  Cell cycle is an indispensable process in the proliferation and development.
Despite significant efforts, global quantification and physical understanding
are still challenging. In this study, we explored the mechanisms of Xenopus
laevis embryonic cell cycle by quantifying the underlying landscape and flux.
We uncovered the irregular Mexican hat landscape of the Xenopus laevis
embryonic cell cycle with several local basins and barriers on the oscillation
path. The local basins characterize the different phases of Xenopus laevis
embryonic cell cycle and the local barriers represent the checkpoints. The
checkpoint mechanism of cell cycle is revealed by the landscape basins and
barriers. While landscape shape determines the stabilities of the states on the
oscillation path, the curl flux force determines the stability of the cell
cycle flow. Replication is fundamental for biology of living. From our
quantitative study here, we see that replication can not proceed without energy
input. In fact, the curl flux originated from energy or nutrition supply
determines the speed of the cell cycle and guarantees the progression. Speed of
cell cycle is a hallmark of cancer. Through landscape and flux analysis, one
can identify the key elements for controlling the speed. This can help to
design effective strategy for drug discovery against cancer.
