#myocytes

Building Muscle

Different types of cells pattern our tissues, each decorated by the thousands of genes and proteins inside them. Transcription factors shape these patterns, helping to switch on sets of distinctive genes in different cells at different times. In these chunks of mouse leg muscle, for example, transcriptions factors like MAF help to create a mosaic of muscle fibres. Coloured stains highlight different type II fibres in red and green in the normal muscle on the left. Investigating further, researchers alter the pattern by removing a version of MAF – changing the balance of fibres (seen on the right). Our own muscles adapt to our lifestyle, changing the makeup of their fibres with the help of transcription factors. Learning more about these and the role of age and diet may help us to maintain healthy muscles for longer, fending off diseases like diabetes and muscular dystrophy.

Written by John Ankers

Image from work by Shunya Sadaki and colleagues

Laboratory Animal Resource Center in Transborder Medical Research Center, and Department of Anatomy and Embryology, Institute of Medicine, University of Tsukuba, Tsukuba, Japan

Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)

Published in Cell Reports, March 2023

Dis-banded

Just like us, fruit flies are stripy beneath the skin. These sarcomeres – repeating bands of stretchy muscle tissue – contain fibres of myosin (highlighted in green) and actin (purple) griping and pulling at each other – as the sarcomeres shorten, the muscle contracts. This is heart muscle from fruit flies (Drosophila), used to investigate common faults in human heart disease. Compared to healthy muscle at the top, the sarcomeres at the bottom are much looser and swollen – in these hearts, researchers used RNA interference to hamper the activity of a protein called filamin, often shown to be altered in heart diseases like hypertrophic cardiomyopathy. Yet altering its activity in a different way – using CRISPR gene editing to change its structure – did not affect the flies as expected. Further studies might aim to solve this mystery, while altering genes and proteins reveals more about what we do, or perhaps don’t, have in common with Drosophila.

Written by John Ankers

Image from work by Flavie Ader and colleagues

Université Paris Cité, Paris, France

Image originally published with a Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0)

Published in Biology Open, September 2022

Building Permission

When a muscle fibre, like the one shown, is injured, its associated stem cells, like the one coloured pink, are keen to start rebuilding. But, they must wait until immune cells have finished clearing up debris. In fact, the immune cells send ‘wait’ signals to the stem cells preventing their activity. Stem cells are impatient, though, and as soon as an injury occurs, they start producing and covering themselves with hyaluronic acid (coloured pale green and seen outlining the stem cell). This carbohydrate goo gradually thickens until it's dense enough to interrupt the immune cells’ signals, essentially giving the stem cells the go-ahead to start work. As humans age, production of hyaluronic acid diminishes, which may explain why injuries in older people take so long to repair. Without a thick gooey barrier to block the immune signals, the stem cells are forced to wait, their building permit denied.

Written by Ruth Williams

Image from work by Kiran Nakka and colleagues

Sprott Center for Stem Cell Research, Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada

Image copyright held by the original authors

Research published in Science, August 2022

Mobile Repairs

Racing to repair our skeletal muscles after injury, satellite cells orbit our stretchy muscle cells, or myofibres, and fuse together to plug gaps. But here scientists reveal another, surprising source of help – the swift movement of the cells’ own nuclei. Daily damage from exercise triggers the myofibre’s multiple myonuclei (highlighted in blue here) to zip along the fibre (yellow and pink), alerted by chemical signals to the area of damage seen at the top left – a bit like the flashing lights on ambulances, only ~10,000 times smaller. At the scene, the myonuclei produce messenger RNA molecules which act as blueprints for proteins involved in cellular reconstruction, helping to rebuild and strengthen the muscle. The next step is to understand how this form of repair is affected by diseases like muscular dystrophy, and what scientists can do to help.

Written by John Ankers

Image from work by William Roman and colleagues

Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisboa, Portugal

Image copyright held by the original authors

Research published in Science, October 2021