Aquaporin (Aqp) 10 water channels in humans allow the free passage of water, glycerol, urea, and boric acid across cells. However, Aqp10.2b in pufferfishes allows only the passage of water and glycerol and not urea and boric acid. Researchers from the Tokyo Institute of Technology sought to understand the evolutionary timeline that resulted in the variable substrate selection mechanisms among Aqp10s. Their results indicate that Aqp10.2 in ray-finned fishes may have reduced or lost urea and boric acid permeabilities through evolution.
Aquaporins (Aqps) are proteins that form water channels in the membranes of living cells, including those of bacteria, fungi, animals, and plants. These channels facilitate water transportation across cells more rapidly than diffusion through the membrane phospholipid bilayer.
Aqp10 belongs to the aquaglyceroporin subfamily of water channels. These proteins facilitate many of our body's physiological processes, including gut function, liver and fat cell metabolism, and skin elasticity. Water and solutes, such as glycerol, urea, and boric acid, get transported through human Aqp10 depending on concentration gradients across the membrane.
Sarcopterygians, which include coelacanths, lungfish, and tetrapods (such as amphibians, reptiles, birds, and mammals), are known to have a single gene that codes for Aqp10. In contrast, actinopterygians, such as ray-finned fishes, have paralogs, or near-identical copies, of the aqp10 gene, such as aqp10.1 and aqp10.2. Interestingly, the ray-finned Japanese pufferfish has paralog called aqp10.2b that shows permeability to water and glycerol but not to urea and boric acid.