The cranial neural crest (CNC) is a population of cells formed at the border between the anterior neural and non-neural ectoderm in vertebrate embryos. These cells undergo a regulated epithelial-mesenchymal transition, emerging from the developing neural tube and migrating throughout the head along defined pathways. CNC cells give rise to a variety of cell types and tissues including the cartilage and skeletal elements of the head and face. Defects in the induction, proliferation, migration and/or differentiation of CNC cells account for a wide range of craniofacial anomalies. Thus, a basic understanding of the molecular events that direct CNC cell development and migratory behavior is critical to understanding the causes of craniofacial defects. ADAM 13 is a member of the ADAMs family of transmembrane glycoproteins, which contain A Disintegrin and A Metalloprotease domain. This protein was identified originally in Xenopus laevis, where it is expressed in CNC cells before and during their migration. ADAM 13 metalloprotease activity is hypothesized to play a critical role in the migratory behaviors of the CNC by modifying the extracellular matrix (ECM) filled spaces through which these cells travel. Therefore, the overall objectives of this study are to establish the functions of ADAM 13 and other members of the ADAM family that are expressed in the neural crest. A primary goal is to establish the mechanism of ADAM 13 involvement in CNC migration. Embryo transcript injection, transgenic methods and transfection will be used to express ADAM 13 wild type and mutant constructs in order to investigate ADAM 13 function in intact Xenopus embryos, cultured explants and single cells. The functional specificities of individual ADAM 13 domains (i.e., metalloprotease, disintegrin, cysteine-rich and cytoplasmic) will also be studied using chimeric ADAM constructs comprised of segments of ADAM 13 and other structurally related ADAMs with differing biological activities. The ADAM 13 cytoplasmic tail has been shown to interact with SH3 domain containing proteins including Src1 and PACSIN-2. PACSIN-2 binding is also associated with a reduction in ADAM 13 functional activity in vivo. Thus, the final aim of the proposed research is to investigate the mechanism by which PACSIN-2 down-regulates ADAM 13 function.
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