Fig. 1. Conservation of an asymmetric enhancer (ASE) of Pitx2 among vertebrates. Structures of the Pitx2 ASE from various vertebrates (located in the last intron of Pitx2) are shown on the left. Red and blue circles represent Foxh1- and Nkx2-binding sites, respectively, with the arrows indicating their orientation. The enhancer activity of each ASE in transgenic mouse assays at E8.2 and 10.5 is summarized on the right. The ASE of zebrafish Pitx2 possesses activity only in the anterior portion of left LPM (asterisk). ND, not determined.