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A formin-nucleated actin aster concentrates cell wall hydrolases for cell fusion in fission yeast.

Dudin O, Bendezú FO, Groux R, Laroche T, Seitz A, Martin SG - J. Cell Biol. (2015)

Bottom Line: In fission yeast cells, the formin Fus1, which nucleates linear actin filaments, is essential for this process.Structured illumination microscopy and live-cell imaging of Fus1, actin, and type V myosins revealed an aster of actin filaments whose barbed ends are focalized near the plasma membrane.Focalization requires Fus1 and type V myosins and happens asynchronously always in the M cell first.

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Affiliation: Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.

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Model for the fusion focus multi-step formation, architecture, and function. (A) Schematic representation of the cell–cell fusion process in fission yeast. Type V myosins first assume a crescent localization, decorating the shmoo tip. Focalization is observed in the h− cell fist and then in the h+ cell. The distance between the two dots then reduces over time, indicating cell wall thinning, until the two structures merge into one and fusion occurs. (B) Illustration of the architecture of the fusion focus. The formin Fus1 nucleates short actin filaments, which are focalized with type V myosins near the plasma membrane. Focalization requires both Fus1 and type V myosins. Longer For3-nucleated cables are also polarized toward the shmoo tip. (C) Model of the function of the fusion focus. For comparison, the wild-type situation is compared with that in fus1Δ cells. In the wild type, glucanases are concentrated at the fusion focus, therefore segregating them from the location of cell wall synthases, which decorate the entire shmoo tip. This geometrical organization permits cell wall thinning and fusion. In absence of Fus1, the localizations of glucanases and cell wall synthases overlap over the shmoo tip, promoting cell growth.
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fig6: Model for the fusion focus multi-step formation, architecture, and function. (A) Schematic representation of the cell–cell fusion process in fission yeast. Type V myosins first assume a crescent localization, decorating the shmoo tip. Focalization is observed in the h− cell fist and then in the h+ cell. The distance between the two dots then reduces over time, indicating cell wall thinning, until the two structures merge into one and fusion occurs. (B) Illustration of the architecture of the fusion focus. The formin Fus1 nucleates short actin filaments, which are focalized with type V myosins near the plasma membrane. Focalization requires both Fus1 and type V myosins. Longer For3-nucleated cables are also polarized toward the shmoo tip. (C) Model of the function of the fusion focus. For comparison, the wild-type situation is compared with that in fus1Δ cells. In the wild type, glucanases are concentrated at the fusion focus, therefore segregating them from the location of cell wall synthases, which decorate the entire shmoo tip. This geometrical organization permits cell wall thinning and fusion. In absence of Fus1, the localizations of glucanases and cell wall synthases overlap over the shmoo tip, promoting cell growth.

Mentions: We studied the formation of the fusion focus by time-lapse microscopy of the entire mating process over several hours, using Myo52 as a marker. In early stages, Myo52 was detected as a pool of dots collectively forming a crescent at the shmoo tips of both partner cells. This crescent then compacted into a single focus in each cell, such that each mating pair showed two dots in close proximity at their contact site (Fig. 3 A; see model in Fig. 6 A). Over time, the distance between the two dots reduced, suggesting progressive degradation of the cell wall between the partner cells (Fig. 3, A and B). The distance between Myo52-tdTomato dots was measured relative to fusion time as defined by entry in the h− cell of GFP driven by an h+ cell-specific promoter (pmap3:GFP). After fusion, the Myo52 focus disassembled within 13.9 ± 4.5 min (n = 20). To measure the distance once the two dots were within the light diffraction limit, we used Myo52 tagged with distinct fluorophores in the two mating partners until focus disassembly. The time between apparent overlap of the two dots to disassembly was 20.7 ± 3.5 min (n = 20). By aligning the two curves on the time of focus disassembly, we conclude that the two Myo52 dots converge into an apparent single dot at the contact between the two cells ∼7 min before fusion pore opening (Fig. 3 B) and are disassembled ∼14 min after fusion.


