Lee, Harksun et al. (2011) International Worm Meeting "Neuronal Regulation of Nictation Behavior in Caenorhabditis elegans."

Kim, Hye-sung, Kim, Heekyeong, Park, Sungsu, Lee, Daehan, Lee, Junho, Hwang, Hyejin, Choi, Myung-kyu, Lee, Harksun, Paik, Young-Ki

[International Worm Meeting, 2011]

Many nematode species, including the free-living nematode Caenorhabditis elegans, exhibit an evolutionarily conserved, developmental stage-specific behavior called nictation, in which daurs stand and wave in three-dimensional loops on a projection. Here we show that nictation is necessary for nematode dispersal, which may be a critical survival strategy under harsh conditions. Using newly established assays for nictation. we showed that acetylcholine is the neurotransmitter required for nictation. By cell-type specific rescue experiments, we found that, among cholinergic neurons, IL2 head neurons were essential for nictation. Optogenetic activation of IL2 neurons using channelrhodopsin increased the nictation ratio and the genetic ablation of IL2 neurons abolished nictation. We also found the cilia structure of IL2 neurons was important for nictation by testing mutants that have defects in cilia structures. We finally demonstrated that nictation is required for transmission of dauers to a new niche using fruit flies as artificial carriers, suggesting a role of nictation as a dispersal and survival strategy under harsh conditions. We anticipate our data to be a starting point for further investigation into how external stimulus or conditions can evoke a specific responsive behavior via rewiring neural circuits at the cellular and molecular levels.

Harksun Lee et al. (2008) "Molecular genetics of nictation"

Hyesung Kim, Seunghee Nam, Junho Lee, Harksun Lee, Myungkyu Choi

[2008]

"When the food is limited or the population is too crowded, C. elegans enters an alternative stage called the dauer. The dauer larvae usually do not move and pharyngeal pumping is almost arrested. The dauer larvae show an unexpected behaviour, nictation. The dauer larvae climb up onto any projections and while standing by their posterior tip, wave in three-dimensional spirals and loops.(Croll, N.A., and Matthews, B. E., 1977, Biology of nematodes) This behaviour is not shown by animals at any other developmental stage. Although C. elegans is known as the free-living organism in the soil, many Caenorhapditis species associate with other species such as snails and insects. Nictation may be critical for transmission of nematodes to a new niche, and thus for their survival. It is known that there are specific neural circuits for specific behaviours such as forward and backward movements, thermotaxis and chemotaxis. The neural circuit involved in nictation is not studied. We want to elucidate the neural circuit involved in the nictation behaviour. We established the behaviour assay of nictation. We will present the identification of genes required for nictation."

Choi, Myung-gyu et al. (2009) International Worm Meeting "Genetic and molecular dissection of nictation."

Lee, Harksun, Lee, Junho, Choi, Myung-gyu

[International Worm Meeting, 2009]

Dauer is an alternative form during C. elegans development. C. elegans enters the dauer stage in adverse environment for long-term survival. Dauers have many unusual features which are not shown in other developmental stages. For example, pharyngeal pumping is almost arrested and fat storage is increased. Behavior pattern is also different. Chemotaxis and thermotaxis do not occur in the dauer stage. In plates, they are lethargic but actively respond to mechanical stimulation. Among many characters of dauers, nictation is a very notable behavior. Nictation is the dauer specific behavior that is observed in three-dimensional space. They can climb up onto any projection and wave their body on the top. Although C. elegans is known as the free-living organism in the soil, many Caenorhabditis species associate with other species such as snails and insects. Nictation would be beneficial behavior for their dispersal to other ecological niche. It was also reported that most of naturally isolated C. elegans were dauer larvae. To identify the genes and neural circuits for nictation, we established nictation assay system and used genetic approach. By screening of pre-existing mutants, we found that the function and development of specific neurons are important for nictation. Further characterization of candidate genes will elucidate the mechanism which underlies this specific behavior. Corresponding author: elegans@snu.ac.kr (J. Lee).

