LvsA, a Protein Related to the Mouse Beige Protein, Is Required for Cytokinesis inDictyostelium

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Abstract
We isolated a Dictyostelium cytokinesis mutant with a defect in a novel locus called large volume sphere A (lvsA). lvsA mutants exhibit an unusual phenotype when attempting to undergo cytokinesis in suspension culture. Early in cytokinesis, they initiate furrow formation with concomitant myosin II localization at the cleavage furrow. However, the furrow is later disrupted by a bulge that forms in the middle of the cell. This bulge is bounded by furrows on both sides, which are often enriched in myosin II. The bulge can increase and decrease in size multiple times as the cell attempts to divide. Interestingly, this phenotype is similar to the cytokinesis failure of Dictyosteliumclathrin heavy-chain mutants. Furthermore, both cell lines cap ConA receptors but form only a C-shaped loose cap. Unlike clathrin mutants,lvsA mutants are not defective in endocytosis or development. The LvsA protein shares several domains in common with the molecules beige and Chediak–Higashi syndrome proteins that are important for lysosomal membrane traffic. Thus, on the basis of the sequence analysis of the LvsA protein and the phenotype of thelvsA mutants, we postulate that LvsA plays an important role in a membrane-processing pathway that is essential for cytokinesis.