Synaptophysin, also known as the major synaptic vesicle protein p38, is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...
that in humans is encoded by the ''SYP''
gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
.
Genomics
The gene is located on the short arm of
X chromosome
The X chromosome is one of the two sex-determining chromosomes ( allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO se ...
(Xp11.23-p11.22). It is 12,406 bases in length and lies on the minus strand. The encoded protein has 313 amino acids with a predicted molecular weight of 33.845
kDa.
Molecular biology
The protein is a
synaptic vesicle
In a neuron, synaptic vesicles (or neurotransmitter vesicles) store various neurotransmitters that are released at the synapse. The release is regulated by a voltage-dependent calcium channel. Vesicles are essential for propagating nerve impu ...
glycoprotein
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as g ...
with four transmembrane domains weighing 38kDa. It is present in
neuroendocrine cells and in virtually all neurons in the
brain
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...
and
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...
that participate in synaptic transmission. It acts as a marker for neuroendocrine tumors, and its ubiquity at the synapse has led to the use of synaptophysin immunostaining for quantification of synapses.
The exact function of the protein is unknown: it interacts with the essential synaptic vesicle protein
synaptobrevin, but when the synaptophysin gene is experimentally inactivated in animals, they still develop and function normally.
Recent research has shown, however, that elimination of synaptophysin in mice creates behavioral changes such as increased exploratory behavior, impaired object novelty recognition, and reduced spatial learning.
Clinical importance
This gene has been implicated in X linked intellectual disability.
Using
immunohistochemistry, synaptophysin can be demonstrated in a range of neural and neuroendocrine tissues,
including cells of the
adrenal medulla and
pancreatic islets. As a specific marker for these tissues, it can be used to identify tumours arising from them, such as
neuroblastoma
Neuroblastoma (NB) is a type of cancer that forms in certain types of nerve tissue. It most frequently starts from one of the adrenal glands but can also develop in the neck, chest, abdomen, or spine. Symptoms may include bone pain, a lump i ...
,
retinoblastoma,
phaeochromocytoma,
carcinoid,
small-cell carcinoma,
medulloblastoma
Medulloblastoma is a common type of primary brain cancer in children. It originates in the part of the brain that is towards the back and the bottom, on the floor of the skull, in the cerebellum, or posterior fossa.
The brain is divided into two ...
and
medullary thyroid carcinoma, among others. Diagnostically, it is often used in combination with
chromogranin A.
See also
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List of human genes
Interactions
Synaptophysin has been shown to
interact with
AP1G1 and
SIAH2.
References
Further reading
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External links
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{{Nerve tissue protein
Glycoproteins
Tumor markers