Limits...
Morphogenesis beyond cytokinetic arrest in Saccharomyces cerevisiae.

Jiménez J, Cid VJ, Cenamor R, Yuste M, Molero G, Nombela C, Sánchez M - J. Cell Biol. (1998)

Bottom Line: This morphogenetic response reflects entry into a new round of the cell cycle: the preference for polarization from the distal pole was lost in bud1 cdc15 double mutants; double cdc15-lyt1 cdc28-4 mutants, defective for START, did not develop apical projections and apical polarization was accompanied by DNA replication.Apical polarization was delayed in cdc15 mutants as compared with budding in control cells and this delay was abolished in a septin mutant.Our results suggest that the delayed M/G1 transition in cdc15 mutants is due to a septin-dependent checkpoint that couples initiation of the cell cycle to the completion of cytokinesis.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Microbiología II, Facultad de Farmacia.

ABSTRACT
The budding yeast lyt1 mutation causes cell lysis. We report here that lyt1 is an allele of cdc15, a gene which encodes a protein kinase that functions late in the cell cycle. Neither cdc15-1 nor cdc15-lyt1 strains are able to septate at 37 degreesC, even though they may manage to rebud. Cells lyse after a shmoo-like projection appears at the distal pole of the daughter cell. Actin polarizes towards the distal pole but the septins remain at the mother-daughter neck. This morphogenetic response reflects entry into a new round of the cell cycle: the preference for polarization from the distal pole was lost in bud1 cdc15 double mutants; double cdc15-lyt1 cdc28-4 mutants, defective for START, did not develop apical projections and apical polarization was accompanied by DNA replication. The same phenomena were caused by mutations in the genes CDC14, DBF2, and TEM1, which are functionally related to CDC15. Apical polarization was delayed in cdc15 mutants as compared with budding in control cells and this delay was abolished in a septin mutant. Our results suggest that the delayed M/G1 transition in cdc15 mutants is due to a septin-dependent checkpoint that couples initiation of the cell cycle to the completion of cytokinesis.

Show MeSH

Related in: MedlinePlus

Microscopic observations by phase–contrast (a–d and h–q), fluorescence (e and f), scanning electron (g), and transmission  electron (r–t) microscopy of haploid and diploid cdc15 mutant strains. (a) Strain L2C24d (cdc15-lyt1) transformed with the pBS9 plasmid bearing the CDC15 gene after 6 h of incubation at 37°C, thus displaying wild-type behavior. (b) Diploid MY1 strain (cdc15-1/cdc15-lyt1) under the same conditions showing abundant chained cells. (c) L2C24d (cdc15-lyt1) strain under the same restrictive conditions.  (d) The same strain incubated in an osmotically stabilized medium (supplemented with 1 M sorbitol) under identical conditions, showing an exacerbated expression of its characteristic apical growth phenotype. (e) Nucleus staining in fixed RNase-treated cells from strain  L2C24d (cdc15-lyt1) after 6 h of incubation at 37°C. (f) Cells from the diploid strain MY1 (cdc15-1/cdc15-lyt1) after the same treatment.  (g) A characteristic asymmetric doublet from the L2C24d (cdc15-lyt1) strain incubated at the restrictive temperature for 6 h. (h–l) Series  showing the development of a cell from the L2C24d (cdc15-lyt1) strain at 37°C. Pictures were taken at 0 h (h), 1 h (i), 2.5 h (j), 3.5 h (k),  and 4.5 h (l). (m–q) Series showing the development of a cell from the MY1 (cdc15-1/cdc15-lyt1) strain in the same conditions. Pictures  were taken at 0 (m), 0.5 h (n), 1.5 (o), 2.5 (p), and 3.5 h (q). (r and s) Section of cells from the L2C24d (cdc15-lyt1) strain after 6 h of incubation at 37°C, showing that septation has not been initiated. (t) A chain of cytokinetic-defective cells from the diploid MY1 (cdc15-1/ cdc15-lyt1) strain under the same conditions. Bars, 8 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2132980&req=5

