Evo-Devo Implications of the Coelacanth Genome

Charles Darwin envisaged evolutionary relationships among forms living and extinct, over wide geographical barriers, and used powerful deductive reasoning and logic to establish the now obvious parallels of natural selection and the principles underlying domestication of plants and animals. Darwin today would no doubt revel in our ability to draw biological inferences from genome sequences, especially for an organism such as the coelacanth, which holds a special place as a living "transitional" form.  A living specimen of the coelacanth was first discovered in 1938 and was an international sensation, as this lineage of lobe-finned fish was thought to have gone extinct nearly 70 million years ago.  We have recently reported the genome sequence of the African coelacanth, Latimeria chalumnae. Protein-coding genes of the coelacanth are significantly more slowly evolving than those of tetrapods, although other features of the coelacanth genome do not appear to be as overtly slowly evolving. Analyses of changes in genes and regulatory elements during the vertebrate adaptation to land highlight genes involved in immunity, nitrogen excretion and the development of fins, tail, ear, eye, brain, and in the sensing of odorants. Functional assays of enhancers involved in the fin-to-limb transition and in the emergence of extra-embryonic tissues demonstrate the importance of the coelacanth genome for informing the evolution of tetrapods and show how evo-devo inferences can be made in a species that is not experimentally tractable.