- Synapsin
The synapsins are a family of
protein s that have long been implicated in the regulation ofneurotransmitter release atsynapse s. Specifically, they are thought to be involved in regulating the number of synaptic vesicles available for release viaexocytosis at any one time.Synapsins are encoded by three different
gene s, synapsin I, II and III, and different neuron terminals will encode different amounts of these; synapsin will make up 1% of total brain protein at any one time.Current studies suggest the following hypothesis for the role of synapsin: synapsins bind synaptic vesicles to components of the
cytoskeleton which prevents them from migrating to the presynaptic membrane and releasing transmitter. During anaction potential , synapsins are phosphorylated by Ca2+/calmodulin-dependent protein kinase II, releasing the synaptic vesicles and allowing them to move to the membrane and release theirneurotransmitter .Gene knockout studies in mice (where the mouse is unable to produce synapsin) have had some surprising results. Mice lacking all three synapsins are prone to seizures, and experiencelearning defects cite journal |author=Rosahl TW, Geppert M, Spillane D, Herz J, Hammer RE, Malenka RC, Sudhof TC |title= Short-term synaptic plasticity is altered in micelacking synapsin I |journal=Cell |volume=75 |pages=661–670 |year=1993 |pmid=7902212 |doi= 10.1016/0092-8674(93)90487-B] . These results suggest that while synapsins are not essential for synaptic function, they do serve an important modulatory role. Conversely, studies usingtransgenic mice in whichneuronal signaling is abolished in specific circuitries showed thatsynaptic activity regulates, but is not essential to maintain, the expression of these proteins cite journal |author=Kihara AH, Santos TO, Paschon V, Matos RJ, Britto LR |title= Lack of photoreceptor signaling alters the expression of specific synaptic proteins in the retina |journal=Neuroscience |volume=151 |pages=995–1005 |year=2008 |pmid=18248909 |doi= 10.1016/j.neuroscience.2007.09.088] .References
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