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Integrative and Comparative Biology Advance Access published online on June 2, 2008
Integrative and Comparative Biology, doi:10.1093/icb/icn048
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oxfordjournals.org.

The midline, oral ectoderm, and the arch-0 problem

Charles B. Kimmel1 and Johann K. Eberhart
Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA

Correspondence: 1E-mail: kimmel{at}uoneuro.uoregon.edu

In most versions of theories of the segmentation of the vertebrate head, a premandibular segment is present rostral to the jaw-forming mandibular segment. These theories posit that in ancient fishes this segment included a gill and a gill-supporting skeleton, which then was modified to support the anterior brain. However, we find no recent evidence for existence of such a premandibular segment. Rather, new findings from studies of fate mapping and gene expression show that the "premandibular" territory is in fact the maxillary region of the mandibular arch. A signaling cascade, beginning with dorsal midline mesoderm in the gastrula and relayed through neural ectoderm and then oral ectoderm, greatly expands the skeletal derivatives of maxillary neural crest in a manner fully consistent with the Gans–Northcutt theory of the vertebrate new head.

From the symposium "Vertebrate Head Segmentation in a Modern Eco-Devo Context" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 2–6, 2008, at San Antonio, Texas.


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