scholarly journals Actin assembly produces sufficient forces for endocytosis in yeast

2019 ◽  
Vol 30 (16) ◽  
pp. 2014-2024 ◽  
Author(s):  
Masoud Nickaeen ◽  
Julien Berro ◽  
Thomas D. Pollard ◽  
Boris M. Slepchenko
Keyword(s):  
Experimental Data ◽  
Plasma Membrane ◽  
Fission Yeast ◽  
Turgor Pressure ◽  
Dendritic Structure ◽  
Yeast Cells ◽  
Cross Linking ◽  
Actin Assembly ◽  
Spatially Resolved ◽  
Single Ring

We formulated a spatially resolved model to estimate forces exerted by a polymerizing actin meshwork on an invagination of the plasma membrane during endocytosis in yeast cells. The model, which approximates the actin meshwork as a visco-active gel exerting forces on a rigid spherocylinder representing the endocytic invagination, is tightly constrained by experimental data. Simulations of the model produce forces that can overcome resistance of turgor pressure in yeast cells. Strong forces emerge due to the high density of polymerized actin in the vicinity of the invagination and because of entanglement of the meshwork due to its dendritic structure and cross-linking. The model predicts forces orthogonal to the invagination that are consistent with formation of a flask shape, which would diminish the net force due to turgor pressure. Simulations of the model with either two rings of nucleation-promoting factors (NPFs) as in fission yeast or a single ring of NPFs as in budding yeast produce enough force to elongate the invagination against the turgor pressure.

scholarly journals Simulation of the mechanics of actin assembly during endocytosis in yeast

2019 ◽  
Author(s):  
Masoud Nickaeen ◽  
Julien Berro ◽  
Thomas D. Pollard ◽  
Boris M. Slepchenko
Keyword(s):  
Experimental Data ◽  
Plasma Membrane ◽  
Fission Yeast ◽  
Turgor Pressure ◽  
Dendritic Structure ◽  
Yeast Cells ◽  
Continuous Approximation ◽  
Actin Assembly ◽  
Spatially Resolved ◽  
Single Ring

We formulated a spatially resolved model to estimate forces exerted by a polymerizing actin meshwork on an invagination of the plasma membrane during endocytosis in yeast cells. The model is a continuous approximation tightly constrained by experimental data. Simulations of the model produce forces that can overcome resistance of turgor pressure in yeast cells. Strong forces emerge due to the high density of polymerized actin in the vicinity of the invagination and because of entanglement of the meshwork due to its dendritic structure and crosslinking. The model predicts forces orthogonal to the invagination that would result in a flask shape that diminishes the net force due to turgor pressure. Simulations of the model with either two rings of nucleation promoting factors as in fission yeast or a single ring of nucleation promoting factors as in budding yeast produce enough force to elongate the invagination against the turgor pressure.

scholarly journals Role of turgor pressure in endocytosis in fission yeast

2014 ◽  
Vol 25 (5) ◽  
pp. 679-687 ◽  
Author(s):  
Roshni Basu ◽  
Emilia Laura Munteanu ◽  
Fred Chang
Keyword(s):  
Cell Wall ◽  
Plasma Membrane ◽  
Fission Yeast ◽  
Turgor Pressure ◽  
Time Lapse ◽  
Actin Assembly ◽  
Latrunculin A ◽  
The Media ◽  
Time Lapse Imaging

Yeast and other walled cells possess high internal turgor pressure that allows them to grow and survive in the environment. This turgor pressure, however, may oppose the invagination of the plasma membrane needed for endocytosis. Here we study the effects of turgor pressure on endocytosis in the fission yeast Schizosaccharomyces pombe by time-lapse imaging of individual endocytic sites. Decreasing effective turgor pressure by addition of sorbitol to the media significantly accelerates early steps in the endocytic process before actin assembly and membrane ingression but does not affect the velocity or depth of ingression of the endocytic pit in wild-type cells. Sorbitol also rescues endocytic ingression defects of certain endocytic mutants and of cells treated with a low dose of the actin inhibitor latrunculin A. Endocytosis proceeds after removal of the cell wall, suggesting that the cell wall does not contribute mechanically to this process. These studies suggest that endocytosis is governed by a mechanical balance between local actin-dependent inward forces and opposing forces from high internal turgor pressure on the plasma membrane.