A formin-nucleated actin aster concentrates cell wall hydrolases for cell fusion in fission yeast.

Dudin O, Bendezú FO, Groux R, Laroche T, Seitz A, Martin SG - J. Cell Biol. (2015)

Model for the fusion focus multi-step formation, architecture, and function. (A) Schematic representation of the cell–cell fusion process in fission yeast. Type V myosins first assume a crescent localization, decorating the shmoo tip. Focalization is observed in the h− cell fist and then in the h+ cell. The distance between the two dots then reduces over time, indicating cell wall thinning, until the two structures merge into one and fusion occurs. (B) Illustration of the architecture of the fusion focus. The formin Fus1 nucleates short actin filaments, which are focalized with type V myosins near the plasma membrane. Focalization requires both Fus1 and type V myosins. Longer For3-nucleated cables are also polarized toward the shmoo tip. (C) Model of the function of the fusion focus. For comparison, the wild-type situation is compared with that in fus1Δ cells. In the wild type, glucanases are concentrated at the fusion focus, therefore segregating them from the location of cell wall synthases, which decorate the entire shmoo tip. This geometrical organization permits cell wall thinning and fusion. In absence of Fus1, the localizations of glucanases and cell wall synthases overlap over the shmoo tip, promoting cell growth.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC4384723&req=5

fig6: Model for the fusion focus multi-step formation, architecture, and function. (A) Schematic representation of the cell–cell fusion process in fission yeast. Type V myosins first assume a crescent localization, decorating the shmoo tip. Focalization is observed in the h− cell fist and then in the h+ cell. The distance between the two dots then reduces over time, indicating cell wall thinning, until the two structures merge into one and fusion occurs. (B) Illustration of the architecture of the fusion focus. The formin Fus1 nucleates short actin filaments, which are focalized with type V myosins near the plasma membrane. Focalization requires both Fus1 and type V myosins. Longer For3-nucleated cables are also polarized toward the shmoo tip. (C) Model of the function of the fusion focus. For comparison, the wild-type situation is compared with that in fus1Δ cells. In the wild type, glucanases are concentrated at the fusion focus, therefore segregating them from the location of cell wall synthases, which decorate the entire shmoo tip. This geometrical organization permits cell wall thinning and fusion. In absence of Fus1, the localizations of glucanases and cell wall synthases overlap over the shmoo tip, promoting cell growth.
Mentions: We studied the formation of the fusion focus by time-lapse microscopy of the entire mating process over several hours, using Myo52 as a marker. In early stages, Myo52 was detected as a pool of dots collectively forming a crescent at the shmoo tips of both partner cells. This crescent then compacted into a single focus in each cell, such that each mating pair showed two dots in close proximity at their contact site (Fig. 3 A; see model in Fig. 6 A). Over time, the distance between the two dots reduced, suggesting progressive degradation of the cell wall between the partner cells (Fig. 3, A and B). The distance between Myo52-tdTomato dots was measured relative to fusion time as defined by entry in the h− cell of GFP driven by an h+ cell-specific promoter (pmap3:GFP). After fusion, the Myo52 focus disassembled within 13.9 ± 4.5 min (n = 20). To measure the distance once the two dots were within the light diffraction limit, we used Myo52 tagged with distinct fluorophores in the two mating partners until focus disassembly. The time between apparent overlap of the two dots to disassembly was 20.7 ± 3.5 min (n = 20). By aligning the two curves on the time of focus disassembly, we conclude that the two Myo52 dots converge into an apparent single dot at the contact between the two cells ∼7 min before fusion pore opening (Fig. 3 B) and are disassembled ∼14 min after fusion.

Bottom Line: In fission yeast cells, the formin Fus1, which nucleates linear actin filaments, is essential for this process.Structured illumination microscopy and live-cell imaging of Fus1, actin, and type V myosins revealed an aster of actin filaments whose barbed ends are focalized near the plasma membrane.Focalization requires Fus1 and type V myosins and happens asynchronously always in the M cell first.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.

Show MeSH
Related in: MedlinePlus