The proper spatial and temporal coordination of mitosis and cytokinesis is essential for maintaining genomic integrity. We describe the identification and characterization of the Saccharomyces cerevisiae IBD1 gene, which encodes a novel protein that regulates the proper nuclear division and bud separation. IBD1 was identified by the limited homology to byr4, a dosage-dependent regulator of cytokinesis in Schizosaccharomyces pombe. IBD1 is not an essential gene, and the knock-out cells show no growth defects except for the reduced mating efficiency . However, upon ectopic expression from an inducible promoter, IBD1 is lethal to the cell and leads to abnormal nuclear division and bud separation. In detail, approximately 90% of the IBD1 overexpressing cells arrest at large bud stages with dividing or divided nuclei. In some IBD1 overexpressing cells, spindle elongation and chromosome separation occur within the mother cell, leading to anucleated and binucleate daughter cells. The anucleated cell can not bud, but the binucleate cell proceeds through another cell cycle(s) to produce a cell with multiple nuclei and multiple buds. Observations of the F-actin and chitin rings in the IBD1 overexpressing cells reveal that these cells lose the polarity for bud site selection and growth or attain the hyper-polarity for growth. Consistent with the phenotypes, the IBD1 overexpressing cells contain a broad range of DNA content, from 2 to 4 N or more. A functional Ibd1p-GFP fusion protein localizes to a single dot at the nuclear DNA boundary in the divided nuclei or to double dots in dividing nuclei, suggesting its localization on the spindle pole body (SPB). The cross-species expressions of IBD1 in S. pombe and byr4 in S. cerevisiae cause defects in shape, implicating the presence of a conserved mechanism for the control of cytokinesis in eukaryotes. We propose that Ibd1p is an SPB associated protein that links proper nuclear division to cytokinesis and bud separation. Copyright (C) 1999 Elsevier Science B.V.
|Number of pages||15|
|Journal||Biochimica et Biophysica Acta - Molecular Cell Research|
|Publication status||Published - 1999 Apr 1|
Bibliographical noteFunding Information:
As the overexpression phenotypes suggest, IBD1 may function in regulating the entry into anaphase and in signaling between nuclear division and the onset of cytokinesis. The role of IBD1 is supported by its possible localization to the spindle pole body. Recent studies proposed the importance of mitotic spindles and the spindle poles in coordinating mitosis and cytokinesis. The potential importance of the spindle pole body in linking between the machinery of mitosis and cytokinesis is being verified in S. pombe . Byr4p, a possible homologue of Ibd1p, is also localized to the spindle pole body as a GFP fusion (K. Song, C. Albright, unpublished data). Byr4p forms a GAP complex with Cdc16p for the Spg1 GTPase to integrate mitosis and cytokinesis in S. pombe , and Spg1p and its target, Cdc7p, are also localized to the SPB [33,35] . These data in S. pombe propose an essential role of the spindle pole body in signaling for the integration of mitosis and cytokinesis. As we describe in this paper, Ibd1p, a potential coordinator of mitosis and cytokinesis in S. cerevisiae , localizes to the spindle pole body, suggesting a conserved role of the spindle pole body in combining nuclear and cytoplasmic divisions. In addition, the major mitotic machinery in all eukaryotes, the cdc2 kinase/cyclin B and the 20S cyclosome/APC, localize to the spindle pole body or its mammalian equivalent, the centrosome [52–54] . Colocalization of the regulators for mitotic progression and for the onset of cytokinesis on the spindle pole body provides the potential significance of the MTOC as a conserved coordinator of mitosis and cytokinesis in all eukaryotes.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology