Cell cycles in the early development of axolotl.

In axolotl embryos, during the course of development, the generation time increases, chiefly on account of a lengthening of the phase of DNA synthesis, the longest in the cell cycle. At the stages of the middle blastula and early gastrula, the G1 phase is shorter than in the G2 phase, while at the neurula stage, the G1 phase is far longer than the G2 phase. Cells of the chordamesoderm pass through the cycle nonuniformly during gastrulation: a period with a very low index of labeled nuclei and slow entry of cells into the S phase gives way to a period of their intensive entry into the S-phase.