Evolutionary sequence conservation is an accepted criterion to identify 
noncoding regulatory sequences. We have used a transposon-based transgenic assay 
in zebrafish to evaluate noncoding sequences at the zebrafish ret locus, 
conserved among teleosts, and at the human RET locus, conserved among mammals. 
Most teleost sequences directed ret-specific reporter gene expression, with many 
displaying overlapping regulatory control. The majority of human RET noncoding 
sequences also directed ret-specific expression in zebrafish. Thus, vast amounts 
of functional sequence information may exist that would not be detected by 
sequence similarity approaches.