THE ROLE OF AP-2 IN CRANIOFACIAL DEVELOPMENT

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DESCRIPTION (provided by applicant): The development of a complex multicellular organism requires precisely regulated patterns of gene expression. Our long-term goal is to learn about these control mechanisms in the context of the AP-2 family of transcription factors, especially Tcfap2a. This gene may provide a link between the genetic and environmental origins of human birth defects. First, chromosomal mapping studies have implicated Tcfap2a as a potential candidate gene for human orofacial clefting. Second, Tcfap2a expression is responsive to the teratogen retinoic acid. These two observations are consistent with the pattern of Tcfap2a expression detected during vertebrate embryogenesis. Tcfap2a is expressed in many tissues undergoing complex morphogenetic changes, especially the neural crest, the face and the limb bud. Moreover, Tcfap2a is a vital component of the regulatory network directing normal vertebrate embryogenesis. Mice heterozygous for the Tcfap2a gene exhibit craniofacial defects including maxillary bending. Tcfap2a-null mice have severe developmental abnormalities: exencephaly and they lack a recognizable face. Detailed studies indicate that six basic developmental programs rely on Tcfap2a: formation of the neural tube, face, eyes, body-wall, heart, and limbs. Tcfap2a is a powerful regulator of craniofacial development. Therefore, to gain insight into the origin of human congenital malformations, especially CLIP, this proposal seeks to determine the regulatory hierarchy by which Tcfap2a controls craniofacial morphogenesis. Three Specific Aims will be undertaken. First, the cis-acting sequences and trans-acting factors responsible for the expression of Tcfap2a in the face will be determined. This aim will reveal the signal transduction pathways that are critical for the normal expression of Tcfap2a in the developing face. Second, since the role of Tcfap2a in craniofacial development is difficult to study in the null mouse (because multiple morphogenic processes shaping the head are disrupted), a novel strain of mouse will be generated in which Tcfap2a expression is removed only from the developing face. This new animal model will reveal the molecular and cellular mechanisms by which Tcfap2a specifically controls craniofacial formation. Third, the target genes through which Tcfap2a controls craniofacial morphogenesis will be identified. Together, these studies will provide valuable insight into both normal facial development and craniofacial malformations.