Evolution of sodium channels and the new view of early nervous system evolution.

Advances in genomics have revealed that many genes implicated in the nervous systems of bilaterians were already present in the last common ancestor (LCA) of animals, and some even before that.(1) (-) (5) This new information coincides with a growing reinterpretation of cnidarian nervous systems which holds that they are 'fundamentally conventional' with regards to bilaterian nervous systems,(6) and do not represent ancient forms. Since in general adult forms are expected to be the most derived features of organisms, the study of non-bilaterian larval forms may be a better way to investigate potential plesiomorphies. We recently showed that voltage-gated sodium channel (Na(v)) genes, which make action potentials in nerves and muscles, were present in the LCA of animals and choanoflagellates, the closest unicellular relatives to animals.(2) This addendum will attempt to put this finding within the context of the new views of nervous system evolution.