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[S4]: Multipotent neural crest‐derived cells in the developing and adult organism
Author(s) -
Sommer L.
Publication year - 2006
Publication title -
international journal of developmental neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.761
H-Index - 88
eISSN - 1873-474X
pISSN - 0736-5748
DOI - 10.1016/j.ijdevneu.2006.09.007
Subject(s) - citation , neural crest , organism , cognitive science , library science , biology , world wide web , computer science , psychology , paleontology , genetics , embryo
The autonomic or visceral nervous system maintains bodily homeostasis through the activity of cardiovascular, respiratory, and digestive organs. Its efferent arm comprises all autonomic ganglia (parasympathetic, sympathetic and enteric) derived from the neural crest as well as their respective preganglionic neurons (or ‘‘general visceral motoneurons’’) located in the hindbrain or spinal cord. It also includes ‘‘special visceral’’ —a.k.a. branchial— motoneurons to muscles of the face, jaw, gills, and pharynx, principally involved in feeding and breathing in aquatic vertebrates, then recruited to more varied functions in terrestrial ones. Strikingly, all these neurons (except sympathetic preganglionics in the spinal cord), irrespective of their origin, phenotype or location express the homeobox gene Phox2b and depend on it for their differentiation. Moreover, Phox2b also controls all visceral afferents. It can thus, be considered as a master gene of the visceral nervous system.We used this unusual specificity to explore the nervous system of the ascidian Ciona intestinalis. In their adult, post-metamorphic form, sea-squirts are fixed animals, devoid of locomotion and consistingmostly of a huge filter-feeding pharynx devoted to both, breathing and feeding, a tiny post-pharyngeal digestive tract, a heart and reproductive organs. They are thus essentially ‘‘visceral’’ creatures. In striking accordance, we show that a great part of the brain of Ciona, a diminutive ‘‘cerebral ganglion’’, which has been considered as a derived feature of ascidians, is in fact made up of motoneurons homologous to vertebrate special visceral (or branchial) motoneurons, on account of their origin from a hindbrain, their diagnostic transcriptional code CiPhox2/ CiTbx20, and the muscular and pharyngeal nature of their target. We propose that Phox2-positive special visceral motoneurons are the ancestral visceral efferents of chordates, on which the vertebrates have elaborated by the addition of peripheral relays derived from the neural crest. This step, strikingly, occurred under the control of the same transcription factor, Phox2b.