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Unformatted text preview: J. Anat. (2005) 207 , pp461–477 © 2005 The Authors Journal compilation © 2005 Anatomical Society of Great Britain and Ireland Blackwel Publishing, Ltd. REVIEW It’s all in your head: new insights into craniofacial development and deformation Minal D. Tapadia, 1 Dwight R. Cordero 2 and Jill A. Helms 1 1 Department of Plastic and Reconstructive Surgery, Stanford University, Stanford, California, USA 2 Department of Obstetrics and Gynecology, Brigham and Women‘s Hospital, Harvard Medical School, Boston, Massachusetts, USA Introduction ‘Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we pretend to assign any reason why this or that part has varied. But when- ever we have the means of instituting a comparison, the same laws appear to have acted in producing the lesser differences between varieties of the same species, and the greater differences between species of the same genus.’ (Darwin, 1859). Charles Darwin did not gild the truth when he candidly pointed out just how imperfect is our knowledge of how morphological diversity is generated. Over the intervening decades we have scrutinized the process of embryonic development and, in doing so, gained a deeper appreciation for the tissue interactions that lie at the basis of morphogenesis. More recently, some of the molecules involved in mediating these tissue inter- actions have been identified and, in a few rare cases, we even have gleaned insights into how species- specific development is controlled. These instances, how- ever, are few and far between and much remains to be accomplished. In this review we will present some of the most recent advances that lie at the heart of understanding the mechanisms controlling normal craniofacial devel- opment, the consequences of when these normal path- ways are disrupted and how this information sheds light on the basis for evolutionary diversity among the species. We choose to focus on morphogenesis of the craniofacial complex for two reasons. First, faces show tremendous phenotypic variation, first evident during the later stages of fetal development. Yet despite these differences in the facial appearance of embryos, they all look remarkably similar during earlier stages of embryogenesis. This suggests that whatever factors influence craniofacial diversity primarily act during a discrete period of embryonic development; and know- ing when diversity first arises is an important first step towards understanding how diversity is generated. The second reason we use craniofacial development as a model is that variations in the craniofacial complex are tightly associated with adaptive radiations into ecological niches. If the relationship between craniofa- cial morphology and speciation is causal (and not merely correlative) then perhaps we can understand how modifying the spatial and temporal patterns of gene expression create diversity within a species....
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This note was uploaded on 05/28/2010 for the course BIOLOGY 03234 taught by Professor Sochacka during the Spring '10 term at Ghent University.
- Spring '10