Piggott, Beverly J. et al. (2009) International Worm Meeting "Dissecting the neural basis for locomotion in freely-behaving worms."

Liu, Jie, Piggott, Beverly J., Feng, Zhaoyang, Xu, X.Z. Shawn

[International Worm Meeting, 2009]

Locomotion represents one of the most basic motor programs in the C. elegans behavioral repertoire. The command interneurons are believed to be the primary drivers of forward and backward locomotion. To better understand the role of these neurons in both sensory and spontaneous behavior, we have developed an automated calcium imaging system that permits simultaneous imaging of neural activity and behavior in freely-moving worms. We have named it the CARIBN system (CAlcium Ratiometric Imaging of Behaving Nematodes). Previous studies have been primarily conducted on restrained or semi-restrained worms that do not exhibit natural behavior. Our system provides a means to temporally examine how neural activity correlates to behavior under standard laboratory conditions where worms freely move on the surface of an NGM plate in an open environment. By using standard laboratory conditions, we can compare our work to the majority of behavioral studies performed by other groups over the past 40 years. We currently focus on the neuron AVA, as it has been implicated as a primary driver of backward locomotion in both spontaneous and sensory induced behaviors. Consistent with other reports, we found that AVA is activated in response to nose touch, osmotic shock, and in spontaneous long reversals. Surprisingly, we do not see a significant AVA activity in spontaneous short reversals. The CARIBN system provides a powerful tool to dissect how genes and neural circuits generate behavior in C. elegans.

Zhang, Xinxing et al. (2021) International Worm Meeting "A cilia-independent function of BBSome mediated by DLK MAPK signaling in C.Elegans."

Liu, Jinzhi, Xu, X.Z. Shawn, Pan, Tong, Liu, Jianfeng, Zhang, Xinxing

[International Worm Meeting, 2021]

Bardet-Biedl Syndrome (BBS) is a genetic disorder affecting primary cilia. BBSome, a protein complex composed of eight BBS proteins, regulates the structure and function of cilia in diverse organisms, and its malfunction causes BBS in humans. Here, we report a new function of BBSome. In a genetic screen conducted in C. elegans to identify genes regulating the photoreceptor LITE-1, a non-ciliary protein expressed in ciliated sensory neurons, we isolated bbs mutants. Functional analysis revealed that BBSome regulates LITE-1 protein stability in a cilia-independent manner. Through another round of genetic screen, we found that this new function of BBSome is mediated by DLK MAPK signaling. We further showed that BBSome regulates the expression of DLK. Interestingly, we found that BBSome also regulates DLK expression in mammalian cells, suggesting a conserved mechanism. These studies identify an unexpected cilia-independent function of BBSome and uncover DLK MAPK signaling as a novel BBSome effector.

Piggott, Beverly J. et al. (2011) International Worm Meeting "Mammalian rhodopsin can functionally substitute for C. elegans photoreceptor to restore light sensitivity in worms."

Piggott, Beverly J., Liu, Jie, Xu, X.Z. Shawn, Gao, Jingwei

[International Worm Meeting, 2011]

We have recently discovered that worms sense light and engage in phototaxis behavior that is essential to their survival. Our work has led to the identification of photoreceptor neurons and molecules in the C. elegans phototransduction pathway. Through electrophysiological interrogation, we discovered that LITE-1 acts in ASJ to transduce light signals through a G protein-mediated process which requires membrane-associated guanylate cyclases. This pathway shares striking similarities to those found in some vertebrate photoreceptor cells. Interestingly, lite-1 belongs to the invertebrate taste receptor family. Discovering that a gustatory receptor could permit light sensation in worms, we wondered if expression of other known light sensing molecules, such as opsins, could function similarly in worms. In other words, could structurally distinct, mammalian opsins, hijack the C. elegans phototransduction machinery to restore photosensory behavior in lite-1 mutants? To this end we made transgenic worms expressing bovine rhodopsin and discovered that it can restore light sensitivity in lite-1 mutants. These findings demonstrate that divergent photoreceptor molecules can share functional homology.

Xiao, Rui et al. (2015) International Worm Meeting "mTORC2 and neuroendocrine signaling modulate C. elegans physiology and aging in a diet-dependent manner."

Xu, X.Z. Shawn, Xiao, Rui, Chun, Lei, Liu, Jianfeng, Friedman, David, Ronan, Elizabeth

[International Worm Meeting, 2015]

Diet affects nearly every aspect of animal life, such as development, metabolism, behavior and aging, both directly by supplying nutrients and indirectly through gut microbiota. C. elegans feeds on bacteria, and like other animals, different bacterial diets induce distinct dietary responses in the worm. However, the lack of certain critical tools hampers the use of worms as a model for dietary signaling. Here, we genetically-engineered the E. coli strain OP50, the standard laboratory diet for C. elegans, making it compatible for double-stranded RNA production. Together with the other bacterial strain HT115, we are able to feed worms different diets while delivering RNAi to interrogate the genetic basis underlying diet-dependent differential modulation of development, metabolism, behavior, and aging. Using comparative RNAi combined with mutant experiemnts, we found that mTORC2, but not mTORC1, modulates a wide range of C. elegans life traits including lifespan in a diet-dependent manner. In addition, neuropeptide signaling may also play important roles in the diet-dependent C. elegans behaviors. Taken together, our results show that neuroendocrine and mTOR pathways are involved in mediating differential dietary responses. This genetic tool (RNAi-competent OP50(xu363)) will greatly facilitate the use of C. elegans as a model for dietary signaling.

