Choi, Woochan et al. (2021) International Worm Meeting "A chemosensory GPCR is required for a concentration-dependent behavioral switch in C. elegans"

Choi, Woochan, Cheon, YongJin, Kim, Kyuhyung, Ryu, Sang Eun, Kim, Seoyeong, Park, Yeon-Ji, Moon, Cheil

[International Worm Meeting, 2021]

C. elegans detects a large number of odorants and elicits a multitude of olfactory behaviors (Bargmann, 1993, Cell). Previous genetic and behavioral experiments have identified a set of signaling genes, including olfactory receptors, but the knowledge is still limited. Specifically, the mechanisms of how the same odorants can elicit either attractive or aversive responses depending on the chemical concentration have not been known in detail. Dimethyl trisulfide (DMTS) is an organic chemical, which smells like garlic and is derived from bacterial decomposition. Here, we show that C. elegans attracts to a low concentration of DMTS via the AWC neurons and avoids a high concentration of DMTS via the ASH neurons. We then find that chemosensory GPCR sri-14 is required for both attraction to a low concentration of DMTS and aversion to a high concentration of DMTS. The defects of DMTS chemotaxis in sri-14 mutants are restored when we expressed the wild-type sri-14 gene to the AWC and ASH neurons for attraction and avoidance, respectively. Ca2+ responses of AWC and ASH upon acute exposure to DMTS are decreased in sri-14 mutants. Moreover, ectopic expression of sri-14 in the ADL neurons is sufficient to elicit Ca2+ responses to DMTS in the ADL neurons. Furthermore, we heterologously expressed the SRI-14 receptor in the mammalian cell and found that these cells confer dose-dependent response upon DMTS exposure, suggesting that SRI-14 is indeed a bona fide DMTS receptor. Next, we investigated how downstream interneurons translate and process DMTS signals from the ASH or AWC neurons to generate alternative behaviors. We found that the AIB interneurons, receiving signals from AWC and ASH neurons, exhibit distinct Ca2+ responses depending upon the concentration of DMTS; the AIB interneurons are activated upon removal of low concentration of DMTS or addition of high concentration of DMTS. Moreover, the sri-14 mutation fully suppresses the AIB Ca2+ response to DMTS odor. Furthermore, we identified that the glr-1 and glr-5 glutamate receptors expressed in AIB are required for different concentration signals from low and high DMTS. Thus, our results demonstrate molecular and circuit mechanisms by which an animal connects chemosensory neurons detecting the same ligand to alternate downstream circuitry to efficiently trigger precise behavioral programs.

Choi, Woochan et al. (2019) International Worm Meeting "The chemosensory GPCR SRI-14 is required for concentration-dependent DMTS odor preference in C. elegans."

Choi, Woochan, Ryu, SangEun, Moon, Cheil, Kim, Kyuhyung, Cheon, YongJin

[International Worm Meeting, 2019]

C. elegans detects a large number of odorants, and elicits a multitude of olfactory behaviors (Bargmann, 1993, Cell). Previous genetic and behavioral experiments have identified set of signaling genes including olfactory receptors, but the knowledge is still limited. Specifically, the mechanisms of how the same odorants can elicit either attractive or aversive responses depending on the chemical concentration have not known in detail. Dimethyl trisulfide (DMTS) is an organic chemical, which smells like garlic and is derived from bacterial decomposition. Here, we showed that C. elegans attracts to low concentration of DMTS via the AWC neurons and avoids to high concentration of DMTS via the ASH neurons. We then performed candidate gene search and found that chemosensory GPCR sri-14 is required for both attraction to low concentration of DMTS and aversion to high concentration of DMTS. The defects of DMTS chemotaxis in sri-14 mutants were restored when we expressed the wild-type sri-14 gene to the AWC and ASH neurons for attraction and avoidance, respectively. Ca2+ responses of AWC and ASH upon acute exposure to DMTS is decreased in sri-14 mutants. Moreover, ectopic expression of sri-14 in the ADL neurons is sufficient to elicit Ca2+ responses to DMTS in the ADL neurons. Furthermore, we heterologously expressed the SRI-14 receptor in the mammalian cell, and found that these cells confer dose-dependent response upon DMTS exposure, suggesting that SRI-14 is indeed a bona fide DMTS receptor. Next, we investigated how downstream interneurons translate and process DMTS signals from the ASH or AWC neurons to generate alternative behaviors. We found that the AIB interneurons, receiving signals from AWC and ASH neurons, exhibit distinct Ca2+ responses depending upon the concentration of DMTS; the AIB interneurons are activated upon removal of low concentration of DMTS or addition of high concentration of DMTS. Moreover, the sri-14 mutation fully suppresses the AIB Ca2+ response to DMTS odor. These results demonstrate that concentration-dependent alternative behaviors are regulated by not sensory receptor but downstream circuit levels.

