A multinucleate cell (also known as multinucleated cell or polynuclear cell) is a eukaryotic cell that has more than one Cell nucleus, 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. Certain organisms may have a multinuclear stage of their life cycle. For example, have a vegetative, multinucleate life stage called a plasmodium.
Multinucleate cells, depending on the mechanism by which they are formed, can be divided into
Some bacteria, such as Mycoplasma pneumoniae, a pathogen of the respiratory tract, may display multinuclear filaments as a result of a delay between genome replication and cellular division.
Terminology
Some biologists use the term "acellular" to refer to multinucleate cell forms (
Syncytium 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 discouraged.
Some use the term "syncytium" in a wide sense, to mean any type of multinucleate cell,
Physiological examples
Syncytia
Syncytia are multinuclear cells that can form either through normal biological processes, such as the mammalian
placenta, or under the influence of certain pathogens, such as HIV, via fusion of the plasma membrane.
Other examples include the skeletal muscle cells of
mammals, the
of
, and the storage cells of
Douglas-fir seeds.
The
granulocyte 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.
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 5 cell nucleus 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.[Hoek, C. van den, Mann, D.G. and Jahns, H.M. (1995). Algae An Introduction to Phycology. Cambridge University Press, Cambridge] Other examples include some , some ,
Placenta
The
placenta, a temporary organ that transports nutrients, oxygen, waste, and other materials between a mother and a developing fetus, is partially composed of a syncytial layer that forms the interface between the foetus and the mother.
In addition to performing simple interface duties, the placental syncytia also acts as a barrier to infection from
Virus,
bacteria, and
protozoa, which is likely due to unique
Cytoskeleton properties of these cells.
Coenocytes
Furthermore, multinucleate cells are produced from specialized
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 (
) and the
schizont of the
Plasmodium parasite which causes
malaria.
Pathological examples
Multinucleated cells can also occur under pathological conditions as the consequence of a disturbed
cell cycle control (e.g., some binucleated cells and metastasizing
tumor cells).
Human Immunodeficiency Virus
As previously mentioned, syncytia may be induced through the actions of HIV, where
are fused by the action of virus-derived
Protein on the
cell membrane.
During viral replication in T
lymphoid cells, large amounts of
viral envelope Glycoprotein (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 neighboring
T-cell receptor, 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.
This interaction is likely specific to CD4+ T-cells, as cells lacking this receptor were unable to form syncytia in laboratory conditions.
Not multinucleate
Although not normally viewed as a case of multinucleation,
share a common cytoplasm by
, and most cells in
animal tissues are in communication with their neighbors via
.
Although endosymbiosis 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 called .
