scholarly journals Chromosome segregation is driven by joint microtubule sliding action of kinesins KIF4A and EG5

2019 ◽  
Author(s):  
Kruno Vukušić ◽  
Renata Buđa ◽  
Ivana Ponjavić ◽  
Patrik Risteski ◽  
Iva M. Tolić
Keyword(s):  
Cell Division ◽  
Molecular Mechanism ◽  
Chromosome Segregation ◽  
Super Resolution ◽  
Human Cells ◽  
Microtubule Stability ◽  
Sliding Mechanism ◽  
Spindle Elongation ◽  
Super Resolution Microscopy

Successful cell division requires proper chromosome segregation during anaphase. Forces required for chromosome segregation in human cells are linked to sliding of antiparallel microtubules and sliding capacity has been demonstrated in vitro for multiple motor proteins, but the molecular mechanism of sliding in the spindle of human cells remains unknown. Using combined depletion and inactivation assays to explore redundancy between multiple targets together with CRISPR technology, we found that PRC1-dependent motor KIF4A/kinesin-4, together with EG5/kinesin-5 motor is essential for spindle elongation in human cells. Photoactivation of tubulin and super-resolution microscopy show that perturbation of both proteins impairs sliding, while decreased midzone microtubule stability cannot explain the observed anaphase arrest. Thus, two independent sliding modules power sliding mechanism that drives spindle elongation in human cells.

scholarly journals SepF is the FtsZ anchor in archaea, with features of an ancestral cell division system

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nika Pende ◽  
Adrià Sogues ◽  
Daniela Megrian ◽  
Anna Sartori-Rupp ◽  
Patrick England ◽  
...  
Keyword(s):  
Cell Division ◽  
Common Ancestor ◽  
Phylogenetic Analyses ◽  
Super Resolution ◽  
Binding Mode ◽  
Last Universal Common Ancestor ◽  
Division Plane ◽  
Multiple Factors ◽  
Universal Common Ancestor ◽  
Super Resolution Microscopy

AbstractMost archaea divide by binary fission using an FtsZ-based system similar to that of bacteria, but they lack many of the divisome components described in model bacterial organisms. Notably, among the multiple factors that tether FtsZ to the membrane during bacterial cell constriction, archaea only possess SepF-like homologs. Here, we combine structural, cellular, and evolutionary analyses to demonstrate that SepF is the FtsZ anchor in the human-associated archaeon Methanobrevibacter smithii. 3D super-resolution microscopy and quantitative analysis of immunolabeled cells show that SepF transiently co-localizes with FtsZ at the septum and possibly primes the future division plane. M. smithii SepF binds to membranes and to FtsZ, inducing filament bundling. High-resolution crystal structures of archaeal SepF alone and in complex with the FtsZ C-terminal domain (FtsZCTD) reveal that SepF forms a dimer with a homodimerization interface driving a binding mode that is different from that previously reported in bacteria. Phylogenetic analyses of SepF and FtsZ from bacteria and archaea indicate that the two proteins may date back to the Last Universal Common Ancestor (LUCA), and we speculate that the archaeal mode of SepF/FtsZ interaction might reflect an ancestral feature. Our results provide insights into the mechanisms of archaeal cell division and pave the way for a better understanding of the processes underlying the divide between the two prokaryotic domains.

Simple topology: FtsK-directed recombination at the dif site

2013 ◽  
Vol 41 (2) ◽  
pp. 595-600 ◽  
Author(s):  
Ian Grainge
Keyword(s):  
Escherichia Coli ◽  
Cell Division ◽  
Chromosome Segregation ◽  
Motor Domain ◽  
Site Specific ◽  
Multifunctional Protein ◽  
Supercoiled Plasmid ◽  
C Terminus ◽  
Dna Translocase

FtsK is a multifunctional protein, which, in Escherichia coli, co-ordinates the essential functions of cell division, DNA unlinking and chromosome segregation. Its C-terminus is a DNA translocase, the fastest yet characterized, which acts as a septum-localized DNA pump. FtsK's C-terminus also interacts with the XerCD site-specific recombinases which act at the dif site, located in the terminus region. The motor domain of FtsK is an active translocase in vitro, and, when incubated with XerCD and a supercoiled plasmid containing two dif sites, recombination occurs to give unlinked circular products. Despite years of research the mechanism for this novel form of topological filter remains unknown.

scholarly journals Radial F-actin Organization During Early Neuronal Development

2018 ◽  
Author(s):  
Durga Praveen Meka ◽  
Robin Scharrenberg ◽  
Bing Zhao ◽  
Theresa König ◽  
Irina Schaefer ◽  
...  
Keyword(s):  
Neuronal Development ◽  
Super Resolution ◽  
Actin Dynamics ◽  
Cell Periphery ◽  
Microtubule Organizing Center ◽  
Actin Organization ◽  
Organizing Center ◽  
Super Resolution Microscopy ◽  
Radial Organization

