A phylogenetic tree of full-length human claudin proteins, indicating the relationships between them. Claudin-10, claudin-18, and claudin-19 have two variants resulting from alternative start sites or splicing (Table 2). Highly similar claudins encoded by genes located in close proximity in the human genome are highlighted in green. As previously suggested , claudins can be divided in two groups in terms of sequence homology (dashed line): the 'classic' human claudins are indicated in red and the 'non-classic' in black. Human claudin protein sequences were obtained from GenBank (see accession numbers in Table 1) and aligned using ClustalW 2.0.11, which was also used to calculate phylogenetic distances. The unrooted tree was obtained using Drawtree in PHYLIP version 3.67.