Yang, Wen et al. (2011) International Worm Meeting "A Mitochondrial Superoxide Signal Triggers Increased Longevity in C. elegans."

Yang, Wen, Hekimi, Siegfried

[International Worm Meeting, 2011]

The nuo-6 and isp-1 genes of C. elegans encode, respectively, subunits of complex I and III of the mitochondrial respiratory chain. Partial loss-of-function mutations in these genes decrease electron transport and greatly increase the longevity of C. elegans by a mechanism that is distinct from that induced by reducing their level of expression by RNAi. Electron transport is a major source of the superoxide anion, which in turn generates several types of toxic reactive oxygen species (ROS), and aging is accompanied by increased oxidative stress, which is an imbalance between the generation and detoxification of ROS. These observations have suggested that the longevity of such mitochondrial mutants might result from a reduction in ROS generation, which would be consistent with the mitochondrial oxidative stress theory of aging. It is difficult to measure ROS directly in living animals, and this has held back progress in determining their function in aging. Here we have adapted a technique of flow cytometry to directly measure ROS levels in isolated mitochondria to show that the generation of superoxide is elevated in the nuo-6 and isp-1 mitochondrial mutants, although overall ROS levels are not, and oxidative stress is low. Furthermore, we show that this elevation is necessary and sufficient to increase longevity, as it is abolished by the antioxidants NAC and vitamin C, and phenocopied by mild treatment with the prooxidant paraquat. Moreover, the results of treating a variety of short- and long-lived mutants with NAC and paraquat suggest that the pathway triggered by mitochondrial superoxide is distinct from previously studied mechanisms, including insulin signalling, dietary restriction, ubiquinone deficiency, the hypoxic response, and hormesis. These findings show that increased superoxide generation acts as a signal to trigger a distinct mechanism that prevents or attenuates the effects of subsequent aging. We propose that superoxide is generated as a protective signal in response to molecular damage sustained during wild-type aging as well. This model provides a new explanation for the well-documented correlation between ROS and the aged phenotype as a gradual increase of molecular damage during aging would trigger a gradually stronger ROS response.

Wen Yang et al. (2003) International Worm Meeting "New lifespan mutants with an Isp-1-like phenotype."

Jingjing Li, Wen Yang, Siegfried Hekimi

[International Worm Meeting, 2003]

We have previously identified over 12 genes (clk and clk-like genes) in which reduction-of-function mutations prolong the animals lifespan. The mutants also share a number of other phenotypes, in particular, a mean slowing down of physiological rates such as the rates of development, reproduction and behavior. The two most extensively characterized of these genes are clk-1 and isp-1. clk-1 encodes an enzyme involved in the biosynthesis of ubiquinone (UQ), a lipid that carries out redox functions at multiple cellular sites, including in the mitochondrial respiratory chain. In clk-1 mutants, UQ is replaced by a biosynthetic precursor, demethoxyubiquinone (DMQ). isp-1 encodes a catalytic subunit of Complex III of the mitochondrial respiratory chain: the nuclearly encoded Rieske iron sulfur protein. In addition, we have identified a mutation in cytochrome b (ctb-1), the mitochondrially encoded subunit of Complex III, which partially suppresses the isp-1(qm150) phenotypes. The increased life span of isp-1 and isp-1;ctb-1 mutants appear to be due to a reduction in the production of reactive oxygen species (ROS) by the mitochondrial respiratory chain. Indeed, these mutants are resistant to killing by paraquat treatment during development. Furthermore, some of the phenotypes of these mutants are relieved by treatments that increase intracellular ROS levels, indicating that these phenotypes are the result of abnormally low levels of ROS. These observations also provide an in vivo demonstration of the role of ROS in regulating growth rates in C. elegans.In order to obtain further insight and genetic tools to study the regulation of ROS production by the mitochondrial respiratory chain, we are carrying out a screen designed to identify mutants with an Isp-1-like phenotype. The development of the F2 progeny of mutagenized animals is synchronized and the developmental rates of the F2 worms are monitored. Animals with very slow development and a very slow defecation cycle period are kept for further analysis. Mutants without obviously deleterious phenotypes, such as small size, transparence, infertility, high levels of embryonic or larval lethality, constipation or movement disorders, are retained for genetic mapping and molecular analysis.

(2017) Toxicol Sci "4-Bromodiphenyl Ether Induces Germ Cell Apoptosis by Induction of ROS and DNA Damage in Caenorhabditis elegans."

[Toxicol Sci, 2017]

The corresponding authorship has been updated to reflect Yang Luan and Jinfu Zhango as co-corresponding authors in the final version.

Fechner S et al. (2018) MicroPubl Biol "The bodies of dpy-10(e128) are twice as stiff as wild type"

Loizeau F, Pruitt B, Nekimken AL, Goodman MB, Fechner S

[MicroPubl Biol, 2018]

DPY-10 is a collagen protein in the nematodes cuticle. Mutations in the dpy-10 gene induce various morphological changes that lead to animals with a dumpy (Dpy) or roller (Rol) phenotype (Levy, Yang and Kramer, 1993).

Ahmad W et al. (2020) Biochem Biophys Res Commun "Prediction of human tau 3D structure, and interplay between O--GlcNAc and phosphorylation modifications in Alzheimer's disease: C.elegans as a suitable model to study these interactions invivo."

Ahmad I, Ahmad W, Shabbiri K

[Biochem Biophys Res Commun, 2020]

Tau protein regulates, maintains and stabilizes microtubule assembly under normal physiological conditions. In certain pathological circumstances, tau is post-translationally modified predominantly via phosphorylation and glycosylation. Hyper-phosphorylation of tau in Alzheimer's disease (AD) resulted in aggregated neurofibrillary tangles (NFTs) formation. Unfortunately, absence of tau 3D structure makes difficult to understand exact mechanism involved in tau pathology. Here by using ab-initio modelling, we predicted a tau 3D structure that not only explains its binding with microtubules but also elucidates NFTs formation. O-linked -N-acetylglucosaminylation (O--GlcNAc) is thought to regulate tau phosphorylation on single or proximal Ser/Thr residues (called as Yin-Yang sites). In this study, we not only validate the previously described three-serine residues (208, 238 and 400) as Yin-Yang sites but also predicted 22 more possible Ser/Thr O-glycosylation sites. Among them seventeen residues were predicted as possible Yin-Yang sites and are proposed to mediate NFT formation in AD. These predicted Yin-Yang sites may act as attractive therapeutic targets for the drug development in AD. Predicted 3D structure of tau₄₄₁ was highly accessible for phosphorylation and hyperphosphorylation, and showed higher surface accessibility for interplay between O--GlcNAc and phosphorylation modifications. Kinases and phosphatases involved in tau phosphorylation are conserved in human and other organisms. Homology modelling revealed conserved catalytic domain for both human and C.elegans O-GlcNAc transferase (OGT), suggesting that transgenic C.elegans expressing human tau may be a suitable model system to study these modifications.

Yee, Callista et al. (2015) International Worm Meeting "The intrinsic apoptosis pathway mediates the pro-longevity response to mitochondrial reactive oxygen species."

Yee, Callista, Yang, Wen, Hekimi, Siegfried

[International Worm Meeting, 2015]

In C. elegans, two mutations that affect mitochondrial electron transport chain subunits (isp-1(qm150) and nuo-6(qm200)) result in increased production of mitochondrial reactive oxygen species (mtROS). Animals carrying these mutations have a significantly increased lifespan relative to the wild type. It has also been shown that treatment with pro-oxidants such as paraquat (PQ) can significantly increase wild type lifespan but is not additive to the lifespan of the two mitochondrial mutants. Furthermore, treatment with antioxidants such as N-acetyl-cysteine (NAC) and Vitamin C can decrease the longevity of these mutants. Using gene arrays, we determined a large overlap of differentially expressed transcripts between isp-1, nuo-6 and paraquat treatment. These and other results suggest that increased levels of mtROS act as a signal to extend lifespan in C. elegans.We were interested in determining the mechanism by which mtROS signalling is sensed and transduced in order to elicit these changes in gene expression. Many processes have been found to require components of the intrinsic apoptotic pathway to perform tasks that do not result in apoptosis, such as cell cycle regulation, neuronal regeneration and mitochondrial fission/fusion. In mammalian studies, components of the intrinsic apoptotic pathway have also been found to be sensitive to ROS, prompting us to test the involvement of this pathway with respect to mtROS-mediated longevity. We found that components of the core intrinsic apoptotic pathway (CED-9, CED-4 and CED-3) are required for the longevity of isp-1 and nuo-6 mutants, as well as for lifespan extension induced by paraquat treatment. In addition, loss of the intrinsic pathway reversed a large portion of the gene expression changes observed in isp-1 and nuo-6 mutants. We found that to induce an effect on longevity the pathway is not stimulated by EGL-1 as for apoptosis, but by CED-13, an alternative BH3-only protein. We observed no effect on developmental apoptosis in isp-1 and nuo-6 mutants or by treatment with paraquat. We conclude that activation of the pathway by mtROS signaling does not affect apoptosis, but instead acts as a defense mechanism to protect against consequences of mitochondrial dysfunction by inducing gene expression changes that promotes survival and modulates stress sensitivity.We are currently using CRISPR/Cas9 to study the molecular mechanisms that allow for a dual role of the pathway: apoptosis and longevity. .

