Behavioral and Synaptic Plasticity Are Impaired upon Lack of the Synaptic Protein SAP47

Abstract

The synapse-associated protein of 47 kDa (SAP47) is a member of a phylogenetically conserved gene family of hitherto unknown function. In Drosophila, SAP47 is encoded by a single gene (Sap47) and is expressed throughout all synaptic regions of the wild-type larval brain; specifically, electron microscopy reveals anti-SAP47 immunogold labeling within 30 nm of presynaptic vesicles. To analyze SAP47 function, we used the viable and fertile deletion mutant Sap47 156 , which suffers from a 1.7 kb deletion in the regulatory region and the first exon. SAP47 cannot be detected by either immunoblotting or immunohistochemistry in Sap47 156 mutants. These mutants exhibit normal sensory detection of odorants and tastants as well as normal motor performance and basic neurotransmission at the neuromuscular junction. However, short-term plasticity at this synapse is distorted. Interestingly, Sap47 156 mutant larvae also show a 50% reduction in odorant-tastant associative learning ability; a similar associative impairment is observed in a second deletion allele (Sap47 201 ) and upon reduction of SAP47 levels using RNA interference. In turn, transgenically restoring SAP47 in Sap47 156 mutant larvae rescues the defect in associative function. This report thus is the first to suggest a function for SAP47. It specifically argues that SAP47 is required for proper behavioral and synaptic plasticity in flies-and prompts the question whether its homologs are required for proper behavioral and synaptic plasticity in other species as well.

Synapsin is required to “boost” memory strength for highly salient events

“…We had found earlier, and have confirmed in this study, that a lack of the Sap47 protein likewise entails a reduction of memory scores to half ( Fig. 5A; Saumweber et al 2011). Notably, the decrements in memory upon a lack of both Synapsin and Sap47 are not additive (Fig.…”

“…The sap47 gene and the Sap47 protein isoforms, as expected, are intact in the syn 97 mutant strain. The sap47 156 mutant strain carries the reported 1.7 kb deletion, which removes part of the promoter region, the first exon, and a small part of the first intron; it therefore is not expressing any Sap47 protein Saumweber et al 2011). In the WT 2 strain, we confirm the expected major Sap47 band at 47 kDa (this band can sometimes be discerned as a double band, Funk et al 2004) a group of weaker bands at 70 kDa, as well as a higher band at 90 kDa.…”

“…emerged from an additional outcrossing of syn 97CS (Godenschwege et al 2004;Michels et al 2005) to wild-type CS for 13 generations. The sap47 156 mutant strain was outcrossed to wild-type CS NF for nine generations Saumweber et al 2011). Outcrossing removes marker genes introduced for mutagenesis and effectively adjusts differences in genetic background that may otherwise distort results (de Belle and Heisenberg 1996) …”

“…Learning and memory finetune the way an animal can act in its environment, e.g., in the search for food. Using odor-sugar reward associative learning in larval Drosophila as a study case, we investigate the role of the Synapsin protein in learning and memory (Scherer et al 2003;Neuser et al 2005;Saumweber et al 2011; for reviews, see Gerber et al 2009;Diegelmann et al 2013).…”

“…2; Scherer et al 2003;Neuser et al 2005;Saumweber et al 2011), an initial attempt to reproduce the reported syn 97 mutant defect in odor-sugar memory failed (Supplemental Fig. S1A,B).…”