scholarly journals The number of cytokinesis nodes in mitotic fission yeast scales with cell volume

2021 ◽  
Author(s):  
Wasim A Sayyad ◽  
Thomas D Pollard
Keyword(s):  
Plasma Membrane ◽  
Fission Yeast ◽  
Large Population ◽  
Yeast Cells ◽  
Wild Type ◽  
Contractile Ring ◽  
Node Number ◽  
Nmt1 Promoter ◽  
Wide Range ◽  
Mutant Cells

Cytokinesis nodes are assemblies of stoichiometric ratios of proteins associated with the plasma membrane, which serve as precursors for the contractile ring during cytokinesis by fission yeast. The total number of nodes is uncertain, because of the limitations of the methods used previously. Here we used the ~140 nm resolution of Airyscan confocal microscopy to resolve a large population of dim, unitary cytokinesis nodes in 3D reconstructions of whole fission yeast cells. Wild-type fission yeast cells make about 200 unitary cytokinesis nodes. Most, but not all of these nodes condense into a contractile ring. The number of cytokinesis nodes scales with cell size in four strains tested, although wide rga4Δ mutant cells form somewhat fewer cytokinesis nodes than expected from the overall trend. The surface density of Pom1 kinase on the plasma membrane around the equators of cells is similar with a wide range of node numbers, so Pom1 does not control cytokinesis node number. However, varying protein concentrations with the nmt1 promoter showed that the numbers of nodes increase above a baseline of about 200 with the total cellular concentration of either Pom1 or the kinase Cdr2.

scholarly journals Rapid adaptation of endocytosis, exocytosis and eisosomes after an acute increase in membrane tension in yeast cells

2018 ◽  
Author(s):  
Joël Lemière ◽  
Yuan Ren ◽  
Julien Berro
Keyword(s):  
Molecular Mechanisms ◽  
Turgor Pressure ◽  
Yeast Cells ◽  
Parallel Mechanisms ◽  
Membrane Tension ◽  
Actin Assembly ◽  
Temporary Reduction ◽  
Tight Connection ◽  
Acute Increase ◽  
Tension Regulation

AbstractDuring clathrin-mediated endocytosis in eukaryotes, actin assembly is required to overcome large membrane tension and turgor pressure. However, the molecular mechanisms that enable the actin machinery to adapt to varying membrane tension remain unclear. Here, we used quantitative microscopy to determine that, upon increased membrane tension, the endocytic actin machinery of fission yeast cells rapidly adapts. We also demonstrate that cells rapidly reduce their membrane tension using three parallel mechanisms. In addition to using their cell wall for mechanical protection, yeast cells disassemble eisosomes to buffer moderate changes in membrane tension on a minute time scale. Meanwhile, a temporary reduction of the rate of endocytosis for 2 to 6 minutes, and an increase in the rate of exocytosis for at least 5 minutes allow cells to add large pools of membrane to the plasma membrane. Our study sheds light on the tight connection between membrane tension regulation, endocytosis and exocytosis in yeast, which are likely conserved among eukaryotes.

scholarly journals Actin cables and the exocyst form two independent morphogenesis pathways in the fission yeast

2011 ◽  
Vol 22 (1) ◽  
pp. 44-53 ◽  
Author(s):  
Felipe O. Bendezú ◽  
Sophie G. Martin
Keyword(s):  
Plasma Membrane ◽  
Fission Yeast ◽  
Long Range ◽  
Cell Types ◽  
Yeast Cells ◽  
Long Range Transport ◽  
Dependent Manner ◽  
Cell Morphogenesis ◽  
Range Transport ◽  
Actin Cables

