A checkpoint that monitors cytokinesis in Schizosaccharomyces pombe.
Cell division in Schizosaccharomyces pombe is achieved through the use of a medially positioned actomyosin ring. A division septum is formed centripetally, concomitant with actomyosin ring constriction. Genetic screens have identified mutations in a number of genes that affect actomyosin ring or septum assembly. These cytokinesis-defective mutants, however, undergo multiple S and M phases and die as elongated cells with multiple nuclei. Recently, we have shown that a mutant allele of the S. pombe drc1(+)/cps1(+) gene, which encodes a 1,3-(beta)-glucan synthase subunit, is defective in cytokinesis but displays a novel phenotype. drc1-191/cps1-191 cells are capable of assembling actomyosin rings and completing mitosis, but are incapable of assembling the division septum, causing them to arrest as binucleate cells with a stable actomyosin ring. Each nucleus in arrested cps1-191 cells is able to undergo S phase but these G(2) nuclei are significantly delayed for entry into the M phase. In this study we have investigated the mechanism that causes cps1-191 to block with two G(2) nuclei. We show that the inability of cps1-191 mutants to proceed through multiple mitotic cycles is not related to a defect in cell growth. Rather, the failure to complete some aspect of cytokinesis may prevent the G(2)/M transition of the two interphase-G(2) nuclei. The G(2)/M transition defect of cps1-191 mutants is suppressed by a mutation in the wee1 gene and also by the dominant cdc2 allele cdc2-1w, but not the cdc2-3w allele. Transient depolymerization of all F-actin structures also allowed a significant proportion of the cps1-191 cells to undergo a second round of mitosis. We conclude that an F-actin and Wee1p dependent checkpoint blocks G(2)/M transition until previous cytokinesis is completed.
Liu
J
J
Cell Division Laboratory, Institute of Molecular Agrobiology, The National University of Singapore, Singapore 117604, Republic of Singapore.
Wang
H
H
Balasubramanian
M K
MK
D000199:Actins / Q000502:physiology; D000205:Actomyosin / Q000235:genetics; D000483:Alleles; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D016195:G2 Phase / Q000187:drug effects / Q000235:genetics; D005964:Glucosyltransferases; D007399:Interphase / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D008938:Mitosis / Q000187:drug effects / Q000235:genetics; D016296:Mutagenesis; D009687:Nuclear Proteins; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000502:physiology; D012568:Schizosaccharomyces / Q000166:cytology* / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D029702:Schizosaccharomyces pombe Proteins; D013696:Temperature; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D018797:Cell Cycle Proteins; D008565:Membrane Proteins; D009687:Nuclear Proteins; D029702:Schizosaccharomyces pombe Proteins; D013844:Thiazoles; D053778:Thiazolidines; D000205:Actomyosin; D005964:Glucosyltransferases; C020570:1,3-beta-glucan synthase; C068689:wee1 protein, S pombe; D011505:Protein-Tyrosine Kinases; C037067:latrunculin A