Biochemistry. A fungal metabolite that interferes with the assembly of microfilaments in the cell. Thereby, it inhibits cellular activities, such as movement, without affecting certain changes that take place in the cell nucleus before cell division.
Cytochalasin B is for example used in the micronucleus test in cell cultures. The cell nucleus is divided however the cell division (cytokinesis) is blocked by cytochalasin B. Thus the cell has two nuclei and sometimes also micronuclei.