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.
-end-


Institute of Science and Technology Austria

Related Nervous System Articles:

Rare cells are 'window into the gut' for the nervous system
Specialized cells in the gut sense potentially noxious chemicals and trigger electrical impulses in nearby nerve fibers, according to a new study led by UC San Francisco scientists.
Study overturns seminal research about the developing nervous system
New research by scientists at the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA overturns a long-standing paradigm about how axons grow during embryonic development.
Sympathetic nervous system is critical in regulating energy expenditure and thermogenesis
New study suggests that your brain, not your white blood cells, keeps you warm.
As fins evolve to help fish swim, so does the nervous system
The sensory system in fish fins evolves in parallel to fin shape and mechanics, and is specifically tuned to work with the fish's swimming behavior, according to new research from the University of Chicago.
Antibodies as 'messengers' in the nervous system
Antibodies are able to activate human nerve cells within milliseconds and hence modify their function -- that is the surprising conclusion of a study carried out at Human Biology at the Technical University of Munich (TUM).
Bioimaging: A clear view of the nervous system
A new and versatile imaging technique enables researchers to trace the trajectories of whole nerve cells and provides extensive insights into the structure of neuronal networks.
In the gut, nervous cells are the 'eyes and ears' of the immune system
A team of scientists in Portugal has discovered, in the mouse gut, a novel process that protects the bowel's lining against inflammation and microbial aggressions -- and fights them when they arise.
Biologists discover new strategy to treat central nervous system injury
Neurobiologists at UC San Diego have discovered how signals that orchestrate the construction of the nervous system also influence recovery after traumatic injury.
Delivery strategies of chemotherapy to the central nervous system
The blood-brain barrier and the blood-tumor barrier remain great obstacles to the drug delivery to brain tumors.
520-million-year-old fossilized nervous system is most detailed example yet found
A 520-million-year-old fossilized nervous system -- so well-preserved that individually fossilized nerves are visible -- is the most complete and best example yet found, and could help unravel how the nervous system evolved in early animals.

Related Nervous System Reading:

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

Setbacks
Failure can feel lonely and final. But can we learn from failure, even reframe it, to feel more like a temporary setback? This hour, TED speakers on changing a crushing defeat into a stepping stone. Guests include entrepreneur Leticia Gasca, psychology professor Alison Ledgerwood, astronomer Phil Plait, former professional athlete Charly Haversat, and UPS training manager Jon Bowers.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".