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Hydrogen sulfide (H₂S) acts as an energy source, a toxin, and a gasotransmitter across diverse biological contexts. We use the robust locomotory responses of Caenorhabditis elegans to high levels of H₂S to elucidate the molecular mechanisms underlying its acute and adaptive responses. We find that the H₂S-evoked behavioral response is shaped by multiple environmental factors including oxygen (O₂) levels and nutritional state and is modulated by various pathways such as insulin, TGF-β, and HIF-1 signaling, as well as by input from O₂-sensing neurons. Prolonged exposure to H₂S activates HIF-1 signaling, leading to the upregulation of stress-responsive genes, including those involved in H₂S detoxification. This promotes an adaptive state in which locomotory speed is reduced in H₂S, while responsiveness to other stimuli is preserved. In mutants deficient in HIF-1 signaling, iron storage, and detoxification mechanisms, animals display a robust initial response but rapidly enter a sleep-like behavior characterized by reduced mobility and diminished responsiveness to subsequent sensory stimuli. Furthermore, while acute production of mitochondria-derived reactive O₂ species (ROS) appears to initiate the avoidance response to H₂S, persistently high ROS promotes an adaptive state, likely by activating various stress-response pathways, without substantially compromising cellular H₂S detoxification capacity. Taken together, our study provides comprehensive molecular insights into the mechanisms through which C. elegans modulates and adapts its response to H₂S exposure.

The Shaker/Kv1 subfamily of voltage-gated potassium (K+) channels is essential for modulating membrane excitability. Their loss results in prolonged depolarization and excessive calcium influx. These channels have also been implicated in a variety of other cellular processes, but the underlying mechanisms remain poorly understood. Through comprehensive screening of K+ channel mutants in C. elegans, we discovered that shk-1 mutants are highly susceptible to bacterial pathogen infection and oxidative stress. This vulnerability is associated with reduced glycogen levels and substantial mitochondrial dysfunction, including decreased ATP production and dysregulated mitochondrial membrane potential under stress conditions. SHK-1 is predominantly expressed and functions in body wall muscle to maintain glycogen storage and mitochondrial homeostasis. RNA-sequencing data reveal that shk-1 mutants have decreased expression of a set of cation-transporting ATPases (CATP), which are crucial for maintaining electrochemical gradients. Intriguingly, overexpressing catp-3, but not other catp genes, restores the depolarization of mitochondrial membrane potential under stress and enhances stress tolerance in shk-1 mutants. This finding suggests that increased catp-3 levels may help restore electrochemical gradients disrupted by shk-1 deficiency, thereby rescuing the phenotypes observed in shk-1 mutants. Overall, our findings highlight a critical role for SHK-1 in maintaining stress tolerance by regulating glycogen storage, mitochondrial homeostasis, and gene expression. They also provide insights into how Shaker/Kv1 channels participate in a broad range of cellular processes.

G protein-coupled receptors (GPCRs) mediate responses to various extracellular and intracellular cues. However, the large number of GPCR genes and their substantial functional redundancy make it challenging to systematically dissect GPCR functions in vivo. Here, we employ a CRISPR/Cas9-based approach, disrupting 1654 GPCR-encoding genes in 284 strains and mutating 152 neuropeptide-encoding genes in 38 strains in C. elegans. These two mutant libraries enable effective deorphanization of chemoreceptors, and characterization of receptors for neuropeptides in various cellular processes. Mutating a set of closely related GPCRs in a single strain permits the assignment of functions to GPCRs with functional redundancy. Our analyses identify a neuropeptide that interacts with three receptors in hypoxia-evoked locomotory responses, unveil a collection of regulators in pathogen-induced immune responses, and define receptors for the volatile food-related odorants. These results establish our GPCR and neuropeptide mutant libraries as valuable resources for the C. elegans community to expedite studies of GPCR signaling in multiple contexts.

Hypoxia alters eating behavior in different animals. In C. elegans, hypoxia induces a strong food leaving response. We found that this behavior was independent of the known O 2 response mechanisms including acute O₂ sensation and HIF-1 signaling of chronic hypoxia response. Mutating egl-3 and egl-21, encoding the neuropeptide pro-protein convertase and carboxypeptidase, led to defects in hypoxia induced food leaving, suggesting that neuropeptidergic signaling was required for this response. However, we failed to identify any neuropeptide mutants that were severely defective in hypoxia induced food leaving, suggesting that multiple neuropeptides act redundantly to modulate this behavior.

