Regulation of the cellular heat shock response in Caenorhabditis elegans by thermosensory neurons

Abstract

Temperature pervasively affects all cellular processes. In response to a rapid increase in temperature, all cells undergo a heat shock response, an ancient and highly conserved program of stress-inducible gene expression, to reestablish cellular homeostasis. In isolated cells, the heat shock response is initiated by the presence of misfolded proteins and therefore thought to be cell-autonomous. In contrast, we show that within the metazoan Caenorhabditis elegans, the heat shock response of somatic cells is not cell-autonomous but rather depends on the thermosensory neuron, AFD, which senses ambient temperature and regulates temperature-dependent behavior. We propose a model whereby this loss of cell autonomy serves to integrate behavioral, metabolic, and stress-related responses to establish an organismal response to environmental change.

Fig. 1

Role of AFD and AIY neurons in the organismal heat shock response. (A) Schematic depiction of genes affecting AFD and AIY function. AFD detects temperature by using the cyclic guanosine 5′-monophosphate (cGMP)–dependent TAX-4/TAX-2 cyclic-nucleotide–gated (CNG) channel. Guanylyl cyclases, gcy-8, gcy-18, and gcy-23, function upstream of tax-4. ODX transcription factor, TTX-1, regulates gcy-8 expression, and AIY function is specified by the LIM homeobox gene, ttx-3. Total hsp70 (C12C8.1) mRNA levels in gcy-8 and ttx-3 mutants relative to wild-type animals before heat shock (pre-H.S.) and 2 hours after heat shock (post-H.S.) at (B) 30°C and (C) 34°C for 15 min. Time course of total (D) hsp70 (C12C8.1), (E) hsp70 (F44E5.4), and (F) hsp16.2 mRNA accumulation after heat shock (34°C; 15 min) in gcy-8 and ttx-3 mutants relative to wild-type animals. mRNA amounts were measured by quantitative reverse transcription polymerase chain reaction (RT-PCR) and normalized to maximal wild-type values. (G) Survival of wild-type, gcy-8, ttx-3, and hsf-1 mutant animals. Error bars indicate ±SE [(B) and (C)] and ±SD [(D) and (E)]. hsp70 (C12C8.1) promoter-GFP reporter expression in (H) wild-type, (I) gcy-8, and (J) ttx-3 mutant animals 2 hours after heat shock (34°C; 15 min). (i) pharynx, (ii) spermatheca, and (iii) intestinal cell. Scale bar = 100 μm.

Fig. 2

Impairment of HSF-1–dependent gene expression in gcy-8 mutants after temperature stress. (A) Total hsp70 (C12C8.1) mRNA, 2 hours after heat shock (34°C; 15 min), in wild-type and gcy-8 mutant animals subjected to RNAi-mediated knockdown of hsf-1 or daf-16. Relative mRNA levels were measured by quantitative RT-PCR and normalized to wild-type values on control RNAi. (B) Total hsp70 (C12C8.1) and cdr-1 mRNA levels in wild-type and gcy-8 mutants after cadmium stress (8). Relative mRNA levels were determined by quantitative RT-PCR and normalization to wild-type values. (C) Relative hsp70 (C12C8.1) mRNA levels in cadmium-treated wild-type animals and gcy-8 mutants subjected to RNAi-mediated knockdown of hsf-1. Relative mRNA levels were determined by quantitative RT-PCR and normalization to wild-type and gcy-8 values on control RNAi. Error bars indicate ±SE.

Fig. 3

AFD-dependent regulation of the cellular heat shock response is modulated by metabolic signals. (A) Relative hsp70 (C12C8.1) mRNA levels before and 2 hours after heat shock (34°C; 15 min) in wild-type and gcy-8 mutant animals grown at low population densities or exposed to dauer pheromone 10 min before and during the 2 hours of recovery after heat shock. Note semi-logarithmic scale. Relative mRNA levels were determined by quantitative RT-PCR and normalized to maximal wild-type values. Error bars indicate ±SE. (B) Model depicting the regulation of the cellular heat shock response by AFD-dependent signaling of temperature and dauer pheromone–dependent signaling of growth conditions.