Genomic structure and evolutionarily conserved non-coding regions (ECRs) of the otp gene. A, Graphical comparison of the otp locus, according to the ECR browser, showing intergenic ECRs (red) and exons (blue) in the zebrafish (genome assembly danRer7), the human (genome assembly hg19) and the mouse (genome assembly mm10). We used the sequence of the otpa gene from zebrafish as the reference. B, A schematic phylogenetic tree of vertebrates. otp ECRs are evident only in gnathostome vertebrates. We noted that some ECRs were absent in the paralogous gene otpb in zebrafish (see text for more details).