Craniofacial development is a uniquely complex morphogenetic process in vertebrate ontogeny, creating evolutionary plasticity but also developmental vulnerability. The head and face are derived from many tissue precursors, which require a precise orchestration of pattern formation, cell migration, proliferation, apoptosis, and inductive interactions to achieve a functional end. Many of these events are mediated by secreted cytokines, whose activity must be precisely regulated to preclude inappropriate cellular responses. Bone Morphogenetic Proteins (BMPs) are a family of secreted ligands which have potent effects on many aspects of craniofacial development, particularly the closely related proteins BMP2 and BMP4. Their activity is thought to be important in the growth or patterning of such diverse tissues as the brain, the skull, the pituitary gland, the teeth, and the precursors of the face. Research from Drosophila and Xenopus indicate that BMP2/4 signal transduction is regulated in large part by antagonistic proteins such as Chordin (Chd) and Noggin (Nog). In frogs, Chd and Nog promote anterior development, and Chd is essential for normal head development in zebrafish. Preliminary work described in this proposal shows that these genes are required for development of the mammalian head. Lack of Chd in an inbred genetic background results in a group of craniofacial skeletal and soft-tissue defects involving neural crest derivatives, similar to those seen in certain human syndromes. Chd and Nog together are required early for head development, but are also involved specifically in development of the forebrain, mouth, nose, mandible, numerous bones of the skull, and other craniofacial tissues. The major aims of this proposal are: 1) to characterize the spatiotemporal expression patterns of Chd and Nog to clarify their roles in craniofacial development; 2) to determine the critical sites and times of action for Chd and Nog in head induction using embryonic stem cell chimeras and tissue recombinants; 3) to determine the functions of these genes in growth and patterning of craniofacial tissues; and 4) to assess whether ectopic BMP signaling reproduces the craniofacial defects of the mutants.
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