Ward, Alex et al. (2009) International Worm Meeting "Eyeless but not blind: Phototransduction in C. elegans."

Liu, Jie, Kang, Lijun, Decaluwe, Brandon, Gao, Jingwei, Xie, Zhixiong, Ma, Di, Ward, Alex, Yu, Yong, Inada, Hitoshi, Mori, Ikue, Xu, X.Z. Shawn, Nishio, Nana

[International Worm Meeting, 2009]

It has long been assumed that the nematode C. elegans lacks the sense of light, mainly because it lives in the soil and does not have eyes. However, we have recently reported the surprising observation that C. elegans in fact possesses a simple visual system and engages in phototaxis behavior that is mediated by photoreceptor cells and light-sensitive channels [1]. Here we elucidate the phototransduction cascade in C. elegans photoreceptor cells through a combination of electrophysiological and behavioral analysis. As is the case with vertebrate photoreceptor cell rods and cones, C. elegans phototransduction is also mediated by G signaling and cGMP-sensitive CNG channels. Interestingly, instead of signaling through phosphodiesterases (PDEs), light-activated G proteins appear to be coupled to guanylate cyclases that produce cGMP, thereby resulting in opening of CNG channels. Our studies identify a new sensory modality in C. elegans and suggest that animals living in dark environments (e.g. soil and caves) may not be presumed to be blind. Our data also reveal a surprising conservation in phototransduction between vertebrates and C. elegans, indicating that C. elegans represents a powerful genetic model for the study of phototransduction. [1] Ward, A.*, Liu, J.*, Feng, Z., and Xu, X.Z.S. (2008) Light-sensitive neurons and channels mediate phototaxis in C. elegans. Nature Neuroscience 11, 916-22 *co-first authors.

Zhang, Bi et al. (2015) International Worm Meeting "Environmental temperature differentially modulates C. elegans longevity through a thermosensitive channel."

Xiao, Rui, He, Yongqun, Xu, X.Z. Shawn, Ronan, Elizabeth A., Zhang, Bi, Liu, Jianfeng

[International Worm Meeting, 2015]

Temperature profoundly affects aging in both poikilotherms and homeotherms. A general belief is that lower temperatures extend lifespan while higher temperatures shorten it. Though this "temperature law" has been widely accepted, it has not been extensively tested. Here, we carefully evaluated the role of temperature in lifespan regulation in C. elegans. We found that while exposure to low temperatures at the adult stage promotes longevity, low temperature treatment at the larval stage surprisingly reduces lifespan. Interestingly, this differential effect of temperature on lifespan in larvae and adults is mediated by the same thermosensitive channel TRPA-1 that signals to the transcription factor DAF-16/FOXO, a master regulator of lifespan. DAF-16/FOXO and TRPA-1 act in larvae to shorten lifespan, but extend lifespan in adulthood. Notably, DAF-16/FOXO differentially regulates gene expression in larvae and adults in a temperature-dependent manner. Our results uncover unexpected complexity underlying temperature modulation of longevity, demonstrating that temperature differentially regulates lifespan at different stages of life.

SN Parrish et al. (1999) International C. elegans Meeting "Investigating the fates of trigger RNAs and target transcripts in RNA-mediated interference"

AZ Fire, SN Parrish

[International C. elegans Meeting, 1999]

We seek to explore the molecular mechanisms responsible for RNA-mediated genetic interference (RNAi). In nematodes, introduction of double-stranded RNA corresponding to a segment of an endogenous genetic locus can result in specific silencing of that locus, essentially producing a knock out phenotype [1]. To date, evidence indicates that this interference reflects a post-transcriptional mechanism, resulting in the loss of the endogenous transcript [2]. Only a few molecules of dsRNA are required per cell to mediate interference, suggesting either an amplification or catalytic aspect of the process [1]. To gain an understanding of the mechanism of RNAi, we are examining the fates of the two key players in this pathway, the endogenous target RNA and the dsRNA effector molecule. First, we are attempting to follow alterations in the endogenous transcripts after the introduction of dsRNA. As a start, we are trying to map possible cleavage events or potential chemical modifications through primer extension and RT PCR of the target transcript. In a complementary set of experiments, we are also examining potential changes in the dsRNA triggering molecule. Through the characterization of the target and effector RNA molecules, we hope to acquire some insight into the mechanism of RNA-triggered silencing. With this knowledge, in conjunction with genetic identification of components in the pathway, it may be possible to unravel the events and intermediates essential for RNAi. 1. Fire, Xu, Montgomery, Kostas, Driver, Mello. Nature 391, 806 2. Montgomery, Xu, and Fire. PNAS 95, 15502

Hung, Wesley L. et al. (2019) International Worm Meeting "A compact circuit of interneurons coordinates two central pattern generators to control forward movement."

