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

Abstract

The formin Fus1 nucleates a novel actin structure in fission yeast, named the actin fusion focus, which consists of an aster of actin filaments whose barbed ends are focalized at a membrane proximal site and serves to focalize cell wall hydrolase delivery for cell fusion.

Spatial focalization of pheromone/MAPK signaling triggers commitment to cell–cell fusion

“…Fission yeast cells efficiently form pairs and fuse when placed in a monolayer on solid medium (Dudin et al 2015;Vjestica et al 2016). Similarly, homothallic yeast cells loaded in a flow chamber successfully formed zygotes in the absence of fluid flow but failed to do so in the presence of flow, which likely perturbed the formation of pheromone gradients (data not shown).…”

“…1E; Dudin et al 2015). Fourth, the second type V myosin Myo51, which accumulates at the fusion focus late in the process (Doyle et al 2009;Dudin et al 2015), was detected in both cells only in committed pairs (Supplemental Fig. S1).…”

“…The Myo52 spot colocalized with the formin Fus1 as well as with Exg3 and Eng2, two glucanases that localize at the fusion focus and are needed to degrade the cell wall during fusion ( Fig. 2F; Dudin et al 2015), suggesting that these led to local cell wall digestion. In agreement with this, osmotic stabilization by addition of 1.2 M sorbitol in the medium efficiently suppressed cell lysis (Fig.…”

“…Similarly, homothallic yeast cells loaded in a flow chamber successfully formed zygotes in the absence of fluid flow but failed to do so in the presence of flow, which likely perturbed the formation of pheromone gradients (data not shown). To test whether the flow directly perturbed fusion in addition to earlier events during mating, we let cell pairs engage in the fusion process in the absence of flow, forming fusion foci characterized by the focal localization of type V myosin Myo52 (Dudin et al 2015), before transiently flowing fresh medium for 10 min (Fig. 1A).…”

“…In fission yeast cells, this is achieved through assembly of the actin fusion focus, a Fus1-dependent aster of linear actin cables that focalizes the myosin V-dependent delivery of cell wall glucanases to the incipient fusion site (Dudin et al 2015). Time-lapse imaging of the fusion focus revealed that this structure forms only in paired cells in contact, suggesting the existence of a signal at close range to trigger fusion focus assembly.…”