Venue: Centre Broca
Do titins rule sarcomeres of insect muscles?
Abstract
Sarcomeres have a stereotypic architecture across animal species. In mammalian muscles, sarcomere length is controlled by the large sarcomere ruler titin spanning from the Z-disc to the M-band. Similarly, non-chordate species such as insects and worms do contain sarcomeres of defined length, varying only between fiber types. However, these species do not contain a large titin molecule spanning across a half sarcomere, hence a simple ruler model cannot generally apply. To investigate how sarcomere length is controlled in non-chordates, we have manipulated the length and elasticity of the Drosophila titin homolog Sallimus (Sls). In Drosophila larval muscles Sls contains a long PEVK spring domain and extends over 2 µm across the I-band linking the Z-disc to the I-band. Surprisingly, we find that genetically reducing the spring domain length of Sls not only changes the I-band length, as expected, but also reduces the A-band and hence myosin filament length. Hence, we hypothesize that a biomechanical feedback mechanism controls sarcomere length in non-chordate species. In support of this mechanism, we have quantified the mechanical forces across Sls in different Drosophila muscle types and find high forces across Sls in sarcomeres with long I-bands, and lower forces in sarcomeres with shorter I-bands.
Frank Schnorrer
Institute for Developmental Biology Marseille
Invited by Gregory Giannone