First published online January 23, 2009
Development 136, 405e (2009)
© The Company of Biologists Limited
Craniofacial development: jaw-dropping insights
Large parts of the craniofacial and pharyngeal skeleton derive from cranial
neural crest cells (NCCs) that migrate from the edge of the dorsal neural tube
(DNT) to populate the pharyngeal arches (PAs - a series of transient
structures that contribute to head and neck formation) and the frontonasal
process (which contributes to the forehead and nose). In this issue, two
papers provide important new insights into the signalling events involved in
this morphogenetic process.
On p. 637, Filippo
Rijli, Denis Duboule and colleagues reveal that the first four PAs share a
common NCC gene expression ground state. NCCs that contribute to individual
PAs express distinct Hox gene combinations that determine PA-specific regional
identities; for example, the NCCs that populate the first PA are Hox-negative.
Previously, these authors have shown that the first and second PA NCCs in mice
share a common Hox-free patterning programme. Now, they demonstrate that
deleting the entire HoxA cluster in cranial NCCs leads to the partial homeotic
transformation of the third and fourth PA towards a first PA identity. Amongst
other effects, this results in the partial quadruplication of Meckel's jaw
cartilage, an evolutionarily ancient structure from which the lower jaw and
middle ear develop. These findings support the idea that all PAs are part of a
single series of segmental structures, and invite the suggestion that the
elaboration of regional identity in such structures on top of a shared gene
expression ground state constitutes a general evolutionary strategy.
In their study, Hiromi Yanagisawa and colleagues turn to later NCC
differentiation events in craniofacial bone development in mice, and report
that endothelial signalling through the transcription factor Hand2 negatively
regulates the differentiation of NCC-derived osteoblasts in PAs (see
p. 615). The authors
demonstrate that a decrease in PA-specific Hand2 expression leads to
accelerated osteoblast differentiation associated with the increased and
ectopic expression of the transcription factor Runx2, a master regulator of
bone differentiation. Based on these and other findings, the authors propose
that a vertebrate-specific domain of Hand2 interacts directly with the
DNA-binding domain of Runx2 to negatively regulate its activity.
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Related articles in Development:
- Hand2 controls osteoblast differentiation in the branchial arch by inhibiting DNA binding of Runx2
- Noriko Funato, Shelby L. Chapman, Marc D. McKee, Hiromasa Funato, Jesse A. Morris, John M. Shelton, James A. Richardson, and Hiromi Yanagisawa
Development 2009 136: 615-625.
[Abstract]
[Full Text]
- Rostral and caudal pharyngeal arches share a common neural crest ground pattern
- Maryline Minoux, Gregory S. Antonarakis, Marie Kmita, Denis Duboule, and Filippo M. Rijli
Development 2009 136: 637-645.
[Abstract]
[Full Text]
