Syn2

SYN2 is a gene that encodes synapsin II, a neuron-specific phosphoprotein of the synapsin family that associates with synaptic vesicles in presynaptic terminals. In humans, SYN2 is expressed predominantly in the brain, with transcripts detected in several regions of the nervous system.

Functionally, synapsin II participates in the regulation of neurotransmitter release by modulating the reserve pool of synaptic vesicles and their availability for exocytosis. It helps tether vesicles to the cytoskeleton and contributes to synapse formation and plasticity. The activity-dependent phosphorylation of synapsin II by kinases such as PKA, CaMKII, and MAPK modulates its interactions with actin and vesicle membranes, thereby influencing vesicle clustering and mobilization in response to neuronal activity.

The SYN2 gene produces multiple protein isoforms, including synapsin IIa and IIb, generated by alternative splicing. These isoforms share conserved N- and C-terminal regions characteristic of the synapsin family, while differences in the central region give rise to distinct expression patterns across development and brain regions.

Localization and interactions center on presynaptic terminals. Synapsin II associates with synaptic vesicles through lipid-binding properties and interacts with components of the cytoskeleton and the SNARE machinery, supporting vesicle docking, mobilization, and timely neurotransmitter release. Its function is intertwined with broader mechanisms of synaptic vesicle cycling and activity-dependent synaptic modulation.

Clinical significance is explored through studies of SYN2 in neuropsychiatric and neurodevelopmental contexts. Variants and dysregulation of synapsin II pathways have been investigated for associations with conditions such as epilepsy and autism spectrum disorders, though causal relationships remain under investigation. Animal models with altered SYN2 expression provide insight into its role in synaptic function and behavior.