[Show abstract][Hide abstract] ABSTRACT: Three populations of myoblasts, embryonic, foetal and adult, appear sequentially during myogenesis. The present study uses retroviruses to mark myoblasts clones in vivo from these populations. Myoblasts labelled at E15 (embryonic) contributed to primary fibres only. The majority of marked primary fibres were slow but a small number of clones contained marked primaries which were no longer slow at E19. Myoblasts labelled at E17 (foetal) fused with both primary and secondary fibres and most clones contained both fast and slow fibres. Similarly, adult myoblasts marked at P0 fused with all fibre types. These results indicate that embryonic myoblasts are restricted to producing only primary fibres which are initially slow but which can convert to being fast. Clones of foetal and adult myoblasts fuse with both primary and secondary fibres which may be either fast or slow.
Full-text · Article · Oct 1999 · Mechanisms of Development
[Show abstract][Hide abstract] ABSTRACT: Adult muscle is composed of different fiber types distinguished by their speed of contraction and metabolism. The generation of these differences is related both to the sequence in which muscle fibers form and to differences between the myogenic cells involved. Fibers form in two successive waves (primary and secondary) whose time of appearance can be correlated with the existence of successive populations of myogenic cells (embryonic and fetal). The differences between fibers arise through an interplay between heritable cellular commitment, where cells are preprogrammed to produce particular types of fiber and influences from the limb environment. The techniques of genetically marking cells and clonal analysis in vivo and in vitro are starting to reveal the relationship between these different influences. Although the process of myogenesis is similar in birds and mammals it is likely that cell autonomous behaviour plays a more important role during avian development as compared to mammals. The identification of muscle specific transcription factors has provided some clues to the mechanisms by which development is controlled but the expression of relatively few of these has been correlated with the sequence of events seen in myogenesis.
No preview · Article · Mar 1998 · The International Journal of Developmental Biology