Molecular basis of infrared detection by snakes

Abstract

Snakes possess a unique sensory system for detecting infrared radiation, enabling them to generate a ‘thermal image’ of predators or prey. Infrared signals are initially received by the pit organ, a highly specialized facial structure that is innervated by nerve fibers of the somatosensory system. How this organ detects and transduces infrared signals into nerve impulses is not known. Here we use an unbiased transcriptional profiling approach to identify TRPA1 channels as infrared receptors on sensory nerve fibers that innervate the pit organ. TRPA1 orthologues from pit bearing snakes (vipers, pythons, and boas) are the most heat sensitive vertebrate ion channels thus far identified, consistent with their role as primary transducers of infrared stimuli. Thus, snakes detect infrared signals through a mechanism involving radiant heating of the pit organ, rather than photochemical transduction. These findings illustrate the broad evolutionary tuning of TRP channels as thermosensors in the vertebrate nervous system.

Cytoplasmic ankyrin repeats of transient receptor potential A1 (TRPA1) dictate sensitivity to thermal and chemical stimuli

“…Recent studies of the capsaicin receptor, TRPV1, suggest that the N-terminal ARD constitutes a binding site for cytoplasmic regulatory factors, such as ATP and calmodulin (17,45), consistent with our findings that the TRPA1 ARD contributes to channel modulation by environmental and endogenous agents. Several TRP channels act as polymodal signal detectors (5, 46), but TRPA1 is unique in that different species use this channel for distinct physiological purposes, generally favoring one modality (thermal or chemical) over the other (10,12). This may reflect evolutionary pressure to reduce background noise from environmental irritants in organisms in which the channel is used primarily for thermoreception, and vice versa.…”

“…Similarly, insect TRPA1 channels are heat-sensitive and contribute to thermal avoidance behaviors (11)(12)(13)(14). In these cases, however, thermosensitivity comes at the expense of chemosensitivity, such that AITC and other chemical irritants still activate these channels but with reduced potency compared with mammalian orthologs (10). Despite clear physiological differences between snake and mammalian TRPA1 channels, they share significant amino acid identity (56%), providing a unique opportunity to exploit sequence comparisons and domain swaps to pinpoint structural elements associated with stimulus detection and/or gating.…”

“…For example, snakes are unique among vertebrates in that their TRPA1 channels are heat-sensitive, which some species (rattlesnakes, boas, and pythons) have exploited to detect infrared radiation (10). Similarly, insect TRPA1 channels are heat-sensitive and contribute to thermal avoidance behaviors (11)(12)(13)(14).…”

Modular thermal sensors in temperature-gated transient receptor potential (TRP) channels

“…In mammals, the neural input on ambient temperature results from specialized groups of neurons that project to the skin. The transducers involve ion channels known as transient receptor potential (TRP) channels (1,2), which constitute an array of biological thermometers responsive over a broad temperature gradient from noxious cold to noxious hot (3).…”

Light-powered molecular logic goes nonlinear

“…For instance, it is thought that birds can image their orientation (or inclination) relative to the earth's magnetic field, thus helping them to navigate during migration (9). Snakes have evolved an incredible system for thermal imaging, not based on the kind of optical layout an engineer would naturally imagine (10).…”