Goulding M (2012) Neuron "Motor neurons that multitask."

Goulding M

[Neuron, 2012]

Animals use a form of sensory feedback termed proprioception to monitor their body position and modify the motor programs that control movement. In this issue of Neuron, Wen etal. (2012) provide evidence that a subset of motor neurons function as proprioceptors in C.elegans, where B-type motor neurons sense body curvature to control the bending movements that drive forward locomotion.

Xu W et al. (2019) Elife "Evolution of Yin and Yang isoforms of a chromatin remodeling subunit precedes the creation of two genes."

Zhao Y, Stevens L, Munoz J, McGrath PT, Long L, Xu W, Felipe I, Ellis RE

[Elife, 2019]

Genes can encode multiple isoforms, broadening their functions and providing a molecular substrate to evolve phenotypic diversity. Evolution of isoform function is a potential route to adapt to new environments. Here we show that <i>de novo</i>, beneficial alleles in the <i>nurf-1</i> gene became fixed in two laboratory lineages of <i>C. elegans</i> after isolation from the wild in 1951, before methods of cryopreservation were developed. <i>nurf-1</i> encodes an ortholog of BPTF, a large (&gt;300kD) multidomain subunit of the NURF chromatin remodeling complex. Using CRISPR-Cas9 genome editing and transgenic rescue, we demonstrate that in <i>C. elegans</i>, <i>nurf-1</i> has split into two, largely non-overlapping isoforms (NURF-1.D and NURF-1.B, which we call Yin and Yang, respectively) that share only two of 26 exons. Both isoforms are essential for normal gametogenesis but have opposite effects on male/female gamete differentiation. Reproduction in hermaphrodites, which involves production of both sperm and oocytes, requires a balance of these opposing Yin and Yang isoforms. Transgenic rescue and genetic position of the fixed mutations suggest that different isoforms are modified in each laboratory strain. In a related clade of <i>Caenorhabditis</i> nematodes, the shared exons have duplicated, resulting in the split of the Yin and Yang isoforms into separate genes, each containing approximately 200 amino acids of duplicated sequence that has undergone accelerated protein evolution following the duplication. Associated with this duplication event is the loss of two additional <i>nurf-1</i> transcripts, including the long-form transcript and a newly identified, highly expressed transcript encoded by the duplicated exons. We propose these lost transcripts are non-functional side products necessary to transcribe the Yin and Yang transcripts in the same cells. Our work demonstrates how gene sharing, through the production of multiple isoforms, can precede the creation of new, independent genes.

Robertson SM et al. (2012) Worm "Our evolving view of Wnt signaling in C. elegans: If two's company and three's a crowd, is four really necessary?"

Robertson SM, Lin R

[Worm, 2012]

In this commentary, we discuss how our recent paper by Yang et al. contributes a new wrinkle to the already somewhat curious Wnt signaling pathway in C. elegans. We begin with a historical perspective on the Wnt pathway in the worm, followed by a summary of the key salient point from Yang et al., 2011, namely demonstration of mutually inhibitory binding of a -catenin SYS-1 to the N-terminus and another -catenin WRM-1 to the C-terminus of the TCF protein POP-1, and a plausible structural explanation for these differential binding specificities. The mutually inhibitory binding creates one population of POP-1 that is bound by WRM-1, phosphorylated by the NLK kinase and exported from the nucleus, and another bound by coactivator SYS-1 that remains in the nucleus. We speculate on the evolutionary history of the four -catenins in C. elegans and suggest a possible link between multiple -catenin gene duplications and the requirement to reduce nuclear POP-1 levels to activate Wnt target genes.

Wilson DL (1998) Journal of Gerontology "Commentary - Survival of C. elegans in axenic culture."

Wilson DL

[Journal of Gerontology, 1998]

Vanfleteren and colleagues present an interesting example of environmental conditions altering the kinetics of survival. Most previous studies of survival in C. elegans have used abundant bacteria as a food source. Such studies have found that the Gompertz function (exponential growth in mortality rate with age) gives a relatively good fit to survival curves, but that there is some deceleration in the rate of growth of mortality later in the life span. Yulong Yang and I have completed dozens of studies of small populations of the wild-type strain, N2, as well as strains TJ401, TJ411, TJ412,and BA713 in the presence of abundant bacteria in liquid or on agar. Survival curves were better fit by Gompertz more often than by Weibull or logistic functions (unpublished observations).