Résumé
This chapter discusses myogenesis in Xenopus embryos. Axial Muscle derives from the somites, which in turn come from mesoderm tissue that is invaginated during gastrulation. The location of the mesoderm as seen during gastrulation is more complicated in Xenopus than in other amphibians. Lineage labeling studies have shown that two blastomeres of the 32-cell stage contribute to the embryonic heart. During gastrulation, the regions of mesoderm destined to form the heart tube are found on either side of the dorsal lip and are distinct from the somitic mesoderm. By the end of gastrulation, these are arranged bilaterally, at the anterior edge of the newly forming neural plate. After gastrulation, it is sometimes useful to be able to dissect embryos into different tissues. Xenopus embryos are large enough that direct biochemical analyses can be carried out on tissues from only a few embryos. Interestingly, tissues among which an induction is taking place tend to be tightly adherent to each other and difficult to separate. A 0.3% solution of commercial collagenase in 1 X modified Barth's saline (MBS) is very helpful in enabling tissues to be separated by gentle action with needles. However, it is essential first to break the very impermeable surface coat of embryos by removing the endoderm.