Figure 2

Phylogeny of the Otop family in amphibians. Maximum-likelihood phylogenetic tree based on the multi-sequence alignment of 19 Otop proteins identified in amphibian, mouse, human, and dog. Proteins are labeled as Xtr_ for X. tropicalis, Xlv_ for X. laevis, mus_ for mouse, homo_ for human, and dog_ for dog. Three distinct clades divide the Otop family into three subfamilies: Otop1, Otop2, and Otop3 (colored red, green, and blue, respectively). Amphibian Otop3 genes appear to have undergone additional gene-duplication events, creating lineage-specific paralogs (designated a to c following the gene symbol). We have applied the same naming convention to the X. tropicalis Otop1 (Otop1a and Otop1b) and Otop2 (Otop2a, Otop2b, and Otop2c) genes, although it is less clear if the duplication events giving rise to these multiple copies occurred in the amphibian lineage or are more ancient (with the genes then getting lost in the mammalian lineage). Branch labels are bootstrap values for 1000 replicates.