Ventral cell rearrangements contribute to anterior. Posterior axis lengthening between neurula and tailbud stages in Xenopus laevis

Studies of morphogenesis in early Xenopus embryos have focused primarily on gastrulation and neurulation. Immediately following these stages is another period of intense morphogenetic activity, the neurula-to-tailbud transition. During this period the embryo is transformed from the spherical shape of the early stages into the long, thin shape of the tailbud stages. While gastrulation and neurulation depend largely on active cell rearrangement and cell shape changes in dorsal tissues, we find that the neurula-to-tailbud transition depends in part on activities of ventral cells. Ventral explains of neurulae lengthen automously as much as the ventral sides of intact embryos, while dorsal explants lengthen less than the dorsal sides of intact embryos. Analyses of cell division, cell shapes, and cell rearrangement by transplantation of labeled cells and by time lapse recordings in live intact embryos concur that cell rearrangements in ventral mesoderm and ectoderm contribute to the autonomous anterior-posterior axis lengthening of ventral explants between neurula and tailbud stages.