The acquisition of cold sensitivity during TRPM8 ion channel evolution

To cope with temperature fluctuations, molecular thermosensors in animals play a piv-otal role in accurately sensing ambient temperature. Transient receptor potential mela-statin 8 (TRPM8) is the most established cold sensor. In order to understand how the evolutionary forces bestowed TRPM8 with cold sensitivity, insights into both emer-gence of cold sensing during evolution and the thermodynamic basis of cold activation are needed. Here, we show that the trpm8 gene evolved by forming and regulating two domains (MHR1-3 and pore domains), thus determining distinct cold-sensitive proper-ties among vertebrate TRPM8 orthologs. The young trpm8 gene without function can be observed in the closest living relatives of tetrapods (lobe -finned fishes), while the mature MHR1-3 domain with independent cold sensitivity has formed in TRPM8s of amphibians and reptiles to enable channel activation by cold. Furthermore, positive selection in the TRPM8 pore domain that tuned the efficacy of cold activation appeared late among more advanced terrestrial tetrapods. Interestingly, the mature MHR1-3 domain is necessary for the regulatory mechanism of the pore domain in TRPM8 cold activation. Our results reveal the domain-based evolution for TRPM8 functions and suggest that the acquisition of cold sensitivity in TRPM8 facilitated terrestrial adapta-tion during the water-to-land transition.

Automated summary

Molecular thermosensors in animals, specifically the TRPM8 gene, play a critical role in accurately sensing and responding to ambient temperature fluctuations. Through the process of evolution, the TRPM8 gene has evolved to form and regulate different domains, allowing for distinct cold-sensitive properties among vertebrate TRPM8 orthologs. The acquisition of cold sensitivity in TRPM8 facilitated terrestrial adaptation during the water-to-land transition.