Evolutionary expansion and anatomical specialization of synapse proteome complexity.

Understanding the origins and evolution of synapses may provide insight into species diversity and the organization of the brain. Using comparative proteomics and genomics, we examined the evolution of the postsynaptic density (PSD) and membrane-associated guanylate kinase (MAGUK)-associated signaling complexes (MASCs) that underlie learning and memory. PSD and MASC orthologs found in yeast carry out basic cellular functions to regulate protein synthesis and structural plasticity. We observed marked changes in signaling complexity at the yeast-metazoan and invertebrate-vertebrate boundaries, with an expansion of key synaptic components, notably receptors, adhesion/cytoskeletal proteins and scaffold proteins. A proteomic comparison of Drosophila and mouse MASCs revealed species-specific adaptation with greater signaling complexity in mouse. Although synaptic components were conserved amongst diverse vertebrate species, mapping mRNA and protein expression in the mouse brain showed that vertebrate-specific components preferentially contributed to differences between brain regions. We propose that the evolution of synapse complexity around a core proto-synapse has contributed to invertebrate-vertebrate differences and to brain specialization.

Neurone specific regulation of dendritic spines in vivo by post synaptic density 95 protein (PSD-95).

Post synaptic density protein 95 (PSD-95) is a postsynaptic adaptor protein coupling the NMDA receptor to downstream signalling pathways underlying plasticity. Mice carrying a targeted gene mutation of PSD-95 show altered behavioural plasticity including spatial learning, neuropathic pain, orientation preference in visual cortical cells, and cocaine sensitisation. These behavioural effects are accompanied by changes in long-term potentiation of synaptic transmission. In vitro studies of PSD-95 signalling indicate that it may play a role in regulating dendritic spine structure. Here, we show that PSD-95 mutant mice have alterations in dendritic spine density in the striatum (a 15% decrease along the dendritic length) and in the hippocampus (a localised 40% increase) without changes in dendritic branch patterns or gross neuronal architecture. These changes in spine density were accompanied by altered expression of proteins known to interact with PSD-95, including NR2B and SAP102, suggesting that PSD-95 plays a role in regulating the expression and activation of proteins found within the NMDA receptor complex. Thus, PSD-95 is an important regulator of neuronal structure as well as plasticity in vivo.

Induction and maintenance of late-phase long-term potentiation in isolated dendrites of rat hippocampal CA1 pyramidal neurones.

Expression of N-methyl-d-aspartate (NMDA) receptor-dependent long-term potentiation (LTP) in the CA1 region of the hippocampus can be divided into an early (1-2 h), protein synthesis-independent phase and a late (>4 h), protein synthesis-dependent phase. In this study we have addressed whether the de novo protein synthesis required for the expression of late-LTP can be sustained solely from the translation of mRNAs located in the dendrites of CA1 pyramidal neurones. Our results show that late-LTP, lasting at least 5 h, can be maintained in hippocampal slices where the dendrites located in stratum radiatum have been isolated from their cell bodies by a microsurgical cut. The magnitude of the potentiation of the slope of field EPSPs in these 'isolated' slices was similar to that recorded in 'intact' slices. Incubation of the slices with the mRNA translation inhibitor cycloheximide or the mammalian target of rapamycin (mTOR) inhibitor rapamycin blocked late-LTP in both 'intact' and 'isolated' slice preparations. In contrast, incubation of slices with the transcription inhibitor, actinomycin D, resulted in a reduction of sustained potentiation, at 4 h, in 'intact' slices while in 'isolated' slices the magnitude of potentiation was similar to that seen in untreated slices. These results indicate that late-LTP can be induced and maintained in 'isolated' dendritic preparations via translation of pre-existing mRNAs.