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.

Due to their post-mitotic state, metabolic demands and often large polarised morphology, the function and survival of neurons is dependent on an efficient cellular waste clearance system both for generation of materials for metabolic processes and removal of toxic components. It is not surprising therefore that deficits in protein clearance can tip the balance between neuronal health and death. Here we discuss how autophagy and lysosome-mediated degradation pathways are disrupted in several neurological disorders. Both genetic and cell biological evidence show the diversity and complexity of vesicular clearance dysregulation in cells, and together may ultimately suggest a unified mechanism for neuronal demise in degenerative conditions. Causative and risk-associated mutations in Alzheimer’s disease, Frontotemporal Dementia, Amyotrophic Lateral Sclerosis, Parkinson’s disease, Huntington’s disease and others have given the field a unique mechanistic insight into protein clearance processes in neurons. Through their broad implication in neurodegenerative diseases, molecules involved in these genetic pathways, in particular those involved in autophagy, are emerging as appealing therapeutic targets for intervention in neurodegeneration.

Ca2+/CaM serine/threonine kinase II (CaMKII) is a central molecule in mechanisms of synaptic plasticity and memory. A vital feature of CaMKII in plasticity is its ability to switch to a calcium (Ca2+) independent constitutively active state after autophosphorylation at threonine 287 (T287). A second pair of sites, T306 T307 in the calmodulin (CaM) binding region once autophosphorylated, prevent subsequent CaM binding and inactivates the kinase during synaptic plasticity and memory. Recently a synaptic molecule called Ca2+/CaM-dependent serine protein kinase (CASK) has been shown to control both sets of CaMKII autophosphorylation events and hence is well poised to be a key regulator of memory. We show deletion of full length CASK or just its CaMK-like and L27 domains disrupts middle-term memory (MTM) and long-term memory (LTM), with CASK function in the α′/β′ subset of mushroom body neurons being required for memory. Likewise directly changing the levels of CaMKII autophosphorylation in these neurons removed MTM and LTM. The requirement of CASK and CaMKII autophosphorylation was not developmental as their manipulation just in the adult α′/β′ neurons was sufficient to remove memory. Overexpression of CASK or CaMKII in the α′/β′ neurons also occluded MTM and LTM. Overexpression of either Drosophila or human CASK in the α′/β′ neurons of the CASK mutant completely rescued memory, confirming that CASK signaling in α′/β′ neurons is necessary and sufficient for Drosophila memory formation and that the neuronal function of CASK is conserved between Drosophila and human. At the cellular level CaMKII overexpression in the α′/β′ neurons increased activity dependent Ca2+ responses while reduction of CaMKII decreased it. Likewise reducing CASK or directly expressing a phosphomimetic CaMKII T287D transgene in the α′/β′ similarly decreased Ca2+ signaling. Our results are consistent with CASK regulating CaMKII autophosphorylation in a pathway required for memory formation that involves activity dependent changes in Ca2+ signaling in the α′/β′ neurons.

Mutations in VPS35 (PARK17) cause autosomal dominant, late onset Parkinson's disease (PD). VPS35 forms a core component of the retromer complex that mediates the retrieval of membrane proteins from endosomes back to either the Golgi or plasma membrane. While aberrant endosomal protein sorting has been linked to several neurodegenerative diseases, the mechanisms by which VPS35 mutations and retromer function contribute to PD pathogenesis are not clear. To address this, we generated transgenic Drosophila that express variant forms of human VPS35 found in PD cases and the corresponding variants of the Drosophila ortholog. We did not find evidence of dominant toxicity from any variant form including the pathogenic D620N mutation, even with aging. However, assessing the ability of Vps35 variants to rescue multiple vps35-mutant phenotypes, we found that the D620N mutation confers a partial loss of function. Recently, VPS35 has been linked to the formation of mitochondria-derived vesicles, which mediate the degradation of mitochondrial proteins and contribute to mitochondrial quality control. This process is also promoted by two other PD-lined genes parkin (PARK2) and PINK1 (PARK6). We demonstrate here that vps35 genetically interacts with parkin but interestingly not with pink1. Strikingly, Vps35 overexpression is able to rescue several parkin-mutant phenotypes. Together these findings provide in vivo evidence that the D620N mutation likely confers pathogenicity through a partial loss of function mechanism and that this may be linked to other known pathogenic mechanisms such as mitochondrial dysfunction.

