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Cytokinesis-based constraints on polarized cell growth in fission yeast.

Bohnert KA, Gould KL - PLoS Genet. (2012)

Bottom Line: Intriguingly, such cells elongated constitutively at new ends unless cytokinesis was perturbed.We posit that such constraints facilitate invasive fungal growth, as cytokinesis mutants displaying bipolar growth defects formed numerous pseudohyphae.Collectively, these data highlight a role for previous cell cycles in defining a cell's capacity to polarize at specific sites, and they additionally provide insight into how a unicellular yeast can transition into a quasi-multicellular state.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute and Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.

ABSTRACT
The rod-shaped fission yeast Schizosaccharomyces pombe, which undergoes cycles of monopolar-to-bipolar tip growth, is an attractive organism for studying cell-cycle regulation of polarity establishment. While previous research has described factors mediating this process from interphase cell tips, we found that division site signaling also impacts the re-establishment of bipolar cell growth in the ensuing cell cycle. Complete loss or targeted disruption of the non-essential cytokinesis protein Fic1 at the division site, but not at interphase cell tips, resulted in many cells failing to grow at new ends created by cell division. This appeared due to faulty disassembly and abnormal persistence of the cell division machinery at new ends of fic1Δ cells. Moreover, additional mutants defective in the final stages of cytokinesis exhibited analogous growth polarity defects, supporting that robust completion of cell division contributes to new end-growth competency. To test this model, we genetically manipulated S. pombe cells to undergo new end take-off immediately after cell division. Intriguingly, such cells elongated constitutively at new ends unless cytokinesis was perturbed. Thus, cell division imposes constraints that partially override positive controls on growth. We posit that such constraints facilitate invasive fungal growth, as cytokinesis mutants displaying bipolar growth defects formed numerous pseudohyphae. Collectively, these data highlight a role for previous cell cycles in defining a cell's capacity to polarize at specific sites, and they additionally provide insight into how a unicellular yeast can transition into a quasi-multicellular state.

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Late cytokinesis mutants phenocopy the new end-growth polarity defects of fic1Δ cells.(A) Quantification of growth patterns for cells of the indicated genotypes. Sample size (n) is provided for each genotype. The percentage of the most prevalent faulty growth pattern is boxed for each genotype. (B) Live-cell DIC movies of cells of the indicated genotypes scored in (A). The most prevalent faulty growth pattern for each genotype is pictured. Solid arrows denote old end growth, whereas dashed arrows indicate new end growth. Birth scars are marked by asterisks. Time points are noted. (C) Quantification of polarity phenotypes of calcofluor-stained cells of the indicated genotypes, with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. All cells were grown at 25°C unless otherwise noted. (D) Quantification of septated cells in (C), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. A dashed gray line marks 20% on the y-axis (Bar = 5 µm).
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pgen-1003004-g006: Late cytokinesis mutants phenocopy the new end-growth polarity defects of fic1Δ cells.(A) Quantification of growth patterns for cells of the indicated genotypes. Sample size (n) is provided for each genotype. The percentage of the most prevalent faulty growth pattern is boxed for each genotype. (B) Live-cell DIC movies of cells of the indicated genotypes scored in (A). The most prevalent faulty growth pattern for each genotype is pictured. Solid arrows denote old end growth, whereas dashed arrows indicate new end growth. Birth scars are marked by asterisks. Time points are noted. (C) Quantification of polarity phenotypes of calcofluor-stained cells of the indicated genotypes, with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. All cells were grown at 25°C unless otherwise noted. (D) Quantification of septated cells in (C), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. A dashed gray line marks 20% on the y-axis (Bar = 5 µm).

Mentions: Because faulty cytokinesis led to persistence of parts of the cell division machinery at fic1Δ division planes, we speculated that these remnants might deter subsequent polarized growth at new ends. If this were the case, one would expect other mutants with late cytokinesis defects to also show erroneous new end growth. Previous data had indicated that Fic1-associated Imp2 contributes to CR disassembly, with imp2Δ cells exhibiting abnormal actin structures flanking previous division sites [51]. Though we had shown that imp2Δ cells are defective in bipolar cell growth (Figure 4A–4C), we wanted to confirm that their growth defect was specific to new ends. Using time-lapse DIC imaging, we found that roughly 75% of imp2Δ cell divisions produced at least one daughter cell that failed at new end growth (Figure 6A). Interestingly, both imp2Δ daughter cells failed at new end growth in the majority of cases (Figure 6A–6B). Therefore, proper disassembly of CR components correlates with new end competency for polarized growth.


