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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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Fic1's C terminus is necessary and sufficient for Fic1's polarity function at the division site.(A) Live-cell bright field (BF) and GFP images of fic1-GFP cells. Localization to cell tips (*), the cytokinetic ring (>), and the division site (#) are marked. (B) Schematic of Fic1 protein domain organization. Residues and fragments of interest are marked. (C) Live-cell BF, GFP (in green), mCherry (mCh) (in magenta), and GFP/mCherry merged images of fic1-GFP sid4-GFP cdc15-mCherry, fic1N-GFP sid4-GFP cdc15-mCherry, and fic1C-GFP sid4-GFP cdc15-mCherry cells. (D) Live-cell images of calcofluor-stained fic1N and fic1C cells. Arrowheads indicate monopolar cells. (E) Quantification of (D), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (F) Quantification of septated cells in (D) and (E), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. (G) Live-cell BF and GFP images of interphase cell tips of fic1-GFP and fic1C-GFP cells (Bars = 5 µm, except for 3G where Bar = 1 µm).
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pgen-1003004-g003: Fic1's C terminus is necessary and sufficient for Fic1's polarity function at the division site.(A) Live-cell bright field (BF) and GFP images of fic1-GFP cells. Localization to cell tips (*), the cytokinetic ring (>), and the division site (#) are marked. (B) Schematic of Fic1 protein domain organization. Residues and fragments of interest are marked. (C) Live-cell BF, GFP (in green), mCherry (mCh) (in magenta), and GFP/mCherry merged images of fic1-GFP sid4-GFP cdc15-mCherry, fic1N-GFP sid4-GFP cdc15-mCherry, and fic1C-GFP sid4-GFP cdc15-mCherry cells. (D) Live-cell images of calcofluor-stained fic1N and fic1C cells. Arrowheads indicate monopolar cells. (E) Quantification of (D), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (F) Quantification of septated cells in (D) and (E), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. (G) Live-cell BF and GFP images of interphase cell tips of fic1-GFP and fic1C-GFP cells (Bars = 5 µm, except for 3G where Bar = 1 µm).

Mentions: Though many cell polarity factors localize to the cell division site in addition to interphase cell tips, only the actions of these proteins at interphase cell tips have been demonstrated to be relevant to polarity regulation. As was observed previously [28], cytoplasmic Fic1-GFP localizes to cell tips during interphase and later to the CR during cell division (Figure 3A). We also detected another pool of Fic1-GFP lining the division site as the CR constricted (Figure 3A). Given this localization pattern and the specific new end growth defect of fic1Δ cells, we asked whether Fic1 affected the timing of NETO via its functions at the cell division site.


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

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

Fic1's C terminus is necessary and sufficient for Fic1's polarity function at the division site.(A) Live-cell bright field (BF) and GFP images of fic1-GFP cells. Localization to cell tips (*), the cytokinetic ring (>), and the division site (#) are marked. (B) Schematic of Fic1 protein domain organization. Residues and fragments of interest are marked. (C) Live-cell BF, GFP (in green), mCherry (mCh) (in magenta), and GFP/mCherry merged images of fic1-GFP sid4-GFP cdc15-mCherry, fic1N-GFP sid4-GFP cdc15-mCherry, and fic1C-GFP sid4-GFP cdc15-mCherry cells. (D) Live-cell images of calcofluor-stained fic1N and fic1C cells. Arrowheads indicate monopolar cells. (E) Quantification of (D), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (F) Quantification of septated cells in (D) and (E), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. (G) Live-cell BF and GFP images of interphase cell tips of fic1-GFP and fic1C-GFP cells (Bars = 5 µm, except for 3G where Bar = 1 µm).
© Copyright Policy
Related In: Results  -  Collection

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

pgen-1003004-g003: Fic1's C terminus is necessary and sufficient for Fic1's polarity function at the division site.(A) Live-cell bright field (BF) and GFP images of fic1-GFP cells. Localization to cell tips (*), the cytokinetic ring (>), and the division site (#) are marked. (B) Schematic of Fic1 protein domain organization. Residues and fragments of interest are marked. (C) Live-cell BF, GFP (in green), mCherry (mCh) (in magenta), and GFP/mCherry merged images of fic1-GFP sid4-GFP cdc15-mCherry, fic1N-GFP sid4-GFP cdc15-mCherry, and fic1C-GFP sid4-GFP cdc15-mCherry cells. (D) Live-cell images of calcofluor-stained fic1N and fic1C cells. Arrowheads indicate monopolar cells. (E) Quantification of (D), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (F) Quantification of septated cells in (D) and (E), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category. (G) Live-cell BF and GFP images of interphase cell tips of fic1-GFP and fic1C-GFP cells (Bars = 5 µm, except for 3G where Bar = 1 µm).
Mentions: Though many cell polarity factors localize to the cell division site in addition to interphase cell tips, only the actions of these proteins at interphase cell tips have been demonstrated to be relevant to polarity regulation. As was observed previously [28], cytoplasmic Fic1-GFP localizes to cell tips during interphase and later to the CR during cell division (Figure 3A). We also detected another pool of Fic1-GFP lining the division site as the CR constricted (Figure 3A). Given this localization pattern and the specific new end growth defect of fic1Δ cells, we asked whether Fic1 affected the timing of NETO via its functions at the cell division site.

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