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Abstract
Fruit fly (Drosophila melanogaster) is one of the most useful animal models to study the causes and effects of hereditary diseases because of its rich genetic resources. It is especially suitable for studying myopathies caused by myosin mutations, because specific mutations can be induced to the flight muscle-specific myosin isoform, while leaving other isoforms intact. Here we describe an X-ray-diffraction-based method to evaluate the structural effects of mutations in contractile proteins in Drosophila indirect flight muscle. Specifically, we describe the effect of the headless myosin mutation, Mhc10-Y97, in which the motor domain of the myosin head is deleted, on the X-ray diffraction pattern. The loss of general integrity of the filament lattice is evident from the pattern. A striking observation, however, is the prominent meridional reflection at d = 14.5 nm, a hallmark for the regularity of the myosin-containing thick filament. This reflection has long been considered to arise mainly from the myosin head, but taking the 6th actin layer line reflection as an internal control, the 14.5-nm reflection is even stronger than that of wild-type muscle. We confirmed these results via electron microscopy, wherein image analysis revealed structures with a similar periodicity. These observations have major implications on the interpretation of myosin-based reflections.
Highlights
Despite the long phylogenic distance between humans and insects, striking similarities exist in the structure of their muscles
Electron microscopy of the flight muscle in this mutant has shown that the rod molecules form thick filaments with hollow centers as in wild type, and that these thick filaments are often surrounded by thin filaments and form a hexagonal lattice, but the integrity of the whole myofibrils is inferior to that in wild type (Cripps et al, 1999)
MOUNTING TECHNIQUES FOR DROSOPHILA FLIGHT MUSCLE The length of the indirect flight muscle fibers of D. melanogaster is only ∼1 mm, and it is very difficult to mount both ends with metal foil clips, as would often be done with longer specimens, while keeping the myofibrils straight. 2-D diffraction patterns from Drosophila flight muscles have been recorded from whole live insects by using two configurations
Summary
Despite the long phylogenic distance between humans and insects, striking similarities exist in the structure of their muscles Both the skeletal or cardiac muscles of vertebrates and somatic muscles of insects are cross-striated, have similar sarcomeric structure and are regulated by the thin-filament-based system involving troponin and tropomyosin. In this respect, Drosophila melanogaster is one of the best-suited model animals to study congenital myopathies that occur in humans, owing to its rich genetic resources and ease of breeding. Electron microscopy of the flight muscle in this mutant has shown that the rod molecules form thick filaments with hollow centers as in wild type, and that these thick filaments are often surrounded by thin filaments and form a hexagonal lattice, but the integrity of the whole myofibrils is inferior to that in wild type (Cripps et al, 1999)
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