Elasmobranch Aqp10 paralogs differ in glycerol permeability

Aquaglyceroporins are water channels that are permeable to uncharged, low-molecular-weight compounds such as glycerol. Aquaglyceroporins are conserved across many species. However, our knowledge of aquaglyceroporins in cartilaginous fish is limited, particularly regarding the functional differences in cartilaginous fish-specific paralogs. We analyzed the evolutionary relationship between Aqp10 paralogs in two elasmobranchs and one holocephalan and compared their solute permeabilities. Molecular phylogenetic and synteny analyses confirmed that the elasmobranch Aqp10 paralogs, Aqp10C1 and Aqp10C2, arose from a cartilaginous-fish-specific tandem gene duplication. The holocephalan lacks Aqp10C1 and possesses two paralogs (Aqp10C2a and Aqp10C2b) probably derived from Aqp10C2. Swelling assays showed that Aqp10C2 maintained glycerol permeability when expressed in Xenopus oocytes. However, the glycerol permeability of Aqp10C1s were lower than those of other paralogs and the activity was similar to those of water-specific aquaporins. Aqp10 function is highly differentiated in elasmobranchs, and Aqp10C1 may have lost its glycerol permeability during a unique evolution through tandem gene duplication and sub/neofunctionalization.