Flightin Is Necessary for Length Determination, Structural Integrity, and Large Bending Stiffness of Insect Flight Muscle Thick Filaments

• Published in: Journal of molecular biology Vol. 395; no. 2; pp. 340 - 348
• Main Authors: Contompasis, John L., Nyland, Lori R., Maughan, David W., Vigoreaux, Jim O.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15-01-2010
• Subjects: Animals; atomic force microscopy; Biomechanical Phenomena; Drosophila; Drosophila melanogaster - genetics; Drosophila melanogaster - physiology; Drosophila melanogaster - ultrastructure; Drosophila Proteins - deficiency; Drosophila Proteins - genetics; Drosophila Proteins - physiology; Filamins; Flight, Animal - physiology; flightin; Genes, Insect; insect flight muscle; Microscopy, Atomic Force; Molecular Motor Proteins - deficiency; Molecular Motor Proteins - genetics; Molecular Motor Proteins - physiology; Muscle Proteins - deficiency; Muscle Proteins - genetics; Muscle Proteins - physiology; Muscle, Skeletal - physiology; Muscle, Skeletal - ultrastructure; Mutation; persistence length; thick filaments; IFM; flightin; fln 0; AFM; thick filaments; persistence length; atomic force microscopy; MyBP-C; SPL; insect flight muscle
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2009.11.021

Despite the fundamental role of thick filaments in muscle contraction, little is known about the mechanical behavior of these filaments and how myosin-associated proteins dictate differences between muscle types. In this study, we used atomic force microscopy to study the morphological and mechanical properties of fully hydrated native thick filaments isolated from indirect flight muscle (IFM) of normal and mutant
Drosophila lacking flightin (
fln
0
). IFM thick filaments from newly eclosed (0–1 h old) wild-type flies have a mean length of 3.04
±
0.05 μm. In contrast, IFM thick filaments from newly eclosed
fln
0
flies are more variable in length and, on average, are significantly longer (3.90
±
1.33 μm) than wild-type filaments from flies of the same age. In the absence of flightin, thick filaments can attain lengths >
300% of wild-type filaments, indicating that flightin is required for setting the proper filament length
in vivo. Filaments lacking flightin are structurally compromised, and filament preparations from fully matured 3- to 5-day-old adult
fln
0
IFM yielded fragments of variable length much shorter than 3.20
±
0.04 μm, the length obtained from wild-type flies of similar age. The persistence length, an index of bending stiffness, was calculated from measurements of filament end-to-end length and contour length. We show that the presence of flightin increases persistence length by more than 40% and that wild-type filaments increase in stiffness with age. These results indicate that flightin fulfills an essential role in defining the structural and mechanical properties of IFM thick filaments.