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Multinucleate cells (also called multinucleated or polynuclear cells) are eukaryotic cells that have more than one nucleus per cell, i.e., multiple nuclei share one common cytoplasm. Mitosis in multinucleate cells can occur either in a coordinated, synchronous manner where all nuclei divide simultaneously or asynchronously where individual nuclei divide independently in time and space. The multinucleate stage in the life cycle of some organisms is called plasmodium.
Although not normally viewed as a case of multinucleation, plant cells share a common cytoplasm by plasmodesmata, and most cells in animal tissues are in communication with their neighbors via gap junctions.
Multinucleate cells, depending on the mechanism they are formed, can be divided into "syncytia" (formed by cell fusion) or "coenocytes" (formed by nuclear division not being followed by cytokinesis).
Some biologists use the term "acellular" to refer to multinucleate cell forms (syncitia and plasmodia), such as to differentiate "acellular" slime molds from the purely "cellular" ones (which do not form such structures). This usage is incorrect and highly misleading to laymen, and as such it is strongly discouraged.
Syncytia (cell fusion without karyogamy)
Multinucleate cells can occur naturally under physiological conditions by the fusion of the plasma membranes of cells thus forming syncytia. Examples include the skeletal muscle cells of mammals, the tapetal cells of plants, and the storage cells of Douglas-fir seeds. The polymorphonuclear leukocytes of mammals are not polynuclear cells, although the lobes of their nuclei are so deeply bifurcated that they can appear so under suboptimal microscopy.
Osteoclasts are multinucleated cells which are found commonly in the human body that aid in the maintenance and repair of the bones by secreting acid that dissolves bone matter. They are typically found to have 5 nuclei per cell, due to the fusion of preosteoclasts.
The chlorarachniophytes form multinucleate cells by fusion, being syncytia and not coenocytes. This syncytia is called plasmodium, in the sense of a multinucleate protoplast without a cell wall which exhibits amoeboid movement. Other examples include some plasmodiophorids, some haplosporidians, and the grex of cellular slime moulds (dictyostelids and acrasids).
Coenocytes (karyokinesis without cytokinesis)
Furthermore, multinucleate cells are produced from specialized cell cycles in which nuclear division occurs without cytokinesis, thus leading to large coenocytes or plasmodia. In filamentous fungi, multinucleate cells may extend over hundreds of meters so that different regions of a single cell experience dramatically different microenvironments. Other examples include, the plasmodia of plasmodial slime molds (myxogastrids) and the schizont of the Plasmodium parasite which causes malaria.
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