Department of Cell Biology, University of Virginia, Charlottsville 22908, USA.
Integrin-mediated cellular adhesion to components of the extracellular matrix (ECM) is important in a number of morphogenetic events that occur during vertebrate embryogenesis. Recent studies suggest that the focal adhesion kinase pp125FAK is involved in the regulation of integrin-dependent signaling processes triggered by cell adhesion to the ECM. We report the cDNA cloning and sequence analysis of the Xenopus homolog of pp125FAK. We also describe temporal and spatial patterns of FAK expression during early development. Xenopus FAK shares greater than 90% identity with its avian and mammalian homologs. FAK mRNA and protein are present in the fertilized egg and in cleavage stage embryos. During gastrulation, FAK protein expression increases significantly and is detected in mesoderm, marginal zone ectoderm, and cells of the blastocoel roof. Later in development, FAK is prominently expressed at intersomitic junctions, in the brain, and in several cranial nerves. Phosphotyrosyl-FAK is first detected during gastrulation, suggesting that the phosphorylation of FAK on tyrosine is developmentally regulated. These data indicate that FAK is likely to participate in a variety of integrin-ECM-dependent signaling events during morphogenesis.