Various DNA content in myotube nuclei during myotomal myogenesis in Hymenochirus boettgeri (Anura: Pipidae).

During myotomal myogenesis in Hymenochirus boettgeri primary myoblasts differentiate into morphologically and functionally mature, mononucleate myotubes. Further muscle development in the studied species is due to fusion of mesenchymal cells with the latter, resulting in the presence of two classes of nuclei in the myotube: large of myotomal origin and small of mesenchymal origin. Densitometric measurements of DNA content revealed that the myotube nuclei at stages 35 reached values close to 4C DNA (3, 3C DNA), while at a later stage (42) the values were equal to 4C. Conversely, the secondary myoblast nuclei following the fusion with the myotube at stage 42 had 2C DNA--a content comparable to that found in erythrocyte nuclei. PCNA (Proliferating Cell Nuclear Antigen)--marker of S-phase of cell cycle, detected in the myotube nuclei (at stages 35, 42) appears during DNA replication.