Mechanism of multinucleate myotomal muscle fibre formation in Hymenochirus boettgeri (Anura, Pipidae) |
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Authors: | M Daczewska |
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Institution: | (1) Department of General Zoology and Laboratory of Evolutionary and Developmental Biology of Vertebrates, Zoological Institute, University of Wrocław, 50-335 Wrocław, Sienkiewicza 21, Poland e-mail: daczew@biol.uni.wroc.pl Tel.:+48-71-3225041, Fax:+48-71-3222817, PL |
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Abstract: | During somitogenesis in Hymenochirus boettgeri, somites separate from non-segmented mesoderm. Somite formation involves changes in position of myotomal cells from perpendicular
to parallel relative to axial organs; the changes are asynchronous and show a dorsoventral gradient. After the rotation has
been completed, the myotomal cells (primary myoblasts) occupy the whole length of the myotomes. MyoD is present in nuclei
of non-segmented mesoderm cells, of myotomal cells during their rotation and of myoblasts occupying the whole length of the
myotomes. The effect of MyoD which activates muscle-specific genes is confirmed by the appearance of skeletal α-actin in mononucleate
myoblasts in which myofibrils and the sarcotubular system develop. Differentiation of primary myoblasts results in development
of mononucleate, morphologically mature myotubes. Differentiating myotubes are initially not accompanied by any other cells.
In further developmental stages, mesenchymal cells appear in intermyotomal fissures and then in myotomes. Their role depends
on their position: mesenchymal cells remaining in the intermyotomal fissures differentiate into fibroblasts while those that
have migrated into the myotomes, between the myotubes, transform into secondary myoblasts. Their myogenic function is evidenced
by the presence of MyoD in their nuclei. These cells fuse with the already existing mononucleate myotubes, resulting in an
increase in their size and number of nuclei.
Accepted: 30 January 2001 |
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