Severe developmental defects in Dictyostelium null mutants for actin-binding proteins

The actin cytoskeleton is implicated in many cellular processes, such as ce ll adhesion, locomotion, contraction and cytokinesis, which are central to any development. The extent of polymerization, cross-linking, and bundling of actin is regulated by several actin-binding proteins. Knock-out mutation s in these proteins have revealed in many cases only subtle, ii. any, defec ts in development, suggesting that the actin system is redundant, with mult iple proteins sharing overlapping functions. The apparent redundancy may, h owever, reflect limitations of available laboratory assays in assessing the developmental role of a given protein. By using a novel assay, which repro duces conditions closer to the natural ones, we have re-examined the effect s of disruption of many actin-binding proteins, and show here that deletion of ol-actinin, interaptin, synexin, 34-kDa actin-bundling protein, and gel ation factor affect to varying degrees the efficiency of Dictyostelium cell s to complete development and form viable spores. No phenotypic defects wer e found in hisactophilin or comitin null mutants. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.