scholarly journals Pulsatile actomyosin contractions underlie Par polarity during the neuroblast polarity cycle

2021 ◽  
Author(s):  
Chet Huan Oon ◽  
Kenneth E. Prehoda
Keyword(s):  
Protein Dynamics ◽  
Myosin Ii ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Par Proteins ◽  
Apical Pole ◽  
Tightly Coupled ◽  
Early Mitosis

AbstractThe Par complex is polarized to the apical cortex of asymmetrically dividing Drosophila neuroblasts. Previously we showed that Par proteins are polarized by apically directed cortical movements that require F-actin (Oon and Prehoda, 2019). Here we report the discovery of cortical actin pulses that begin before the Par complex is recruited to the cell cortex and ultimately become tightly coupled to Par protein dynamics. Pulses are initially unoriented in interphase but are rapidly directed towards the apical pole in early mitosis, shortly before the Par protein aPKC accumulates on the cortex. The movements of cortical aPKC that lead to its polarization are precisely correlated with cortical actin pulses and F-actin disruption coincides with immediate loss of movement followed by depolarization. We find that myosin II is a component of the cortical pulses, suggesting that actomyosin pulsatile contractions initiate and maintain apical Par polarity during the neuroblast polarity cycle.

scholarly journals Generation of stress fibers through myosin-driven re-organization of the actin cortex

2020 ◽  
Author(s):  
JI Lehtimäki ◽  
EK Rajakylä ◽  
S Tojkander ◽  
P Lappalainen
Keyword(s):  
De Novo ◽  
Myosin Ii ◽  
Focal Adhesions ◽  
Stress Fibers ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Cellular Processes ◽  
Actin Cortex ◽  
Muscle Myosin ◽  
Subsequent Stabilization

SummaryContractile actomyosin bundles, stress fibers, govern key cellular processes including migration, adhesion, and mechanosensing. Stress fibers are thus critical for developmental morphogenesis. The most prominent actomyosin bundles, ventral stress fibers, are generated through coalescence of pre-existing stress fiber precursors. However, whether stress fibers can assemble through other mechanisms has remained elusive. We report that stress fibers can also form without requirement of pre-existing actomyosin bundles. These structures, which we named cortical stress fibers, are embedded in the cell cortex and assemble preferentially underneath the nucleus. In this process, non-muscle myosin II pulses orchestrate the reorganization of cortical actin meshwork into regular bundles, which promote reinforcement of nascent focal adhesions, and subsequent stabilization of the cortical stress fibers. These results identify a new mechanism by which stress fibers can be generated de novo from the actin cortex, and establish role for stochastic myosin pulses in the assembly of functional actomyosin bundles.

scholarly journals Generation of stress fibers through myosin-driven reorganization of the actin cortex

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Jaakko I Lehtimäki ◽  
Eeva Kaisa Rajakylä ◽  
Sari Tojkander ◽  
Pekka Lappalainen
Keyword(s):  
De Novo ◽  
Myosin Ii ◽  
Focal Adhesions ◽  
Stress Fibers ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Cellular Processes ◽  
Actin Cortex ◽  
Muscle Myosin ◽  
Subsequent Stabilization

Contractile actomyosin bundles, stress fibers, govern key cellular processes including migration, adhesion, and mechanosensing. Stress fibers are thus critical for developmental morphogenesis. The most prominent actomyosin bundles, ventral stress fibers, are generated through coalescence of pre-existing stress fiber precursors. However, whether stress fibers can assemble through other mechanisms has remained elusive. We report that stress fibers can also form without requirement of pre-existing actomyosin bundles. These structures, which we named cortical stress fibers, are embedded in the cell cortex and assemble preferentially underneath the nucleus. In this process, non-muscle myosin II pulses orchestrate the reorganization of cortical actin meshwork into regular bundles, which promote reinforcement of nascent focal adhesions, and subsequent stabilization of the cortical stress fibers. These results identify a new mechanism by which stress fibers can be generated de novo from the actin cortex and establish role for stochastic myosin pulses in the assembly of functional actomyosin bundles.

scholarly journals Isotropic actomyosin dynamics promote organization of the apical cell cortex in epithelial cells

2014 ◽  
Vol 207 (1) ◽  
pp. 107-121 ◽  
Author(s):  
Christoph Klingner ◽  
Anoop V. Cherian ◽  
Johannes Fels ◽  
Philipp M. Diesinger ◽  
Roland Aufschnaiter ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Apical Membrane ◽  
Myosin Ii ◽  
Apical Cell ◽  
Cell Cortex ◽  
Apical Surface ◽  
Cortical Actin ◽  
Cellular Mechanics ◽  
Apical Cell Membrane ◽  
Spatially Correlated

