Applying our Drosophila nanobody toolbox to study Drosophila titin homologs (Loreau et al. 2022, eLife), we revealed a staggered organisation of the two Drosophila titin homologs and found that one of the Drosophila titins extends over a length of 2.5 µm in larval sarcomeres (Schueder et al. 2022, eLife). This is significant as before our work the longest natively stretched sarcomeric protein was considered to be human titin, with a length of < 2 µm.
For the first time, our cryo-ET structures of mouse psoas muscle revealed the three-dimensional organization of the sarcomere, the different organization of myosin double heads and uncovered that alpha-actinin forms an irregular mesh of double cross-links between antiparallel actin filaments (Wang, Grange et al. 2021, Cell). Our recent cryo-ET structure of the thin filament from skeletal mouse muscle (Wang, Grange et al. 2022, Science) represents the highest resolution structure of a filament determined in situ and the only pseudo-atomic structure determined from tissues after cryo focused-ion-laser beam milling to date. Fundamentally, this study represents a leap in capability for structural biology and the ability to perform atomic-level structural analyses within native tissue will be at the forefront of molecular diagnostics in the years to come. In general our results highlight the strength of our synergistic approach integrating information from fly, fish and mammalian sarcomeres. In the next funding period we expect to obtain structures of the thick filament in relaxed and contracted states and of other sarcomeric domains from Drosophila, zebrafish and mouse. In addition, we plan to put our focus on objective 3, namely the investigation of the sarcomere structure and maintenance during muscle ageing.
