title: F-actin ring formation and the role of F-actin cables in the fission yeast Schizosaccharomyces pombe.
abstract: Cells of the fission yeast Schizosaccharomyces pombe divide by the contraction of the F-actin ring formed at the medial region of the cell. We investigated the process of F-actin ring formation in detail using optical sectioning and three-dimensional reconstruction fluorescence microscopy. In wild-type cells, formation of an aster-like structure composed of F-actin cables and accumulation of F-actin cables were recognized at the medial cortex of the cell during prophase to metaphase. The formation of the aster-like structure seemed to initiate from branching of the longitudinal F-actin cables at a site near the spindle pole bodies, which had been duplicated but not yet separated. A single cable extended from the aster and encircled the cell at the equator to form a primary F-actin ring during metaphase. During anaphase, the accumulated F-actin cables were linked to the primary F-actin ring, and then all of these structures seemed to be packed to form the F-actin ring. These observations suggest that formation of the aster-like structure and the accumulation of the F-actin cables at the medial region of the cell during metaphase may be required to initiate the F-actin ring formation. In the nda3 mutant, which has a mutation in ss-tubulin and has been thought to be arrested at prophase, an F-actin ring with accumulated F-actin cables similar to that of anaphase wild-type cells was formed at a restrictive temperature. Immediately after shifting to a permissive temperature, this structure changed into a tightly packed ring. This suggests that the F-actin ring formation progresses beyond prophase in the nda3 cells once the cells enter prophase. We further examined F-actin structures in both cdc12 and cdc15 early cytokinesis mutants. As a result, Cdc12 seemed to be required for the primary F-actin ring formation during prophase, whereas Cdc15 may be involved in both packing the F-actin cables to form the F-actin ring and rearrangement of the F-actin after anaphase. In spg1, cdc7 and sid2 septum initiation mutants, the F-actin ring seemed to be formed in order.
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Tokyo, 153-8902, Japan.
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Arai
authors.forename: Issei
authors.initials: I
authors.lastname: Mabuchi
mesh_terms: D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D002455:Cell Division / Q000502:physiology*; D048429:Cell Size / Q000502:physiology; D003599:Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D020409:Molecular Motor Proteins / Q000502:physiology; D009154:Mutation / Q000502:physiology; D015388:Organelles / Q000378:metabolism* / Q000648:ultrastructure; D010641:Phenotype; D012568:Schizosaccharomyces / Q000166:cytology* / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D013696:Temperature
chemical_list: D000199:Actins; D020409:Molecular Motor Proteins