Key result
Nanobodies combined with DNA-PAINT super-resolution microscopy revealed that Sallimus bridges across the flight muscle I-band and Projectin is located at the beginning of the A-band, with their ends overlapping.
Why the study?
The instructive role of titins for sarcomeric architecture outside of vertebrates is not well understood.
The study reveals a staggered organization of Drosophila titin homologs Sallimus and Projectin at the I-band/A-band border, providing insights into sarcomeric architecture and force transduction in flight muscles.
Titin's role outside vertebrates remains unclear; leaves open whether similar mechanisms determine sarcomere architecture in invertebrates.
Sarcomeres are the force producing units of all striated muscles. Their nanoarchitecture critically depends on the large titin protein, which in vertebrates spans from the sarcomeric Z-disc to the M-band and hence links actin and myosin filaments stably together. This ensures sarcomeric integrity and determines the length of vertebrate sarcomeres. However, the instructive role of titins for sarcomeric architecture outside of vertebrates is not as well understood. Here, we used a series of nanobodies, the Drosophila titin nanobody toolbox, recognising specific domains of the two Drosophila titin homologs Sallimus and Projectin to determine their precise location in intact flight muscles. By combining nanobodies with DNA-PAINT super- resolution microscopy, we found that, similar to vertebrate titin, Sallimus bridges across the flight muscle I-band, whereas Projectin is located at the beginning of the A- band. Interestingly, the ends of both proteins overlap at the I-band/A-band border, revealing a staggered organisation of the two Drosophila titin homologs. This architecture may help to stably anchor Sallimus at the myosin filament and hence ensure efficient force transduction during flight.
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Schueder et al. (2022) studied Drosophila flight muscle sarcomere architecture. Nanobodies combined with DNA-PAINT super-resolution microscopy was evaluated on Precise location of Sallimus and Projectin domains in intact flight muscles. Nanobodies combined with DNA-PAINT super-resolution microscopy revealed that Sallimus bridges across the flight muscle I-band and Projectin is located at the beginning of the A-band, with their ends overlapping.
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