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First published online August 12, 2008
doi: 10.1242/10.1242/dev.019778

Development 135, 2905-2916 (2008)
Published by The Company of Biologists 2008
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Dlx genes pattern mammalian jaw primordium by regulating both lower jaw-specific and upper jaw-specific genetic programs

Juhee Jeong1,*, Xue Li2, Robert J. McEvilly3, Michael G. Rosenfeld3, Thomas Lufkin4 and John L. R. Rubenstein1,*

1 Department of Psychiatry, Nina Ireland Laboratory of Developmental Neurobiology, University of California San Francisco, 1550 4th street, San Francisco, CA 94158, USA.
2 Department of Surgery/Urology and Department of Pathology, Children's Hospital of Boston, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA.
3 Howard Hughes Medical Institute, Department of Medicine, University of California, San Diego, School of Medicine, 9500 Gilman Drive, La Jolla, CA 92093, USA.
4 Genome Institute of Singapore, 60 Biopolis Street, Singapore 138672, Singapore.

* Authors for correspondence (emails: john.rubenstein{at}ucsf.edu; juhee.jeong{at}ucsf.edu)

Accepted 26 June 2008

Dlx transcription factors are implicated in patterning the mammalian jaw, based on their nested expression patterns in the first branchial arch (primordium for jaw) and mutant phenotypes; inactivation of Dlx1 and Dlx2 (Dlx1/2-/-) causes defects in the upper jaw, whereas Dlx5/6-/- results in homeotic transformation of the lower jaw into upper jaw. Therefore, the `Dlx codes' appear to regionalize the jaw primordium such that Dlx1/2 regulate upper jaw development, while Dlx5/6 confer the lower jaw fate. Towards identifying the genetic pathways downstream of Dlx5/6, we compared the gene expression profiles of the wild-type and Dlx5/6-/- mouse mandibular arch (prospective lower jaw). We identified 20 previously unrecognized Dlx5/6-downstream genes, of which 12 were downregulated and 8 upregulated in the mutant. We found a Dlx-regulated transcriptional enhancer in close proximity to Gbx2, one of the Dlx5/6-downstream genes, strongly suggesting that Gbx2 is a direct target of Dlx5/6. We also showed that Pou3f3 is normally expressed in the maxillary (prospective upper jaw) but not mandibular arch, is upregulated in the mandibular arch of Dlx5/6-/-, and is essential for formation of some of the maxillary arch-derived skeleton. A comparative analysis of the morphological and molecular phenotypes of various Dlx single and double mutants revealed that Dlx1, 2, 5 and 6 act both partially redundantly and antagonistically to direct differential expression of downstream genes in each domain of the first branchial arch. We propose a new model for Dlx-mediated mammalian jaw patterning.

Key words: Dlx, Gbx2, Pou3f3, Craniofacial, Branchial arch, Jaw, Mouse






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