TALIN REQUIRES BETA-INTEGRIN, BUT NOT VINCULIN, FOR ITS ASSEMBLY INTOFOCAL ADHESION-LIKE STRUCTURES IN THE NEMATODE CAENORHABDITIS-ELEGANS

In cultured cells, the 230-kDa protein talin is found at discrete plas ma membrane foci known as focal adhesions, sites that anchor the intra cellular actin cytoskeleton to the extracellular matrix. The regulated assembly of focal adhesions influences the direction of cell migratio ns or the reorientation of cell shapes. Biochemical studies of talin h ave shown that it binds to the proteins integrin, vinculin, and actin in vitro. To understand the function of talin in vivo and to correlate its in vitro and in vivo biochemical properties, various genetic appr oaches have been adopted. With the intention of using genetics in the study of talin, we identified a homologue to mouse talin in a genetic model system, the nematode Caenorhabditis elegans. C. elegans talin is 39% identical and 59% similar to mouse talin. In wild-type adult C. e legans, talin colocalizes with integrin, vinculin, and alpha-actinin i n the focal adhesion-like structures found in the body-wall muscle. By examining the organization of talin in two different C. elegans mutan t strains that do not make either beta-integrin or vinculin, we were a ble to determine that talin does not require vinculin for its initial organization at the membrane, but that it depends critically on the pr esence of integrin for its initial assembly at membrane foci.