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First published online 11 July 2007
doi: 10.1242/dev.007567

Development 134, 2981-2989 (2007)
Published by The Company of Biologists 2007
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Hox patterning of the vertebrate rib cage

Daniel C. McIntyre1, Sabita Rakshit1, Alisha R. Yallowitz2, Luke Loken1, Lucie Jeannotte3, Mario R. Capecchi4 and Deneen M. Wellik1,*

1 Division of Molecular Medicine and Genetics, Department of Internal Medicine, University of Michigan Medical Center, 109 Zina Pitcher, Ann Arbor, MI 48109-2200, USA.
2 Department of Cellular and Developmental Biology, University of Michigan Medical Center, 109 Zina Pitcher, Ann Arbor, MI 48109-2200, USA.
3 Centre de Recherche en Cancérologie de l'Université Laval, Centre Hospitalier Universitaire de Québec, Québec, G1R 2J6, Canada.
4 Department of Human Genetics, University of Utah, and Howard Hughes Medical Institute, Salt Lake City, UT 84112, USA.

* Author for correspondence (e-mail: dwellik{at}umich.edu)

Accepted 12 June 2007

Unlike the rest of the axial skeleton, which develops solely from somitic mesoderm, patterning of the rib cage is complicated by its derivation from two distinct tissues. The thoracic skeleton is derived from both somitic mesoderm, which forms the vertebral bodies and ribs, and from lateral plate mesoderm, which forms the sternum. By generating mouse mutants in Hox5, Hox6 and Hox9 paralogous group genes, along with a dissection of the Hox10 and Hox11 group mutants, several important conclusions regarding the nature of the `Hox code' in rib cage and axial skeleton development are revealed. First, axial patterning is consistently coded by the unique and redundant functions of Hox paralogous groups throughout the axial skeleton. Loss of paralogous function leads to anterior homeotic transformations of colinear regions throughout the somite-derived axial skeleton. In the thoracic region, Hox genes pattern the lateral plate-derived sternum in a non-colinear manner, independent from the patterning of the somite-derived vertebrae and vertebral ribs. Finally, between adjacent sets of paralogous mutants, the regions of vertebral phenotypes overlap considerably; however, each paralogous group imparts unique morphologies within these regions. In all cases examined, the next-most posterior Hox paralogous group does not prevent the function of the more-anterior Hox group in axial patterning. Thus, the `Hox code' in somitic mesoderm is the result of the distinct, graded effects of two or more Hox paralogous groups functioning in any anteroposterior location.

Key words: Hox code, Anteroposterior (AP) patterning, Developmental genetics, Posterior prevalence, Vertebral column, Primaxial/abaxial


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Cracking the rib cage code

Development 2007 134: e1603. [Full Text]  





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