Xu, Suhong et al. (2011) International Worm Meeting "Calcium signaling is required for epidermal wound repair in C. elegans."

Xu, Suhong, Chisholm, Andrew D, Hsiao, Tiffany I

[International Worm Meeting, 2011]

Epidermal wound repair in general involves several coordinated responses, including actomyosin based closure of the wound, repair of the permeability barrier, and cutaneous innate immune responses. C. elegans has a remarkable ability to repair and respond to epidermal wounds, such as those inflicted by injection needles or nematode-penetrating fungi. Wounding of the epidermis by injection needles or laser damage activates a cutaneous innate immune response via p38/PMK-1 signaling (Refs. 1, 2). This p38 MAPK pathway is important for survival post-wounding (Ref. 3) but does not appear to be involved in wound closure or barrier repair. We are interested in the triggers and effectors of wound closure and barrier repair. Studies of wound repair in single cells have implicated calcium as a key second messenger pathway in response to damage. In C. elegans epidermal calcium signaling is involved in epidermal enclosure (Ref. 4), but the role of calcium in the mature epidermis is well known. Using genetically encoded calcium sensors we find that needle or laser wounding triggers a rapid and robust calcium wave that spreads from the injury site through the epidermis. The speed of travel of the calcium wave suggest it results from calcium-induced calcium release from internal stores. Dominant-negative fragments of the inositol trisphosphate receptor ITR-1 ("IP3 sponges") reduce the amplitude of the wound-triggered transient. IP3 sponges and calcium chelators reduce survival post-wounding, suggesting calcium signals are important for wound repair. To identify genes involved in the initiation or transduction of the calcium signal we are screening the ~400 C. elegans genes with domains implicated in calcium binding or flux (the 'calciome'). We find that the TRPM channel GTL-2 is important for epidermal calcium dynamics and survival post wounding. GTL-2 is expressed in the epidermis (T. Stawicki and Y. Jin, personal communication) and can function cell autonomously to regulate epidermal calcium. gtl-2 mutants display normal induction of epidermal innate immune responses to wounding, suggesting GTL-2 acts in parallel to the p38 MAPK pathway. Conversely, we find that calcium signaling, but not the p38 pathway, is important for actomyosin mediated closure of epidermal wounds. In summary, epidermal wounding appears to trigger multiple signal transduction pathways in the epidermis that must cooperate for effective wound healing. References: 1.Pujol et al, 2008 Current Biology 18, 481-489 2.Ziegler et al, 2009, Cell Host & Microbe 5, 341-352 3.Tong et al, PNAS, 2009, 106, 1457-1461 4.Thomas-Virnig et al, 2004, Current Biology 14, 1882-1887.

Xu, Suhong et al. (2015) International Worm Meeting "Epidermal wounding induces mitochondrial ROS production that promotes wound repair in C. elegans."

Xu, Suhong, Chisholm, Andrew D

[International Worm Meeting, 2015]

All organisms have evolved stress response pathways that allow them to switch into an alerted state and protect them from environmental challenges. Skin wounds are acute stresses that can be fatal unless tissue homeostasis is efficiently restored. Wounding of barrier epithelia such as the epidermis causes loss of bodily fluids and can result in opportunistic infection at the wound site. C. elegans is able to tolerate needle wounds such as those inflicted during microinjections, yet the mechanisms that detect and respond epidermal damage have only recently become apparent. Wounding of the worm epidermis by microinjection needle or laser triggers a p38 MAPK dependent innate immune response that defends against opportunistic infection at wounds . In addition to this innate immune response, we previously reported that wounding triggers a cytosolic Ca2+ response which is required for actin polymerization dependent epidermal wound closure. Here we describe an intracellular cytoprotective role for mitochondrial reactive oxygen species (mtROS) in response to wounding in C. elegans epidermis. We show that epidermal mitochondria become fragmented and generate ROS superoxide locally after injury. Reducing mtROS levels by treatment with mitochondrial targeted antioxidants inhibits wound closure. Conversely, genetic or pharmacological elevation of mtROS accelerates wound closure in the wild type, and can rescue the wound closure defects of mutants such as TRPM/gtl-2. mtROS act downstream of wound-triggered Ca2+ influx. We find that the Mitochondrial Calcium Uniporter MCU-1 is essential for rapid mitochondrial Ca2+ uptake and mtROS production after wounding. mtROS can promote actin-based wound closure by local inhibition of Rho GTPase activity via a redox-sensitive motif. Our findings identify mtROS as an important second messenger signal in restoring tissue homeostasis after injury.

Fire A et al. (1994) Worm Breeder's Gazette "Vectorology I: New lacZ Vectors (Building a Better Gene Trap)."

Fire A, Xu SQ

[Worm Breeder's Gazette, 1994]

Vectorology I: New lacZ vectors ("building a better gene trap") Andrew Fire and SiQun Xu Carnegie Institution of Washington, Baltimore, Md 21210

Niethammer P (2014) Dev Cell "Stress heals."