Although cortical actin plays an important role in cellular mechanics and morphogenesis, there is surprisingly little information on cortex organization at the apical surface of cells. In this paper, we characterize organization and dynamics of microvilli (MV) and a previously unappreciated actomyosin network at the apical surface of Madin–Darby canine kidney cells. In contrast to short and static MV in confluent cells, the apical surfaces of nonconfluent epithelial cells (ECs) form highly dynamic protrusions, which are often oriented along the plane of the membrane. These dynamic MV exhibit complex and spatially correlated reorganization, which is dependent on myosin II activity. Surprisingly, myosin II is organized into an extensive network of filaments spanning the entire apical membrane in nonconfluent ECs. Dynamic MV, myosin filaments, and their associated actin filaments form an interconnected, prestressed network. Interestingly, this network regulates lateral mobility of apical membrane probes such as integrins or epidermal growth factor receptors, suggesting that coordinated actomyosin dynamics contributes to apical cell membrane organization.

scholarly journals Pan1p, End3p, and Sla1p, Three Yeast Proteins Required for Normal Cortical Actin Cytoskeleton Organization, Associate with Each Other and Play Essential Roles in Cell Wall Morphogenesis

2000 ◽  
Vol 20 (1) ◽  
pp. 12-25 ◽  
Author(s):  
Hsin-Yao Tang ◽  
Jing Xu ◽  
Mingjie Cai
Keyword(s):  
Cell Wall ◽  
Actin Cytoskeleton ◽  
Normal Cell ◽  
Cell Cortex ◽  
Repeat Region ◽  
Cortical Actin ◽  
Cytoskeleton Organization ◽  
Eh Domain ◽  
Actin Cytoskeleton Organization ◽  
Cell Wall Morphogenesis

ABSTRACT The EH domain proteins Pan1p and End3p of budding yeast have been known to form a complex in vivo and play important roles in organization of the actin cytoskeleton and endocytosis. In this report, we describe new findings concerning the function of the Pan1p-End3p complex. First, we found that the Pan1p-End3p complex associates with Sla1p, another protein known to be required for the assembly of cortical actin structures. Sla1p interacts with the first long repeat region of Pan1p and the N-terminal EH domain of End3p, thus leaving the Pan1p-End3p interaction, which requires the second long repeat of Pan1p and the C-terminal repeat region of End3p, undisturbed. Second, Pan1p, End3p, and Sla1p are also required for normal cell wall morphogenesis. Each of the Pan1-4, sla1Δ, andend3Δ mutants displays the abnormal cell wall morphology previously reported for the act1-1 mutant. These cell wall defects are also exhibited by wild-type cells overproducing the C-terminal region of Sla1p that is responsible for interactions with Pan1p and End3p. These results indicate that the functions of Pan1p, End3p, and Sla1p in cell wall morphogenesis may depend on the formation of a heterotrimeric complex. Interestingly, the cell wall abnormalities exhibited by these cells are independent of the actin cytoskeleton organization on the cell cortex, as they manifest despite the presence of apparently normal cortical actin cytoskeleton. Examination of several act1 mutants also supports this conclusion. These observations suggest that the Pan1p-End3p-Sla1p complex is required not only for normal actin cytoskeleton organization but also for normal cell wall morphogenesis in yeast.

scholarly journals Mechanism of the formation of contractile ring in dividing cultured animal cells. II. Cortical movement of microinjected actin filaments.

1990 ◽  
Vol 111 (5) ◽  
pp. 1905-1911 ◽  
Author(s):  
L G Cao ◽  
Y L Wang
Keyword(s):  
Actin Filaments ◽  
Average Rate ◽  
Rat Kidney ◽  
Equatorial Region ◽  
Cell Cortex ◽  
Polar Regions ◽  
Cortical Actin ◽  
Animal Cells ◽  
Contractile Ring ◽  
Directional Movement

The contractile ring in dividing animal cells is formed primarily through the reorganization of existing actin filaments (Cao, L.-G., and Y.-L. Wang. 1990. J. Cell Biol. 110:1089-1096), but it is not clear whether the process involves a random recruitment of diffusible actin filaments from the cytoplasm, or a directional movement of cortically associated filaments toward the equator. We have studied this question by observing the distribution of actin filaments that have been labeled with fluorescent phalloidin and microinjected into dividing normal rat kidney (NRK) cells. The labeled filaments are present primarily in the cytoplasm during prometaphase and early metaphase, but become associated extensively with the cell cortex 10-15 min before the onset of anaphase. This process is manifested both as an increase in cortical fluorescence intensity and as movements of discrete aggregates of actin filaments toward the cortex. The concentration of actin fluorescence in the equatorial region, accompanied by a decrease of fluorescence in polar regions, is detected 2-3 min after the onset of anaphase. By directly tracing the distribution of aggregates of labeled actin filaments, we are able to detect, during anaphase and telophase, movements of cortical actin filaments toward the equator at an average rate of 1.0 micron/min. Our results, combined with previous observations, suggest that the organization of actin filaments during cytokinesis probably involves an association of cytoplasmic filaments with the cortex, a movement of cortical filaments toward the cleavage furrow, and a dissociation of filaments from the equatorial cortex.

