Fig. 1.

Evolution of solute carrier 12 (SLC12) proteins. A: cluster dendogram of human SLC12A cotransporters. The two major branches of cation-chloride cotransporters (CCC) separated early during evolution. Functionally uncharacterized CCC9 separated early from the Na⁺-dependent branch of cation-chloride cotransporters. In a similar fashion, CCC8 separated early from the Na⁺-independent K-Cl cotransporters. The human Na⁺-independent cotransporters are more closely related to one another than are the Na⁺-dependent cotransporters. NKCC2, Na-K-2Cl cotransporter 2. B: cluster dendogram illustrating separation of the Na⁺-independent cation-chloride cotransporters during vertebrate evolution. Although multiple “K-Cl like” cotransporters are found in roundworms and arthropods, the modern K-Cl cotransporters diverged early during vertebrate evolution. The amino acid sequences used to create the dendograms in both A and B were aligned using Vector Nti Suite software (version 6.0; Invitrogen/Life Technologies), saved as a text file, and then reformatted for use with Promlk, a software component of the Phylogeny Inference Package (PHYLIP; http://evolution.gs.washington.edu/phylip.html). Length of tree branches can be compared with the reference bar, which represents 0.1 amino acid substitutions per site. Dm, Drosophila melanogaster; Ce, Caenorhabditis elegans.