Microtubule and actin-dependent movement of the formin cdc12p in fission yeast

Although a number of gene products involved in cytokinesis have been identi fied, still little is known about how these proteins are localized to the p roper site and assembled into a ring structure. How is the plane of cell di vision is positioned in the cell? Schizosaccharomyces pombe are simple rod- shaped eukaryotic cells that divide by medial fission using a medial contra ctile ring. S. pombe cdc12p encodes a member of the formin gene family, pro teins with conserved roles in cytokinesis and actin organization. cdc12p is required specifically for the formation of the medial ring and is located in this ring during mitosis. Time-lapse microscopy of cells expressing GFP- cdc12p protein fusions reveals that during interphase, S. pombe cdc12p is p resent in a discrete, motile cytoplasmic particle that moves using both act in and microtubules. At the onset of mitosis, the spot moves to the future site of cell division and spreads out into a ring. These studies demonstrat e that a cytokinesis factor may travel on both microtubule and actin networ ks to the site of contractile ring assembly. These findings suggest a poten tial mechanism for how the mitotic spindle positions the cell division plan e in animal cells. Microsc. Res. Tech. 49:161-167, 2000. (C) 2000 Wiley-Lis s, Inc.