Kim, SeoYeong et al. (2021) International Worm Meeting "Construction of the map of odorants and olfactory neurons in C. elegans"

Choi, Woochan, Kim , Kyuhyung, Kim, Seoyeong

[International Worm Meeting, 2021]

Animals must recognize and discriminate among thousands of chemicals to generate the correct behavioral response. Understanding basic design of a sensory system in simple animals gives the opportunity to elucidate detailed molecular and neural mechanisms underlying sensory responses in higher animals. The small nematode Caenorhabditis elegans detects many odorants via a few neuron pairs, including the AWC neurons, and elicit a multitude of olfactory behaviors (Bargmann, 1993, Cell). Due to the established connectome, the olfactory system of C. elegans provides an excellent model system in which to explore the circuit mechanisms underlying olfactory processing at the single-cell resolution. Previous genetic and behavioral experiments have identified a set of signaling genes, including olfactory receptors, but the knowledge is still limited. Here we are trying to construct a comprehensive map of odorants and olfactory neurons in C. elegans. We first screened volatile chemicals that are not tested previously and found that animals respond to a set of volatile chemicals, including acetic acid, acetoin, formaldehyde, 1-propanol, or 2-propanol. We further identified that the AWC neurons are required for chemotactic responses to these chemicals. We then measured intracellular Ca2+ transients in response to 3,4-hexanedione, acetic acid, heptanoic acid, and (-)-pulegone in AWC-specific GCaMP3 transgenic worms and found that AWC alters Ca2+ activities in response to 3,4-hexanedione, heptanoic acid, and (-)-pulegone. Overall, this study indicates that C. elegans olfactory systems detect a large spectrum of volatile chemicals via the distinct chemosensory neuron-type.

Chen J et al. (2016) Food Funct "Extracts of Tsai Tai (Brassica chinensis): enhanced antioxidant activity and anti-aging effects both in vitro and in Caenorhabditis elegans."

Xiang L, Liu X, Huang Z, Zhou X, Xiang Y, Zhang J, Chen J, Liu Y, He X

[Food Funct, 2016]

Tsai Tai is one of the most widely consumed Brassica vegetables in Asian countries because of its good taste and its nutritional benefits. This study evaluated the antioxidant capacity and possible associated health benefits of 3 Tsai Tai (Brassica chinensis) varieties, namely, Hon Tsai Tai, Pak Choi and Choi Sum. The DPPH radical scavenging ability and reducing power assays were performed to evaluate the in vitro activities of the extracts. Caenorhabditis elegans was used as an in vivo model for evaluation of beneficial health effects, including antioxidant activity and delayed aging. In vitro, the Hon Tsai Tai extract exhibited higher antioxidant activities than Pak Choi and Choi Sum, and the total phenolic contents were significantly correlated with the DPPH and RP values. In vivo, the three assayed Tsai Tai extracts significantly increased resistance against paraquat-induced oxidative stress with an increase in survival rates from 15% to 28% compared with controls. However, only the extract from Hon Tsai Tai significantly prolonged the lifespan of Caenorhabditis elegans, with an 8% increase in the mean lifespan with respect to controls. Further evidence of antioxidant protection was obtained by assessing ROS production via the DCF assay. The analyses of intracellular SOD activity and MDA content confirmed the existence of an antioxidant protective effect. These results suggest that Tsai Tai might serve as a good source of natural antioxidants, and in particular, Hon Tsai Tai could be explored as a potential dietary supplement to retard aging.

(2019) Development "The people behind the papers - Sungwook Choi."

[Development, 2019]

The control of timing in development is crucial, both within and between tissues. Heterochrony involves shifts in the rate of development of some tissues relative to others, and although the first heterochronic genes were identified in <i>Caenorhabditis elegans</i> in the early 1980s, their role in inter-tissue developmental coordination is still not completely understood. A new paper in Development tackles this problem with an analysis of the role of <i>lin-28</i>, a key heterochronic gene, in worm fertility. We caught up with Sungwook Choi, first author and recently graduated PhD student in Victor Ambros' lab at the University of Massachusetts Medical School in Worcester, to find out more.

Birsoy, Bilge et al. (2009) International Worm Meeting "Right Way to Have Sex."

