AP 2 AND CRANIOFACIAL DEVELOPMENT

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DESCRIPTION (adapted from the Investigator's abstract): The development of a mammalian embryo requires precisely regulated patterns of gene expression. This is accomplished, in part, by a regulatory network of transcription factors that modulate the rate of gene expression. Aberrant transcription factor activity can lead to developmental abnormalities and oncogenesis. A comprehensive analysis of how these proteins act is vital to understand development and disease. The Principal Investigator's long term goal is to learn about these control mechanisms in the context of the transcription factor AP-2. The AP-2 gene may provide a link between the genetic and environmental origins or human birth defects. First, chromosomal mapping studies have implicated AP-2 as a potential candidate gene for human orofacial clefting. Second, AP-2 expression is responsive to the teratogen retinoic acid (RA). These two observations are consistent with the pattern of AP-2 is expressed in many issues undergoing complex morphogenetic changes, especially in the neural crest, the frontonasal process and the limb bud. Moreover, AP-2 is a vital component of the regulatory network directing normal vertebrate embryogenesis. Mice heterozygous for the AP-2 gene exhibit craniofacial defects including maxillary and dental malformations. Mice that lack both AP-2 alleles have sever and pleiotropic developmental abnormalities. In particular, AP-2 knockout mice exhibit exencephaly and lack recognizable face. Detailed studies indicate that five basic developmental programs rely on AP- expression. These include formation of the neural tube, face, eyes, body wall and limbs. AP-2 is one of the most powerful regulators of craniofacial development so far identified. Therefore, to gain insight into the origin of human congenital malformations, this proposal seeks to determine the regulatory hierarchy by which AP-2 controls craniofacial morphogenesis. Three specific aims will be undertaken. First, the cis- acting sequences and trans-acting factors responsible for the expression of AP-2 in the facial prominences will be determined. This aim will reveal the signal transduction pathways that are critical for the normal expression of AP-2 in the developing face. Second, since the role of AP-2 in craniofacial development is difficult to study in the knockout mouse (because multiple morphogenic processes shaping the head are disrupted), a novel strain of mouse will be generated in which AP-2 expression in removed only from the developing face. This new animal model will reveal the molecular and cellular mechanisms by which AP-2 specifically controls craniofacial formation. Third, the target genes through which AP-2 controls craniofacial morphogenesis will be identified. Together, these studies will provide valuable insight into both normal facial development and craniofacial deformity.