Cytochalasin B is a poison produced by fungi, known as a mycotoxin. It is able to permeate cell membranes, allowing it to damage cells without membrane damage. Once inside, it can execute a variety of negative effects due to its ability to shorten actin filaments.
Actin is a protein used in the construction of cell structures, such as microfilaments. Cytochalasin B blocks actin units from being added to filaments, halting their growth. Microfilaments are essential to cytoplasmic division, so cytochalasin B effectively keeps cells from dividing. This mycotoxin also causes nuclear extrusion, or a deformation of the cell nucleus, by the same mechanism.
Microfilaments help to hold deoxyribonucleic acid (DNA) in place inside of the cell. The action of cytochalasin B on these filaments, therefore, causes DNA to fragment. The extension of actin filaments also plays a role in cell movement and phagocytosis, a process cells use to take up foreign objects. Studies have shown that the presence of different cytochalasins inhibit both of these actions, as well.
Through a similar mechanism, cytochalasin B prevents the transport of glucose and other sugars across cell membranes. It also prevents platelets from aggregating, or joining together. When platelets aggregate to close wounds, their actin filaments actually shorten. By binding to the end of actin filaments, this cytochalasin also prevents the filament units from dissociating, effectively stopping filament contraction.
Cytochalasin B has found some commercial use in cloning experiments. In the nuclear transfer process, egg cells without nuclei receive nuclei from a foreign organism. The recipient egg cells are treated with a stain containing this mycotoxin. The cytochalasin makes the cell walls smoother. The subsequent lack of resistance allows micro-needles to easily inject a nucleus into the cell without rupturing it.
To conserve resources, or if they are infected, cells will sometimes undergo a programmed death known as apoptosis. This process consists of the cell cleaving its DNA, and undergoing changes in form. While cytochalasin B does not prevent the cleavage of DNA, it does prevent the apoptotic body from forming, essentially arresting the process.
Cytochalasin B is not produced by many fungi, but is commercially available due to its many uses. In addition to cloning, researchers use it to learn about the actions of microfilaments and their importance. Cell signaling studies also use this compound to remove certain receptors from cell membranes. This can help researchers determine what role these receptors play in cellular activities.