Drosophila have been used in classical conditioning experiments for over 40 years, thus greatly facilitating our understanding of memory, including the elucidation of the molecular mechanisms involved in cognitive diseases [1][2][3][4][5][6][7]

Obesity is a major public health problem. An in-depth knowledge of the molecular mechanisms of oro-sensory detection of dietary lipids may help fight it. Humans and rodents can detect fatty acids via lipido-receptors, such as CD36 and GPR120. We studied the implication of the MAPK pathways, in particular, ERK1/2, in the gustatory detection of fatty acids. Linoleic acid, a dietary fatty acid, induced via CD36 the phosphorylation of MEK1/2-ERK1/2-ETS-like transcription factor-1 cascade, which requires Fyn-Src kinase and lipid rafts in human taste bud cells (TBCs). ERK1/2 cascade was activated by Ca signaling via opening of the calcium-homeostasis modulator-1 (CALHM1) channel. Furthermore, fatty acid-evoked Ca signaling and ERK1/2 phosphorylation were decreased in both human TBCs after small interfering RNA knockdown of CALHM1 channel and in TBCs from Calhm1 mice. Targeted knockdown of ERK1/2 by small interfering RNA or PD0325901 (MEK1/2 inhibitor) in the tongue and genetic ablation of Erk1 or Calhm1 genes impaired preference for dietary fat in mice. Lingual inhibition of ERK1/2 in healthy volunteers also decreased orogustatory sensitivity for linoleic acid. Our data demonstrate that ERK1/2-MAPK cascade is regulated by the opening of CALHM1 Ca channel in TBCs to modulate orogustatory detection of dietary lipids in mice and humans.-Subramaniam, S., Ozdener, M. H., Abdoul-Azize, S., Saito, K., Malik, B., Maquart, G., Hashimoto, T., Marambaud, P., Aribi, M., Tordoff, M. G., Besnard, P., Khan, N. A. ERK1/2 activation in human taste bud cells regulates fatty acid signaling and gustatory perception of fat in mice and humans.

Alzheimer’s disease (AD) is the most common form of dementia and is characterized by intracellular neurofibrillary tangles of hyperphosphorylated Tau, including the 0N4R isoform and accumulation of extracellular amyloid beta (Aβ) plaques. However, less than 5% of AD cases are familial, with many additional risk factors contributing to AD including aging, lifestyle, the environment and epigenetics. Recent epigenome-wide association studies (EWAS) of AD have identified a number of loci that are differentially methylated in the AD cortex. Indeed, hypermethylation and reduced expression of the Ankyrin 1 ( ANK1 ) gene in AD has been reported in the cortex in numerous different post-mortem brain cohorts. Little is known about the normal function of ANK1 in the healthy brain, nor the role it may play in AD. We have generated Drosophila models to allow us to functionally characterize Drosophila Ank2 , the ortholog of human ANK1 and to determine its interaction with human Tau and Aβ. We show expression of human Tau 0N4R or the oligomerizing Aβ 42 amino acid peptide caused shortened lifespan, degeneration, disrupted movement, memory loss, and decreased excitability of memory neurons with co-expression tending to make the pathology worse. We find that Drosophila with reduced neuronal Ank2 expression have shortened lifespan, reduced locomotion, reduced memory and reduced neuronal excitability similar to flies overexpressing either human Tau 0N4R or Aβ42. Therefore, we show that the mis-expression of Ank2 can drive disease relevant processes and phenocopy some features of AD. Therefore, we propose targeting human ANK1 may have therapeutic potential. This represents the first study to characterize an AD-relevant gene nominated from EWAS.

In humans KCNQ2/3 heteromeric channels form an M-current that acts as a brake on neuronal excitability, with mutations causing a form of epilepsy. The M-current has been shown to be a key regulator of neuronal plasticity underlying associative memory and ethanol response in mammals. Previous work has shown that many of the molecules and plasticity mechanisms underlying changes in alcohol behaviour and addiction are shared with those of memory. We show that the single KCNQ channel in Drosophila (dKCNQ) when mutated show decrements in associative short- and long-term memory, with KCNQ function in the mushroom body α/βneurons being required for short-term memory. Ethanol disrupts memory in wildtype flies, but not in a KCNQ null mutant background suggesting KCNQ maybe a direct target of ethanol, the blockade of which interferes with the plasticity machinery required for memory formation. We show that as in humans, Drosophila display age-related memory impairment with the KCNQ mutant memory defect mimicking the effect of age on memory. Expression of KCNQ normally decreases in aging brains and KCNQ overexpression in the mushroom body neurons of KCNQ mutants restores age-related memory impairment. Therefore KCNQ is a central plasticity molecule that regulates age dependent memory impairment.