Synaptophysin is an integral membrane glycoprotein found within the small synaptic vesicles in brain and endocrine cells. Studies with synaptophysin antibodies show that it is one of the most abundant small vesicle proteins, constituting approximately 7% of the total vesicle. Synaptophysin antibodies were used to monitor synaptophysin and synaptobrevin complexes in mature nerve terminals, where it was found that the dual complex associated with other fusion proteins such as syntaxin and SNAP25 to allow the SNARE complex to form, and therefore enable vesicle membrane fusion (1). Using synaptophysin antibodies for immunofluorescence and immunoEM (electron microscope) studies, Tixier-Vidal, et. al. showed that synaptophysin is released from the golgi apparatus in a vesicular form and transported to nerve endings (2). While it has been strongly implicated in nerve terminal function, McMahon’s group studied knockout mice with synaptophysin antibodies and were surprised to find synaptophysin was not essential for neurotransmitter release, suggesting either a redundant or more subtle function then analyzed in their experiments (3).Nevertheless, there is some evidence that immunofluoresence microscopy with synaptophysin antibodies using synaptophysin as a novel marker in NE (neuroendocrine) neoplasms may be helpful (4).
