Drosophila nonmuscle myosin II is required for rapid cytoplasmic transport during oogenesis and for axial nuclear migration in early embryos

The X-linked Drosophila gene spaghetti squash (sqh) encodes the regulatory light chain of nonmuscle myosin II. To assess the requirement for myosin II in oogenesis and early embryogenesis, we induced homozygous germline clones of the hypomorphic mutation sqh1 in otherwise heterozygous mothers. Developing oocytes in such sqh1 germline clones often failed to attain full size due to a defect in ‘dumping’, the rapid phase of cytoplasmic transport from nurse cells. In contrast to other dumpless mutants described to date, sqh1 egg chambers showed no evidence of ring canal obstruction, and no obvious alteration in the actin network. However the distribution of myosin II was abnormal. We conclude that the molecular motor responsible for cytoplasmic dumping is supplied largely, if not exclusively, by nurse cell myosin II and we suggest that regulation of myosin activity is one means by which cytoplasmic transport may be controlled during oocyte development. The eggs resulting from sqh1 clones, though smaller than normal, began development but exhibited an early defect in axial migration of cleavage nuclei towards the posterior pole of the embryo, in a similar manner to that seen in early cleavage eggs in which the actin cytoskeleton is disrupted. Thus both nurse cell dumping and axial migration require a maternally supplied myosin II.

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Drosophila nonmuscle myosin II is required for cytoplasmic transport during oogenesis

Biology of the Cell ◽

10.1016/s0248-4900(98)80274-8 ◽

1998 ◽

Vol 90 (1) ◽

pp. 115-115

Author(s):

Pascale Jordan ◽

Anne Royou ◽

Annie Glatigny ◽

Roger Karess

Keyword(s):

Myosin Ii ◽

Nonmuscle Myosin ◽

Cytoplasmic Transport ◽

Nonmuscle Myosin Ii

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Expansion and concatenation of nonmuscle myosin IIA filaments drive cellular contractile system formation during interphase and mitosis

Molecular Biology of the Cell ◽

10.1091/mbc.e15-10-0725 ◽

2016 ◽

Vol 27 (9) ◽

pp. 1465-1478 ◽

Cited By ~ 70

Author(s):

Aidan M. Fenix ◽

Nilay Taneja ◽

Carmen A. Buttler ◽

John Lewis ◽

Schuyler B. Van Engelenburg ◽

...

Keyword(s):

Actin Filaments ◽

Molecular Motor ◽

Myosin Ii ◽

Cell Movement ◽

Nonmuscle Myosin ◽

Contractile Ring ◽

Contractile System ◽

Nonmuscle Myosin Ii ◽

Dividing Cells ◽

Contractile Forces

Cell movement and cytokinesis are facilitated by contractile forces generated by the molecular motor, nonmuscle myosin II (NMII). NMII molecules form a filament (NMII-F) through interactions of their C-terminal rod domains, positioning groups of N-terminal motor domains on opposite sides. The NMII motors then bind and pull actin filaments toward the NMII-F, thus driving contraction. Inside of crawling cells, NMIIA-Fs form large macromolecular ensembles (i.e., NMIIA-F stacks), but how this occurs is unknown. Here we show NMIIA-F stacks are formed through two non–mutually exclusive mechanisms: expansion and concatenation. During expansion, NMIIA molecules within the NMIIA-F spread out concurrent with addition of new NMIIA molecules. Concatenation occurs when multiple NMIIA-Fs/NMIIA-F stacks move together and align. We found that NMIIA-F stack formation was regulated by both motor activity and the availability of surrounding actin filaments. Furthermore, our data showed expansion and concatenation also formed the contractile ring in dividing cells. Thus interphase and mitotic cells share similar mechanisms for creating large contractile units, and these are likely to underlie how other myosin II–based contractile systems are assembled.