Cell morphogenesis depends on polarized exocytosis. One widely held model posits that long-range transport and exocyst-dependent tethering of exocytic vesicles at the plasma membrane sequentially drive this process. Here, we describe that disruption of either actin-based long-range transport and microtubules or the exocyst did not abolish polarized growth in rod-shaped fission yeast cells. However, disruption of both actin cables and exocyst led to isotropic growth. Exocytic vesicles localized to cell tips in single mutants but were dispersed in double mutants. In contrast, a marker for active Cdc42, a major polarity landmark, localized to discreet cortical sites even in double mutants. Localization and photobleaching studies show that the exocyst subunits Sec6 and Sec8 localize to cell tips largely independently of the actin cytoskeleton, but in a cdc42 and phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2)–dependent manner. Thus in fission yeast long-range cytoskeletal transport and PIP2-dependent exocyst represent parallel morphogenetic modules downstream of Cdc42, raising the possibility of similar mechanisms in other cell types.

scholarly journals Sterol biosensor reveals LAM-family Ltc1-dependent sterol flow to endosomes upon Arp2/3 inhibition

2020 ◽  
Vol 219 (6) ◽  
Author(s):  
Magdalena Marek ◽  
Vincent Vincenzetti ◽  
Sophie G. Martin
Keyword(s):  
Electron Microscopy ◽  
Plasma Membrane ◽  
Schizosaccharomyces Pombe ◽  
Fission Yeast ◽  
Biological Membranes ◽  
Time Lapse ◽  
Vesicular Trafficking ◽  
Actin Assembly ◽  
Contact Sites ◽  
Family Protein

Sterols are crucial components of biological membranes, which are synthetized in the ER and accumulate in the plasma membrane (PM). Here, by applying a genetically encoded sterol biosensor (D4H), we visualize a sterol flow between PM and endosomes in the fission yeast Schizosaccharomyces pombe. Using time-lapse and correlative light-electron microscopy, we found that inhibition of Arp2/3-dependent F-actin assembly promotes the reversible relocalization of D4H from the PM to internal sterol-rich compartments (STRIC) labeled by synaptobrevin Syb1. Retrograde sterol internalization to STRIC is independent of endocytosis or an intact Golgi, but depends on Ltc1, a LAM/StARkin-family protein localized to ER-PM contact sites. The PM in ltc1Δ cells over-accumulates sterols and upon Arp2/3 inhibition forms extended ER-interacting invaginations, indicating that sterol transfer contributes to PM size homeostasis. Anterograde sterol movement from STRIC is independent of canonical vesicular trafficking but requires Arp2/3, suggesting a novel role for this complex. Thus, transfer routes orthogonal to vesicular trafficking govern the flow of sterols in the cell.

scholarly journals Pivot-and-bond model explains microtubule bundle formation

2017 ◽  
Author(s):  
Marcel Prelogović ◽  
Lora Winters ◽  
Ana Milas ◽  
Iva M. Tolić ◽  
Nenad Pavin
Keyword(s):  
Fission Yeast ◽  
Physical Mechanism ◽  
Spindle Pole ◽  
Yeast Cells ◽  
Cross Linking ◽  
Stable Bundle ◽  
Wild Type ◽  
Microtubule Bundle ◽  
Angular Movement ◽  
Bond Model

ABSTRACTDuring mitosis, bundles of microtubules form a spindle, but the physical mechanism of bundle formation is still not known. Here we show that random angular movement of microtubules around the spindle pole and forces exerted by passive cross-linking proteins are sufficient for the formation of stable microtubule bundles. We test these predictions by experiments in wild-type and ase1Δ fission yeast cells. In conclusion, the angular motion drives the alignment of microtubules, which in turn allows the cross-linking proteins to connect the microtubules into a stable bundle.

