SYT1 (Synaptotagmin 1) is an integral membrane protein found on synaptic vesicles. As a calcium ion sensor, it participates in the regulation of vesicular trafficking and exocytosis at the synaptic active zone and regulates neuronal release probability (binding of Ca2+ triggers synaptic neurotransmitter release). In immunohistochemistry of cancer, it is a neural marker used to typify the neural subtype of glioblastoma. In normal tissue, it has membranous positivity in neurons of the central nervous system. References: Cancer Cell. 2010 Jan 19;17(1):98-110, PMID: 20129251; Nature. 2001 Mar 1;410(6824):41-9, PMID:11242035;