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Establishing neuronal identity in vertebrate neurogenic placodes

Baker, Clare V. H. and Bronner-Fraser, Marianne (2000) Establishing neuronal identity in vertebrate neurogenic placodes. Development, 127 (14). pp. 3045-3056. ISSN 0950-1991.

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The trigeminal and epibranchial placodes of vertebrate embryos form different types of sensory neurons. The trigeminal placodes form cutaneous sensory neurons that innervate the face and jaws, while the epibranchial placodes (geniculate, petrosal and nodose) form visceral sensory neurons that innervate taste buds and visceral organs. In the chick embryo, the ophthalmic trigeminal (opV) placode expresses the paired homeodomain transcription factor Pax3 from very early stages, while the epibranchial placodes express Pax2. Here, we show that Pax3 expression in explanted opV placode ectoderm correlates at the single cell level with neuronal specification and with commitment to an opV fate. When opV (trigeminal) ectoderm is grafted in place of the nodose (epibranchial) placode, Pax3-expressing cells form Pax3-positive neurons on the same schedule as in the opV placode. In contrast, Pax3-negative cells in the grafted ectoderm are induced to express the epibranchial placode marker Pax2 and form neurons in the nodose ganglion that express the epibranchial neuron marker Phox2a on the same schedule as host nodose neurons. They also project neurites along central and peripheral nodose neurite pathways and survive until well after the main period of cell death in the nodose ganglion. The older the opV ectoderm is at the time of grafting, the more Pax3-positive cells it contains and the more committed it is to an opV fate. Our results suggest that, within the neurogenic placodes, there does not appear to be a two-step induction of 'generic' neurons followed by specification of the neuron to a particular fate. Instead, there seems to be a one-step induction in which neuronal subtype identity is coupled to neuronal differentiation.

Item Type:Article
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URLURL TypeDescription
Bronner-Fraser, Marianne0000-0003-4274-1862
Additional Information:Copyright © 2000 by Company of Biologists. Accepted 28 April; published on WWW 22 June 2000. Thanks to Domingos Henrique and Jean-François Brunet for the Pax2 and Phox2a in situ probes respectively. We are very grateful to Andy Groves and Helen McBride for discussion and helpful comments on the manuscript. This work was supported by NS-36585 and NS-13815 (M.B.-F.) and by American Heart Association Fellowship 1171-F11 (C.V.H.B.).
Funding AgencyGrant Number
American Heart Association1171-F11
Subject Keywords:Placodes, Trigeminal placode, nodose placode, Pax2, Pax3, Phox2a, Chick, Quail, Sensory neurons
Issue or Number:14
Record Number:CaltechAUTHORS:BAKdev00
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11891
Deposited By: Archive Administrator
Deposited On:08 Oct 2008 23:29
Last Modified:03 Oct 2019 00:23

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