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Assembly of thick filaments and myofibrils occurs in the absence of the myosin head
Author(s) -
Cripps Richard M.,
Suggs Jennifer A.,
Bernstein Sanford I.
Publication year - 1999
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/18.7.1793
Subject(s) - biology , myofibril , myosin , myosin head , head (geology) , actin , biophysics , microbiology and biotechnology , anatomy , biochemistry , myosin light chain kinase , paleontology
We investigated the importance of the myosin head in thick filament formation and myofibrillogenesis by generating transgenic Drosophila lines expressing either an embryonic or an adult isoform of the myosin rod in their indirect flight muscles. The headless myosin molecules retain the regulatory light‐chain binding site, the α‐helical rod and the C‐terminal tailpiece. Both isoforms of headless myosin co‐assemble with endogenous full‐length myosin in wild‐type muscle cells. However, rod polypeptides interfere with muscle function and cause a flightless phenotype. Electron microscopy demonstrates that this results from an antimorphic effect upon myofibril assembly. Thick filaments assemble when the myosin rod is expressed in mutant indirect flight muscles where no full‐length myosin heavy chain is produced. These filaments show the characteristic hollow cross‐section observed in wild type. The headless thick filaments can assemble with thin filaments into hexagonally packed arrays resembling normal myofibrils. However, thick filament length as well as sarcomere length and myofibril shape are abnormal. Therefore, thick filament assembly and many aspects of myofibrillogenesis are independent of the myosin head and these processes are regulated by the myosin rod and tailpiece. However, interaction of the myosin head with other myofibrillar components is necessary for defining filament length and myofibril dimensions.