Myofilin, a protein in the thick filaments of insect muscle

Thick filaments in striated muscle are myosin polymers with a length and diameter that depend on the fibre type. In invertebrates, the length of the thick filaments varies widely in different muscles and additional proteins control filament assembly. Thick filaments in asynchronous insect flight mus...

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Bibliographic Details
Published in:	Journal of cell science Vol. 118; no. 7; pp. 1527 - 1536
Main Authors:	Qiu, Feng, Brendel, Sigrun, Cunha, Paulo M. F, Astola, Nagore, Song, Bauzhen, Furlong, Eileen E. M, Leonard, Kevin R, Bullard, Belinda
Format:	Journal Article
Language:	English
Published:	England 01-04-2005
Subjects:	Alternative Splicing Amino Acid Sequence Animals Anopheles Cloning, Molecular Drosophila Drosophila Proteins - chemistry Drosophila Proteins - genetics Drosophila Proteins - metabolism Filamins Hemiptera Insect Proteins - chemistry Insect Proteins - genetics Insect Proteins - metabolism Lethocerus Molecular Sequence Data Muscle Proteins - chemistry Muscle Proteins - genetics Muscle Proteins - metabolism Muscle, Skeletal - chemistry Muscle, Skeletal - ultrastructure Protein Isoforms - chemistry Protein Isoforms - genetics Protein Isoforms - metabolism Recombinant Proteins - genetics
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Summary:	Thick filaments in striated muscle are myosin polymers with a length and diameter that depend on the fibre type. In invertebrates, the length of the thick filaments varies widely in different muscles and additional proteins control filament assembly. Thick filaments in asynchronous insect flight muscle have an extremely regular structure, which is likely to be essential for the oscillatory contraction of these muscles. The factors controlling the assembly of thick filaments in insect flight muscle are not known. We previously identified a thick filament core protein, zeelin 1, in Lethocerus flight and non-flight muscles. This has been sequenced, and the corresponding proteins in Drosophila and Anopheles have been identified. The protein has been re-named myofilin. Zeelin 2, which is on the outside of Lethocerus flight muscle thick filaments, has been sequenced and because of the similarity to Drosophila flightin, is re-named flightin. In Drosophila flight muscle, myofilin has a molecular weight of 20 kDa and is one of five isoforms produced from a single gene. In situ hybridisation of Drosophila embryos showed that myofilin RNA is first expressed late in embryogenesis at stage 15, a little later than myosin. Antibody to myofilin labelled the entire A-band, except for the H-zone, in cryosections of flight and non-flight muscle. The periodicity of myofilin in Drosophila flight muscle thick filaments was found to be 30 nm by measuring the spacing of gold particles in labelled cryosections; this is about twice the 14.5 nm spacing of myosin molecules. The molar ratio of myofilin to myosin in indirect flight muscle is 1:2, which is the same as that of flightin. We propose a model for the association of these proteins in thick filaments, which is consistent with the periodicity and stoichiometry. Myofilin is probably needed for filament assembly in all muscles, and flightin for stability of flight muscle thick filaments in adult flies.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0021-9533 1477-9137
DOI:	10.1242/jcs.02281