AbstractThe centrosome is thought to be the major neuronal microtubule-organizing center (MTOC) in early neuronal development, producing microtubules with a radial organization. In addition, albeit in vitro, recent work showed that isolated centrosomes could serve as an actin-organizing center (Farina et al., 2016), raising the possibility that neuronal development may, in addition, require a centrosome-based actin radial organization. Here we report, using super-resolution microscopy and live-cell imaging, F-actin organization around the centrosome with dynamic F-actin aster-like structures with F-actin fibers extending and retracting actively. Photoconversion/photoactivation experiments and molecular manipulations of F-actin stability reveal a robust flux of somatic F-actin towards the cell periphery. Finally, we show that somatic F-actin intermingles with centrosomal PCM-1 satellites. Knockdown of PCM-1 and disruption of centrosomal activity not only affect F-actin dynamics near the centrosome but also in distal growth cones. Collectively the data show a radial F-actin organization during early neuronal development, which might be a cellular mechanism for providing peripheral regions with a fast and continuous source of actin polymers; hence sustaining initial neuronal development.

scholarly journals ZapA tetramerization is required for midcell localization and ZapB interaction in Escherichia coli

2019 ◽  
Author(s):  
Nils Y. Meiresonne ◽  
Tanneke den Blaauwen
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Bacterial Cell Division ◽  
Cellular Processes ◽  
Interaction Partners ◽  
Associated Proteins

AbstractBacterial cell division is guided by FtsZ treadmilling precisely at midcell. FtsZ itself is regulated by FtsZ associated proteins (Zaps) that couple it to different cellular processes. ZapA is known to enhance FtsZ bundling but also forms the synchronizing link with chromosome segregation through ZapB and matS bound MatP. ZapA exists as dimers and tetramers in the cell. Using the ZapAI83E mutant that only forms dimers, this paper investigates the effects of ZapA multimerization state on its interaction partners and cell division. By employing (fluorescence) microscopy and Förster Resonance Energy Transfer in vivo it is shown that; dimeric ZapA is unable to complement a zapA deletion strain and localizes diffusely through the cell but still interacts with FtsZ that is not part of the cell division machinery. Dimeric ZapA is unable to recruit ZapB, which localizes in its presence unipolarly in the cell. Interestingly, the localization profiles of the chromosome and unipolar ZapB anticorrelate. The work presented here confirms previously reported in vitro effects of ZapA multimerization in vivo and further places it in a broader context by revealing the strong implications for ZapB localization and ter linkage.

scholarly journals Hyperphosphorylated tau self-assembles into amorphous aggregates eliciting TLR4-dependent inflammatory responses

2021 ◽  
Author(s):  
David Klenerman ◽  
Jonathan Meng ◽  
Yu Zhang ◽  
Dominik Saman ◽  
Suman De ◽  
...  
Keyword(s):  
Inflammatory Responses ◽  
Mechanistic Model ◽  
Super Resolution ◽  
Hyperphosphorylated Tau ◽  
Toll Like Receptor ◽  
Wild Type ◽  
Toll Like Receptor 4 ◽  
Soluble Aggregates ◽  
Super Resolution Microscopy

Abstract Soluble aggregates of the microtubule-associated protein tau have been challenging to assemble and characterize, despite their important role in the development of tauopathies. We found that sequential hyperphosphorylation by PKA in conjugation with either GSK3-β or SAPK4 enabled recombinant wild-type (WT) tau of isoform 0N4R to spontaneously polymerize into small amorphous aggregates in vitro. We employed tandem mass spectrometry to determine the phosphorylation sites and the degree of phosphorylation, and super-resolution microscopy and electron microscopy to characterize the morphology of aggregates formed. Functionally, in comparison with the unmodified aggregates, which require heparin induction to assemble, these self-assembled hyperphosphorylated tau aggregates more efficiently disrupt membrane bilayers and induce Toll-like receptor 4 (TLR4)-dependent inflammatory responses. Together, our results demonstrate that tau hyperphosphorylation is potentially damaging to cells, providing a mechanistic model of how hyperphosphorylation of tau aggregates drives neuroinflammation in tauopathies.

scholarly journals Mutant EGFR is a preferred SMURF2 substrate of ubiquitination: role in enhanced receptor stability and TKI sensitivity

2020 ◽  
Author(s):  
Paramita Ray ◽  
Krishnan Raghunathan ◽  
Aarif Ahsan ◽  
Uday Sankar Allam ◽  
Shirish Shukla ◽  
...  
Keyword(s):  
Growth Factor Receptor ◽  
Super Resolution ◽  
Receptor Internalization ◽  
Stochastic Optical Reconstruction Microscopy ◽  
Steady State Levels ◽  
Epidermal Growth ◽  
Optical Reconstruction ◽  
Super Resolution Microscopy