Son, Sangwon et al. (2015) International Worm Meeting "Study of transcriptome regulating a dispersal behavior in C. elegans."

Lee, Junho, Lee, Harksun, Son, Sangwon

[International Worm Meeting, 2015]

Many nematodes including C. elegans show nictation behavior by which a worm stands on its tail and waves its head in three dimension. Nematodes show nictation behavior only in dauer stage, which is an alternative stage for long-term survival in harsh environments. In the previous study, we discovered that nictation is a dispersal strategy to reach a new niche, and is initiated by IL2 head neurons. IL2 neurons show a distinct morphology in dauer stage compared to that in non-dauer, and this different morphology and behavior pattern implies that the gene expression in IL2 neurons should be changed at dauer stage. Here we are analyzing IL2 specific transcriptome in dauer stage, by mRNA tagging methods. In one approach, we use FLAG-tagged poly-A tail binding protein (PABP), and mRNA-FLAG::PABP complexes in IL2 can be purified using FLAG antibody. Another approach is TU-tagging method. An enzyme called UPRT which is originated from Toxoplasma gondii can convert uracils in RNA to thio-uracils. IL2-specific expression of UPRT would make the RNAs expressed in IL2 neurons have thio-uracils, and after biotinylation process they can be purified using biotin-streptavidin interaction. By analyzing IL2 specific transcriptome in dauer stage we expect to find novel genes regulating nictation behavior.

Abate JP et al. (2009) Cell Metab "Life is short, if sweet."

Blackwell TK, Abate JP

[Cell Metab, 2009]

Insulin is essential for glucose homeostasis, but reducing its activity delays the aging process in model organisms. In this issue of Cell Metabolism, Lee et al. (2009) show how these effects of insulin signaling intersect when glucose is fed to C. elegans.

Lee C et al. (2017) Bio Protoc "Single-molecule RNA Fluorescence in situ Hybridization (smFISH) in Caenorhabditis elegans."

Sorensen EB, Lee C, Seidel HS, Lynch TR, Crittenden SL, Kimble J

[Bio Protoc, 2017]

Single-molecule RNA fluorescence <i>in situ</i> hybridization (smFISH) is a technique to visualize individual RNA molecules using multiple fluorescently-labeled oligonucleotide probes specific to the target RNA ( Raj <i>et al.</i>, 2008 ; Lee <i>et al.</i>, 2016a ). We adapted this technique to visualize RNAs in the <i>C. elegans</i> whole adult worm or its germline, which enabled simultaneous recording of nascent transcripts at active transcription sites and mature mRNAs in the cytoplasm ( Lee <i>et al.</i>, 2013 and 2016b). Here we describe each step of the smFISH procedure, reagents, and microscope settings optimized for <i>C. elegans</i> extruded gonads.

Dawes-Hoang RE et al. (2003) Dev Cell "Bringing classical embryology to C elegans gastrulation."

Zallen JA, Wieschaus EF, Dawes-Hoang RE

[Dev Cell, 2003]

In a recent paper, Lee and Goldstein develop an explant assay that recapitulates key aspects of gastrulation in C. elegans and permits classical embryological manipulations. The resulting detailed analysis of cell behavior will ultimately extend to broader issues, such as, whether morphogenesis can be described as the sum of single-cell events or if unique phenomena emerge at the multicellular level.

Kim, Nari et al. (2013) International Worm Meeting "The regulation of nictation, a dispersal behavior in C. elegans, by insulin-like molecules."

Kim, Nari, Lee, Harksun, Lee, Junho, Lee, Daehan, Choi, Myung-kyu

[International Worm Meeting, 2013]

Nictation is a dauer-specific behavior in which a dauer climbs up pointed places, then stands on its tail and waves its head. We previously reported that nictation is a dispersal behavior performed by dauers for the purpose of transmission to a new environment for their survival and reproduction. Dauer formation is regulated by guanylyl cyclase, TGF-b-like, insulin-like pathways, which are evolutionarily conserved. As reported in many studies, Insulin-like signaling (ILS) is involved in various behaviors such as pathogen avoidance, food-associated learning and mate searching. However, the involvement of ILS genes on the nictation behavior has not been reported. A recent report that ILS mediates synaptic plasticity led to a hypothesis that ILS can affect synaptic plasticity of neurons regulating nictation. To test this hypothesis, we are trying to examine ILS mutants with micro-dirt chips assay and clarify roles of ILS component genes on nictation behavior.

