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Nutrient-responsive and DAF-16/FoxO target H1 histone HIL-1 promotes resistance to starvation and bacterial pathogens in Caenorhabditis elegans

ABSTRACT: Insulin/IGF-1 signaling (IIS) mediates metabolic and developmental acclimation to stressful conditions including starvation. The transcription factor DAF-16/FoxO actuates many of the physiological effects of reduced IIS, yet the specific contributions of DAF-16 target genes to stress resistance remain poorly understood. We explore the function of C. elegans H1 linker histone variant hil-1/H1.0, a DAF-16 target that is upregulated during starvation. The HIL-1 sequence is divergent from the other eight annotated C. elegans H1 variants, and the others are not so highly responsive to nutrient availability and DAF-16 activity, suggesting distinct function. Using knock-in reporters, we find that HIL-1 is expressed ubiquitously in nuclei of L1 and dauer larvae during starvation, but that expression is largely undetectable in fed larvae. Disrupting hil-1 activity through mutation or auxin-inducible degradation led to reduced growth after extended L1 starvation, revealing reduced starvation resistance. RNA-seq of hil-1 mutants showed that hil-1 affects expression of relatively few genes. However, hil-1 activates genes involved in the innate immune response, Pseudomonas aeruginosa infection, and components of the nipi-3/TRIB1 immunity pathway. hil-1 mutants display compromised survival upon exposure to P. aeruginosa under reduced IIS, and genes activated by hil-1 promote resistance to P. aeruginosa. Together these results suggest that DAF-16/FoxO activates transcription of hil-1 during starvation to promote resistance to starvation and pathogens. We demonstrate conditional regulation of an H1 histone, and we reveal a novel mechanism for how IIS promotes stress resistance by identifying a histone variant that connects nutrient sensing to immunity.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE318171 | GEO | 2026/05/27

REPOSITORIES: GEO

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Project description:Post-embryonic development of the nematode C. elegans is governed by nutrient availability. L1-stage larvae remain in a state of developmental arrest after hatching until they feed. This “L1 arrest” (or "L1 diapause") is associated with increased stress resistance, supporting starvation survival. Loss of the transcription factor daf-16/FOXO, an effector of insulin/IGF signaling, results in arrest-defective and starvation-sensitive phenotypes. We show that daf-16/FOXO regulates L1 arrest cell-nonautonomously, suggesting that insulin/IGF signaling regulates at least one additional signaling pathway. We used mRNA-seq to identify candidate signaling molecules affected by daf-16/FOXO during L1 arrest. daf-16/FOXO had overlapping but distinct effects on gene expression in L1 arrest compared to daf-2/InsR adults. Notably, dbl-1/TGF-β, a ligand for the Sma/Mab pathway, and daf-36, which encodes an upstream component of the daf-12/NHR steroid hormone signaling pathway, were up-regulated during L1 arrest in a daf-16/FOXO mutant. Using genetic epistasis analysis, we show that dbl-1/TGF-β and daf-12/NHR steroid hormone signaling pathways are required for the daf-16/FOXO arrest-defective phenotype, suggesting that daf-16/FOXO represses dbl-1/TGF-β and daf-36. The dbl-1/TGF-β and daf-12/NHR pathways have not previously been shown to affect L1 development, but we found that disruption of these pathways delayed L1 development in fed larvae, consistent with these pathways promoting development in starved daf-16/FOXO mutants. Though the dbl-1/TGF-β and daf-12/NHR pathways are epistatic to daf-16/FOXO for the arrest-defective phenotype, disruption of these pathways does not suppress starvation sensitivity of daf-16/FOXO mutants. This observation uncouples starvation survival from developmental arrest, indicating that DAF-16/FOXO targets distinct effectors for each phenotype, and revealing that inappropriate development during starvation does not cause the early demise of daf-16/FOXO mutants. Overall, this study shows that daf-16/FOXO promotes developmental arrest cell-nonautonomously by repressing pathways that promote larval development.

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Nutrient-responsive and DAF-16/FoxO target H1 histone HIL-1 promotes resistance to starvation and bacterial pathogens in Caenorhabditis elegans

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