This presumably prevents nuclear fusion from occurring during mitosis in the multinucleate syncytium. The plates are covered by the epidermis, which consists of a smooth syncytium. Astrocytes are linked by gap junctions, creating an electrically coupled (functional) syncytium. This is a special type of syncytium. Digestion is accomplished by means of a syncytium that forms a vacuole around ingested food. Recruitment of bystander cells into the syncytium leads to significant regression of the tumor. Another important vertebrate syncytium is in the placenta of placental mammals. This method involves the action of morphogen gradients within the syncytium. A classic example of a syncytium is the formation of skeletal muscle. It also plays a role in the formation and expression of HLA-G in the syncytium. An increase in intracellular calcium concentration can propagate outwards through this functional syncytium. Inhibition of syncytium formation occurred with an IC50 of 150 micrograms/ml. This fusion leads to the formation of a large multi-nuclear structure (syncytium). It is also unique among model organisms in that cleavage occurs in a syncytium. Each syncytium obeys the all or none law.