Choi, Myung-kyu et al. (2013) International Worm Meeting "Elucidation of a neuronal mechanism of nictation, a dispersal behavior, in C. elegans."

Choi, Myung-kyu, Park, Dongjun, Lee, Harksun, Lee, Junho, Lee, Daehan

[International Worm Meeting, 2013]

Charles Darwin described that invertebrates can be dispersed by hitch-hiking on other animals. However, a neuronal and molecular mechanism of such dispersal behaviors is not studied well. As a means to dispersal, C. elegans exhibits dauer-specific behavior called nictation: standing and waving at the tip of three-dimensional objects. We have shown that nictation is carried out to facilitate relocation to a favorable environment. We also demonstrated that acetylcholine in IL2 ciliated neurons is important for nictation. According to the observation that dauers only nictate in three-dimensional objects such as micro-dirt chips, we have speculated that mechanical stimuli rather than chemical ones provide initial clues to nictation. Now we are searching for external signals that can activate IL2 neurons. For searching better habitats, individuals must make a decision between exploration and exploitation. Nictation is a decision making behavior because nictation is the outcome of the decision of dauers on whether they ambush or cruise. It is known that a neuromodulatory system can offer flexibility to the output of neural circuits. So, we have also established mutant screening about genes involved in neuromodulation. The results will show that stage-specific alteration in neural substrate can affect stage-specific, dispersal behavior.

Schroeder, Nathan et al. (2013) International Worm Meeting "Reversible dendrite arborization in dauers is regulated by KPC-1/furin."

Barr, Maureen, Lee, Junho, Schroeder, Nathan, Lee, Harksun, Androwski, Rebecca, Rashid, Alina

[International Worm Meeting, 2013]

Neuroplasticity in response to adverse environmental conditions can entail both hypertrophy and resorption of dendrites. How dendrite remodeling occurs in response to unfavorable environmental conditions is unclear. We discovered that the six IL2 sensory neurons undergo dendrite remodeling during development of the stress-resistant dauer stage. Based on our findings we divide the IL2 neurons into two separate anatomical classes. The four IL2Q (quadrant) neurons undergo extensive dendritic arborization and a shift from bipolar to multipolar neurons during dauer formation. The two IL2Ls (lateral) extend only a single additional process during dauer formation. During dauer recovery, the IL2 arbor retracts, leaving behind remnant branches in post-dauer L4 and adult animals. We isolated a mutation in kpc-1 (kex2/subtilisin-like proprotein convertase), from a forward genetic screen, which results in disorganized and truncated IL2Q arbors. In mammals, the KPC-1 homolog furin is responsible for the cleavage and activation of numerous proproteins associated with various pathologies including neurodegenerative diseases. While broadly expressed in C. elegans, kpc-1 is upregulated in dauer IL2 neurons and acts cell autonomously in the regulation of dauer-specific arborization. The IL2s are required for nictation behavior. We found that kpc-1 mutant dauers are defective for nictation. kpc-1 is also required for multidendritic neuron morphology and behavior during non-dauer stages (See Rashid et al. abstract) suggesting that, similar to furin, KPC-1 plays multiple roles in C. elegans. We are currently searching for potential substrates of KPC-1 that affect dauer-specific IL2 remodeling (See Androwski et al. abstract). The C. elegans IL2 sensory neurons provide a paradigm to study stress-induced reversible neuroplasticity, and the role of environmental and developmental cues in this process. Our discovery of KPC-1 as required for dendrite morphogenesis provides insight into the role of proprotein convertases in nervous system development.