Synaptophysin

Synaptophysin is a membrane glycoprotein of small synaptic vesicles that is highly enriched in presynaptic terminals of neurons and neuroendocrine cells. It is encoded by the SYP gene and is approximately 38 kDa in size. The protein contains four transmembrane domains and is located on the vesicle membrane with cytoplasmic tails that participate in vesicle cycling. Synaptophysin co-localizes with other synaptic vesicle proteins and is widely used as an immunohistochemical marker for presynaptic terminals in both central and peripheral nervous tissue.

Although the precise function is not completely resolved, synaptophysin is believed to play a role in synaptic vesicle biogenesis, docking, and recycling, and in the regulation of neurotransmitter release. It interacts with components of the vesicle cycle, such as synaptobrevin (VAMP); genetic disruption of SYP in animal models results in altered synaptic vesicle pools and neurotransmitter release, supporting a role in vesicle dynamics.

Clinically, synaptophysin is a standard marker for neurons and neuroendocrine differentiation. Immunostaining for synaptophysin helps identify neuronal tissue in histopathology and is used to characterize neuroendocrine tumors, including certain carcinomas and pituitary tumors. Its expression is typically absent in glial tumors, aiding differential diagnosis.

Synaptophysin belongs to a family of synaptic vesicle proteins and is widely studied as a tool in neuroscience research and pathology to study synaptic architecture and neuronal differentiation.