CLONING OF A XENOPUS-LAEVIS CDNA-ENCODING FOCAL ADHESION KINASE (FAK)AND EXPRESSION DURING EARLY DEVELOPMENT

Focal adhesion kinase (FAK) is a widely produced nonreceptor protein-t yrosine kinase thought to participate in signalling pathways activated in response to cell interaction with the extracellular matrix. Fibron ectin-dependent cell adhesion mediated by integrin receptors plays a c ritical role in mesodermal cell migration during amphibian gastrulatio n in early development. As a first step toward understanding the role of FAK in Xenopus laevis (Xl) early development, we isolated cDNAs enc oding Xl FAK and deduced the entire amino acid (aa) sequence. Xl FAK h as 89-91% overall identity to the homologs previously described from m ouse, human and chicken sources. Within the catalytic domain, the aa i dentity is about 97%. Northern blot analysis revealed that abundant ma ternal FAK transcript is present in Xl eggs, with levels decreasing sl ightly through cleavage and early blastula stages. At early gastrulati on, the FAK mRNA level becomes modestly elevated, followed by a steady decline through late gastrulation. The mRNA level undergoes a further drop at the neurula stage, then begins a steady increase through the tailbud and tadpole stages. These data indicate that the steady-state level of FAK mRNA is regulated during Xl early development, and are co nsistent with a proposed role for FAK in the process of gastrulation.