysteine containing domain (H-box and NC domain, respectively). EGL-26 along with other eukaryotic proteins belongs to a distinct subclass of NlpC/P60-related putative enzymes. The mammalian proteins lecithin: retinol acyltransferase or LRAT and H-ras revertant 107 or H-Rev107 are the most closely related to EGL-26. Both LRAT and H-Rev107 contain putative transmembrane domains in addition to the H-box and NC domains. Although EGL-26 contains no putative transmembrane domains, it is localized at the apical membrane of cells where it is expressed. Proper localization of LRAT within the retinal pigment epithelium is essential for its function. Significantly, an S-F substitution at amino acid 275 of EGL-26 found in the egl-26 (n481) allele causes mislocalization of an EGL-26::GFP fusion leading to general cytoplasmic expression as opposed to normal apical membrane localization. The corresponding Serine residue is conserved in both LRAT and H-Rev107. We are attempting to analyze the relationship between the mammalian proteins and EGL-26 by attempting a rescue of egl-26 mutants by expression of either LRAT or H-Rev107 or both. We plan to test the importance of membrane localization by restoring membrane localization to EGL-26n481 via addition of alternative membrane localization signals.

Schwartz, Hillel et al. (2013) International Worm Meeting "Developing Heterorhabditis nematodes as an experimental system for the study of mutualistic symbiosis."

Schwartz, Hillel, Sternberg, Paul

[International Worm Meeting, 2013]

Entomopathogenic nematodes of the genus Heterorhabditis are insect killers that live in mutually beneficial symbiosis with pathogenic Photorhabdus bacteria. Photorhabdus is rapidly lethal to insects and to other nematodes, including C. elegans, but is required for Heterorhabditis growth in culture and for the insect-killing that defines the entomopathogenic lifestyle. The symbiosis between Heterorhabditis and Photorhabdus offers the potential to study the molecular genetic basis of their cooperative relationship. We developing tools to make such studies more feasible: we have been studying multiple nematodes of the genus Heterorhabditis and developing tools for the molecular genetic analysis of Heterorhabditis bacteriophora. Many species of Heterorhabditis and variants of Photorhabdus have been isolated; some pairings show specificity in their ability to establish a symbiotic relationship. To better understand these interactions and other variations in the lifestyles of Heterorhabditis, we have sequenced H. indica, H. megidis, H. sonorensis, and H. zealandica; a H. bacteriophora genome sequence is available. A comparison of these closely related species may help us to identify mechanisms that regulate the response to bacterial interactions and to find variations that correlate with differences in lifestyle or bacterial compatibility. In addition to genomics, we are developing H. bacteriophora as a laboratory organism. H. bacteriophora grows well on plates, has been reported to be susceptible to RNAi and transgenesis, and can develop as a selfing hermaphrodite, and so should be a powerful system for the molecular genetic study of the aspects of biology to which it is uniquely well suited, most prominently symbiosis. This potential is severely diminished by inconvenient sex determination: the self-progeny of hermaphrodites are mostly females with some males; at low density, their progeny are almost exclusively females. We have screened for and isolated a constitutively hermaphroditic mutant for use in molecular genetic studies of symbiosis. This mutant also offers the opportunity to explore the basis of hermaphrodite sex determination in H. bacteriophora.

Schwartz H et al. (2010) Aging, Metabolism, Stress, Pathogenesis, and Small RNAs, Madison, WI "Towards a SNP map for Heterorhabditis bacteriophora"

Sternberg P, Schwartz H

[Aging, Metabolism, Stress, Pathogenesis, and Small RNAs, Madison, WI, 2010]

