In biology, a syncytium is a large region of cytoplasm that contains many nuclei. A syncytium can form in two ways. Many insects such as the model organism Drosophila melanogaster lay eggs that initially develop as syncytial blastoderms, i.e early on the embryos exhibit incomplete cell division. In particular, the nuclei undergo S-phase (they replicate their DNA) and sister chromatids get pulled apart and re-assembled into nuclei containing full sets of homologous chromosomes, but cytokinesis is absent. Thus, the nuclei multiply in a common cytoplasmic space of the zygote. Large skeletal muscle fibers form by the fusion of thousands of myocytes. Biology is a branch of science, dealing with the study of life. ... Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells and contains the nuclear genes which form most of the cells genetic material. ... Embryos (and one tadpole) of the wrinkled frog (Rana rugosa). ... Cells in culture, stained for keratin (red) and DNA (green). ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... A cell that has almost completed cytokinesis. ... This article or section does not cite its references or sources. ... A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, attached to the skeleton. ...

The early embryo syncytium of invertebrates such as Drosophila is important for syncitial specification of cell differentiation. The egg cell cytoplasm contains localized mRNA molecules such as those that encode the transcription factors Bicoid and Nanos. Bicoid protein is expressed in a gradient that extends from the anterior end of the early embryo while Nanos protein is concentrated at the posterior end (antero-posterior axis). At first, the nuclei of the early embryo rapidly and synchronously divide in the syncytial blastoderm an then migrate through the cytoplasm and position themselves in a monolayer around the periphery, leaving only a small number of nuclei in the center of the egg, which will become yolk nuclei. The position of the nuclei along the embryonic axes determines the relative exposure of different amounts of Bicoid, Nanos, and other morphogens. Those nuclei with more Bicoid will activate genes that promote differentiation of cells into head and thorax structures. Nuclei exposed to more Nanos will activate genes responsible for differentiation of posterior regions, such as the abdomen and germ cells. The same principles hold true for the specification of the dorso-ventral axis – higher concentration of nuclear Dorsal protein on the ventral side of the egg specify the ventral fate, whereas absence thereof allows dorsal fates. After the nuclei are positioned in a monolayer underneath the egg membrane, the membrane begins to slowly invaginate, thus separating the nuclei into cellular compartments; during this period, the egg is called a cellular blastoderm. The pole cells – the germline anlage – are the first cells to separate fully. Binomial name Drosophila melanogaster Meigen, 1830 Drosophila melanogaster Meigen , 1830 (Black-bellied Dew-lover) a dipteran (two-winged) insect, is the species of fruit fly that is commonly used in genetic experiments; it is among the most important model organisms. ... The interaction of mRNA in a eukaryote cell. ... In the context of genetics, a transcription factor is a regulatory protein that initiates the transcription of certain genes upon binding with DNA. The binding of a transcription factor to a specific DNA sequence can result in either an increased rate of transcription of the gene, known as activated transcription... Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ... A morphogen is a substance governing the shapes of tissues, organs and entire organisms and the positions of the various specialized cell types - morphogenesis. ... Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ...

The syncytium of skeletal muscle is important because it allows rapid coordinated contraction of muscles along their entire length. Action potentials propagate along the surface of the muscle fiber from the point of synaptic contact with a motoneuron. Another important vertebrate syncytium is in the placenta of placental mammals. Embryo-derived cells that form the interface with the maternal blood stream fuse together to form a multi-nucleated barrier. This is probably important in order to limit the exchange of migratory cells between the developing embryo and the body of the mother, as some blood cells are specialized to be able to insert themselves between adjacent epithelial cells. The syncitial epithelium of the placenta does not provide such an access path from the maternal circulation into the embryo. A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... Illustration of the major elements in a prototypical synapse. ... In vertebrates, motoneurons (also called motor neurons) are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. ... The placenta is an ephemeral (temporary) organ present only in female placental mammals during gestation (pregnancy). ... White Blood Cells redirects here. ... In zootomy, epithelium is a tissue composed of a layer of cells. ...

Syncytia can also form when cells are infected with certain types of virus such as HIV and paramyxoviruses. During infection, viral fusion proteins used by the virus to enter the cell are transported to the cell surface where they can cause the host cell membrane to fuse with neighbouring cells. The human immunodeficiency virus (HIV) A bacteriophage virus A virus is a submicroscopic parasitic particle that infects cells in biological organisms. ... Human immunodeficiency virus (commonly known as HIV, and formerly known as HTLV-III and lymphadenopathy-associated virus) is a retrovirus that primarily infects vital components of the human immune system such as CD4+ T cells, macrophages and dendritic cells. ... Genera See text Paramyxoviruses are viruses of the Paramyxoviridae family of the Mononegavirales order; they are negative-sense single-stranded RNA viruses responsible for a number of human and animal diseases. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ...

See also

• Syncytiotrophoblast