The emergence of jaws in primitive fish allowed vertebrates to become top predators. What is less appreciated is another evolutionary innovation that may have been just as important for the success of early vertebrates: the formation of covers to protect and pump water over the gills. In a new study published in the Proceedings of the National Academy of Sciences (PNAS), USC Stem Cell scientists and their collaborators have identified a key modification to the genome that led to the evolution of gill covers more than 430 million years ago.
The scientists started by creating zebrafish with mutations in a gene called Pou3f3. Strikingly, fish lacking this gene, or the DNA element controlling its activity in the