Figure 2: Microscopic observations by phase–contrast (a–d and h–q), fluorescence (e and f), scanning electron (g), and transmission electron (r–t) microscopy of haploid and diploid cdc15 mutant strains. (a) Strain L2C24d (cdc15-lyt1) transformed with the pBS9 plasmid bearing the CDC15 gene after 6 h of incubation at 37°C, thus displaying wild-type behavior. (b) Diploid MY1 strain (cdc15-1/cdc15-lyt1) under the same conditions showing abundant chained cells. (c) L2C24d (cdc15-lyt1) strain under the same restrictive conditions. (d) The same strain incubated in an osmotically stabilized medium (supplemented with 1 M sorbitol) under identical conditions, showing an exacerbated expression of its characteristic apical growth phenotype. (e) Nucleus staining in fixed RNase-treated cells from strain L2C24d (cdc15-lyt1) after 6 h of incubation at 37°C. (f) Cells from the diploid strain MY1 (cdc15-1/cdc15-lyt1) after the same treatment. (g) A characteristic asymmetric doublet from the L2C24d (cdc15-lyt1) strain incubated at the restrictive temperature for 6 h. (h–l) Series showing the development of a cell from the L2C24d (cdc15-lyt1) strain at 37°C. Pictures were taken at 0 h (h), 1 h (i), 2.5 h (j), 3.5 h (k), and 4.5 h (l). (m–q) Series showing the development of a cell from the MY1 (cdc15-1/cdc15-lyt1) strain in the same conditions. Pictures were taken at 0 (m), 0.5 h (n), 1.5 (o), 2.5 (p), and 3.5 h (q). (r and s) Section of cells from the L2C24d (cdc15-lyt1) strain after 6 h of incubation at 37°C, showing that septation has not been initiated. (t) A chain of cytokinetic-defective cells from the diploid MY1 (cdc15-1/ cdc15-lyt1) strain under the same conditions. Bars, 8 μm.

Mentions: An interesting observation was made when studying the lytic phenotype of cdc15ts strains: lysed cells were seldom symmetrical doublets. 96.9% of lysed cells in a given population of the L2C24d cdc15-lyt1 strain showed an asymmetrical morphology after 5 h at 37°C: one of the cells in the doublet had developed a more or less conspicuous apical structure (Fig. 2 c, e, g, h–l, and s). This phenotype was precluded by introduction of the pBS9 plasmid, bearing the CDC15 gene (Fig. 2 a). To determine whether it was the mother, daughter, or either that was developing the apical projection, we grew a culture of the same strain at 24°C and then shifted some cells to a YPD microsheet and kept them under observation at 37°C in a thermostatted microscope. With this approach, we observed that the aberrant structure that seemed to precede cell lysis occurred in the daughter cell (Fig. 2, h–l). All 37 cells under these conditions behaved identically. Further support to the conclusion that it was essentially the daughter cell that developed the structure was provided by the staining of bud scars with calcofluor white. In 34 out of 35 scar-bearing doublets, the cell showing the apical shmoo-like structure never had chitin scars, suggesting that it was the newborn one. In turn, when present, scars were always situated on the nonaberrant cell of the doublet (data not shown).


Morphogenesis beyond cytokinetic arrest in Saccharomyces cerevisiae.

Jiménez J, Cid VJ, Cenamor R, Yuste M, Molero G, Nombela C, Sánchez M - J. Cell Biol. (1998)

Microscopic observations by phase–contrast (a–d and h–q), fluorescence (e and f), scanning electron (g), and transmission  electron (r–t) microscopy of haploid and diploid cdc15 mutant strains. (a) Strain L2C24d (cdc15-lyt1) transformed with the pBS9 plasmid bearing the CDC15 gene after 6 h of incubation at 37°C, thus displaying wild-type behavior. (b) Diploid MY1 strain (cdc15-1/cdc15-lyt1) under the same conditions showing abundant chained cells. (c) L2C24d (cdc15-lyt1) strain under the same restrictive conditions.  (d) The same strain incubated in an osmotically stabilized medium (supplemented with 1 M sorbitol) under identical conditions, showing an exacerbated expression of its characteristic apical growth phenotype. (e) Nucleus staining in fixed RNase-treated cells from strain  L2C24d (cdc15-lyt1) after 6 h of incubation at 37°C. (f) Cells from the diploid strain MY1 (cdc15-1/cdc15-lyt1) after the same treatment.  (g) A characteristic asymmetric doublet from the L2C24d (cdc15-lyt1) strain incubated at the restrictive temperature for 6 h. (h–l) Series  showing the development of a cell from the L2C24d (cdc15-lyt1) strain at 37°C. Pictures were taken at 0 h (h), 1 h (i), 2.5 h (j), 3.5 h (k),  and 4.5 h (l). (m–q) Series showing the development of a cell from the MY1 (cdc15-1/cdc15-lyt1) strain in the same conditions. Pictures  were taken at 0 (m), 0.5 h (n), 1.5 (o), 2.5 (p), and 3.5 h (q). (r and s) Section of cells from the L2C24d (cdc15-lyt1) strain after 6 h of incubation at 37°C, showing that septation has not been initiated. (t) A chain of cytokinetic-defective cells from the diploid MY1 (cdc15-1/ cdc15-lyt1) strain under the same conditions. Bars, 8 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132980&req=5