Bloss, Tim, Birsoy, Bilge, Rothman, Joel H., Downes, Joanna C., Choi, Shin Sik

[International Worm Meeting, 2009]

While the mechanism that breaks left-right (L-R) anatomical asymmetry (handedness) has been described in C. elegans, we have found that at least one additional mechanism must exist to establish other handedness cues that generates L-R differences in the deployment of alternative cell death pathways (see abstract from our lab by Choi et al.). To assess whether such a system might affect a behavior in the worm, we investigated whether male mating behavior exhibits L-R handedness. Upon recognizing a hermaphrodite, males initiate backward locomotion and continuously scan along the hermaphrodite''s body. When their tails reach either the head or tail of the hermaphrodite, males turn to maintain contact and then continue backward locomotion on the opposite side of the hermaphrodite. We found that this turning behavior shows a distinct right-handed bias: when individual males were allowed to mate with lin-2(e1309) vulvaless hermaphrodites, >70% of the turns when made over the hermaphrodites'' body (away from the agar surface) and >55% of turns when made under the hermaphrodites'' body (toward the agar surface) are right-handed. To determine whether this bias in turning direction correlated with L-R asymmetry in the male mating structure, which results from stochastic EGL-1-dependent loss of sensory rays (Choi et al. abstract), we examined the turning bias in egl-1(n1084n3082) mutants. We were surprised to find that, although wild-type males lack rays more frequently on the right, the right-hand turning bias is actually increased in the egl-1 mutant, in which no rays are lost and therefore rays are always symmetrically arranged. Thus, the intrinsic turning bias is even more apparent in males with symmetric mating structures. To assess whether this L-R behavioral bias is dependent on anatomical handedness, we analyzed gpa-16(it143) mutants in which the L-R asymmetry of the internal organs is reversed as a result of the reversal in the early embryonic symmetry break. Males with reversed anatomical asymmetry showed a virtually identical right hand bias in turning, demonstrating that a handedness-determining system that is independent of the previously described L-R symmetry breaking event must control this behavior. These findings raise the possibility that, analogous to brain laterality in humans, functionally L-R asymmetry in the C. elegans motor nervous system may be independent of anatomical handedness.

Young-Ki Paik et al. (2006) East Asia C. elegans Meeting "A Comprehensive Proteomic Analysis of Dauer and Cholesterol Signaling Pathway in Caenorhabditis elegans"

Mi Jeong Jeong, Young-Ki Paik, Keun Na, Pan-Young Jeong

[East Asia C. elegans Meeting, 2006]

With the availability of its complete genome sequence and unique biological features relevant to human disease, C. elegans has become an invaluable model organism for the studies of proteomics, leading to the elucidation of nematode gene function. We have focused on two key metabolic regulators of C. elegans: dauer-inducing pheromone (daumone; Jeong et al., 2005, Nature, 433, 541-545) and cholesterol (Choi et al, 2003, MCP, 2, 1086-95). First, using various proteomic tools including 2D-LC-MS/MS and DIGE, we analyzed proteomic profiles upon treatment of daumone, which signals C. elegans to enter the dauer stage, an enduring and non-ageing stage of the nematode life cycle. We found that there are multi-level changes in protein expression in the area of energy metabolism (decreased) and oxidative defense system (increased), suggesting that differential changes in various metabolic pathways appear to accommodate this non-aged state. This proteomic data was also paralleled with DNA microarray studies, which provided a window for direct comparison of proteomic and genomic profiles in dauer state. Second, we have launched a global C. elegans proteome project (CEPP) in order to analyze a comprehensive map of proteins involved in cholesterol signaling pathway in embryonic stage of C. elegans. In this talk, we will discuss a few lessons as well as some progress obtained from the pilot phase with respect to data management and functional annotation in C. elegans

Kim, Sungjong et al. (2015) International Worm Meeting "Genetic screens for IL2 lineage-specific regulators in Caenorhabditis elegans."

Kim, Sungjong, Lee, Junho, Ahn, Soungyub, Swoboda, Peter, Park, Dongjun

[International Worm Meeting, 2015]

Ciliated IL2 sensory neuron is important for nictation, a dauer specific behavior. We previously reported that dauers in which IL2 neurons were genetically ablated could not nictate(1). IL2 sensory neurons consist of six cell bodies. Each cell body has a unique embryonic lineage. Neural progenitors divide asymmetrically into two lineages; one lineage becomes IL2 neurons and the other lineage divides into two sublineages, again. Two divided sublineages generate IL1 sensory neurons and apoptotic cells. However, no lineage-specific regulator has been identified in neurogenesis of IL2 yet. In this study, we tried to find genes that regulate these asymmetrical cell divisions. At first, We labeled IL1 and IL2 neurons with fluorescent markers dsRED and GFP, respectively. We treated worms with EMS for random mutagenesis. Then we sorted out candidate mutant worms with COPAS biosort. which optically analyzes and sorts living multicellular organisms on the basis of fluorescent protein expression patterns and other optical signatures, at rates up to about 100 organisms per second(2). We try to find out the genes which can regulate mutational phenomenon. Our study will contribute to elucidating the mechanism of IL2 development and/or differentiation.(1) H. Lee, M. Choi, et al., (2012) Nictation, a dispersal behavior of the nematode Caenorhabditis elegans, is regulated by IL2 neurons, Nature Neuroscience Volume 15, 107-112(2) Rock Pulak, (2006) Techniques for Analysis, Sorting, and Dispensing of C. elegans on the COPAS&trade; Flow-Sorting System, Methods in Molecular Biology Volume 351, pp 275-286.

