Cell cycle remodeling requires cell-cell interactions in developing Xenopus embryos.

Flow cytometric analysis has revealed a general remodeling of the cell cycle in developing Xenopus embryos. During early gastrulation the cell cycle is dominated by S phase, with 82% of all interphase nuclei in the S phase fraction. As development proceeds over the next 60 hours, a gradual decline in S phase cells is proportional to an increase in the number of cells in G1. By the late tailbud stage, 85% of all nuclei are found in the G1 fraction, approximating the cell cycle profile of adult somatic cells. Cell cycle remodeling occurs on schedule even in embryos that have been dissociated into a loose mound of cells which remain in close proximity to one another. However, cells that have been widely separated by manual dispersion do not undergo remodeling. These dispersed cells maintain an S phase-dominated cell cycle and continue to show patterns of blastula and gastrula gene expression at least 30 hours beyond gastrulation. We conclude that cell cycle remodeling occurs in the absence of an intact embryo but requires the inductive influences associated with a community of cells.