Skeletal muscles are built from small contractile units, the sarcomeres.
Many of these sarcomeres are connected in a well-ordered series to form myofibrils that span from one muscle end to the other. Contractions of these sarcomeres result in contraction of the entire muscle.
Scientists at the Max Planck Institute of Biochemistry (MPIB) in Munich-Martinsried recently identified a key mechanism how this muscle architecture is built during development.
“Mechanical tension is the essential trigger” explains Frank Schnorrer, group leader at the MPIB. “If tension is eliminated, no regular myofibrils, but only short, random protein assemblies can form. Such muscles are entirely non-functional”.
In order to move the body, skeletal muscles are pulling on the skeleton. For efficient muscle and skeletal movements it is essential that the muscle contracts only along a defined axis, for instance for the leg movement along the thigh. Such a directed contraction is achieved by the myofibrils that span through the entire length of the muscle.
At both ends, the myofibrils are anchored to the tendon cells, which themselves are linked to the skeleton. “Thereby, the entire force is transduced from the muscle to the skeleton,” Frank Schnorrer describes. How can the regular architecture of a many hundred sarcomeres long myofibril be built along a defined axis during muscle development?
PhD student Manuela Weitkunat and PostDoc Aynur Kaya-Çopur were investigating this question in the fruit fly Drosophila melanogaster. They discovered that shortly after the Drosophila flight muscles contact their tendons, mechanical tension is established.
This tension buildup occurs before sarcomeres are formed and reaches through the entire muscle-tendon-skeleton system. This tension axis equips the muscle with positional information along which the sarcomeres must form.
Absence of tension results in chaos
By using genetic mutations in the fly, the scientists of the Muscle Dynamics group have been able to block the attachment of flight muscles to tendons and thus eliminate tension formation in the system. As a consequence, muscles could not build long regular myofibrils anymore but instead distribute the sarcomeric protein complexes chaotically.
In order to directly test the influence of mechanical tension, the scientists used a laser to cut the tendons off the muscle. This strategy of tension release also led to a major defect in sarcomere and myofibril formation. “Based on these results, we are suggesting a new model of myofibril formation, which proposes tension dependent self-assembly of the sarcomeric components,” explains Frank Schnorrer.
“When a certain tension threshold is reached, myofibril formation is triggered. If tension is compromised, the sarcomeric components have no spatial information and assemble chaotically.”
As human muscles also contain myofibrils that are built by periodically arrayed sarcomeres, it is likely that a similar tension-based assembly model may also apply during human muscle development, so the scientists think. These results have now been published in the journal Current Biology.
M. Weitkunat, A. Kaya-Çopur, S.W. Grill and and F. Schnorrer: Tension and force-resistant attachment are essential for myofibrillogenesis in Drosophila flight muscle. Current Biology, March 13, 2014.
Dr. Frank Schnorrer
Max Planck Institute of Biochemistry
Am Klopferspitz 18
Max Planck Institute of Biochemistry
Am Klopferspitz 18
Tel. +49 89 8578-2824
http://www.biochem.mpg.de/4137023/067_schnorrer_muskelentwicklung - complete press release
http://www.biochem.mpg.de/schnorrer - website of the Research Group "Muscle Dynamics" (Frank Schnorrer)
Anja Konschak | Max-Planck-Institut
Rainbow colors reveal cell history: Uncovering β-cell heterogeneity
22.09.2017 | DFG-Forschungszentrum für Regenerative Therapien TU Dresden
The pyrenoid is a carbon-fixing liquid droplet
22.09.2017 | Max-Planck-Institut für Biochemie
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy