Abstract

Failure of facial prominence fusion causes cleft lip and palate (CL/P), a common human birth defect. Several potential mechanisms can be envisioned that would result in CL/P, including failure of prominence growth and/or alignment as well as a failure of fusion of the juxtaposed epithelial seams. Here, using geometric morphometrics, we analyzed facial outgrowth and shape change over time in a novel mouse model exhibiting fully penetrant bilateral CL/P. This robust model is based upon mutations in Tfap2a, the gene encoding transcription factor AP-2α, which has been implicated in both syndromic and non-syndromic human CL/P. Our findings indicate that aberrant morphology and subsequent misalignment of the facial prominences underlies the inability of the mutant prominences to fuse. Exencephaly also occured in some of the Tfap2a mutants and we observed additional morphometric differences that indicate an influence of neural tube closure defects on facial shape. Molecular analysis of the CL/P model indicates that Fgf signaling is misregulated in the face, and that reducing Fgf8 gene dosage can attenuate the clefting pathology by generating compensatory changes. Furthermore, mutations in either Tfap2a or Fgf8 increase variance in facial shape, but the combination of these mutations restores variance to normal levels. The alterations in variance provide a potential mechanistic link between clefting and the evolution and diversity of facial morphology. Overall, our findings suggest that CL/P can result from small gene-expression changes that alter the shape of the facial prominences and uncouple their coordinated morphogenesis, which is necessary for normal fusion.

Highlights

  • Orofacial clefts are common human birth defects, with cleft lip with or without cleft palate (CL/P) occurring in about one in 700 births, and cleft palate only (CP) presenting about half as frequently (Mossey and Modell, 2012)

  • This study describes the generation of a new and a fully penetrant mouse model of CL/P caused by mutations in Tfap2a, a gene linked to human CL/P

  • We describe a new mouse model of CL/P caused by mutations in Tfap2a, the gene encoding transcription factor AP-2α

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Summary

Introduction

Orofacial clefts are common human birth defects, with cleft lip with or without cleft palate (CL/P) occurring in about one in 700 births, and cleft palate only (CP) presenting about half as frequently (Mossey and Modell, 2012). Studies of unaffected parents of children with CL/P using cephalometry, or more recently detailed three-dimensional (3D) morphometrics, show distinct differences in facial shape compared with unaffected families (McIntyre and Mossey, 2002; Nakasima and Ichinose, 1983; Wyszynski, 2002; Weinberg et al, 2006; Weinberg et al, 2009). These differences hold true for many different racial and ethnic backgrounds, and often include a more concave face. Studies on CL/P have not advanced as far, in part because, until recently, there were few models that displayed CL/P with high penetrance

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