Comparison of Pax1/9 locus reveals 500-Myr-old syntenic block and evolutionary conserved noncoding regions

Identification of conserved genomic regions within and between different genomes is crucial when studying genome evolution. Here, we described regions of strong synteny conservation between vertebrate deuterostomes (tetrapods and teleosts) and invertebrate deuterostomes (amphioxus and sea urchin). The shared gene contents across phylogenetically distant species demonstrate that the conservation of the regions stemmed from an ancestral segment instead of a series of independent convergent events. Comparison of the syntenic regions allows us to postulate the primitive gene organization in the last common ancestor of deuterostomes and the evolutionary events that occurred to the 3 distinct lineages of sea urchin, amphioxus, and vertebrates after their separation. In addition, alignment of the syntenic regions led to the identification of 8 noncoding evolutionarily conserved regions shared between amphioxus and vertebrates. To our knowledge, this is the first report of conserved noncoding sequences shared by vertebrates and nonvertebrates. These noncoding sequences have high possibility of being elements that regulate neighboring genes. They are likely to be a factor in the maintenance of conserved synteny over long phylogenetic distance in different deuterostome lineages.