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 tested the function of type V myosins during cell fusion. Myosin V deletion strains (myo51Δ and myo52Δ and the double myo51Δmyo52Δ mutant, noted myoVΔ throughout) fused inefficiently with wild-type cells and were fusion defective when crossed to fus1Δ (Fig. 4 A). We note that myoVΔ cells fused more efficiently with h+ than h− wild-type partners (not depicted), as also observed for fus1Δ × wild type (Fig. 4, compare A and H), though the significance of this observation is currently unknown. Homothallic myoVΔ cells were also fusion defective. However, even myoVΔ double mutant displayed efficient mating pair formation (similar to their ability to polarize during mitotic growth; Motegi et al., 2001; Win et al., 2001; Bendezú and Martin, 2011), suggesting the observed fusion defect is not caused by prior cell polarization defects. The stronger phenotype of the myoVΔ double mutant, compared with each single mutant, indicates that Myo51 and Myo52 contribute at least partially overlapping function to cell fusion. Fus1 displayed a broader localization in myosin V mutants, especially in the double mutant in which it localized over the entire surface at the contact zone (Fig. 4, B and C). Similarly, actin accumulation at the fusion site spread along the contact zone in the double myoVΔ mutant (Fig. 4 D). Thus, type V myosins are required for focalization of the formin Fus1 and of actin filaments in the focus. As we have shown in Fig. 2 (D and E) that Fus1 is required for myosin V focalization, we conclude that actin fusion focus formation relies on positive reinforcement between formin and type V myosins.
Affiliation: Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.