Sufficient supply of oxygen (O₂) to tissue is essential for survival of aerobicanimals. In mammals, there are constant homeostatic regulation mechanisms that act on different time scales to maintain optimal O₂ delivery to tissues. The ability to detect and respond to acute oxygen shortages is indispensable to aerobic life. However, the molecular mechanisms and circuits underlying this capacity are poorly understood.

We characterize the locomotory response of feeding Caenorhabditis elegans (C. elegans) to 1% O₂. Acute hypoxia triggers a bout of turning maneuvers followed by a persistent switch to rapid forward movement as animals seek to avoid and escape hypoxia. Increasing cGMP signaling inhibits escape from 1% O₂, and that cGMP activates the protein kinase G, EGL-4, which in turn enhances neuroendocrine secretion to inhibit acute response to 1% O₂. A primary source of cGMP is the guanylyl cyclase, GCY-28. In addition, increasing mitochondrial reactive oxygen species (ROS), abrogate acute hypoxia response. Up-regulation of mitochondrial ROS increases cGMP levels, which contribute to the reduced hypoxia response. Our results implicate ROS and precise regulation of intracellular cGMP in the modulation of acute response to hypoxia by C. elegans.

In addition, we found that FMRFamide-related peptides FLP-1 plays a role in hypoxia evoked locomotory response. Our data showed that FLP-1 secretion from AVK interneurons acts on AVA and other neurons through DMSR-4, DMSR7, and DMSR-8 GPCR receptors to maintain baseline speed and to promote locomotory response to hypoxia.

We also found that hypoxia could induce food leaving behavior in C. elegans. Animals quickly escaped from the bacterial lawn when exposed to 1% O₂. The known O₂ response mechanisms cannot explain this phenotype, instead, neuropeptidergic signalling seems to be required for this behaviour.

It's known that pro-inflammatory cytokine ILC-17.1, the homologue of mammalian IL-17s, act as a neuromodulator involved in hyperoxia sensing in C. elegans. We found that it was not involved in acute hypoxia response. Instead, ILC-17.1 could modulate lifespan and damage defense mechanisms against stress in C. elegans by triggering an inhibitory network to constrain the activity of the nuclear hormone receptor, NHR-49.

In summary, our research can provide molecular and neurological understanding of how O₂ is sensed by animals. Additionally, it further emphasis C. elegans as a good model to understand oxygen sensing

The ability to detect and respond to acute oxygen (O2) shortages is indispensable to aerobic life. The molecular mechanisms and circuits underlying this capacity are poorly understood. Here, we characterize the behavioral responses of feeding Caenorhabditis elegans to approximately 1% O2. Acute hypoxia triggers a bout of turning maneuvers followed by a persistent switch to rapid forward movement as animals seek to avoid and escape hypoxia. While the behavioral responses to 1% O2 closely resemble those evoked by 21% O2, they have distinct molecular and circuit underpinnings. Disrupting phosphodiesterases (PDEs), specific G proteins, or BBSome function inhibits escape from 1% O2 due to increased cGMP signaling. A primary source of cGMP is GCY-28, the ortholog of the atrial natriuretic peptide (ANP) receptor. cGMP activates the protein kinase G EGL-4 and enhances neuroendocrine secretion to inhibit acute responses to 1% O2. Triggering a rise in cGMP optogenetically in multiple neurons, including AIA interneurons, rapidly and reversibly inhibits escape from 1% O2. Ca2+ imaging reveals that a 7% to 1% O2 stimulus evokes a Ca2+ decrease in several neurons. Defects in mitochondrial complex I (MCI) and mitochondrial complex I (MCIII), which lead to persistently high reactive oxygen species (ROS), abrogate acute hypoxia responses. In particular, repressing the expression of isp-1, which encodes the iron sulfur protein of MCIII, inhibits escape from 1% O2 without affecting responses to 21% O2. Both genetic and pharmacological up-regulation of mitochondrial ROS increase cGMP levels, which contribute to the reduced hypoxia responses. Our results implicate ROS and precise regulation of intracellular cGMP in the modulation of acute responses to hypoxia by C. elegans.