TRPM8 thermosensation in ectotherms mediates both skin colour and locomotor performance responses to cold temperature

<p>Thermoregulation is a homeostatic process to maintain an organism's internal temperature within a physiological range compatible with life. In ectotherms, body temperature fluctuates with that of the environment, with both physiological and behavioral responses employed to modify body temperature. Changing skin colour/reflectance and locomotor activity are both well-recognized temperature regulatory mechanisms, but little is known of the participating thermosensor/s. We find that <em>Xenopus laevis</em> tadpoles put in the cold exhibit a temperature-dependent and rapid melanosome aggregation in melanophores, which lightens the skin. To identify the cold-sensor, we focused on <em>transient receptor potential</em> (trp) channel genes from group 1 (TRPA, TRPM, TRPV and TRPC families). Of particular interest were TRPM family members, known as cold sensors. mRNAs for several TRPMs are present in <em>Xenopus</em> tails, and TRPM8 protein is present in skin melanophores. Temperature-induced melanosome aggregation is mimicked by the Trpm8 agonist menthol (WS12) and blocked by the Trpm8 antagonist PF05105679. The degree of skin lightening induced by cooling or the WS12 TRPM8 agonist correlates with the extent of alterations in locomotor performance. We propose that TRPM8 serves as a cool thermosensor in ectotherms that helps coordinate skin lightening and behavioural locomotor performance as adaptive thermoregulatory responses to cold.</p>