Integrated genomic, transcriptomic, and microsomal metabolic profiling of cytochrome P450s in squirrels.

Squirrels (family Sciuridae; hereafter referred to as sciurids) are frequently treated with veterinary medical products, such as fipronil, a topically applied insecticide used for ectoparasite control; however, fundamental information on their drug-metabolizing capacity remains limited. In this study, we examined whether hepatic cytochrome P450 (CYP) profiles and microsomal fipronil metabolism differ among sciurids, Eurasian red squirrel (Sciurus vulgaris orientis), Siberian flying squirrel (Pteromys volans orii), Pallas's squirrel (Callosciurus erythraeus), and laboratory rodents (Mus musculus and Rattus norvegicus). We integrated sequence, expression, and functional analyses with a primary focus on CYP2C and CYP3A, key enzymes involved in xenobiotic metabolism. No clear evidence of sciurid-specific loss or major divergence was detected in CYP2C/3A, and microsomal fipronil metabolic efficiency did not differ significantly among the examined species. RNA sequencing (RNA-Seq) revealed distinct hepatic CYP expression profiles beyond CYP2C/3A; notably, CYP2B represented <1% of total major CYP expression in the Eurasian red squirrel, a proportion lower than that observed in laboratory rodents. These findings provide baseline information on hepatic CYP profiles and microsomal fipronil metabolism in sciurids and may support future comparative studies of wildlife drug metabolism.