During neural development, immature nerve cells extend axons and dendrites toward their targets then form connections with other cells. At the tip of these extending fibers is the growth cone, a structure with finger-like protrusions called filopodia.
As the growth cone moves like an amoeba through the environment, the filopodia detect chemical guidance cues that steer it in the right direction. These processes are dependent on rearrangements of the actin cytoskeleton, a protein scaffold inside the cell.
Now, a team of researchers led by Hiroyuki Kamiguchi of the RIKEN Brain Science Institute has shown that nerve fibers turn clockwise in the absence of external clues, when growing on flat two-dimensional surfaces, because the filopodia rotate of their own accord.
The researchers first confirmed that nerve fibers from the hippocampus of embryonic rats turn rightwards when grown on a two-dimensional substrate, but grow straight when embedded in a three-dimensional gel. Addition of the fungal toxin cytochalasin D, which stops elongation of actin filaments, prevented the turning of fibers growing on a flat surface, showing that the turning is dependent on the cytoskeleton.
Hypothesizing that filopodia rotate autonomously, the researchers developed a new technique to directly observe the movements in three dimensions. They embedded hippocampal neurons in a gel, so the nerve fibers grew vertically towards the lens of an upright microscope. This revealed that individual filopodia tended to rotate counter-clockwise. This rotation generates a leftward force on the surface, causing the growth cone to turn to the right.
The researchers then tested whether or not this turning is powered by myosins, the motor proteins responsible for actin-based cellular movements. They transfected hippocampal neurons with three different full-length myosins (Va, Vb and Vc), as well as shortened forms of them that prevent endogenous myosin molecules from binding actin filaments. All were fused to, or co-expressed with, a fluorescent protein to allow easy visualization.
As expected, filopodial rotation was blocked in neurons expressing the shortened myosins, but could be rescued by transfecting the cells with myosins Va and Vb, but not myosin Vc. The rightwards rotation was also observed in neurons from the cerebral cortex, thalamus and cerebellum, suggesting that this is a general mechanism.
Commenting on the findings, Kamiguchi says that: “Rotating filopodia would probe a larger volume of the environment and contribute to the precise perception of cues by the growth cone.”Alternatively, the rotations could promote nerve bundle formation, by enabling new fibers to twine around older ones.
The corresponding author for this highlight is based at the Laboratory for Neuronal Growth Mechanisms, RIKEN Brain Science Institute
1. Tamada, A., Kawase, S., Murakami, F., & Kamiguchi, H. Autonomous right-screw rotation of growth cone filopodia drives neurite turning. Journal of Cell Biology published online 1 February 2010 (doi:10.1083/jcb.200906043).
gro-pr | Research asia research news
What happens in the cell nucleus after fertilization
06.12.2016 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt
Researchers uncover protein-based “cancer signature”
05.12.2016 | Universität Basel
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
06.12.2016 | Materials Sciences
06.12.2016 | Medical Engineering
06.12.2016 | Power and Electrical Engineering