Formation of Regulator/Target Gene Relationships During Evolution

The study examined the evolution of Foxn1-like forkhead/winged-helix transcription factor genes, which have been maintained as a single copy throughout chordate evolution. It was found that fish and mouse Foxn1-like genes were functionally equivalent in activating hair keratin genes, indicating no significant functional changes over hundreds of millions of years. However, the Foxn1-like gene from the cephalochordate Branchiostoma lanceolatum was inactive in this function due to changes outside the DNA binding and transcriptional activation domains. The findings suggested that cis-regulatory regions of genes evolved more rapidly than protein coding regions, and changes in these regions did not necessarily require corresponding changes in transcription factor proteins for the development of new regulator/target gene relationships.