Mechanical signaling through membrane tension induces somal translocation during neuronal migration.

Neurons migrate in a saltatory manner by repeating two distinct steps: extension of the leading process and translocation of the cell body. The former step is critical for determining the migratory route in response to extracellular guidance cues. In the latter step, neurons must generate robust forces that translocate the bulky soma against mechanical barriers of the surrounding three-dimensional environment.

Adhesion-clutch between DCC and netrin-1 mediates netrin-1-induced axonal haptotaxis.

The growth cone, a motile structure located at the tip of growing axons, senses extracellular guidance cues and translates them into directional forces that drive axon outgrowth and guidance. Axon guidance directed by chemical cues on the extracellular adhesive substrate is termed haptotaxis. Recent studies reported that netrin-1 on the substrate functions as a haptotactic axon guidance cue.

Bayesian traction force estimation using cell boundary-dependent force priors.

Understanding the principles of cell migration necessitates measurements of the forces generated by cells. In traction force microscopy (TFM), fluorescent beads are placed on a substrate's surface and the substrate strain caused by the cell traction force is observed as displacement of the beads. Mathematical analysis can estimate traction force from bead displacement.

Guided axon outgrowth of neurons by molecular gradients generated from femtosecond laser-fabricated micro-holes.

Objective: Transplantation of scaffold-embedded guided neurons has been reported to increase neuronal regeneration following brain injury. However, precise axonal integration between host and transplant neurons to form functional synapses remains a major problem. Thus, a high-precision tool to actuate neuronal axon outgrowth in real-time conditions is required to attain robust axon regeneration.

Dephosphorylation of neural wiring protein shootin1 by PP1 phosphatase regulates netrin-1-induced axon guidance.

Axon pathfinding is an essential step in neuronal network formation. Shootin1a is a clutch-linker molecule that is mechanically involved in axon outgrowth and guidance. It was previously shown that concentration gradients of axon guidance molecule netrin-1 in the extracellular environment elicit asymmetrically localized Pak1 kinase-mediated phosphorylation of shootin1a within axonal growth cones, which is higher on the netrin-1 source side.

Mechanical regulation of synapse formation and plasticity.

Dendritic spines are small protrusions arising from dendrites and constitute the major compartment of excitatory post-synapses. They change in number, shape, and size throughout life; these changes are thought to be associated with formation and reorganization of neuronal networks underlying learning and memory. As spines in the brain are surrounded by the microenvironment including neighboring cells and the extracellular matrix, their protrusion requires generation of force to push against these structures.

Analyses of Actin Dynamics, Clutch Coupling and Traction Force for Growth Cone Advance.

To establish functional networks, neurons must migrate to their appropriate destinations and then extend axons toward their target cells. These processes depend on the advances of growth cones that located at the tips of neurites. Axonal growth cones generate driving forces by sensing their local microenvironment and modulating cytoskeletal dynamics and actin-adhesion coupling (clutch coupling).

Simultaneous analyses of clutch coupling and actin polymerization in dendritic spines of rodent hippocampal neurons during chemical LTP.

Dendritic spine enlargement by synaptic activation is thought to increase synaptic efficacy underlying learning and memory. This process requires forces generated by actin polymerization and actin-adhesion coupling (clutch coupling). Here, we describe a protocol to monitor actin filament retrograde flow and actin polymerization within spines using a standard epi-fluorescence microscope.

Mechanosensitive axon outgrowth mediated by L1-laminin clutch interface.

Mechanical properties of the extracellular environment modulate axon outgrowth. Growth cones at the tip of extending axons generate traction force for axon outgrowth by transmitting the force of actin filament retrograde flow, produced by actomyosin contraction and F-actin polymerization, to adhesive substrates through clutch and cell adhesion molecules. A molecular clutch between the actin filament flow and substrate is proposed to contribute to cellular mechanosensing.

Shootin1a-mediated actin-adhesion coupling generates force to trigger structural plasticity of dendritic spines.

Dendritic spines constitute the major compartments of excitatory post-synapses. They undergo activity-dependent enlargement, which is thought to increase the synaptic efficacy underlying learning and memory. The activity-dependent spine enlargement requires activation of signaling pathways leading to promotion of actin polymerization within the spines.

Forces to Drive Neuronal Migration Steps.

To establish and maintain proper brain architecture and elaborate neural networks, neurons undergo massive migration. As a unique feature of their migration, neurons move in a saltatory manner by repeating two distinct steps: extension of the leading process and translocation of the cell body. Neurons must therefore generate forces to extend the leading process as well as to translocate the cell body.

An Artificial Amphiphilic Peptide Promotes Endocytic Uptake by Inducing Membrane Curvature.

Membrane curvature plays a pivotal role in cellular life, including cellular uptake and membrane trafficking. The modulation of membrane curvature provides a novel means of manipulating cellular events. In this report, we show that a nine-residue amphiphilic peptide (R6W3) stimulates endocytic uptake by inducing membrane curvature.

Shootins mediate collective cell migration and organogenesis of the zebrafish posterior lateral line system.

