Amultinucleate cell (also known asmultinucleated cell orpolynuclear cell) is aeukaryotic cell that has more than onenucleus, i.e., multiple nuclei share one commoncytoplasm.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. Certain organisms may have a multinuclear stage of their life cycle. For example,slime molds have a vegetative, multinucleate life stage called aplasmodium.[1]
Multinucleate cells, depending on the mechanism by which they are formed, can be divided into[2][3] "syncytia" (formed bycell fusion) or "coenocytes" (formed bynuclear division not followed bycytokinesis).[4]
Somebacteria, such asMycoplasma pneumoniae, apathogen of therespiratory tract, may display multinuclear filaments as a result of a delay between genome replication andcellular division.[5]
Some biologists use the term "acellular" to refer to multinucleate cell forms (syncitia andplasmodia), such as to differentiate "acellular" slime molds from the purely "cellular" ones (which do not form such structures).[6][7][8] This usage is incorrect and highly misleading tolaymen, and as such it is discouraged.
Some use the term "syncytium" in a wide sense, to mean any type of multinucleate cell,[9] while others differentiate the terms for each type.[10]
Syncytia are multinuclear cells that can form either through normal biological processes, such as the mammalianplacenta, or under the influence of certain pathogens, such asHIV, via fusion of the plasma membrane.[11][12] Other examples include theskeletal muscle cells ofmammals, thetapetal cells ofplants, and the storage cells ofDouglas-fir seeds.[13] Thepolymorphonuclear leukocytes of mammals are not polynuclear cells, although the lobes of their nuclei are so deeply bifurcated that they can appear so under non-optimal microscopy.
Osteoclasts are multinuclear cells that 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 5nuclei per cell, due to the fusion of preosteoclasts.
Thechlorarachniophytes form multinucleate cells by fusion, being syncytia and not coenocytes. This syncytia is calledplasmodium, in the sense of a multinucleateprotoplast without acell wall which exhibitsamoeboid movement.[14] Other examples include someplasmodiophorids, somehaplosporidians,[15] and thegrex ofcellular slime moulds (dictyostelids andacrasids).
Theplacenta, a temporary organ that transports nutrients, oxygen, waste, and other materials between a mother and a developing fetus, is partially composed of asyncytial layer that forms the interface between the foetus and the mother.[16] In addition to performing simple interface duties, the placental syncytia also acts as a barrier to infection fromviruses,bacteria, andprotozoa, which is likely due to uniquecytoskeletal properties of these cells.[16]
Furthermore, multinucleate cells are produced from specializedcell cycles in which nuclear division occurs without cytokinesis, thus leading to large coenocytes or plasmodia. Infilamentous fungi, multinucleate cells may extend over hundreds of meters so that different regions of a single cell experience dramatically different microenvironments. Other examples include, theplasmodia ofplasmodial slime molds (myxogastrids) and theschizont of thePlasmodiumparasite which causesmalaria.
Multinucleated cells can also occur under pathological conditions as the consequence of a disturbedcell cycle control (e.g., somebinucleated cells and metastasizingtumor cells).
As previously mentioned, syncytia may be induced through the actions of HIV, whereT-cells are fused by the action of virus-derivedproteins on thecell membrane.[12] During viral replication in Tlymphoid cells, large amounts ofviral envelopeGlycoprotein (Env) are synthesized and trafficked to the cell membrane where they can be incorporated into new virus particles. However, some of the Env molecules interact with neighboringT-cell receptors, which brings the cells into close enough proximity to enable trigger events culminating in the fusion of two host cells, likely due to the close contact of the two plasma membranes.[17] This interaction is likely specific toCD4+ T-cells, as cells lacking this receptor were unable to form syncytia in laboratory conditions.[18]
Although not normally viewed as a case of multinucleation,plant cells share a common cytoplasm byplasmodesmata, and most cells inanimal tissues are in communication with their neighbors viagap junctions.[19]
Althoughendosymbiosis among eukaryotes can result in multiple nuclei in a cell, these are not considered "multinucleate" because the nuclei are not surrounded by the same cytoplasm. These extra nuclei are callednucleomorphs.