Lee, Daehan et al. (2011) International Worm Meeting "Tracing the genetic basis of the nictation behavior by QTL mapping."

Lee, Junho, Lee, Daehan

[International Worm Meeting, 2011]

Given harsh conditions such as high temperature, starvation and high population density, Caenorhabditis elegans enters an alternative developmental stage called dauer. Dauer larvae exhibit specific behavior called nictation - when a dauer confronts filamentous matter or rough surface, it stands and waves its body on the protruding ending. Nictation is a conserved behavior among nematodes, and may have been adopted as a strategy for phoresy, necromeny and parasitism. However, little is known about the genetic and neural basis of nictation. Unlike in laboratory conditions, wild strains of C. elegans habituate in fluctuating environments and they are usually isolated as dauer larvae even in a rich environment like compost soil. They are also often isolated from terrestrial isopod species, probably associated by nictation. Previously, we showed that mutants with defects in nictation could not be transported to new E. coli lawn by fruit flies in which condition these mutant dauers cannot recover from the dauer stage and reproduce. Nictation may facilitate transfer to new habitat in wild environment, which may greatly affect its survivorship and reproduction. Presumably, depending on its habitat condition, different wild isolates might have gone through different selection for nictation. In this work, we show phenotypic variations of nictation among wild isolates. By quantitative trait loci(QTL) mapping, we will trace the genetic basis of the phenotypic variation, and ultimately elucidate development and evolution of nictation.

Lee, Daehan et al. (2015) International Worm Meeting "Natural variation and developmental plasticity of hitchhiking behavior in C. elegans."

Kruglyak, Leonid, Lee, Harksun, Andersen, Erik, Lee, Daehan, Lee, Boyun, Yang, Heeseung, Kim, Heekyeong, Lee, Junho, Paik, Young-Ki, Kim, Jun

[International Worm Meeting, 2015]

Under harsh conditions, Caenorhabditis elegans develops to an alternative non-feeding stage called dauer. Dauer larvae display a prominent stage-specific behavior called nictation, a waving and standing behavior. Nictation facilitates dauers to hitchhike onto other animals, which in turn helps dauers to transfer to new habitats. Nictation was reported several decades ago, nonetheless underlying regulatory mechanisms on this behavior are only recently beginning to be studied. Here, we explore genetic and environmental factors affecting the hitchhiking behavior of C. elegans. We revealed the existence of natural variation in nictation behavior among wild isolates, and mapped nict-1 QTL involved in the variation displayed in N2 and CB4856. Meanwhile, we also screened environmental cues that might influence the hitchhiking ability of dauers. We found that feeding pathogenic bacteria Pseudomonas aeruginosa produces nictation-enhanced dauers. In addition, we investigated responsible signaling pathways for developmental plasticity of nictation behavior in response to environmental conditions. Our study will provide new insights on genetic basis for regulation of hitchhiking behavior, which plays a critical role in the survival and evolution of the species.

Lee, Daehan et al. (2014) Evolutionary Biology of Caenorhabditis and Other Nematodes "TO RIDE OR NOT TO RIDE: GENETIC BASIS FOR NATURAL VARIATION OF C. elegans HITCHHIKING BEHAVIOR"

Kruglyak, Leonid, Andersen, Erik C., Lee, Daehan, Lee, Junho, Paik, Young-Ki, Kim, Heekyeong

[Evolutionary Biology of Caenorhabditis and Other Nematodes, 2014]

In parasitic nematodes, cruising (widely foraging) and ambushing (sit-and-wait) are two main dispersal strategies for survival and host finding. Free living nematode use similar strategies. Given harsh conditions, Caenorhabditis elegans develops to a dauer larva, which can either cruise or display an ambushing behavior called nictation. This behavior may facilitate dispersal of dauers to new habitats in the wild environment through phoresy - using other animals as a transportation vehicle. Therefore, nictation may greatly affect the survivorship and reproduction of C. elegans. However, this ambushing strategy decreases the probability of finding new habitats by the cruising strategy. Thus, the decision making between cruising and nictating might be selected in nature. In this work, we characterized natural variation in nictation behavior among C. elegans wild isolates. By linkage mapping, we identified a major-effect quantitative trait locus (QTL) and a candidate gene for nictation behavior. This QTL might underlie natural variation of the C. elegans hitchhiking behavior in the wild. Our work clearly defines a specific QTL that may have an important evolutionary role by modulating decision making probability for a specific 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.

Bhattacharya, Abhishek et al. (2015) International Worm Meeting "Stress induced plasticity of the C. elegans electrical synapse network."

