Genome‐wide identification and solute selectivity of aquaporins in the sharpnose sevengill shark, Heptranchias perlo

The aquaporin genes (aqps) are widely distributed among vertebrates. In cartilaginous fish, aqp3 and aqp10 are duplicated, whereas many species have lost aqp8. While the solute permeability of aquaglyceroporins and Aqp8 exhibits significant diversity, systematic evaluations of their activity within species are limited. Consequently, we conducted a comprehensive analysis of the aqps in various cartilaginous fish genome databases. Our analysis revealed that the sharpnose sevengill shark (Heptranchias perlo) and North Pacific spiny dogfish (Squalus suckleyi) possess all aqp genes found in cartilaginous fish, rendering them suitable for comparative analysis of Aqp activity. The activity of all aquaglyceroporins and Aqp8 in the sharpnose sevengill shark was analyzed using Xenopus oocyte swelling assays. The water permeability of Aqp3c2, Aqp8, Aqp9, Aqp10c1, and Aqp10c2; the glycerol permeability of Aqp3c2, Aqp9, and Aqp10c2; the urea permeability of Aqp3c2, Aqp8, Aqp9, and Aqp10c2; and the boric acid permeability of Aqp8 and Aqp9 were determined. The urea and boric acid permeabilities of Aqp9 were higher than those of other Aqps. Our results provide genomic evidence for the loss of aqp7 and further elucidate the diversification of aqp8 in cartilaginous fishes. Moreover, the urea permeability of Aqp9 suggests a functional role in their unique urea-based osmoregulation strategy.