Synapsin is an evolutionarily conserved presynaptic phosphoprotein. It<br />is encoded by only one gene in the Drosophila genome and is expressed<br />throughout the nervous system. It regulates the balance between reserve<br />and releasable vesicles, is required to maintain transmission upon heavy<br />demand, and is essential for proper memory function at the behavioral<br />level. Task-relevant sensorimotor functions, however, remain intact in<br />the absence of Synapsin. Using an odor-sugar reward associative learning<br />paradigm in larval Drosophila, we show that memory scores in mutants<br />lacking Synapsin (syn97) are lower than in wild-type animals only when<br />more salient, higher concentrations of odor or of the sugar reward are<br />used. Furthermore, we show that Synapsin is selectively required for<br />larval short-term memory. Thus, without Synapsin Drosophila larvae can<br />learn and remember, but Synapsin is required to form memories that match<br />in strength to event salience-in particular to a high saliency of odors,<br />of rewards, or the salient recency of an event. We further show that the<br />residual memory scores upon a lack of Synapsin are not further decreased<br />by an additional lack of the Sap47 protein. In combination with mass<br />spectrometry data showing an up-regulated phosphorylation of Synapsin in<br />the larval nervous system upon a lack of Sap47, this is suggestive of a<br />functional interdependence of Synapsin and Sap47.
Kleber, J., Chen, Y. C., Michels, B., Saumweber, T., Schleyer, M., Kähne, T., … Gerber, B. (2016). Synapsin is required to “boost” memory strength for highly salient events. Learning and Memory, 23(1), 9–20. https://doi.org/10.1101/lm.039685.115