A formin-nucleated actin aster concentrates cell wall hydrolases for cell fusion in fission yeast.
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.
Affiliation: Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.Show MeSH
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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.
Affiliation: Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.