Critical Reviews in Oral Biology & Medicine, Vol 6, 202-217, Copyright © 1995 by International & American Associations for Dental Research
Programmed cell death and cell transformation in craniofacial development
C. F. Shuler
University of Southern California, School of Dentistry, Center for Craniofacial Molecular Biology, Los Angeles 90033, USA.
Fusion of branchial arch derivatives is an essential component in the
development of craniofacial structures. Bilaterally symmetric branchial
arch processes fuse in the midline to form the mandible, lips, and palate.
The mechanism for fusion requires several different morphologic and
molecular events prior to the completion of the mesenchymal continuity
between opposing tissue processes. The ectodermal covering of the branchial
arches is one of the cell types that has an important role during
craniofacial development. The surface epithelia provide the initial
adherence between the processes; however, this population of cells is
ultimately absent from the fusion zone. The medial edge epithelium of the
secondary palatal shelves is one example of such an epithelium that must
disappear from the fusion zone of the secondary palate during development
in order to complete palatal fusion. The mechanisms for removal of the
epithelial cells from the fusion zone could include either programmed cell
death, epithelial-mesenchymal transformation, or migration to adjacent
epithelia. All three of these fates have been hypothesized as a mechanism
for the removal of the palatal medial edge epithelia. The processes of
programmed cell death, epithelial-mesenchymal transformation, and
epithelial migration are reviewed with respect to both palatal fusion and
results reported in other model systems.