ABSTRACTWe previously reported that differential protein degradation of TKI-sensitive [L858R, del(E746-A750)] and resistant (T790M) epidermal growth factor receptor (EGFR) mutants upon erlotinib treatment correlates with drug sensitivity. However, the molecular mechanism remains unclear. We also reported SMAD ubiquitination regulatory factor 2 (SMURF2) ligase activity is important in stabilizing EGFR. Here, using in vitro and in vivo ubiquitination assays, mass spectrometry, and super-resolution microscopy, we show SMURF2-EGFR functional interaction is critical in receptor stability and TKI sensitivity. We found that L858R/T790M EGFR is a preferred substrate of SMURF2-UBCH5 (an E3-E2) complex-mediated K63-linked polyubiquitination, which preferentially stabilizes mutant receptor. We identified four lysine (K) residues (K721, 846, 1037 and 1164) as the sites of ubiquitination and replacement of K to acetylation-mimicking asparagine (Q) at K1037 position in L858R/T790M background converts the stable protein sensitive to erlotinib-induced degradation. Using STochastic Optical Reconstruction Microscopy (STORM) imaging, we show that SMURF2 presence allows longer membrane retention of activated EGFR upon EGF treatment, whereas, siRNA-mediated SMURF2 knockdown fastens receptor endocytosis and lysosome enrichment. In an erlotinib-sensitive PC9 cells, SMURF2 overexpression increased EGFR levels with improved erlotinib tolerance, whereas, SMURF2 knockdown decreased EGFR steady state levels in NCI-H1975 and PC9-AR cells to overcome erlotinib and AZD-9291 resistance respectively. Additionally, by genetically altering the SMURF2-UBCH5 complex formation destabilized EGFR. Together, we propose that SMURF2-mediated preferential polyubiquitination of L858R/T790M EGFR may be competing with acetylation-mediated receptor internalization to provide enhanced receptor stability and that disruption of the E3-E2 complex may be an attractive alternate to overcome TKI resistance.

scholarly journals Binding of the RNA Chaperone Hfq on Target mRNAs Promotes the Small RNA RyhB-Induced Degradation in Escherichia coli

2021 ◽  
Vol 7 (4) ◽  
pp. 64
Author(s):  
David Lalaouna ◽  
Karine Prévost ◽  
Seongjin Park ◽  
Thierry Chénard ◽  
Marie-Pier Bouchard ◽  
...  
Keyword(s):  
Complex Formation ◽  
Super Resolution ◽  
Rnase E ◽  
Rna Chaperone ◽  
Target Mrnas ◽  
Mrna Targets ◽  
Super Resolution Microscopy

Many RNA-RNA interactions depend on molecular chaperones to form and remain stable in living cells. A prime example is the RNA chaperone Hfq, which is a critical effector involved in regulatory interactions between small RNAs (sRNAs) and cognate target mRNAs in Enterobacteriaceae. While there is a great deal of in vitro biochemical evidence supporting the model that Hfq enhances rates or affinities of sRNA:mRNA interactions, there is little corroborating in vivo evidence. Here we used in vivo tools including reporter genes, co-purification assays, and super-resolution microscopy to analyze the role of Hfq in RyhB-mediated regulation, and we found that Hfq is often unnecessary for efficient RyhB:mRNA complex formation in vivo. Remarkably, our data suggest that a primary function of Hfq is to promote RyhB-induced cleavage of mRNA targets by RNase E. Moreover, our work indicates that Hfq plays a more limited role in dictating regulatory outcomes following sRNAs RybB and DsrA complex formation with specific target mRNAs. Our investigation helps evaluate the roles played by Hfq in some RNA-mediated regulation.

scholarly journals Single depolymerizing and transport kinesins stabilize microtubule ends

2020 ◽  
Author(s):  
Alexandra Ciorîtă ◽  
Michael Bugiel ◽  
Swathi Sudhakar ◽  
Erik Schäffer ◽  
Anita Jannasch
Keyword(s):  
Cell Division ◽  
Molecular Mechanism ◽  
Regulatory Function ◽  
Microtubule Depolymerization ◽  
Stabilization Mechanism ◽  
The Stability ◽  
Kinesin Superfamily ◽  
Dependent Mechanism ◽  
Dependent Interaction

ABSTRACTMicrotubules are highly dynamic cellular filaments and many intracellular processes like cell division depend on an accurate control of their length. Among other factors, microtubule length is actively modulated by motors from the kinesin superfamily. For example, yeast kinesin-8, Kip3, depolymerizes microtubules in a collective manner by a force- and length-dependent mechanism. However, whether single motors depolymerize or stabilize microtubule ends is unclear. Here, using interference reflection microscopy, we measured the influence of single kinesin motors on the stability of microtubules in an in vitro assay. Surprisingly, using unlabeled, stabilized microtubules, we found that both single kinesin-8 and non-depolymerizing kinesin-1 transport motors stabilized microtubule ends further by reducing the spontaneous microtubule depolymerization rate. Since we observed this effect for two very different kinesins, it implies a more general stabilization mechanism. For Kip3, this behavior is contrary to the collective force-dependent depolymerization activity of multiple motors. The complex, concentration-dependent interaction with microtubule ends provides new insights into the molecular mechanism of kinesin-8 and its regulatory function of microtubule length.

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