The Dictyostelium LIM domain-containing protein LIM2 is essential for proper chemotaxis and morphogenesis

We have identified limB, a gene encoding a novel LIM domain-containing prot ein, LIM2, in a screen for genes required for morphogenesis. limB null cell s aggregate, although poorly, but they are unable to undergo morphogenesis, and the aggregates arrest at the mound stage. limB null cells exhibit an a berrant actin cytoskeleton and have numerous F-actin-enriched microspikes. The cells exhibit poor adhesion to a substratum and do not form tight cell- cell agglomerates in suspension. Furthermore, limB null cells are unable to properly polarize in chemoattractant gradients and move very poorly. Expre ssion of limB from a prestalk-specific but not a prespore-specific promoter complements the morphogenetic defects of the limB null strain, suggesting that the limB null cell developmental defect results from an inability to p roperly sort prestalk cells. LIM2 protein is enriched in the cortex of wild -type cells, although it does not colocalize with the actin cytoskeleton. O ur analysis indicates that LIM2 is a new regulatory protein that functions to control rearrangements of the actin cytoskeleton and is required for cel l motility and chemotaxis. Our findings may be generally applicable to unde rstanding pathways that control cell movement and morphogenesis in all mult icellular organisms. Structure function studies on the LIM domains are pres ented.