Journal Club – March 2019

Peeling Actomyosin Bundles, Tubulin Accretion, and Mapping the Primary Cilium


Must Reads

Directionality Of Dynein Is Controlled By The Angle And Length Of Its Stalk

Can et al. | Nature
Dynein motors possess an uncanny ability to walk toward the microtubule minus end.  This minus end directionality is critical for retrograde intracellular transport (among other cellular functions) and is at the center of a number of human health and disease concerns.  In this study, Can et al. dissect the mechanistic underpinnings of dynein directionality by engineering a plus end-directed dynein in Saccharomyces cerevisiae. With single molecule studies, the authors discover that changing the length and angle of the coiled-coil stalk can reverse dynein directionality, and argue in support of the “linker swing vector” model.


Microtubules Form By Progressively Faster Tubulin Accretion, Not By Nucleation-Elongation

Rice, Moritz, and Agard | bioRxiv
Spontaneous microtubule nucleation is a rare event that has eluded researchers (and confounded our scientific illustrators here at PurSolutions) in large part because of the structural complexity of the hollow microtubule.  Rice, Moritz, and Agard argue that the notion of a “critical nucleus” is oversimplified, and explore biochemical models that more accurately portray nucleation and assembly events.  The authors describe a de novo microtubule assembly pathway that proceeds via the formation of 2D sheet-like structures that, like crystals, grow faster the larger they become.  This “accretion” model offers a new framework for conceptualizing the unique kinetics of microtubule self-assembly.


Designing A Chemical Inhibitor For The AAA Protein Spastin Using Active Site Mutations

Cupido et al. | Nature Chemical Biology
Microtubule severing enzymes including spastin, fidgetin, and katanin have a remarkable ability to break microtubules along their lengths.  Chemical inhibitors of these enzymes would unlock new insights into the role of microtubule severing in dynamic cellular processes and is an especially valuable research goal given that microtubule severing enzymes belong to the AAA ATPase superfamily.  In this study, Cupido et al. design the first chemical inhibitor of spastin, spastazoline, along with inhibitor-resistant point mutations as tools for probing spastin phenotypes in living cells.

Labeling of the microtubule cytoskeleton in a human cell line
Dr. Jeffrey A.J. van Haren | UCSF
Nikon Small World in Motion Competition

Cytoskeleton Methodology

Thao Nguyen, Tim Mitchison, and Martin Wühr provide detailed immunofluorescence protocols for imaging microtubule assemblies in whole-mount embryos, where large cellular volumes present unique microscopy challenges. (Vertebrate Embryogenesis | Methods in Molecular Biology)


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Conference Watch

Gordon Research Conference | Motile and Contractile Systems
Principles of Cytoskeletal Organization from Single Molecules to Organisms
July 28 – August 2, 2019
New London, New Hampshire


Journal Club Picks

  • Kinetochore proteins function outside of mitosis during neuronal development as revealed by two research studies.  Cheerambathur et al. and Zhao et al. | Dev Cell
  • High-resolution mapping of the primary cilium provides a 3D reconstruction of the membrane surface and underlying axoneme architecture.  Yoon et al. | Biophys J
  • Centrosomal microtubule organization regulates neurogenesis in the subventricular zone during development.  Carmargo Ortega et al. | Nature
  • Tropomyosin isoforms specifically tune actin filament length and treadmilling.  Jansen and Goode | MBoC
  • Two novel dynein adapters are the first identified to combine a Rab GTPase domain and a dynein–dynactin activator domain on a single polypeptide.  Wang et al. | JCB
  • A complete force-extensibility curve of thick filaments from intact vertebrate skeletal muscle elicits discussion of the sliding filament theory.  Ma et al. | Biophys J (comment to the editor by Reconditi et al., response by Ma et al.)
  • Artificially-induced asymmetric cell divisions in sea urchin zygotes uncover a role of weakening microtubule centering forces in moving the cell division plane.  Sallé et al. | JCB (spotlight by Alper and Zanic)
  • Structural analysis of yeast kinetochores with electron cryotomography in vivo reveals partial Dam1 rings, challenging traditional models for microtubule-driven chromosome movement.  Ng et al. | JCB
  • Isogenic cell lines with varied kinesin-5 activity reveal cellular responses to a gradient of centromere tension.  Mukherjee et al. | Dev Cell
  • Cooperative transport of cargo by two kinesin motors is influenced by microtubule reattachment rates.  Arpağ et al. | Biophys J
  • Detyrosinated microtubules serve as hubs for lysosomes, facilitating their fusion with autophagosomes to trigger autophagy.  Mohan et al. | JCB
  • Peeling bundles of actin and myosin during cytokinesis maintain uniform tension during actomyosin ring contraction.  Cheffings et al. | MBoC
  • Actomyosin contractility in cancer cells regulates the secretion of factors that modulate the tumor immune microenvironment and drive disease progression.  Georgouli et al. | Cell