Niethammer P

[Dev Cell, 2014]

Reactive oxygen species (ROS) are generated as a response to cellular stress and regulate processes including cellular signaling and wound healing. In this issue of Developmental Cell, Xu and Chisholm (2014) demonstrate that mitochondrial ROS are required for proper wound healing in Caenorhabditis elegans through controlling the redox state of actin regulators.

Bonini NM (2001) Dev Cell "Stores to die for."

Bonini NM

[Dev Cell, 2001]

Genes that regulate apoptosis are well defined. In contrast, it has not been clear what genes are central to necrotic cell loss. In the September 27th issue of Neuron, Xu et al. (2001) report a critical role for genes that regulate storage and release of Ca2+ from the endoplasmic reticulum as important to necrotic-like cellular degeneration in Caenorhabditis elegans.

Tang, Ngang Heok et al. (2019) International Worm Meeting "Regulation of axon regeneration by the mRNA decay factors."

Tang, Ngang Heok, Kim, Kyung Won, Yeo, Gene, Blazie, Stephen, Chisholm, Andrew, Jin, Yishi, Xu, Suhong, Yee, Brian

[International Worm Meeting, 2019]

mRNA decay factors regulate mRNA turnover by recruiting non-translating mRNAs and targeting them for translational repression, decapping and degradation, yet it remains poorly understood how mRNA decay factors function in vivo to regulate specific cellular processes. We found that mRNA decay factors form cytoplasmic puncta in C. elegans neurons and have opposing roles in axon regrowth. While decapping enzymes such as DCAP-1/2 promote axon regrowth after injury, translational repressors such as CAR-1 and CGH-1 inhibit axon regrowth in adult animals. We find that enhanced axon regeneration in a translational repressor mutant is dependent on mitochondrial functions. We show that axon injury triggers a transient mitochondrial calcium influx, which is more sustained in animals lacking translational repressors. We use genome-wide seCLIP to identify mRNA targets of translational repression in neurons, among which a regulator of mitochondrial calcium influx appears to be a direct target. Loss of translational repression leads to elevated mRNA levels for the mitochondrial calcium regulator. Moreover, the enhanced axon regrowth and sustained axonal calcium elevation observed in translational repressor mutants is dependent on mitochondrial calcium influx regulators. Our results reveal specific roles for mRNA decay regulation in neurons and a novel pathway that controls axon regeneration through mitochondrial calcium uptake.

Fire A et al. (1998) Nature "Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans."

Fire A, Mello CC, Kostas SA, Montgomery MK, Driver SE, Xu SQ

[Nature, 1998]

Experimental introduction of RNA into cells can be used in certain biological systems to interfere with the function of an endogenous gene. Such effects have been proposed to result from a simple antisense mechanism that depends on hybridization between the injected RNA and endogenous messenger RNA transcripts. RNA interference has been used in the nematode Caenorhabditis elegans to manipulate gene expression. Here we investigate the requirements for structure and delivery of the interfering RNA. To our surprise, we found that double-stranded RNA was substantially more effective at producing interference than was either strand individually. After injection into adult animals, purified single strands had at most a modest effect, whereas double-stranded mixtures caused potent and specific interference. The effects of this interference were evident in both the injected animals and their progeny. Only a few molecules of injected double-stranded RNA were required per affected cell, arguing against stochiometric interference with endogenous mRNA and suggesting that there could be a catalytic or amplification component in the interference process.AD - Carnegie Institution of Washington, Department of Embryology, Baltimore, Maryland 21210, USA. fire@mail1.ciwemb.eduFAU - Fire, AAU - Fire AFAU - Xu, SAU - Xu SFAU - Montgomery, M KAU - Montgomery MKFAU - Kostas, S AAU - Kostas SAFAU - Driver, S EAU - Driver SEFAU - Mello, C CAU - Mello CCLA - engPT - Journal ArticleCY - ENGLANDTA - NatureJID - 0410462RN - 0 (Calmodulin-Binding Proteins)RN - 0 (Helminth Proteins)RN - 0 (Muscle Proteins)RN - 0 (RNA, Antisense)RN - 0 (RNA, Double-Stranded)RN - 0 (twitchin)SB - IM

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

Voia, Anna et al. (2022) MicroPubl Biol

Labbe, Jean-Claude, Voia, Anna, Poupart, Vincent

[MicroPubl Biol, 2022]

Plants of the Mimosa genus are studied and used for their bioactive properties. Among bioactive phytochemicals are quercetin and myricetin, which have been demonstrated to act as antioxidants in many contexts (Taheri et al. 2020; Xu et al. 2019), including in C. elegans (Buchter et al. 2013; Grnz et al. 2012; Sugawara and Sakamoto 2020). Other phytochemicals from these plants, such as the triterpenoid phytosterol lupeol, have been shown to have antioxidant properties but have not been as extensively characterized in model organisms (Liu et al. 2021; Shai et al. 2009). Here we employed the nematode C. elegans to assess whether lupeol elicits antioxidant response in vivo . Using reporter assays for oxidative stress, we find that treatment of animals with lupeol rescues some of the effects resulting from treatment with the prooxidant paraquat. Our results demonstrate that lupeol displays antioxidant properties in vivo in C. elegans .