The zebrafish sensory posterior lateral line is an excellent model system to study collective cell migration and organogenesis. Shootin1 is a cytoplasmic protein involved in neuronal polarization and axon guidance. Previous studies have shown that shootin1 couples actin filament retrograde flow with extracellular adhesive substrates at the leading edge of axonal growth cones, thereby producing mechanical force for the migration and guidance of axonal growth cones.

An influenza-derived membrane tension-modulating peptide regulates cell movement and morphology via actin remodeling.

Tension in cell membranes is closely related to various cellular events, including cell movement and morphogenesis. Therefore, modulation of membrane tension can be a new approach for manipulating cellular events. Here, we show that an amphipathic peptide derived from the influenza M2 protein (M2[45-62]) yields lamellipodia at multiple sites in the cell.

Rab33a and Rab33ba mediate the outgrowth of forebrain commissural axons in the zebrafish brain.

Rab small GTPases play key roles in intracellular membrane trafficking. Rab33a promotes axon outgrowth of cultured rat hippocampal neurons by mediating the anterograde axonal transport of Golgi-derived vesicles and the concomitant exocytosis of these vesicles at the growth cone. However, the functions of Rab33 in vivo are unclear.

Shootin1b Mediates a Mechanical Clutch to Produce Force for Neuronal Migration.

As an essential step for brain morphogenesis, neurons migrate via mechanical interactions with components of their environment such as neighboring cells and the extracellular matrix. However, the molecular mechanism by which neurons exert forces on their environment during migration remains poorly understood. Here, we show that shootin1b is expressed in migrating mouse olfactory interneurons and accumulates at their leading process growth cone.

Gradient-reading and mechano-effector machinery for netrin-1-induced axon guidance.

Growth cones navigate axonal projection in response to guidance cues. However, it is unclear how they can decide the migratory direction by transducing the local spatial cues into protrusive forces. Here we show that knockout mice of display abnormal projection of the forebrain commissural axons, a phenotype similar to that of the axon guidance molecule netrin-1.

Grip and slip of L1-CAM on adhesive substrates direct growth cone haptotaxis.

Chemical cues presented on the adhesive substrate direct cell migration, a process termed haptotaxis. To migrate, cells must generate traction forces upon the substrate. However, how cells probe substrate-bound cues and generate directional forces for migration remains unclear.

Actin Waves: Origin of Cell Polarization and Migration?

Actin filaments and associated proteins undergo wave-like movement in various cell types. Recent studies with cutting-edge analyses, including live-cell imaging, biophysical monitoring and manipulation, and mathematical modeling, have highlighted roles of 'actin waves' in cellular protrusion, polarization, and migration. The prevailing models to explain the wave-like dynamics of actin filaments involve an activator-inhibitor mechanism.

Identification of a shootin1 isoform expressed in peripheral tissues.

Shootin1 is a brain-specific cytoplasmic protein involved in neuronal polarity formation and axon outgrowth. It accumulates at the leading edge of axonal growth cones, where it mediates the mechanical coupling between F-actin retrograde flow and cell adhesions as a clutch molecule, thereby producing force for axon outgrowth. In this study, we report a novel splicing isoform of shootin1 which is expressed not only in the brain but also in peripheral tissues.

Shootin1-cortactin interaction mediates signal-force transduction for axon outgrowth.

Motile cells transduce environmental chemical signals into mechanical forces to achieve properly controlled migration. This signal-force transduction is thought to require regulated mechanical coupling between actin filaments (F-actins), which undergo retrograde flow at the cellular leading edge, and cell adhesions via linker "clutch" molecules. However, the molecular machinery mediating this regulatory coupling remains unclear.

Actin Migration Driven by Directional Assembly and Disassembly of Membrane-Anchored Actin Filaments.

Actin and actin-associated proteins migrate within various cell types. To uncover the mechanism of their migration, we analyzed actin waves, which translocate actin and actin-associated proteins along neuronal axons toward the growth cones. We found that arrays of actin filaments constituting waves undergo directional assembly and disassembly, with their polymerizing ends oriented toward the axonal tip, and that the lateral side of the filaments is mechanically anchored to the adhesive substrate.

Conversion of a signal into forces for axon outgrowth through Pak1-mediated shootin1 phosphorylation.

Soluble guidance cues can direct cellular protrusion and migration by modulating adhesion and cytoskeletal dynamics. Actin filaments (F-actins) polymerize at the leading edge of motile cells and depolymerize proximally [1, 2]; this, together with myosin II activity, induces retrograde flow of F-actins [3-5]. It has been proposed that the traction forces underlying cellular motility may be regulated by the modulation of coupling efficiency between F-actin flow and the extracellular substrate via "clutch" molecules [6-10].

Rab33a mediates anterograde vesicular transport for membrane exocytosis and axon outgrowth.

Axon outgrowth requires plasma membrane expansion, which results from post-Golgi vesicular transport and fusion. However, the molecular mechanisms regulating post-Golgi vesicular trafficking for membrane expansion and axon outgrowth remain unclear. Here, we show that Rab33a expression became upregulated during axon outgrowth of cultured rat hippocampal neurons.