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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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Constitutive NETO signaling does not fully rescue cytokinesis-based growth polarity defects.(A) Quantification of growth patterns for wild-type and tea1-for3 cells. Sample size (n) is provided for each genotype. (B) Quantification of times from septum splitting to initiation of tip growth at previous division sites for tea1-for3 cells. Times were carried into the next cell cycle where applicable. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers). n>200. (C) Data for tea1-for3 cells in (B) grouped according to the amount of time needed for the mother cell to complete septation. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers) for each category. (D) Live-cell DIC movies of tea1-for3 cells with different times needed to complete septation. The time of septum splitting of the mother cell is marked as point zero. The initiation of tip growth at previous division sites is denoted by yellow arrows. Tip growth at these sites was also scored for cells that did not initiate such growth until the subsequent cell cycle. (E) Live-cell images of calcofluor-stained tea1-for3 and tea1-for3 fic1Δ cells. Arrowheads indicate monopolar cells. (F) Quantification of (E), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (G) Quantification of septated cells in (E) and (F), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category (Bars = 5 µm).
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pgen-1003004-g008: Constitutive NETO signaling does not fully rescue cytokinesis-based growth polarity defects.(A) Quantification of growth patterns for wild-type and tea1-for3 cells. Sample size (n) is provided for each genotype. (B) Quantification of times from septum splitting to initiation of tip growth at previous division sites for tea1-for3 cells. Times were carried into the next cell cycle where applicable. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers). n>200. (C) Data for tea1-for3 cells in (B) grouped according to the amount of time needed for the mother cell to complete septation. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers) for each category. (D) Live-cell DIC movies of tea1-for3 cells with different times needed to complete septation. The time of septum splitting of the mother cell is marked as point zero. The initiation of tip growth at previous division sites is denoted by yellow arrows. Tip growth at these sites was also scored for cells that did not initiate such growth until the subsequent cell cycle. (E) Live-cell images of calcofluor-stained tea1-for3 and tea1-for3 fic1Δ cells. Arrowheads indicate monopolar cells. (F) Quantification of (E), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (G) Quantification of septated cells in (E) and (F), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category (Bars = 5 µm).

Mentions: To analyze tea1-for3 cells in real-time, we performed time-lapse DIC imaging. As expected, most tea1-for3 cells underwent NETO before the next cell division (Figure 8A), with nearly 75% of new ends initiating growth within 50 minutes of septum splitting (Figure 8B). Nonetheless, some tea1-for3 outliers took much longer to extend at tips created by cell division (Figure 8B). After grouping the times needed for tip growth to occur at previous division sites relative to the amount of time needed for the mother cell to complete cytokinesis, we found that newly-formed tips that took longer to initiate growth had been formed by more inefficient cytokinesis (Figure 8C–8D). As distal tip growth continued in cells undergoing division (Figure 8D) and appeared unimpeded by additional factors, these findings suggested that faulty cytokinesis imposes constraints at previous division sites that counteract positive polarizing cues. We corroborated this model by expressing the Tea1-For3 fusion in fic1Δ cells. Although tea1-for3 cells were mostly bipolar, tea1-for3 fic1Δ cells showed a high percentage of monopolar growth (Figure 8E–8G). These findings confirmed that efficient completion of cytokinesis is critical for new end growth, even when signaling networks responsible for NETO are prematurely activated.


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

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

Constitutive NETO signaling does not fully rescue cytokinesis-based growth polarity defects.(A) Quantification of growth patterns for wild-type and tea1-for3 cells. Sample size (n) is provided for each genotype. (B) Quantification of times from septum splitting to initiation of tip growth at previous division sites for tea1-for3 cells. Times were carried into the next cell cycle where applicable. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers). n>200. (C) Data for tea1-for3 cells in (B) grouped according to the amount of time needed for the mother cell to complete septation. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers) for each category. (D) Live-cell DIC movies of tea1-for3 cells with different times needed to complete septation. The time of septum splitting of the mother cell is marked as point zero. The initiation of tip growth at previous division sites is denoted by yellow arrows. Tip growth at these sites was also scored for cells that did not initiate such growth until the subsequent cell cycle. (E) Live-cell images of calcofluor-stained tea1-for3 and tea1-for3 fic1Δ cells. Arrowheads indicate monopolar cells. (F) Quantification of (E), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (G) Quantification of septated cells in (E) and (F), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category (Bars = 5 µm).
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pgen-1003004-g008: Constitutive NETO signaling does not fully rescue cytokinesis-based growth polarity defects.(A) Quantification of growth patterns for wild-type and tea1-for3 cells. Sample size (n) is provided for each genotype. (B) Quantification of times from septum splitting to initiation of tip growth at previous division sites for tea1-for3 cells. Times were carried into the next cell cycle where applicable. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers). n>200. (C) Data for tea1-for3 cells in (B) grouped according to the amount of time needed for the mother cell to complete septation. Data are presented in box-and-whisker plots showing the median (line in the box), 25th–75th percentiles (box), and 5th–95th percentiles (whiskers) for each category. (D) Live-cell DIC movies of tea1-for3 cells with different times needed to complete septation. The time of septum splitting of the mother cell is marked as point zero. The initiation of tip growth at previous division sites is denoted by yellow arrows. Tip growth at these sites was also scored for cells that did not initiate such growth until the subsequent cell cycle. (E) Live-cell images of calcofluor-stained tea1-for3 and tea1-for3 fic1Δ cells. Arrowheads indicate monopolar cells. (F) Quantification of (E), with three trials per genotype and n>300 for each trial. Data are presented as mean ± SEM for each category. (G) Quantification of septated cells in (E) and (F), with three trials per genotype and n>200 for each trial. Data are presented as mean ± SEM for each category (Bars = 5 µm).
Mentions: To analyze tea1-for3 cells in real-time, we performed time-lapse DIC imaging. As expected, most tea1-for3 cells underwent NETO before the next cell division (Figure 8A), with nearly 75% of new ends initiating growth within 50 minutes of septum splitting (Figure 8B). Nonetheless, some tea1-for3 outliers took much longer to extend at tips created by cell division (Figure 8B). After grouping the times needed for tip growth to occur at previous division sites relative to the amount of time needed for the mother cell to complete cytokinesis, we found that newly-formed tips that took longer to initiate growth had been formed by more inefficient cytokinesis (Figure 8C–8D). As distal tip growth continued in cells undergoing division (Figure 8D) and appeared unimpeded by additional factors, these findings suggested that faulty cytokinesis imposes constraints at previous division sites that counteract positive polarizing cues. We corroborated this model by expressing the Tea1-For3 fusion in fic1Δ cells. Although tea1-for3 cells were mostly bipolar, tea1-for3 fic1Δ cells showed a high percentage of monopolar growth (Figure 8E–8G). These findings confirmed that efficient completion of cytokinesis is critical for new end growth, even when signaling networks responsible for NETO are prematurely activated.

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