An enteric neuron ionotropic receptor regulates salt stress resistance
Summary
This Nature study identifies a single enteric (pharyngeal) neuron in Caenorhabditis elegans, I3, that senses ingested monovalent and divalent cations and drives organismal resistance to high-salt stress. Salt detection relies on an ionotropic receptor-like tuning subunit GLR-9 together with the IR25a-like co-receptor GLR-7. Activation of I3 triggers two modes of signalling: cholinergic output that protects against acute high-salt exposure, and peptidergic (FLP-6) signalling required for acclimatisation-dependent tolerance. GLR-9/GLR-7 are necessary and sufficient for salt responses, and I3 signalling reprogrammes gene expression in distant tissues (gut, epidermis) to up-regulate osmoprotective factors such as glycerol biosynthetic enzymes and secreted protective peptides.
Key Points
- GLR-9 (tuning subunit) and GLR-7 (co-receptor) localise to the lumen-facing sensory ending of the single I3 pharyngeal neuron and act as a salt-detecting complex.
- I3 responds cell-autonomously to a range of cations (Na+, K+, NH4+, Ca2+ etc.) but not to equiosmolar sugars, indicating cation-specific sensing rather than general osmolarity detection.
- Loss of glr-9 or glr-7 makes worms hypersensitive to high salt; rescuing glr-9 in I3 restores tolerance, showing sufficiency and necessity.
- I3 uses cholinergic signalling for immediate protection against acute salt shock, and FLP-6 neuropeptide signalling during acclimatisation to produce longer-term salt tolerance.
- Salt-evoked I3 signalling changes expression in distal tissues (e.g. gpdh-1, pgph-2, trehalase genes, fipr-26), and these transcriptional programmes are required for full acclimatisation and recovery.
- Heterologous co-expression of GLR-9 with GLR-7 isoforms in HEK293T cells produces salt-evoked calcium responses, supporting receptor sufficiency in a non-native system.
- The work demonstrates a chemosensory role for ionotropic receptor-like proteins in nematodes, extending the known chemosensory functions of IR-like receptors beyond arthropods.
Content summary
The authors combine cellular imaging, genetics, electrophysiology-like calcium assays in HEK cells, behavioural assays and RNA-sequencing to map the pathway from salt detection to organismal tolerance. GLR-9::GFP is expressed exclusively in I3 and concentrates at its pharyngeal lumen-exposed ending. I3’s calcium signal is triggered by multiple salts and abolished in glr-9 or glr-7 nulls. Reintroducing glr-9 specifically to I3 rescues responses and survival. Functional dissection shows acute tolerance needs vesicular acetylcholine release from I3, whereas acclimatisation depends on peptidergic signalling (FLP-6). RNA-seq after short-term salt acclimatisation reveals a GLR-9-dependent subset of osmotolerance genes (glycerol production enzymes, trehalase paralogues, secreted peptides and cuticle components) that likely underlie improved survival. glr-9 mutants show misregulated basal transcription and slower recovery after salt stress, implying tonic low-salt signalling by I3 helps maintain homeostasis.
Context and relevance
This paper defines an interoceptive sensory pathway — an enteric neuron directly sampling ingested ions — that couples local detection to systemic transcriptional and physiological changes. It links molecular sensory recognition (ionotropic receptor complex) to neurally mediated endocrine outputs and tissue-level remodelling, offering a compact model of how animals detect and adapt to specific internal chemical stresses. The findings are relevant to researchers studying interoception, sensory receptor evolution, enteric nervous system function, osmoregulation and stress-response gene networks. It also suggests that IR-like chemoreceptors have retained functional roles across protostomes, not only in insects.
Why should I read this?
Short version: it’s neat. A single gut neuron reads the salt in the food, flips two different signalling switches (fast acetylcholine and slower peptide), and rewires the worm so it survives salty shocks. If you care about how senses inside the body control whole-organism stress responses — this paper saves you days of slogging through mutants and messy transcriptomes. It’s a tidy mechanistic story with clear genetic, imaging and transcriptomic evidence.
Author style
Punchy: the study delivers a crisp chain of evidence from receptor to behaviour and gene expression. If you work on sensory biology, stress physiology or receptor evolution, give this one your attention — the details matter and the mechanisms are actionable.