Alignment of known regulatory elements. (A) Sequence of Krx20 binding sites in different species. Krox20 binding sites are involved in Hox2 regulation and they are conserved in HoxA and B clusters from human, mouse, pufferfish, and HoxA from tilapia. Both Krx20 and the “box a” are widely conserved. The degree of identity is 67% among the species in this comparison. (B) Alignment of sequences of the “box a” motif.