Molecular Evolutionary Analysis of the HCRTR Gene Family in Vertebrates.

Hypocretin system is composed of hypocretins (hcrts) and their receptors (hcrtrs), which has multiple vital functions. Hypocretins work via hypocretin receptors and it is reported that functional differentiation occurred in hcrtrs. It is necessary to figure out the evolution process of hypocretin receptors. In our study, we adopt a comprehensive approach and various bioinformatics tools to analyse the evolution process of HCRTR gene family. It turns out that the second round of whole genome duplication in early vertebrate ancestry and the independent round in fish ancestry may contribute to the diversity of HCRTR gene family. HCRTR1 of fishes and mammals are not the same receptor, which means that there are three members in the family. HCRTR2 is proved to be the most ancient one in HCRTR gene family. After duplication events, the structure of HCRTR1 diverged from HCRTR2 owing to relaxed selective pressure. Negative selection is the predominant evolutionary force acting on the HCRTR gene family but HCRTR1 of mammals is found to be subjected to positive selection. Our study gains insight into the molecular evolution process of HCRTR gene family, which contributes to the further study of the system.