Phylogenetic analysis of ABCG subfamily proteins. The phylogram was constructed by the neighbor-joining method, based on the amino acid alignment (ClustalW) of full-length Abcg2 proteins from human (Hosa-ABCG2), mouse (Mumu-Abcg2), dog (Cafa-Abcg2), cow (Bota-Abcg2), chicken (Gaga-Abcg2), pufferfish (Teni-Abcg2), and zebrafish (zAbcg2a, b, c, and d). For comparison, the Abcg1 proteins from human, mouse, and dog; Abcg4 proteins from human, mouse, dog, and zebrafish; Abcg5 proteins from mouse; and Abcg8 proteins from human, mouse, and zebrafish are also shown. The Abcg5 protein from mouse was used as an out-group. The numbers at the relevant branches refer to bootstrap values of 1000 replications.