Multinucleated

Multinucleated refers to a cell or cellular structure that contains more than one nucleus within a shared cytoplasm. Multinucleation can arise when nuclei divide without cytokinesis (karyokinesis without cytokinesis) or when individual cells fuse, producing a single, multinucleated cell. It is distinct from polyploid cells, which have multiple genome copies within a single nucleus rather than multiple nuclei.

Multinucleation occurs in several physiological contexts. In skeletal muscle, myoblasts fuse during development and repair to form multinucleated muscle fibers that can span long distances and coordinate contraction. Osteoclasts, the bone-resorbing cells, are also multinucleated, formed by the fusion of mononuclear precursors. In the placenta, the syncytiotrophoblast is a multinucleated layer that facilitates nutrient and gas exchange between mother and fetus.

Mechanisms underlying multinucleation vary by tissue. Muscle fusion involves specific fusogenic proteins, such as myomaker and myomixer, that promote plasma membrane merging. Osteoclast formation is driven by signals like RANKL and M-CSF that stimulate precursor cell fusion. Multinucleation can also occur as a response to injury or infection, in which multinucleated giant cells derive from macrophage fusion and participate in granulomatous inflammation.

Clinical and diagnostic relevance varies with context. Normal multinucleation is essential for the function of skeletal muscle, osteoclasts, and placental tissue. Abnormal or excessive multinucleation can be observed in certain diseases or tumors, including giant cell–forming lesions. Histological examination typically reveals discrete nuclei within a common cytoplasm, distinguishing multinucleated cells from mononuclear cells.