Biology subjects

Loreau, V.

Publications and source records attributed to Loreau, V..

4 recordsLinked to original sources

bioRxiv2024

Muscle growth by sarcomere divisions

The sarcomere is the elementary contractile unit of muscles. Adult muscle cells chain thousands of sarcomeres into long periodic myofibrils that attach to the skeleton. How new sarcomeres are added during muscle growth is unknown. By live imaging and high-throughput image analysis, we have now tracked sarcomeric components during Drosophila muscle development and discovered that individual sarcomeres divide along the myofibril tension axis into daughter sarcomeres. This way, new sarcomeres can be inserted into contractile and mechanically intact myofibrils. We propose that sarcomere division is triggered by tension and local sarcomere damage originating from skeletal growth and muscle contractions. Sarcomere divisions repair damaged sarcomeres, ensure their mechanical integrity and synchronise sarcomere addition with skeletal growth during animal development.

developmental biology↗

bioRxiv2024

Titin-dependent biomechanical feedback tailors sarcomeres to specialised muscle functions in insects

Sarcomeres are the contractile units of muscles that enable animals to move. Insect muscles are remarkable examples because they use extremely different contraction frequencies (ranging from [~]1 to 1000 Hz) and amplitudes for flying, walking and crawling. This is puzzling because sarcomeres are built from essentially the same actin-myosin components. We show here that the giant protein titin is the key to this functional specialisation. I-band titin spans and determines the length of the sarcomeric I-band, and occurs in muscle-type-specific isoforms. Surprisingly, it also rules the length of the force-generating myosin filament in a force feedback mechanism, even though it is not present there. We provide evidence for this model and its validity beyond insects. SummaryHere we identified a mechanical mechanism that instructs sarcomeres to fulfill the specific needs of different muscle types.

developmental biology↗

bioRxiv2024

PatternJ: an ImageJ toolset for the automated and quantitative analysis of regular spatial patterns found in sarcomeres, axons, somites, and more

Regular spatial patterns are ubiquitous forms of organization in nature. In animals, regular patterns can be found from the cellular scale to the tissue scale, and from early stages of development to adulthood. To understand the formation of these patterns, how they form and mature, and how they are affected by perturbations, a precise quantitative description of the patterns is essential. However, accessible tools that offer in-depth analysis without the need for computational skills are lacking for biologists. Here we present PatternJ, a novel toolset to analyze regular pattern organizations precisely and automatically. This toolset, to be used with the popular imaging processing program ImageJ/Fiji, facilitates the extraction of key geometric features within and between pattern repeats. We validated PatternJ on simulated data and tested it on images of sarcomeres in insect muscles and cardiomyocytes, actin rings in neurons, and somites in zebrafish embryos obtained using confocal fluorescence microscopy, STORM, electron microscopy, and bright-field imaging. We show that the toolset delivers subpixel feature extraction reliably even with images of low signal-to-noise ratio. PatternJs straightforward use and functionalities make it valuable for various scientific fields requiring quantitative pattern analysis, including the sarcomere biology of muscles or the patterning of mammalian axons, speeding up discoveries with the bonus of high reproducibility.

biophysics↗

bioRxiv2022

A nanobody toolbox to investigate localisation and dynamics of Drosophila titins

Measuring the positions and dynamics of proteins in intact tissues or whole animals is key to understand protein function. However, to date this is still a challenging task, as accessibility of large antibodies to dense tissues is often limited and fluorescent proteins inserted close to a domain of interest may affect function of the tagged protein. These complications are particularly present in the muscle sarcomere, arguably one of the most protein dense structures in nature, which makes studying morphogenesis at molecular resolution challenging. Here, we have employed an efficient pipeline to generate a nanobody toolbox specifically recognising various domains of two large Drosophila titin homologs, Sallimus and Projectin. We demonstrate the superior labelling qualities of our nanobodies compared to conventional antibodies in intact muscle tissue. Applying our nanobody toolbox to larval muscles revealed a gigantic Sallimus isoform stretched more than 2 {micro}m to bridge the sarcomeric I-band. Furthermore, N- and C-terminal nanobodies against Projectin identified an unexpected polar orientation of Projectin covering the myosin filaments in larval muscles. Finally, expression of a Sallimus nanobody in living larval muscles confirmed the high affinity binding of nanobodies to target epitopes in living tissue and hence demonstrated their power to reveal the in vivo dynamics of sarcomeric protein domains. Together, our toolbox substantiates the multiple advantages of nanobodies to study sarcomere biology. It may inspire the generation of similar toolboxes for other large protein complexes in Drosophila or mammals.

developmental biology↗