Although most cells that compose
animal organs contain single nuclei, certain kinds of cells are multinucleated.
Multi nucleation is known to be caused by either cell fusion (as in skeletal muscle or placental trophoblast) or mitosis without cytokinesis (as in
hepatocytes or myocytes) and is thought to be a process of tissue/cell growth.
In this case, the numbers of chromosome copies and nuclei in each cell
increase. In other cases of tissue/cell growth such as cell division and endo replication (chromosomal doubling without karyokinesis), only a single nucleus per cell exists. It is known that binucleation of hepatocytes or
myocytes occurs according to the growth of individuals. In rat hepatocytes, the
proportion of binucleate cells increase in the transition from suckling to
weaning, and the rate of binucleation is controlled by nutrient signaling. In
rat myocytes, cells predominantly binucleate by 10 days after birth. However,
the functional benefits for organs by increasing the number of nuclei are
largely unclear.