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Electrostatic and bending energies predict staggering and splaying in nonmuscle myosin II minifilaments

10.1101/2020.03.20.000265 ◽

2020 ◽

Cited By ~ 1

Author(s):

Tom Kaufmann ◽

Ulrich S. Schwarz

Keyword(s):

Elasticity Theory ◽

Stochastic Dynamics ◽

Molecular Motor ◽

Myosin Ii ◽

Super Resolution ◽

Live Cells ◽

Sequence Information ◽

Nonmuscle Myosin ◽

Resolution Limit ◽

Nonmuscle Myosin Ii

AbstractRecent experiments with super-resolution live cell microscopy revealed that nonmuscle myosin II minifilaments are much more dynamic than formerly appreciated, often showing plastic processes such as splitting, concatenation and stacking. Here we combine sequence information, electrostatics and elasticity theory to demonstrate that the parallel staggers at 14.3, 43.2 and 72 nm have a strong tendency to splay their heads away from the minifilament, thus potentially initiating the diverse processes seen in live cells. In contrast, the straight antiparallel stagger with an overlap of 43 nm is very stable and likely initiates minifilament nucleation. Using stochastic dynamics in a newly defined energy landscape, we predict that the optimal parallel staggers between the myosin rods are obtained by a trial-and-error process in which two rods attach and re-attach at different staggers by rolling and zipping motion. The experimentally observed staggers emerge as the configurations with the largest contact times. We find that contact times increase from isoforms C to B to A, that A-B-heterodimers are surprisingly stable and that myosin 18A should incorporate into mixed filaments with a small stagger. Our findings suggest that nonmuscle myosin II minifilaments in the cell are first formed by isoform A and then convert to mixed A-B-filaments, as observed experimentally.Author summaryNonmuscle myosin II (NM2) is a non-processive molecular motor that assembles into minifilaments with a typical size of 300 nm to generate force and motion in the actin cytoskeleton. This process is essential for many cellular processes such as adhesion, migration, division and mechanosensing. Due to their small size below the resolution limit, minifilaments are a challenge for imaging with traditional light microscopy. With the advent of super-resolution microscopy, however, it has become apparent that the formation of NM2-minifilaments is much more dynamic than formerly appreciated. Modeling the electrostatic interaction between the rigid rods of the myosin monomers has confirmed the main staggers observed in experiments, but cannot explain these high dynamics. Here we complement electrostatics by elasticity theory and stochastic dynamics to show that the parallel staggers are likely to splay away from the main axis of the minifilament and that monomers attach and deattach with rolling and zipping motions. Based on the sequences of the different NM2-isoforms, we predict that isoform A forms the most stable homofilaments and that A-B-heterofilaments are also very stable.

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Drosophila nonmuscle myosin II has multiple essential roles in imaginal disc and egg chamber morphogenesis

Development ◽

10.1242/dev.122.5.1499 ◽

1996 ◽

Vol 122 (5) ◽

pp. 1499-1511 ◽

Cited By ~ 11

Author(s):

K.A. Edwards ◽

D.P. Kiehart

Keyword(s):

Myosin Ii ◽

Cell Sheet ◽

Follicle Cell ◽

Nonmuscle Myosin ◽

Filamentous Actin ◽

Nonmuscle Myosin Ii ◽

Egg Chambers ◽

Mutant Phenotypes ◽

Shape Changes ◽

Drosophila Embryos

Morphogenesis is characterized by orchestrated changes in the shape and position of individual cells. Many of these movements are thought to be powered by motor proteins. However, in metazoans, it is often difficult to match specific motors with the movements they drive. The nonmuscle myosin II heavy chain (MHC encoded by zipper is required for cell sheet movements in Drosophila embryos. To determine if myosin II is required for other processes, we examined the phenotypes of strong and weak larval lethal mutations in spaghetti squash (sqh), which encodes the nonmuscle myosin II regulatory light chain (RLC). sqh mutants can be rescued to adulthood by daily induction of a sqh cDNA transgene driven by the hsp70 promoter. By transiently ceasing induction of the cDNA, we depleted RLC at specific times during development. When RLC is transiently depleted in larvae, the resulting adult phenotypes demonstrate that RLC is required in a stage-specific fashion for proper development of eye and leg imaginal discs. When RLC is depleted in adult females, oogenesis is reversibly disrupted. Without RLC induction, developing egg chambers display a succession of phenotypes that demonstrate roles for myosin II in morphogenesis of the interfollicular stalks, three morphologically and mechanistically distinct types of follicle cell migration, and completion of nurse cell cytoplasm transport (dumping). Finally, we show that in sqh mutant tissues, MHC is abnormally localized in punctate structures that do not contain appreciable amounts of filamentous actin or the myosin tail-binding protein p127. This suggests that sqh mutant phenotypes are chiefly caused by sequestration of myosin into inactive aggregates. These results show that myosin II is responsible for a surprisingly diverse array of cell shape changes throughout development.

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