Heterorhabditis bacteriophora is a species of insect-parasitic nematode that lives in mutually beneficial symbiosis with pathogenic Photorhabdus luminescens bacteria. P. luminescens bacteria are lethal to insects and to other nematodes, including the soil nematode Caenorhabditis elegans, but are required for H. bacteriophora growth. The symbiosis between H. bacteriophora and P. luminescens therefore offers the potential to study the molecular genetic basis of their cooperative relationship. We are interested in developing tools to make such studies more feasible; in particular, we propose to generate tools for genetic mapping in H. bacteriophora. We will test independent isolates of H. bacteriophora to ensure that the isolates are cross-fertile. We will then examine the abilities of these isolates to grow on and to become infected with different wild-type and mutant Photorhabdus bacteria. From these tests we will select an isolate on which we will use next-generation high-throughput sequencing technology for the purpose of refining the existing draft genome sequence and for the creation of a SNP map. We anticipate that this SNP map will enable us and the wider insect-parasitic nematode community to identify induced mutations and natural variations affecting the interactions between H. bacteriophora nematodes and pathogenic Photorhabdus bacteria.

Chu, Yu-De et al. (2013) International Worm Meeting "An RNAi-based screen for the DExD/H-box RNA helicases involved in Caenorhabditis elegans microRNA function."

Chan, Shih-Peng, Chen, Shin-Kai, Chu, Yu-De, Chen, Guan-Rong, Huang, Tao

[International Worm Meeting, 2013]

MicroRNAs (miRNAs) are small non-coding regulatory RNAs that regulate gene expression at the post-transcriptional level and are involved in a broad spectrum of biological processes. Rearrangements of inter- or intra-molecular RNA structures and conformational changes of ribonucleoprotein complexes in the multiple processes of the miRNA pathway have led to the involvement of RNA helicase activities but little is known so far. In eukaryotes, RNA helicases generally belong to the superfamily 2 (SF2) in helicase classification, especially the DExD/H-box helicase family. The DExD/H-box proteins have been shown in association with many cellular processes involving RNA. To better understand the possible roles of DExD/H-box RNA helicases in miRNA function, we employed RNAi screen to identify genetic interaction between C. elegans DExD/H-box RNA helicases and the let-7 miRNA, which controls the timing of cell cycle exit and terminal differentiation. In addition to the RNA helicase p72, a component of Drosha Microprocessor complex, and CGH-1 that has been reported to facilitate the function of miRNA-induced silencing complex (miRISC), we found several DExD/H-box RNA helicases, which are involved in ribosomal RNA processing, pre-mRNA splicing and mRNA surveillance, may also take part in miRNA biogenesis and/or function. (Support: National Science Council, Taiwan. NSC 100-2311-B-002-006-MY3).

Alexandre Neves et al. (2006) Development & Evolution Meeting "A Notch-GATA Transcription Code for Endoderm-Specific Gene Activation in C.elegans"

James Priess, Alexandre Neves

[Development & Evolution Meeting, 2006]

Several Notch interactions occur in rapid succession during early C.elegans embryogenesis, each resulting in a distinct fate. We have previously shown that ref-1, a gene distantly related to Drosophila E(spl), is a direct Notch target in all these interactions. We show here that ref-1 expression is controlled by multiple, Notch-dependent enhancers that are specific for each interaction. We have identified a 150bp enhancer that is specific to Notch interactions in the endoderm, and found similar enhancers with the same activity in C.briggsae and C.remanei. The endoderm enhancer contains multiple, conserved binding sites for LAG-1/Su(H) and GATA transcription factors. We demonstrate that all LAG-1/Su(H) and GATA sites are required for full activity of this enhancer. We provide evidence that a GATA transcription factor called ELT-2 is a cooperative factor for Notch in the endoderm. Ectopic expression of ELT-2 in non-endodermal lineages caused activation of the endoderm enhancer only in Notch-signaled cells, suggesting that the presence of the cooperative factor dictates in which Notch interaction a Notch-dependent enhancer becomes responsive in vivo. Previous studies in Drosophila showed that synergy between Su(H) and the bHLH transcription factor Daughterless requires a specific configuration of Su(H) sites, known as a Su(H) paired site, SPS. The endoderm enhancer contains a putative SPS. However, we find that Notch-GATA synergy does not require a SPS, and instead requires a non-SPS configuration of oriented LAG-1/Su(H) sites. Thus, it appears that that each configuration couples Notch signaling with a specific class of transcription factor.