scholarly journals Dia- and Rok-dependent enrichment of capping proteins in a cortical region

2021 ◽  
Author(s):  
Anja Schmidt ◽  
Long Li ◽  
Zhiyi Lv ◽  
Shuling Yan ◽  
Jörg Großhans
Keyword(s):  
Myosin Ii ◽  
Rho Kinase ◽  
Cortical Region ◽  
Protein Enrichment ◽  
Cortical Actin ◽  
Capping Protein ◽  
Capping Proteins ◽  
Muscle Myosin ◽  
Drosophila Embryos

Rho signaling with its major targets the formin Dia, Rho kinase (Rok) and non-muscle myosin II control turnover, amount and contractility of actomyosin. Much less investigated has been a potential function for the distribution of F-actin plus and minus ends. In syncytial Drosophila embryos Rho1 signaling is high between actin caps, i. e. the cortical intercap region. Capping protein binds to free plus ends of F-actin to prevent elongation of the filament. Capping protein has served as a marker to visualize the distribution of F-actin plus ends in cells and in vitro. Here, we probed the distribution of plus ends with capping protein in syncytial Drosophila embryos. We found that Capping proteins are specifically enriched in the intercap region similar to Dia and MyoII but distinct from overall F-actin. The intercap enrichment of Capping protein was impaired in dia mutants and embryos, in which Rok and MyoII activation was inhibited. Our observations reveal that Dia and Rok/MyoII control Capping protein enrichment and support a model that Dia and Rok/MyoII control the organization of cortical actin cytoskeleton downstream of Rho1 signaling.

scholarly journals Polar relaxation by dynein-mediated removal of cortical myosin II

2020 ◽  
Vol 219 (8) ◽  
Author(s):  
Bernardo Chapa-y-Lazo ◽  
Motonari Hamanaka ◽  
Alexander Wray ◽  
Mohan K. Balasubramanian ◽  
Masanori Mishima
Keyword(s):  
Recent Work ◽  
Molecular Mechanism ◽  
Molecular Mechanisms ◽  
Myosin Ii ◽  
Cell Cortex ◽  
Cleavage Furrow ◽  
Contractile Ring ◽  
C Elegans ◽  
Polar Cell

Nearly six decades ago, Lewis Wolpert proposed the relaxation of the polar cell cortex by the radial arrays of astral microtubules as a mechanism for cleavage furrow induction. While this mechanism has remained controversial, recent work has provided evidence for polar relaxation by astral microtubules, although its molecular mechanisms remain elusive. Here, using C. elegans embryos, we show that polar relaxation is achieved through dynein-mediated removal of myosin II from the polar cortexes. Mutants that position centrosomes closer to the polar cortex accelerated furrow induction, whereas suppression of dynein activity delayed furrowing. We show that dynein-mediated removal of myosin II from the polar cortexes triggers a bidirectional cortical flow toward the cell equator, which induces the assembly of the actomyosin contractile ring. These results provide a molecular mechanism for the aster-dependent polar relaxation, which works in parallel with equatorial stimulation to promote robust cytokinesis.

Sla1p couples the yeast endocytic machinery to proteins regulating actin dynamics

2002 ◽  
Vol 115 (8) ◽  
pp. 1703-1715 ◽  
Author(s):  
Derek T. Warren ◽  
Paul D. Andrews ◽  
Campbell W. Gourlay ◽  
Kathryn R. Ayscough
Keyword(s):  
Immunofluorescence Microscopy ◽  
Fluid Phase ◽  
Actin Dynamics ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Binding Studies ◽  
Endocytic Machinery ◽  
Single Complex ◽  
Actin Patch ◽  
First Time

Sla1p is a protein required for cortical actin patch structure and organisation in budding yeast. Here we use a combination of immunofluorescence microscopy and biochemical approaches to demonstrate interactions of Sla1p both with proteins regulating actin dynamics and with proteins required for endocytosis. Using Sla1p-binding studies we reveal association of Sla1p with two proteins known to be important for activation of the Arp2/3 complex in yeast, Abp1p and the yeast WASP homologue Las17p/Bee1p. A recent report of Sla1p association with Pan1p puts Sla1p in the currently unique position of being the only yeast protein known to interact with all three known Arp2/3-activating proteins in yeast. Localisation of Sla1p at the cell cortex is, however, dependent on the EH-domain-containing protein End3p, which is part of the yeast endocytic machinery. Using spectral variants of GFP on Sla1p(YFP) and on Abp1p (CFP) we show for the first time that these proteins can exist in discrete complexes at the cell cortex. However, the detection of a significant FRET signal means that these proteins also come close together in a single complex, and it is in this larger complex that we propose that Sla1p binding to Abp1p and Las17p/Bee1p is able to link actin dynamics to the endocytic machinery. Finally, we demonstrate marked defects in both fluid-phase and receptor-mediated endocytosis in cells that do not express SLA1, indicating that Sla1p is central to the requirement in yeast to couple endocytosis with the actin cytoskeleton.

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