Nav: Home

Friction shapes zebrafish embryos

March 27, 2017

A simple ball of cells is the starting point for humans -- and zebrafish. At the end of embryonic development, however, a fish and a human look very different. The biochemical signals at play have been studied extensively. How mechanical forces on the other hand shape the embryo is the subject of a study by Carl-Philipp Heisenberg, Professor at the Institute of Science and Technology Austria (IST Austria), and his group, including first author and postdoc Michael Smutny. In their study, published today in Nature Cell Biology, the researchers show that friction between moving tissues generates force. This force shapes the nervous system of the zebrafish embryo, a popular animal model of embryonic development. "We show that friction is generated by forming tissues sliding against each other, and that this force is a key mechanism for regulating morphogenesis during embryo development," Carl-Philipp Heisenberg explains.

As the embryo develops, cells move and tissues are rearranged. Mechanical forces drive this morphogenesis. So far, however, it has been poorly understood how these forces are generated and integrated with other signals. In the present study, Heisenberg and his group studied the mechanical forces that are at work when the central nervous system (CNS) of the zebrafish develops. The neural anlage, the precursor of the neural tube, develops from one of three germ layers, the neurectoderm. However, the other two germ layers, the mesoderm and endoderm, have been shown to be crucial for the proper morphogenesis of the neurectoderm. When the neural anlage develops, the germ layers of the ball-shaped embryo move in opposite directions. The mesoderm and endoderm -- also referred to collectively as mesendoderm - move to one pole of the embryo, the so-called animal pole, while the overlying neurectoderm slides against them to move to the opposite pole, the vegetal pole.

Heisenberg and his group found that this movement is important for positioning the neural anlage correctly. As the tissues slide against each other, the cells in the neurectoderm that will form the neural anlage change their direction of movement. They switch track and move towards the animal pole, the same direction as the underlying mesendoderm. The researchers found that in embryos where the mesendoderm is absent, these neurectoderm cells do not reorient. Instead, all neurectoderm cells move to the vegetal pole and the neural anlage is incorrectly positioned. When the mesendoderm cells move more slowly than normal, the neural anlage also ends up at the wrong position.

Now, to find what the underlying mechanism was, the researchers built a theoretical model based on their observation. By modelling the forces at work in the embryo, they found that the movement of neurectoderm against mesendoderm causes friction to arise. Michael Smutny explains how friction arises: "When the tissues slide against each other, friction arises, similar to when you rub a balloon against a sweater. In the case of the zebrafish embryo, the tissues contact each other directly via E-cadherin, a protein that reaches out of the cells. When these linker proteins rub against each other, friction builds up between the tissues."

The scientists confirmed the importance of E-cadherin by rebuilding the system in the lab: they cultured a layer of ectoderm cells in a dish and moved it in one direction, while pushing a bead coated with E-cadherin in the opposite direction. As a result, the ectoderm cells re-orient in the same way as observed in the embryo. This finding that mesendoderm cells directly affect the movement of neurectoderm cells through friction forces shows for the first time that friction is a key regulator of tissue morphogenesis in the embryo.

Neurectoderm morphogenesis defects are one of the most common birth defects in humans. The finding that friction forces that emerge at the interface between the forming germ layers play a key role in neurectoderm morphogenesis indicate a previously unrecognized mechanism that might underlie those birth defects.

Institute of Science and Technology Austria

Related Nervous System Articles:

Discovery concerning the nervous system overturns a previous theory
It appears that when our nervous system is developing, only the most viable neurons survive, while immature neurons are weeded out and die.
Nanocapsule reaches cancer that has spread to central nervous system in mice
Researchers developed a drug delivery system that can break through the blood-brain barrier in mice.
Autonomic nervous system appears to function well regardless of mode of childbirth
'In a low-risk group of babies born full-term, the autonomic nervous system and cortical systems appear to function well regardless of whether infants were exposed to labor prior to birth,' says Sarah B.
First step to induce self-repair in the central nervous system
Injured axons instruct Schwann cells to build specialized actin spheres to break down and remove axon fragments, thereby starting the regeneration process.
First complete wiring diagram of an animal's nervous system
In a study published online today in Nature, researchers at Albert Einstein College of Medicine describe the first complete wiring diagram of the nervous system of an animal, the roundworm Caenorhabditis elegans, used by scientists worldwide as a model organism.
Scientists unlock new role for nervous system in regeneration
Biologists have developed a computational model of flatworm regeneration to answer an important question in regeneration research - what are the signals that determine the rebuilding of specific anatomical structures?
Study identifies new approach to repairing damaged peripheral nervous system
A new understanding of cell migration may eventually help in the treatment of neurodegenerative diseases -- and even allow children to 'get out of their wheelchairs and live an enhanced quality of life.'
Research gives new insight into the evolution of the nervous system
Pioneering research has given a fascinating fresh insight into how animal nervous systems evolved from simple structures to become the complex network transmitting signals between different parts of the body.
Researchers solve mystery of how ALL enters the central nervous system
A research team led by Duke Cancer Institute scientists has found that this blood cancer infiltrates the central nervous system not by breaching the blood-brain barrier, but by evading the barrier altogether.
The VIPs of the nervous system
Biologists at Washington University in St Louis unlocked a cure for jet lag in mice by activating a small subset of the neurons involved in setting daily rhythms.
More Nervous System News and Nervous System Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.