Hobert, Oliver, Lee, Junho, Lee, Daehan, Bhattacharya, Abhishek

[International Worm Meeting, 2015]

Stress induced plasticity of the nervous system allows animals to adapt to changing environments by modulating their behavior. We are studying the nervous system rewiring in response to environmental cues by investigating the hibernation-like alternative diapause state of C. elegans, the dauer state. In adverse environmental conditions, mainly starvation, population density and high temperature, C. elegans larvae molt into dauer, which not only show altered morphology, but also show a remarkably altered responsiveness to various environmental cues and strikingly different locomotory behavior. However, the neuronal circuit responsible for these altered behaviors and the molecular mechanism responsible for the circuit remodelling is poorly understood. We focused our study on innexin (inx) genes, which encode the functional units of invertebrate electrical synapses. In a screen, using fosmid-based fluorescent reporter transgenes, for neuronally expressed inx genes that show altered expression in dauer, we have identified the cellular specificity of inx-6 expression is altered in dauer. In replete condition, inx-6 is only expressed in pharynx throughout life. In dauer, inx-6 expression is additionally turned on in the glutametergic interneuron pair AIB, which regulates locomotion during chemotaxis and odortaxis, by promoting reversals and turns. Furthermore, the inx-6 expression in AIB is reversible. As animals recover from dauer stage, inx-6 expression disappears from AIB. Another diapause stage, the starvation-induced L1-diapause, shows similar plasticity of inx-6 expression in AIB. Using a temperature sensitive inx-6(rr5) allele, we identified that INX-6 activity is required for nictation, a dauer specific dispersal behavior that is also conserved in parasitic nematodes. We also observed that the loss of INX-6 activity and similarly ablation of AIB affects locomotion speed and locomotory quiescence, specifically in dauer. I will present our data on the molecular composition of the INX-6-synapses in dauer-AIB and preliminary results en route to identifying the synaptic partners of dauer-AIB for INX-6-mediated synapses. I will also present our data on the transcriptional control of the inx-6 expression plasticity in the dauer nervous system that provides cellular specificity and also integrates environmental cues. Our studies provide insights into the process of stress induced nervous system plasticity at different levels of gene regulation, circuits and behaviors. .

Angeles Albores, David et al. (2015) International Worm Meeting "Preparing Panagrellus redivivus for molecular genetics."

Lee, Daehan, Angeles Albores, David, Sternberg, Paul, Lee, Junho

[International Worm Meeting, 2015]

Panagrellus redivivus is a free-living nematode that is evolutionarily distant from C. elegans being in clade IV versus clade V respectively . Although the species has been known since the 1700s, it is used more for toxicology and fish food than for biological analysis. Sternberg, Horvitz and Sulston worked out the post-embryonic and partial embryonic lineages in the 1980s, and a draft genome has been published. We are studying P. redivivus intensely in preparation for molecular genetics studies. We complete the description of the life cycle of this species by confirmation of a dauer larva stage, which is absent in the British lab strain, but present in a natural isolate from Korea. We show functional analogy of the P. redivivus distal tip cell (DTC) to the C. elegans DTC and also show functional conservation of the cholinergic system in regulation of male tail flexion in P. redivivus. We demonstrate qualitative results of key cell ablations in the mail tail of P. redivivus on mating behavior, and present preliminary results concerning attempts at transgenesis and RNAi in this beautiful worm. .

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.

Zhang, Gaotian et al. (2021) International Worm Meeting "The genetic architectures of gene expression variation in wild C. elegans"

Hahnel, Steffen, Andersen, Erik, Roberto, Nicole, Zhang, Gaotian, Lee, Daehan

[International Worm Meeting, 2021]

Natural variation in gene expression is a major source of phenotypic diversity among individuals. Genetic variants underlying gene expression differences are known as expression quantitative trait loci (eQTL). In Caenorhabditis elegans, both local eQTL (located close to the genes they influence) and distant eQTL (located farther away from the genes they influence) have been identified using linkage analysis from a panel of recombinant inbred advanced intercross lines (RIAILs) between the laboratory reference strain, N2, and a wild strain, CB4856. However, the eQTL detected using RIAILs were limited to genetic variants between N2 and CB4856. Here, we investigated the natural variation in gene expression of 205 genetically distinct C. elegans wild strains by performing RNA-sequencing on synchronized young adult hermaphrodites. We obtained reliable expression of 25,896 protein-coding transcripts (16,106 genes). We used genome-wide association (GWA) analysis to identify 3,342 local eQTL for 3,342 transcripts (2,777 genes), and 2,835 distant eQTL for 2,206 transcripts (2,082 genes). We found that most of the narrow-sense heritability for transcript expression variation is explained by detected eQTL. Of the 2,835 distant eQTL, 1,670 eQTL significantly clustered in 54 hotspots across the C. elegans genome. We will further explore causal genes underlying these distant eQTL hotspots and their functions. Additionally, we applied mediation analysis to the eQTL data and other organism-level quantitative traits to elucidate the genetic effects on phenotypic variation mediated by gene expression. For instance, instead of relying on time-consuming investigations of rare genetic variants missed in GWA studies and prior knowledge of the trait as published in our study of C. elegans responses to benzimidazoles (Hahnel et al. 2018), the significant mediating effect of the expression of ben-1, the causal gene, was quickly and successfully identified by mediation analysis. Our results suggest that mediation analysis using expression data facilitates identification of causal genes in GWA studies in C. elegans.

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.