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

Abstract

Thermoregulation is a homeostatic process to maintain an organism’s internal temperature within a physiological range compatible with life. In poikilotherms, 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 Xenopus laevis tadpoles put in the cold exhibit a temperature-dependent, systemic, and rapid melanosome aggregation in melanophores, which lightens the skin. Cooling also induces a reduction in the locomotor performance. To identify the cold-sensor, we focus on transient receptor potential (trp) channel genes from a Trpm family. mRNAs for several Trpms are present in Xenopus tails, and Trpm8 protein is present in skin melanophores. Temperature-induced melanosome aggregation is mimicked by the Trpm8 agonist menthol (WS12) and blocked by a Trpm8 antagonist. The degree of skin lightening induced by cooling is correlated with locomotor performance, and both responses are rapidly regulated in a dose-dependent and correlated manner by the WS12 Trpm8 agonist. We propose that TRPM8 serves as a cool thermosensor in poikilotherms that helps coordinate skin lightening and behavioural locomotor performance as adaptive thermoregulatory responses to cold.

Cold-induced skin darkening does not protect amphibian larvae from UV-associated DNA damage

“…L. peronii larvae acclimated to cooler temperatures elicited a darkening response, supporting some but not all studies on factors influencing melanin dispersion in amphibians (Norris and Milstead, 1967;Kats and van Dragt, 1986;Moriya and Miyashita, 1989;Fernandez and Bagnara, 1991;Jenks et al, 2007;Malik et al, 2023). Against our hypothesis, darker larvae acclimated to dark backgrounds did not have reduced levels of DNA damage in the form of whole-body or skin CPDs following UVR exposure compared to lighter larvae.…”

Cold‐induced skin darkening does not protect amphibian larvae from UV‐associated DNA damage

“…L. peronii larvae acclimated to cooler temperatures elicited a darkening response, supporting some but not all studies on factors influencing melanin dispersion in amphibians (Fernandez & Bagnara, 1991;Jenks et al, 2007;Kats & van Dragt, 1986;Liedtke et al, 2023;Malik et al, 2023;Moriya & Miyashita, 1989;Nilsson Sköld et al, 2013;Norris & Milstead, 1967;Rodríguez-Rodríguez et al, 2020). Against our hypothesis, darker larvae acclimated to black backgrounds did not have reduced levels of DNA damage in the form where the presence of increased melanin also did not influence DNA damage (Lesser et al, 2001) or improve survival (Belden & Blaustein, 2002) following UVR exposure.…”

Novel observations of “freeze resistance” and dynamic blue and green dorsal coloration in frozen and thawing Dryophytes chrysoscelis

“…Dorsal color change in anurans is most commonly studied in the context of camouflage and predation avoidance (Choi & Jang, 2014; Nielsen & Dyck, 1978), often associated with seasonal variation in leaf cover and color (Wente & Phillips, 2003). Amphibians also have the ability to adjust skin color in minutes to hours in response to stress (Kindermann et al, 2013), during mating (Kindermann et al, 2014), for communication (de Luna et al, 2010), and to help regulate body temperature and hydration (Malik et al, 2023; Stegen et al, 2004). Among those circumstances, the stress response is the only one that seems applicable to the animals in our study, but even the stress response may not explain our findings given that the neurohormonal mechanisms that mediate this response are suppressed in cold and frozen frogs.…”