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Role of polo kinase and Mid1p in determining the site of cell division in fission yeast.

Bähler J, Steever AB, Wheatley S, Wang Yl, Pringle JR, Gould KL, McCollum D - J. Cell Biol. (1998)

Bottom Line: Upon overexpression of Plo1p, Mid1p exits the nucleus prematurely and displays a reduced mobility on gels similar to that of the hyperphosphorylated form observed previously in mitotic cells.Plo1p localizes to the spindle pole bodies and spindles of mitotic cells and also to the medial ring at the time of its formation.Given its previously known functions in mitosis and the timing of cytokinesis, Plo1p is thus implicated as a key molecule in the spatial and temporal coordination of cytokinesis with mitosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA.

ABSTRACT
The fission yeast Schizosaccharomyces pombe divides symmetrically using a medial F-actin- based contractile ring to produce equal-sized daughter cells. Mutants defective in two previously described genes, mid1 and pom1, frequently divide asymmetrically. Here we present the identification of three new temperature-sensitive mutants defective in localization of the division plane. All three mutants have mutations in the polo kinase gene, plo1, and show defects very similar to those of mid1 mutants in both the placement and organization of the medial ring. In both cases, ring formation is frequently initiated near the cell poles, indicating that Mid1p and Plo1p function in recruiting medial ring components to the cell center. It has been reported previously that during mitosis Mid1p becomes hyperphosphorylated and relocates from the nucleus to a medial ring. Here we show that Mid1p first forms a diffuse cortical band during spindle formation and then coalesces into a ring before anaphase. Plo1p is required for Mid1p to exit the nucleus and form a ring, and Pom1p is required for proper placement of the Mid1p ring. Upon overexpression of Plo1p, Mid1p exits the nucleus prematurely and displays a reduced mobility on gels similar to that of the hyperphosphorylated form observed previously in mitotic cells. Genetic and two-hybrid analyses suggest that Plo1p and Mid1p act in a common pathway distinct from that involving Pom1p. Plo1p localizes to the spindle pole bodies and spindles of mitotic cells and also to the medial ring at the time of its formation. Taken together, the data indicate that Plo1p plays a role in the positioning of division sites by regulating Mid1p. Given its previously known functions in mitosis and the timing of cytokinesis, Plo1p is thus implicated as a key molecule in the spatial and temporal coordination of cytokinesis with mitosis.

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Medial ring formation in elongated cells. cdc25-22 (strain YDM152; wt),  cdc25-22 pom1-Δ1 (strain  JB120), and cdc25-22 mid1-ΔF (strain JB43) cells, all expressing GFP-Cdc4p fusion  protein and growing exponentially at 25°C, were shifted  to 36°C for 4 hr, returned to  25°C, and observed 45 min  later.
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Figure 4: Medial ring formation in elongated cells. cdc25-22 (strain YDM152; wt), cdc25-22 pom1-Δ1 (strain JB120), and cdc25-22 mid1-ΔF (strain JB43) cells, all expressing GFP-Cdc4p fusion protein and growing exponentially at 25°C, were shifted to 36°C for 4 hr, returned to 25°C, and observed 45 min later.

Mentions: If actin is not recruited efficiently to the middle of the cell in the plo1 and mid1 mutants, it might then begin to form filaments at the cell ends, where it is most concentrated in interphase cells. This might explain the frequent origination of the Cdc4p-containing structures at the cell ends in these mutants (see above). In this case, the effect might be more dramatic in highly elongated cells. Therefore, we examined medial ring formation in cdc25-22 mutant cells, which become highly elongated at the restrictive temperature due to a block in late G2 (Thuriaux et al., 1980; Mitchison and Nurse, 1985) and undergo cytokinesis synchronously upon return to permissive temperature. When cdc25-22 single-mutant cells were blocked at restrictive temperature for 4 h and then returned to permissive temperature, 66 of 66 cells examined developed a Cdc4p-containing ring at the cell center (Fig. 4, wt). Similarly, in cdc25-22 pom1-Δ1 double mutants, 69 of 69 cells examined formed rings at or near the cell center (Fig. 4, pom1-Δ; see Discussion). In contrast, 82 of 91 cdc25-22 mid1-ΔF double-mutant cells examined formed rings and filaments close to the very ends of the cells (Fig. 4, mid1-Δ), consistent with the hypothesis that Mid1p (and presumably Plo1p) is required for recruitment of actin from the cell ends to the cell center at the time of ring formation.


