Cytochalasin B is an inhibitor of actin polymerization, which binds to the positive (+) terminal of F- actin and prevents the function of F- actin. Cytochalasin D (CD) or B (dihydrocytochalasin B (DCB) has studied the function of actin, and found that actin constitutes microfilament of cytoskeleton in cytoplasm, which is related to many life activities such as cytoplasmic flow, deformation movement, cell morphology maintenance, cell membrane dynamic change and organelle movement. Actin in the nucleus may be related to the localization and directional movement of the nucleus, the formation of cleavage furrow during cytokinesis and the maintenance of multiline chromosome structure. The results obtained by injecting anti-actin antibody or actin binding protein show that actin can affect chromosome condensation, chromosome structural state adjustment and gene transcription. There are few reports about whether actin is involved in cell cycle regulation.

Cytochalasin B was injected into synchronized Plasmodium physarum polycephalum, and the mitotic process was observed under light and electron microscope. It was found that the mitotic time of physarum polycephalum was delayed, and the mitotic time of S phase samples injected with CB was delayed by 35 minutes. Compared with the sample without CB treatment. Samples injected with CB in the early G2 phase were delayed for 20 minutes. In G2 metaphase, the injection was delayed for 45 minutes; The delay of injection for 60 minutes in the late G2 phase indicates that the inhibition of actin function significantly affects mitosis. The whole time course and dynamic changes of nuclear structure of CB-treated samples after mitosis are basically the same as those of untreated samples, indicating that the influence of CB-treated samples on mitosis may be mainly to delay the start of mitosis. CB treatment in the late G2 stage has the most obvious effect on mitotic initiation, which indicates that there may be a mitotic checkpoint in physarum polycephalum in the late G2 stage.