Pxl1p, a Paxillin-related Protein, Stabilizes the Actomyosin Ring during Cytokinesis in Fission Yeast

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Abstract
Paxillins are a family of conserved LIM domain-containing proteins that play important roles in the function and integrity of the actin cytoskeleton. Although paxillins have been extensively characterized by cell biological and biochemical approaches, genetic studies are relatively scarce. Here, we identify and characterize a paxillin-related protein Pxl1p in the fission yeast Schizosaccharomyces pombe. Pxl1p is a component of the fission yeast actomyosin ring, a structure that is essential for cytokinesis. Cells deleted for pxl1 display a novel phenotype characterized by a splitting of the actomyosin ring in late anaphase, leading to the formation of two rings of which only one undergoes constriction. In addition, the rate of actomyosin ring constriction is slower in the absence of Pxl1p. pxl1Δ mutants display strong genetic interactions with mutants defective in IQGAP-related protein Rng2p and mutants defective in components of the fission yeast type II myosin machinery. Collectively, these results suggest that Pxl1p might cooperate with type II myosin and Rng2p-IQGAP to regulate actomyosin ring constriction as well as to maintain its integrity during constriction.