Figure 3 : Differential ammonia excretion in the gills of mudskippers.

From: Mudskipper genomes provide insights into the terrestrial adaptation of amphibious fishes

Figure 3

(a) An overview of ammonia excretion pathways in the gills illustrates the differential ammonia excretion in mudskippers. The core pathway comprises Na+–K+–Cl co-transporter (NKCC), Na+K+–ATPase (NKA), carbonic anhydrase (CA), cystic fibrosis transmembrane conductance regulator (CFTR), Na+/H+ exchanger (NHE) 3, H+–ATPase-V-type-B-subunit (H–ATPase), anion exchanger (AE), glycosylated Rhesus protein b (Rhbg) and c (Rhcg1 and Rhcg2). The black star represents genes with positive selection in both BP and PM, whereas the white and red stars indicate genes that are positively selected specifically in BP and PM, respectively. (bd) Three-dimensional views of Rhcg1 proteins in BP (b), PM (c) and PS (d) highlight several PM- and PS-specific amino-acid substitutions. The red squares indicate the central pore of the channel for transporting NH3, which includes the conserved Phe-Gate (F145, F250) and Twin-His (H200, H359). Three genetic variations around the central pore, Leu328Cys, Leu342Phe and Val361Met in PM and PS, may be related to a more-efficient NH3 diffusion system in PM and PS suited for a land-dominant lifestyle.