ABSTRACT
An in vitro method is described whereby it is possible to perform transection and extirpation experiments on the young mouse embryo.
Mouse embryos having 4 – 7 (rarely 8) somites at the beginning of culture were incubated for 18 – 20 hr. Intact embryos added 6 – 10 somites, the number depending on the number at the beginning of culture. Other systems, particularly gut and heart, showed even greater differentiation.
The axial level at which they were transected determined the ways in which the transected embryos differed from the intact embryos. Notochord lengths in the cut embryos varied with the experiment but the base of the notochord was always present and at the same level. The neural folds closed or remained open depending on whether or not somitic mesoderm fused under them. Fusion of somitic mesoderm was affected by the presence or absence of notochord. The number of new somites formed, however, was unaffected by the experimental manipulations and all were found to come from cells located anterior to the node at the beginning of culture. Gut differentiation was unchanged.
The results of all experiments were similar to those obtained from experiments in the chick.