cGMP dynamics that underlies thermosensation in temperature-sensing neuron regulates thermotaxis behavior in C. elegans

Abstract

Living organisms including bacteria, plants and animals sense ambient temperature so that they can avoid noxious temperature or adapt to new environmental temperature. A nematode C. elegans can sense innocuous temperature, and navigate themselves towards memorize past cultivation temperature (Tc) of their preference. For this thermotaxis, AFD thermosensory neuron is pivotal, which stereotypically responds to warming by increasing intracellular Ca2+ level in a manner dependent on the remembered past Tc. We aimed to reveal how AFD encodes the information of temperature into neural activities. cGMP synthesis in AFD is crucial for thermosensation in AFD and thermotaxis behavior. Here we characterized the dynamic change of cGMP level in AFD by imaging animals expressing a fluorescence resonance energy transfer (FRET)-based cGMP probe specifically in AFD and found that cGMP dynamically responded to both warming and cooling in a manner dependent on past Tc. Moreover, we characterized mutant animals that lack guanylyl cyclases (GCYs) or phosphodiesterases (PDEs), which synthesize and hydrolyze cGMP, respectively, and uncovered how GCYs and PDEs contribute to cGMP and Ca2+ dynamics in AFD and to thermotaxis behavior.

Feedforward and feedback mechanisms cooperatively regulate rapid experience-dependent response adaptation in a single thermosensory neuron type

“…Both T* cGMP and T* Calcium adapted to a significantly higher temperature within 3 mins of the temperature upshift from 15°C to 25°C (Figure 1C-D, Figure S1A-B), and continued to shift upwards upon further exposure to 25°C for up to 30 mins (Figure 1C-D, Figure S1A-B). As reported previously (18, 19, 25, 26), both T* cGMP and T* Calcium adapted to their final values upon overnight growth at 25°C (Figure 1C-D, Figure S1A-B). T* Calcium adaptation was similar at the AFD sensory endings and soma indicating that rapid adaptation occurs at the sensory endings themselves (Figure S1C).…”

“…To distinguish between these models, we shifted adult animals from 15ºC to 25ºC for different periods of time, and compared T*cGMP and T*Calcium in AFD neurons expressing the genetically encoded FlincG3 or GCaMP6s cGMP and calcium sensors, respectively (18,19,25) (Figure 1B). Both T*cGMP and T*Calcium adapted to a significantly higher temperature within 3 mins of the temperature upshift from 15ºC to 25ºC (Figure 1C As reported previously (18,19,25,26), both T*cGMP and T*Calcium adapted to their final values upon overnight growth at 25ºC (Figure 1C-D, Figure S1A-B). T*Calcium adaptation was similar at the AFD sensory endings and soma indicating that rapid adaptation occurs at the sensory endings themselves (Figure S1C).…”

“…Mutations in the tax-4 CNG channel α subunit largely abrogate temperature-evoked calcium dynamics in AFD (18). We were unable to generate a strain expressing the FlincG3 cGMP sensor in AFD in tax-4 mutants (also see (26)). Two independent tax-2 CNG channel β subunit mutants retained partial temperature-evoked calcium responses in AFD although these responses were highly variable (Figure S3A).…”

“…As in other sensory neurons, thermotransduction in AFD is mediated via cyclic nucleotide and calcium signaling (21,22) (Figure 1A). Warming temperatures above the adapted temperature threshold activates a trio of rGCs, increases intracellular cGMP levels and opens cyclic nucleotide-gated (CNG) channels to permit calcium influx and neuronal depolarization (17,(23)(24)(25)(26). This response is terminated via hydrolysis of cGMP by multiple PDEs (26,27) (Figure 1A).…”

“…Warming temperatures above the adapted temperature threshold activates a trio of rGCs, increases intracellular cGMP levels and opens cyclic nucleotide-gated (CNG) channels to permit calcium influx and neuronal depolarization (17,(23)(24)(25)(26). This response is terminated via hydrolysis of cGMP by multiple PDEs (26,27) (Figure 1A). We recently showed that long-term adaptation to a new warm growth temperature is mediated in part via calcium-dependent expression changes in multiple genes in AFD including the thermosensor rGCs (10,28,29).…”