Making enhancers from spare parts of the genome

Metazoan genomes contain tens of thousands of regions for which there has been recent experimental evidence for the binding of transcription factors and cofactors [1]. Many of these regions are conserved, sometimes through hundreds of millions of years of evolutionary history, as in the case of enhancers regulating early embryonic development [2]. There are numerous examples that show how new regulatory behavior can appear through modifi cation of existing functional elements. At the same time, most known enhancers, including the most conserved ones, are unique sequences with no similarity to any of the elements that serve other functions, and there is increasing evidence showing that important functions are driven by regulatory elements that are poorly conserved, and showing a lineagespecific accelerate