Overview Cell Structures Cell Migration Cell Division  

Assembly of Myofibrils in Developing Myotubes

McKenna et al., J. Cell Biol. 103:2163-2171 (1986)

Mature muscle cells contain highly organized myofibrils, which consist of well aligned sarcomeres. During embryonic development, sarcomere assembly starts as randomly distributed contractile units, which gradually turn into an organized array of myofibrils. To study this process, fluorescently labeled alpha-actinin was microinjected into developing chick myotubes to label the Z-lines (where actin filaments are anchored) and their precursors.

Merger of Punctate Z-Bodies

Precursors of Z-lines are punctate structures referred to as Z-bodies. During development these Z-bodies merge into short lines with a characteristic spacing. Neighboring short Z-lines then merge to form long Z-lines across the myotube. Recording time, 4 hours.

Correction of Misalignment and Registration of Neighboring Myofibrils

The alignment of Z-lines is a trial-and-error process: Z-lines of neighboring myofibrils constantly associate and dissociate. Misaligned associations are unstable and are gradually replaced by correct, more stable associations. Recording time, 4 hours (upper), 7.5 hours (lower).