Figure 2: Microscopic observations by phase–contrast (a–d and h–q), fluorescence (e and f), scanning electron (g), and transmission electron (r–t) microscopy of haploid and diploid cdc15 mutant strains. (a) Strain L2C24d (cdc15-lyt1) transformed with the pBS9 plasmid bearing the CDC15 gene after 6 h of incubation at 37°C, thus displaying wild-type behavior. (b) Diploid MY1 strain (cdc15-1/cdc15-lyt1) under the same conditions showing abundant chained cells. (c) L2C24d (cdc15-lyt1) strain under the same restrictive conditions. (d) The same strain incubated in an osmotically stabilized medium (supplemented with 1 M sorbitol) under identical conditions, showing an exacerbated expression of its characteristic apical growth phenotype. (e) Nucleus staining in fixed RNase-treated cells from strain L2C24d (cdc15-lyt1) after 6 h of incubation at 37°C. (f) Cells from the diploid strain MY1 (cdc15-1/cdc15-lyt1) after the same treatment. (g) A characteristic asymmetric doublet from the L2C24d (cdc15-lyt1) strain incubated at the restrictive temperature for 6 h. (h–l) Series showing the development of a cell from the L2C24d (cdc15-lyt1) strain at 37°C. Pictures were taken at 0 h (h), 1 h (i), 2.5 h (j), 3.5 h (k), and 4.5 h (l). (m–q) Series showing the development of a cell from the MY1 (cdc15-1/cdc15-lyt1) strain in the same conditions. Pictures were taken at 0 (m), 0.5 h (n), 1.5 (o), 2.5 (p), and 3.5 h (q). (r and s) Section of cells from the L2C24d (cdc15-lyt1) strain after 6 h of incubation at 37°C, showing that septation has not been initiated. (t) A chain of cytokinetic-defective cells from the diploid MY1 (cdc15-1/ cdc15-lyt1) strain under the same conditions. Bars, 8 μm.
Mentions: An interesting observation was made when studying the lytic phenotype of cdc15ts strains: lysed cells were seldom symmetrical doublets. 96.9% of lysed cells in a given population of the L2C24d cdc15-lyt1 strain showed an asymmetrical morphology after 5 h at 37°C: one of the cells in the doublet had developed a more or less conspicuous apical structure (Fig. 2 c, e, g, h–l, and s). This phenotype was precluded by introduction of the pBS9 plasmid, bearing the CDC15 gene (Fig. 2 a). To determine whether it was the mother, daughter, or either that was developing the apical projection, we grew a culture of the same strain at 24°C and then shifted some cells to a YPD microsheet and kept them under observation at 37°C in a thermostatted microscope. With this approach, we observed that the aberrant structure that seemed to precede cell lysis occurred in the daughter cell (Fig. 2, h–l). All 37 cells under these conditions behaved identically. Further support to the conclusion that it was essentially the daughter cell that developed the structure was provided by the staining of bud scars with calcofluor white. In 34 out of 35 scar-bearing doublets, the cell showing the apical shmoo-like structure never had chitin scars, suggesting that it was the newborn one. In turn, when present, scars were always situated on the nonaberrant cell of the doublet (data not shown).

Bottom Line: This morphogenetic response reflects entry into a new round of the cell cycle: the preference for polarization from the distal pole was lost in bud1 cdc15 double mutants; double cdc15-lyt1 cdc28-4 mutants, defective for START, did not develop apical projections and apical polarization was accompanied by DNA replication.Apical polarization was delayed in cdc15 mutants as compared with budding in control cells and this delay was abolished in a septin mutant.Our results suggest that the delayed M/G1 transition in cdc15 mutants is due to a septin-dependent checkpoint that couples initiation of the cell cycle to the completion of cytokinesis.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Microbiología II, Facultad de Farmacia.

ABSTRACT
The budding yeast lyt1 mutation causes cell lysis. We report here that lyt1 is an allele of cdc15, a gene which encodes a protein kinase that functions late in the cell cycle. Neither cdc15-1 nor cdc15-lyt1 strains are able to septate at 37 degreesC, even though they may manage to rebud. Cells lyse after a shmoo-like projection appears at the distal pole of the daughter cell. Actin polarizes towards the distal pole but the septins remain at the mother-daughter neck. This morphogenetic response reflects entry into a new round of the cell cycle: the preference for polarization from the distal pole was lost in bud1 cdc15 double mutants; double cdc15-lyt1 cdc28-4 mutants, defective for START, did not develop apical projections and apical polarization was accompanied by DNA replication. The same phenomena were caused by mutations in the genes CDC14, DBF2, and TEM1, which are functionally related to CDC15. Apical polarization was delayed in cdc15 mutants as compared with budding in control cells and this delay was abolished in a septin mutant. Our results suggest that the delayed M/G1 transition in cdc15 mutants is due to a septin-dependent checkpoint that couples initiation of the cell cycle to the completion of cytokinesis.

Show MeSH
Related in: MedlinePlus