Role of polo kinase and Mid1p in determining the site of cell division in fission yeast.

Bähler J, Steever AB, Wheatley S, Wang Yl, Pringle JR, Gould KL, McCollum D - J. Cell Biol. (1998)

Medial ring formation in elongated cells. cdc25-22 (strain YDM152; wt),  cdc25-22 pom1-Δ1 (strain  JB120), and cdc25-22 mid1-ΔF (strain JB43) cells, all expressing GFP-Cdc4p fusion  protein and growing exponentially at 25°C, were shifted  to 36°C for 4 hr, returned to  25°C, and observed 45 min  later.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132972&req=5

Figure 4: Medial ring formation in elongated cells. cdc25-22 (strain YDM152; wt), cdc25-22 pom1-Δ1 (strain JB120), and cdc25-22 mid1-ΔF (strain JB43) cells, all expressing GFP-Cdc4p fusion protein and growing exponentially at 25°C, were shifted to 36°C for 4 hr, returned to 25°C, and observed 45 min later.
Mentions: If actin is not recruited efficiently to the middle of the cell in the plo1 and mid1 mutants, it might then begin to form filaments at the cell ends, where it is most concentrated in interphase cells. This might explain the frequent origination of the Cdc4p-containing structures at the cell ends in these mutants (see above). In this case, the effect might be more dramatic in highly elongated cells. Therefore, we examined medial ring formation in cdc25-22 mutant cells, which become highly elongated at the restrictive temperature due to a block in late G2 (Thuriaux et al., 1980; Mitchison and Nurse, 1985) and undergo cytokinesis synchronously upon return to permissive temperature. When cdc25-22 single-mutant cells were blocked at restrictive temperature for 4 h and then returned to permissive temperature, 66 of 66 cells examined developed a Cdc4p-containing ring at the cell center (Fig. 4, wt). Similarly, in cdc25-22 pom1-Δ1 double mutants, 69 of 69 cells examined formed rings at or near the cell center (Fig. 4, pom1-Δ; see Discussion). In contrast, 82 of 91 cdc25-22 mid1-ΔF double-mutant cells examined formed rings and filaments close to the very ends of the cells (Fig. 4, mid1-Δ), consistent with the hypothesis that Mid1p (and presumably Plo1p) is required for recruitment of actin from the cell ends to the cell center at the time of ring formation.

Bottom Line: Upon overexpression of Plo1p, Mid1p exits the nucleus prematurely and displays a reduced mobility on gels similar to that of the hyperphosphorylated form observed previously in mitotic cells.Plo1p localizes to the spindle pole bodies and spindles of mitotic cells and also to the medial ring at the time of its formation.Given its previously known functions in mitosis and the timing of cytokinesis, Plo1p is thus implicated as a key molecule in the spatial and temporal coordination of cytokinesis with mitosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA.

ABSTRACT
The fission yeast Schizosaccharomyces pombe divides symmetrically using a medial F-actin- based contractile ring to produce equal-sized daughter cells. Mutants defective in two previously described genes, mid1 and pom1, frequently divide asymmetrically. Here we present the identification of three new temperature-sensitive mutants defective in localization of the division plane. All three mutants have mutations in the polo kinase gene, plo1, and show defects very similar to those of mid1 mutants in both the placement and organization of the medial ring. In both cases, ring formation is frequently initiated near the cell poles, indicating that Mid1p and Plo1p function in recruiting medial ring components to the cell center. It has been reported previously that during mitosis Mid1p becomes hyperphosphorylated and relocates from the nucleus to a medial ring. Here we show that Mid1p first forms a diffuse cortical band during spindle formation and then coalesces into a ring before anaphase. Plo1p is required for Mid1p to exit the nucleus and form a ring, and Pom1p is required for proper placement of the Mid1p ring. Upon overexpression of Plo1p, Mid1p exits the nucleus prematurely and displays a reduced mobility on gels similar to that of the hyperphosphorylated form observed previously in mitotic cells. Genetic and two-hybrid analyses suggest that Plo1p and Mid1p act in a common pathway distinct from that involving Pom1p. Plo1p localizes to the spindle pole bodies and spindles of mitotic cells and also to the medial ring at the time of its formation. Taken together, the data indicate that Plo1p plays a role in the positioning of division sites by regulating Mid1p. Given its previously known functions in mitosis and the timing of cytokinesis, Plo1p is thus implicated as a key molecule in the spatial and temporal coordination of cytokinesis with mitosis.

Show MeSH
Related in: MedlinePlus