DDLIM IS A CYTOSKELETON-ASSOCIATED PROTEIN INVOLVED IN THE PROTRUSIONOF LAMELLIPODIA IN DICTYOSTELIUM

DdLim, a multi-domain member of the cysteine-rich family of LIM domain proteins, was isolated from Dictyostelium cells where it localizes in lamellipodia and at sites of membrane ruffling. The transcription and expression of DdLim are developmentally regulated, and the timing of its increased association with the actin cytoskeleton coincides with t he acquisition in starved cells of a motile, chemotactic behavior. Veg etative cells that overexpress DdLim contain large lamella and exhibit ruffling at the cortex. The high frequency of large, multinucleated m utant cells found in suspension culture suggests that excess DdLim int erferes with cytokinesis. DdLim was also identified as a protein in a Dictyostelium cell lysate that associated indirectly, but in a guanosi ne triphosphate-dependent manner, with a GST-rac1 fusion protein. The data presented suggest that DdLim acts as an adapter protein at the cy toskeleton-membrane interface where it is involved in a receptor-media ted rac1-signaling pathway that leads to actin polymerization in lamel lipodia and ultimately cell motility.