Centralization of the deuterostome nervous system predates chordates.
The origin of the chordate central nervous system (CNS) is unknown. One theory is that a CNS was present in the first bilaterian and that it gave rise to both the ventral cord of protostomes and the dorsal cord of deuterostomes. Another theory proposes that the chordate CNS arose by a dramatic process of dorsalization and internalization from a diffuse nerve net coextensive with the skin of the animal, such as enteropneust worms (Hemichordata, Ambulacraria) are supposed to have. We show here that juvenile and adult enteropneust worms in fact have a bona fide CNS, i.e., dense agglomerations of neurons associated with a neuropil, forming two cords, ventral and dorsal. The latter is internalized in the collar as a chordate-like neural tube. Contrary to previous assumptions, the greater part of the adult enteropneust skin is nonneural, although elements of the peripheral nervous system (PNS) are found there. We use molecular markers to show that several neuronal types are anatomically segregated in the CNS and PNS. These neuroanatomical features, whatever their homologies with the chordate CNS, imply that nervous system centralization predates the evolutionary separation of chordate and hemichordate lineages.
Nomaksteinsky
Marc
M
Department of Biology, Ecole Normale Supérieure, 75005 Paris, France; CNRS UMR 8542, 75005 Paris, France.
Röttinger
Eric
E
Dufour
Héloïse D
HD
Chettouh
Zoubida
Z
Lowe
Chris J
CJ
Martindale
Mark Q
MQ
Brunet
Jean-François
JF
D000717:Anatomy, Comparative; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002490:Central Nervous System / Q000033:anatomy & histology*; D043344:Chordata / Q000033:anatomy & histology*; D003001:Cloning, Molecular; D006254:Hawaii; D007448:Invertebrates / Q000033:anatomy & histology*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D009419:Nerve Tissue Proteins; D014157:Transcription Factors