Rapid adaptation of endocytosis, exocytosis and eisosomes after an acute increase in membrane tension in yeast cells

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Joël Lemière ◽  
Yuan Ren ◽  
Julien Berro
Keyword(s):  
Molecular Mechanisms ◽  
Turgor Pressure ◽  
Yeast Cells ◽  
Parallel Mechanisms ◽  
Membrane Tension ◽  
Actin Assembly ◽  
Temporary Reduction ◽  
Tight Connection ◽  
Acute Increase ◽  
Tension Regulation

During clathrin-mediated endocytosis in eukaryotes, actin assembly is required to overcome large membrane tension and turgor pressure. However, the molecular mechanisms by which the actin machinery adapts to varying membrane tension remain unknown. In addition, how cells reduce their membrane tension when they are challenged by hypotonic shocks remains unclear. We used quantitative microscopy to demonstrate that cells rapidly reduce their membrane tension using three parallel mechanisms. In addition to using their cell wall for mechanical protection, yeast cells disassemble eisosomes to buffer moderate changes in membrane tension on a minute time scale. Meanwhile, a temporary reduction of the rate of endocytosis for 2 to 6 minutes, and an increase in the rate of exocytosis for at least 5 minutes allow cells to add large pools of membrane to the plasma membrane. We built on these results to submit the cells to abrupt increases in membrane tension and determine that the endocytic actin machinery of fission yeast cells rapidly adapts to perform clathrin-mediated endocytosis. Our study sheds light on the tight connection between membrane tension regulation, endocytosis and exocytosis.

scholarly journals Forces that shape fission yeast cells

2017 ◽  
Vol 28 (14) ◽  
pp. 1819-1824 ◽  
Author(s):  
Fred Chang
Keyword(s):  
Fission Yeast ◽  
Cell Biology ◽  
Cell Shape ◽  
Turgor Pressure ◽  
Cell Types ◽  
Yeast Cells ◽  
Animal Cells ◽  
Cellular Mechanics ◽  
Cellular Processes ◽  
Micrometer Scale

One of the major challenges of modern cell biology is to understand how cells are assembled from nanoscale components into micrometer-scale entities with a specific size and shape. Here I describe how our quest to understand the morphogenesis of the fission yeast Schizosaccharomyces pombe drove us to investigate cellular mechanics. These studies build on the view that cell shape arises from the physical properties of an elastic cell wall inflated by internal turgor pressure. Consideration of cellular mechanics provides new insights into not only mechanisms responsible for cell-shape determination and growth, but also cellular processes such as cytokinesis and endocytosis. Studies in yeast can help to illuminate approaches and mechanisms to study the mechanobiology of the cell surface in other cell types, including animal cells.

scholarly journals The Cell Biology of Fission Yeast Septation

2016 ◽  
Vol 80 (3) ◽  
pp. 779-791 ◽  
Author(s):  
Juan C. García Cortés ◽  
Mariona Ramos ◽  
Masako Osumi ◽  
Pilar Pérez ◽  
Juan Carlos Ribas
Keyword(s):  
Cell Wall ◽  
Plasma Membrane ◽  
Fission Yeast ◽  
Cell Biology ◽  
Turgor Pressure ◽  
Ring Closure ◽  
Wall Structure ◽  
Local Defect ◽  
Cleavage Furrow ◽  
Fungal Cell

SUMMARYIn animal cells, cytokinesis requires the formation of a cleavage furrow that divides the cell into two daughter cells. Furrow formation is achieved by constriction of an actomyosin ring that invaginates the plasma membrane. However, fungal cells contain a rigid extracellular cell wall surrounding the plasma membrane; thus, fungal cytokinesis also requires the formation of a special septum wall structure between the dividing cells. The septum biosynthesis must be strictly coordinated with the deposition of new plasma membrane material and actomyosin ring closure and must occur in such a way that no breach in the cell wall occurs at any time. Because of the high turgor pressure in the fungal cell, even a minor local defect might lead to cell lysis and death. Here we review our knowledge of the septum structure in the fission yeastSchizosaccharomyces pombeand of the recent advances in our understanding of the relationship between septum biosynthesis and actomyosin ring constriction and how the two collaborate to build a cross-walled septum able to support the high turgor pressure of the cell. In addition, we discuss the importance of the septum biosynthesis for the steady ingression of the cleavage furrow.

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