Park, Dongjun et al. (2013) International Worm Meeting "Genetic screens for IL2 lineage-specific regulators in Caenorhabditis elegans."

Park, Dongjun, Lee, Junho, Swoboda, Peter

[International Worm Meeting, 2013]

Ciliated IL2 sensory neuron is important for nictation, a dauer specific behavior. We previously reported that dauers in which IL2 neurons were genetically ablated could not nictate(1). IL2 sensory neurons consist of six cell bodies. Each cell body has a unique embryonic lineage. Neural progenitors divide asymmetrically into two lineages; One lineage becomes IL2 neurons and the other lineage divides into two sublineages, again. Two divided sublineages generate IL1 sensory neurons and apoptotic cells. However, any lineage-specific regulator has not been identified in neurogenesis of IL2 yet. In this study, we tried to find the genes that regulate these asymmetrical cell divisions. At first, we labeled IL1 and IL2 neurons with fluorescent markers dsRED and GFP, respectively. We treated worms with EMS for random mutagenesis. Then we sorted out candidate mutant worms with COPAS biosort. which optically analyzes and sorts living multicellular organisms on the basis of fluorescent protein expression patterns and other optical signatures, at rates up to about 100 organisms per second(2). We selected two mutant lines. One mutant line has only dsRED signals and the other lines has ectopic GFP signals that are positioned posterior to the normal positions. We try to find out which genes regulate these mutational phenomenon. Our study will contribute to elucidating the mechanism of IL2 development and/or differentiation. (1) H. Lee, M. Choi, et al., (2012) Nictation, a dispersal behavior of the nematode Caenorhabditis elegans, is regulated by IL2 neurons, Nature Neuroscience Volume 15, 107-112 (2) Rock Pulak, (2006) Techniques for Analysis, Sorting, and Dispensing of C. elegans on the COPAS Flow-Sorting System, Methods in Molecular Biology Volume 351, pp 275-286.

Choi, Y.S. et al. (2017) International Worm Meeting "Investigating the role of MUT-2 in transgenerational gene silencing triggered by neuronal double-stranded RNAs."

Choi, Y.S., Edwards, Lanelle, DiBello, Aubrey, Jose, Antony

[International Worm Meeting, 2017]

Studies in C. elegans have shown that dsRNA expressed in neurons can transmit a signal to the germline of an animal to cause silencing of a germline gene in that animal and in its descendants. The molecular details of how mobile RNA is processed, exported, and transmitted from neurons to the germline are poorly understood. Tissue-specific rescue experiments using repetitive transgenes suggest that MUT-2, a putative RNA nucleotidyltransferase, is sufficient in the sending cells for gene silencing by mobile dsRNA. One hypothesis suggested by this finding is that forms of RNA that are modified by MUT-2 move between cells. Alternatively, use of repetitive transgenes could have led to misexpression in receiving cells and MUT-2 might function only in receiving cells. Distinguishing between these possibilities requires the development of better reagents and methods for the analysis of MUT-2 and small RNAs. In the absence of MUT-2, transposons are activated, leading to progressive mutagenesis in the background, which could complicate interpretations. Indeed, when we generated new deletions of mut-2 using CRISPR-based genome editing and analyzed three independently propagated mut-2(-) deletion lines, we did not detect the previously reported reduced brood size. To examine possible changes in small RNAs that result from loss of mut-2, we have developed a sensitive northern blotting approach that can detect RNAs as short as 14 nt and thus effectively complement RNA-seq (1). Finally, we are defining the neurons that can export dsRNA to elicit the most effective and enduring transgenerational gene silencing through a large-scale effort called the Transgenerational Brain Initiative using cohorts of ~35 undergraduates each year. This effort will create and characterize a collection of strains expressing dsRNA, reporter genes, and MUT-2 from single copy transgenes in different subsets of neurons. Collectively, with these tools, we will establish where MUT-2 acts to initiate transgenerational gene silencing triggered by neuronal dsRNA. 1. Choi et al., Nucleic Acids Research, 2017.