Cytokinesis-based constraints on polarized cell growth in fission yeast.

Bohnert KA, Gould KL - PLoS Genet. (2012)

Late cytokinesis mutants phenocopy the new end-growth polarity defects of fic1Δ cells.(A) Quantification of growth patterns for cells of the indicated genotypes. Sample size (n) is provided for each genotype. The percentage of the most prevalent faulty growth pattern is boxed for each genotype. (B) Live-cell DIC movies of cells of the indicated genotypes scored in (A). The most prevalent faulty growth pattern for each genotype is pictured. Solid arrows denote old end growth, whereas dashed arrows indicate new end growth. Birth scars are marked by asterisks. Time points are noted. (C) Quantification of polarity phenotypes of calcofluor-stained cells of the indicated genotypes, with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. All cells were grown at 25°C unless otherwise noted. (D) Quantification of septated cells in (C), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. A dashed gray line marks 20% on the y-axis (Bar = 5 µm).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475658&req=5

pgen-1003004-g006: Late cytokinesis mutants phenocopy the new end-growth polarity defects of fic1Δ cells.(A) Quantification of growth patterns for cells of the indicated genotypes. Sample size (n) is provided for each genotype. The percentage of the most prevalent faulty growth pattern is boxed for each genotype. (B) Live-cell DIC movies of cells of the indicated genotypes scored in (A). The most prevalent faulty growth pattern for each genotype is pictured. Solid arrows denote old end growth, whereas dashed arrows indicate new end growth. Birth scars are marked by asterisks. Time points are noted. (C) Quantification of polarity phenotypes of calcofluor-stained cells of the indicated genotypes, with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. All cells were grown at 25°C unless otherwise noted. (D) Quantification of septated cells in (C), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. A dashed gray line marks 20% on the y-axis (Bar = 5 µm).
Mentions: Because faulty cytokinesis led to persistence of parts of the cell division machinery at fic1Δ division planes, we speculated that these remnants might deter subsequent polarized growth at new ends. If this were the case, one would expect other mutants with late cytokinesis defects to also show erroneous new end growth. Previous data had indicated that Fic1-associated Imp2 contributes to CR disassembly, with imp2Δ cells exhibiting abnormal actin structures flanking previous division sites [51]. Though we had shown that imp2Δ cells are defective in bipolar cell growth (Figure 4A–4C), we wanted to confirm that their growth defect was specific to new ends. Using time-lapse DIC imaging, we found that roughly 75% of imp2Δ cell divisions produced at least one daughter cell that failed at new end growth (Figure 6A). Interestingly, both imp2Δ daughter cells failed at new end growth in the majority of cases (Figure 6A–6B). Therefore, proper disassembly of CR components correlates with new end competency for polarized growth.

Bottom Line: Intriguingly, such cells elongated constitutively at new ends unless cytokinesis was perturbed.We posit that such constraints facilitate invasive fungal growth, as cytokinesis mutants displaying bipolar growth defects formed numerous pseudohyphae.Collectively, these data highlight a role for previous cell cycles in defining a cell's capacity to polarize at specific sites, and they additionally provide insight into how a unicellular yeast can transition into a quasi-multicellular state.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute and Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.

ABSTRACT
The rod-shaped fission yeast Schizosaccharomyces pombe, which undergoes cycles of monopolar-to-bipolar tip growth, is an attractive organism for studying cell-cycle regulation of polarity establishment. While previous research has described factors mediating this process from interphase cell tips, we found that division site signaling also impacts the re-establishment of bipolar cell growth in the ensuing cell cycle. Complete loss or targeted disruption of the non-essential cytokinesis protein Fic1 at the division site, but not at interphase cell tips, resulted in many cells failing to grow at new ends created by cell division. This appeared due to faulty disassembly and abnormal persistence of the cell division machinery at new ends of fic1Δ cells. Moreover, additional mutants defective in the final stages of cytokinesis exhibited analogous growth polarity defects, supporting that robust completion of cell division contributes to new end-growth competency. To test this model, we genetically manipulated S. pombe cells to undergo new end take-off immediately after cell division. Intriguingly, such cells elongated constitutively at new ends unless cytokinesis was perturbed. Thus, cell division imposes constraints that partially override positive controls on growth. We posit that such constraints facilitate invasive fungal growth, as cytokinesis mutants displaying bipolar growth defects formed numerous pseudohyphae. Collectively, these data highlight a role for previous cell cycles in defining a cell's capacity to polarize at specific sites, and they additionally provide insight into how a unicellular yeast can transition into a quasi-multicellular state.

Show MeSH
Related in: MedlinePlus