title: Evolution of Heat Sensors Drove Shifts in Thermosensation between Xenopus Species Adapted to Different Thermal Niches.
abstract: Temperature is one of the most critical environmental factors affecting survival, and thus species that inhabit different thermal niches have evolved thermal sensitivities suitable for their respective habitats. During the process of shifting thermal niches, various types of genes expressed in diverse tissues, including those of the peripheral to central nervous systems, are potentially involved in the evolutionary changes in thermosensation. To elucidate the molecular mechanisms behind the evolution of thermosensation, thermal responses were compared between two species of clawed frogs (Xenopus laevis and Xenopus tropicalis) adapted to different thermal environments. X. laevis was much more sensitive to heat stimulation than X. tropicalis at the behavioral and neural levels. The activity and sensitivity of the heat-sensing TRPA1 channel were higher in X. laevis compared with those of X. tropicalis The thermal responses of another heat-sensing channel, TRPV1, also differed between the two Xenopus species. The species differences in Xenopus TRPV1 heat responses were largely determined by three amino acid substitutions located in the first three ankyrin repeat domains, known to be involved in the regulation of rat TRPV1 activity. In addition, Xenopus TRPV1 exhibited drastic species differences in sensitivity to capsaicin, contained in chili peppers, between the two Xenopus species. Another single amino acid substitution within Xenopus TRPV1 is responsible for this species difference, which likely alters the neural and behavioral responses to capsaicin. These combined subtle amino acid substitutions in peripheral thermal sensors potentially serve as a driving force for the evolution of thermal and chemical sensation.
authors.affiliation: From the Division of Cell Signaling, Okazaki Institute for Integrative Bioscience, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan, the Department of Physiological Sciences, SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan, and sshigeru@nips.ac.jp.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Saito
authors.affiliation: the Department of Veterinary Pharmacology, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Ohkita
authors.affiliation: From the Division of Cell Signaling, Okazaki Institute for Integrative Bioscience, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan.
authors.forename: Claire T
authors.initials: CT
authors.lastname: Saito
authors.affiliation: the Department of Veterinary Pharmacology, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: From the Division of Cell Signaling, Okazaki Institute for Integrative Bioscience, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan, the Department of Physiological Sciences, SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan, and.
authors.forename: Makoto
authors.initials: M
authors.lastname: Tominaga
authors.affiliation: the Department of Veterinary Pharmacology, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan tohta@muses.tottori-u.ac.jp.
authors.forename: Toshio
authors.initials: T
authors.lastname: Ohta
mesh_terms: D000064:Acclimatization / Q000235:genetics / Q000502:physiology*; D019943:Amino Acid Substitution; D000818:Animals; D017089:Ankyrin Repeat; D005075:Biological Evolution; D020013:Calcium Signaling; D019143:Evolution, Molecular; D005260:Female; D006367:HeLa Cells; D006801:Humans; D009865:Oocytes / Q000378:metabolism; D010802:Phylogeny; D051381:Rats; D013045:Species Specificity; D050916:TRPV Cation Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D013697:Thermosensing / Q000235:genetics / Q000502:physiology*; D050051:Transient Receptor Potential Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D014981:Xenopus / Q000235:genetics / Q000502:physiology*; D029867:Xenopus Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D014982:Xenopus laevis / Q000235:genetics / Q000502:physiology
chemical_list: D050916:TRPV Cation Channels; C550099:TRPV1 protein, Xenopus; D050051:Transient Receptor Potential Channels; D029867:Xenopus Proteins
keywords: Xenopus; electrophysiology; functional evolution; molecular basis; molecular evolution; receptor structure-function; thermal sensor; transient receptor potential channels (TRP channels)