The role of Plo1 kinase in mitotic commitment and septation in Schizosaccharomyces pombe

Abstract

Plo1-associated casein kinase activity peaked during mitosis before septation. Phosphatase treatment abolished this activity. Mitotic Plo1 activation had a requirement for prior activation of M-phase promoting factor (MPF), suggesting that Plo1 does not act as a mitotic trigger kinase to initiate MPF activation during mitotic commitment. A link between Plo1 and the septum initiating network (SIN) has been suggested by the inability of plo1D cells to septate and the proli®c septation following plo1 + overexpression. Interphase activation of Spg1, the G protein that modulates SIN activity, induced septation but did not stimulate Plo1-associated kinase activity. Conversely, SIN inactivation did not affect the mitotic stimulation of Plo1-associated kinase activity. plo1.ts4 cells formed a misshapen actin ring, but rarely septated at 36°C. Forced activation of Spg1 enabled plo1.ts4 mutant cells, but not cells with defects in the SIN component Sid2, to convert the actin ring to a septum. The ability of plo1 + overexpression to induce septation was severely compromised by SIN inactivation. We propose that Plo1 acts before the SIN to control septation.

Yeast polo-like kinases: functionally conserved multitask mitotic regulators

“…However, Plo1 localizes to the SPB after mitotic entry and delocalizes from it following APC activation (Mulvihill et al, 1999). Close examination of Plo1 activities with synchronous cultures revealed that Plo1 activation occurs in a biphasic manner; the first phase of Plo1 activity coincides with actin ring formation in prophase, whereas the second peak precedes septum formation late in mitosis (Tanaka et al, 2001). These data suggest that timely activation and dynamic subcellular localization of Plo1 are critical for regulating Plo1 function.…”

Roles of Pdk1p, a Fission Yeast Protein Related to Phosphoinositide-dependent Protein Kinase, in the Regulation of Mitosis and Cytokinesis

“…These include 1) mitotic abnormalities caused by the formation of a monopolar mitotic spindle; 2) misplaced actomyosin rings; and 3) cytokinesis defects associated with the formation of multinucleate cells with back-to-back nuclei, similar to that observed in SIN mutants (Ohkura et al, 1995;Bähler et al, 1998;Tanaka et al, 2001). The plo1 ts mutants used in this study display all the abovementioned phenotypes at the restrictive temperature of 36°C but rarely do so at the permissive temperature of 24°C.…”

A ‘marker switch’ approach for targeted mutagenesis of genes in Schizosaccharomyces pombe

“…The architecture of the filamentous actin ring that implements cytokinesis was defective in both the plo1.ts4 and plo1.ts18 mutant strains (Figure 3; Tanaka et al, 2001). At 25 • C both strains had an actin ring that correctly bisected the cell perpendicular to the long axis of the cell (Marks and Hyams, 1985).…”

“…pombe 593 in plo1.ts18 mutant cells was much larger than normal and appeared to randomly bisect the cell in a manner that was highly reminiscent of the plo1.1, plo1.24C and plo1.25 mutations reported by Bähler et al (1998a; Figure 3B). The ability of plo1.ts4 to use the F-actin ring to deposit septal material was severely compromised when the strain was grown in minimal medium (Tanaka et al, 2001); 4 h after the temperature was changed from 25 • C to 36 • C, 49% of cells contained multiple nuclei but had no septa (Tanaka et al, 2001). The few septa that did form in plo1.ts4 cells were misshapen and asymmetric (Tanaka et al, 2001).…”

“…The ability of plo1.ts4 to use the F-actin ring to deposit septal material was severely compromised when the strain was grown in minimal medium (Tanaka et al, 2001); 4 h after the temperature was changed from 25 • C to 36 • C, 49% of cells contained multiple nuclei but had no septa (Tanaka et al, 2001). The few septa that did form in plo1.ts4 cells were misshapen and asymmetric (Tanaka et al, 2001).…”