Synaptophysin

Synaptophysin, also known as the major synaptic vesicle protein p38, is a is_associated_with::protein that in humans is encoded by the SYP is_associated_with::gene.

Genomics
The gene is located on the short arm of is_associated_with::X chromosome (Xp11.23-p11.22). It is 12,406 bases in length and lies on the Crick (minus) strand. The encoded protein has 313 amino acids with a predicted molecular weight of 33.845 kDa.

Molecular biology
The protein is a is_associated_with::synaptic vesicle is_associated_with::glycoprotein with four transmembrane domains weighing 38kDa. It is present in neuroendocrine cells and in virtually all neurons in the is_associated_with::brain and is_associated_with::spinal cord 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 is_associated_with::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 mental retardation.

Using is_associated_with::immunohistochemistry, synaptophysin can be demonstrated in a range of neural and neuroendocrine tissues, including cells of the is_associated_with::adrenal medulla and is_associated_with::pancreatic islets. As a specific marker for these tissues, it can be used to identify tumours arising from them, such as is_associated_with::neuroblastoma, is_associated_with::retinoblastoma, is_associated_with::phaeochromocytoma, is_associated_with::carcinoid, is_associated_with::small-cell carcinoma, is_associated_with::medulloblastoma and is_associated_with::medullary thyroid carcinoma, among others. Diagnostically, it is often used in combination with is_associated_with::chromogranin A.

Interactions
Synaptophysin has been shown to interact with is_associated_with::AP1G1 and is_associated_with::SIAH2.