Sathaseevan, Anson, Meng, Jun, Zhen, Mei, Chang, Maggie M., Hung, Wesley L., Miller III, David M., Lu, Yangning, Wang, Ying, McWhirter, Rebecca, Luo, Linjiao

[International Worm Meeting, 2019]

In C. elegans, there are two central pattern generators (CPGs) that contribute to forward movement - the head CPG that controls the head swing, through currently unidentified neurons, and the body CPGs, which resides in the B-type motor neurons (Xu et al., 2017). The frequency and amplitude of the head swing and body undulation are tightly coupled to allow smooth, sinusoidal forward movement. We show here that the descending interneurons, AVG and RIF, play a critical role in two aspects of forward movement: forward speed modulation and head-body coordination. While AVG is not essential for locomotion, the loss of AVG results in animals with reduced forward speed and an increased tendency to remain in a pausing/resting state. Conversely, optogenetic activation of AVG alone rapidly increases forward velocity. This effect requires gap junction-mediated activation of RIFL/R, which subsequently activates the premotor interneurons AVBL/R to increase activity of the forward movement-driving B motor neurons. When head swinging is inhibited, body undulation is decreased. Conversely, increased head swinging frequency leads to increased body undulation frequency to potentiate higher forward velocity. This suggests communication between the head and body CPGs. Our preliminary results suggest that AVG may also be required to coordinate the head and body CPGs. Activation of AVG was sufficient to drive body bends even when head swinging was inhibited. Increased head swinging is not able change body undulation when AVG is ablated. We propose that the descending interneuron circuit (AVG-RIF-AVB) permits generation of adaptive forward movement by modulating forward speed and linking the head and body CPGs. Xu, T. et. al. PNAS May 8, 2018 115 (19) E4493-E4502

William M Winston et al. (2001) International C. elegans Meeting "A Screen for Mutations that Enhance and Suppress Systemic RNAi"

Christina Molodowitch, William M Winston, Craig P Hunter

[International C. elegans Meeting, 2001]

One of the hallmarks of RNAi in C. elegans is the systemic effect: injecting gene specific dsRNA into one tissue interferes with the expression of that gene in other tissues (Fire, A. et. al, 1998). In order to elucidate the mechanisms of systemic RNAi, we have developed an assay that has allowed us to identify mutants that are specifically suppressed in their ability to execute systemic RNAi, but are still able to maintain cell autonomous RNAi. This assay has also been used to identify mutants that are apparently enhanced for RNAi. We have screened approximately 600,000 genomes in search of suppressor mutants and approximately 100,000 genomes for enhancer mutants. Towards our goal of identifying the genes necessary for systemic RNAi, we are placing the mutations into complementation groups, mapping representative mutants to linkage groups, and characterizing the gene and tissue specificity of the suppressor mutants. Fire, A., Xu, S., Montgomery, M.K., Kostas, S.A., Driver, S.E., Mello, C.C. (1998) Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans . Nature 19;391(6669):806-11

Rauthan, M. et al. (2017) International Worm Meeting "MicroRNA regulation of nicotine-dependent behavior in C. elegans."

Rauthan, M., Ronan, E.A., Gong, J., Xu, X.Z.S., Liu, J., Wescott, S.

[International Worm Meeting, 2017]

Tobacco smoking is the leading cause of preventable death in developed nations. Nicotine is the principle addictive substance in cigarettes. Chronic exposure to nicotine up-regulates nAChRs and is thought to play a critical role in the primary steps of nicotine dependence, but the underlying mechanisms are not well understood. We have previously developed a C. elegans model of nicotine dependent behavior, and shown that the nAChR gene acr-15 is required for acute response to nicotine (Feng et al., 2006). Here we identify a key role for microRNA in regulating nicotine-dependent behavior by modulating nAChR expression in C. elegans. Specifically, we show that chronic nicotine treatment down-regulates microRNA machinery, leading to up-regulation of another nAChR gene that is specifically required for nicotine withdrawal behavior. This effect is mediated by a microRNA that recognizes the 3'UTR of nAChR transcripts. These observations uncover an interesting phenomenon that different nAChRs mediate distinct aspects of nicotine dependence in C. elegans. Our results reveal a functional link between nicotine, microRNA, nAChRs, and nicotine-dependent behavior. Reference(s): 1. Feng, Z., Li, W., Ward, A., Piggott, B.J., Larkspur, E., Sternberg, P.W., and Xu, X.Z.S. (2006). A C. elegans model of nicotine-dependent behavior: regulation by TRP family channels. Cell 127, 621-633.