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FINE STRUCTURE AND SIZE DISTRIBUTION OF FREE THICK FILAMENTS IN EARLY FIBRILLOGENESIS OF ASCIDIAN TADPOLE
Author(s) -
TERAKADO KIYOSHI
Publication year - 1975
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1111/j.1440-169x.1975.00355.x
Subject(s) - protein filament , myofibril , biophysics , myosin , intermediate filament , treadmilling , electron microscope , tadpole (physics) , chemistry , anatomy , materials science , biology , microfilament , optics , cytoskeleton , composite material , cell , physics , biochemistry , particle physics
The development and the size distribution of free thick filaments which accumulate in the early stages of myofibril formation in somitic myoblasts of the ascidian tadpole were studied by electron microscopy. Such filaments appeared in the cell cortex but, rather dominantly, the aggregates of these thick filaments and filamentous structures were observed in the interior of the cell. The aggregate consisted of some of the following elements: filamentous structures (20–60 A in diameter); free thick filaments (60–220 A); dense Z‐band precursor materials; bundles of thick (140–160 A) and thin (60–70 A) filaments; and ribosomal clusters. The free thick filaments were variable in diameter and showed long lateral projections (300–600 A) and tapered ends. The variation curve in diameter of the free thick filaments indicates a continuous size distribution, suggesting the continuous growth of these filaments by polymerization of myosin molecules. Free thick filaments thicker than myosin filaments which were found within myofibrils were present; their significance is discussed in relation to myosin filament formation.