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Evolution of basal deuterostome nervous systems

TitleEvolution of basal deuterostome nervous systems
Publication TypeJournal Article
Year of Publication2015
AuthorsHolland LZ
JournalJournal of Experimental Biology
Date Published2015/02
Type of ArticleReview
ISBN Number0022-0949
Accession NumberWOS:000349833800016
KeywordsAmphioxus; body plans; Cephalochordate; chordate body; common origin; Deuterostomes; developmental; Echinoderm; evolution; expression; Hemichordate; insights; Nervous system; phylogeny; saccoglossus-kowalevskii; sea-urchin embryo; vertebrate head

Understanding the evolution of deuterostome nervous systems has been complicated by the by the ambiguous phylogenetic position of the Xenocoelomorpha (Xenoturbellids, acoel flat worms, nemertodermatids), which has been placed either as basal bilaterians, basal deuterostomes or as a sister group to the hemichordate/echinoderm clade (Ambulacraria), which is a sister group of the Chordata. None of these groups has a single longitudinal nerve cord and a brain. A further complication is that echinoderm nerve cords are not likely to be evolutionarily related to the chordate central nervous system. For hemichordates, opinion is divided as to whether either one or none of the two nerve cords is homologous to the chordate nerve cord. In chordates, opposition by two secreted signaling proteins, bone morphogenetic protein (BMP) and Nodal, regulates partitioning of the ectoderm into central and peripheral nervous systems. Similarly, in echinoderm larvae, opposition between BMP and Nodal positions the ciliary band and regulates its extent. The apparent loss of this opposition in hemichordates is, therefore, compatible with the scenario, suggested by Dawydoff over 65 years ago, that a true centralized nervous system was lost in hemichordates.

Short TitleJ. Exp. Biol.
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