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 ce ll 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 nucle i are found in the G1 fraction, approximating the cell cycle profile o f adult somatic cells. Cell cycle remodeling occurs on schedule even i n embryos that have been dissociated into a loose mound of cells which remain in close proximity to one another. However, cells that have be en widely separated by manual dispersion do not undergo remodeling. Th ese dispersed cells maintain an S phase-dominated cell cycle and conti nue 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 i nfluences associated with a community of cells. (C) 1994 Wiley-Liss, I nc.