Cell cycle analysis and synchronization of the Xenopus cell line XL2

We have determined the length of the cell cycle and its different phases in a permanent Xenopus tadpole cell line, XL2. Following BrdU labeling, the total length of the cell cycle was estimated as 28 h. The different phases of the cell cycle, G1, S, G2, and M were, respectively, 14 h, 10 h 45 min, 2 h 30 min, and 54 min. Knowing these parameters, we were able to develop methods that selectively enrich cells in different phases of the cycle. Treatment with aphidicolin resulted in a S phase block in which more than 85% of the cells showed S phase chromosomes. Almost 60% of the cells were arrested in mitosis after a double block with aphidicolin/nocodazole or aphidicolin/ALLN (acetyl-leucyl-leucyl-norleucinal) treatment. This synchronization protocol will greatly facilitate studies of biochemical events associated with specific gene regulation through the cell cycle. Our synchronization protocol does not disturb cell metabolism as the expression of cyclin B2 during the cell cycle is in agreement with the results obtained with mammalian cells.