Since long time some Brain Mind & Life’s
neuroscientists maintained the relevance of the Central Nervous System
morphological evolution from an external site of the simplest animal body, or surface-nerve-net,
to the interior of the skeleton as in the mammals, as connected to ectodermal
differentiation, with the adaptation of the homologues of some skin-nerve genes
as vertebrates genes like Emx-1. faces this problem in
the interesting article that will appear in the next month number of Nature
Review Neuroscience (, Early central
nervous system evolution: an era of skin brains? Nature Review Neuroscience. Vol 4 No 8, August 2003). Until
recently, it was assumed that the ancestral nerve net or surface-nerve-net
became localized as all or part of the CNS in the basal groups of bilaterally
symmetrical animals. However, in the enteropneust hemichordate Saccoglossus,
expression of homologues of vertebrate CNS anteroposterior patterning genes is
not limited to the nerve tracts, but extends widely throughout the ectoderm,
implying that the CNS of this animal includes the entire basiepidermal nerve
net. Holland discusses the implications of this discovery for CNS
evolution.
BM&L-July 2003