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The amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD)–linked RNA-binding protein called FUS (fused in sarcoma) has been implicated in several aspects of RNA regulation, including mRNA translation. The mechanism by which FUS affects the translation of polyribosomes has not been established. Here we show that FUS can associate with stalled polyribosomes and that this association is sensitive to mTOR (mammalian target of rapamycin) kinase activity. Specifically, we show that FUS association with polyribosomes is increased by Torin1 treatment or when cells are cultured in nutrient-deficient media, but not when cells are treated with rapamycin, the allosteric inhibitor of mTORC1. Moreover, we report that FUS is necessary for efficient stalling of translation because deficient cells are refractory to the inhibition of mTOR-dependent signaling by Torin1. We also show that ALS-linked FUS mutants R521G and P525L associate abundantly with polyribosomes and decrease global protein synthesis. Importantly, the inhibitory effect on translation by FUS is impaired by mutations that reduce its RNA-binding affinity. These findings demonstrate that FUS is an important RNA-binding protein that mediates translational repression through mTOR-dependent signaling and that ALS-linked FUS mutants can cause a toxic gain of function in the cytoplasm by repressing the translation of mRNA at polyribosomes.

Heterozygous GRN (progranulin) mutations cause frontotemporal dementia (FTD) due to haploinsufficiency, and increasing progranulin levels is a major therapeutic goal. Several microRNAs, including miR-29b, negatively regulate progranulin protein levels. Antisense oligonucleotides (ASOs) are emerging as a promising therapeutic modality for neurological diseases, but strategies for increasing target protein levels are limited. Here, we tested the efficacy of ASOs as enhancers of progranulin expression by sterically blocking the miR-29b binding site in the 3’ UTR of the human GRN mRNA. We found 16 ASOs that increase progranulin protein in a dose-dependent manner in neuroglioma cells. A subset of these ASOs also increased progranulin protein in iPSC-derived neurons and in a humanized GRN mouse model. In FRET-based assays, the ASOs effectively competed miR-29b from binding to the GRN 3’ UTR RNA. The ASOs increased levels of newly synthesized progranulin protein by increasing its translation, as revealed by ribosomal profiling. Together, our results demonstrate that ASOs can be used to effectively increase target protein levels by partially blocking miR binding sites. This ASO strategy may be therapeutically feasible for progranulin-deficient FTD as well as other conditions of haploinsufficiency.

Genetic mutations in nitrogen permease regulator-like 2 (NPRL2) are associated with a wide spectrum of familial focal epilepsies, autism, and sudden unexpected death of epileptics (SUDEP), but the mechanisms by which NPRL2 contributes to these effects are not well known. NPRL2 is a requisite subunit of the GAP activity toward Rags 1 (GATOR1) complex, which functions as a negative regulator of mammalian target of rapamycin complex 1 (mTORC1) kinase when intracellular amino acids are low. Here, we show that loss of NPRL2 expression in mouse excitatory glutamatergic neurons causes seizures before death, consistent with SUDEP in humans with epilepsy. Additionally, the absence of NPRL2 expression increases mTORC1-dependent signal transduction and significantly alters amino acid homeostasis in the brain. Loss of NPRL2 reduces dendritic branching and increases the strength of electrically stimulated action potentials (APs) in neurons. The increased AP strength is consistent with elevated expression of epilepsy-linked, voltage-gated sodium channels in the NPRL2-deficient brain. Targeted deletion of NPRL2 in primary neurons increases the expression of sodium channel

BackgroundThe medial prefrontal cortex (mPFC) is part of a complex circuit controlling stress responses by sending projections to different limbic structures including the nucleus accumbens (NAc) and ventral tegmental area (VTA). However, the impact of chronic stress on NAc- and VTA-projecting mPFC neurons is still unknown and the distinct contribution of these pathways to stress responses in males and females is unclear.MethodsBehavioral stress responses were induced by 21 days of chronic variable stress (CVS) in male and female C57BL6 mice. An inter-sectional viral approach was used to label both pathways and assess the functional, morphological, and transcriptional adaptations in NAc- and VTA-projecting mPFC neurons in stressed males and females. Using chemogenetic approaches, we modified neuronal activity of NAc-projecting mPFC neurons to decipher their contribution to stress phenotypes.ResultsCVS induced depressive-like behaviors in males and females. NAc- and VTA-projecting mPFC neurons exhibited sex-specific functional, morphological, and transcriptional alterations. The functional changes were more severe in females in NAc-projecting mPFC neurons while males exhibited more drastic reductions in dendritic complexity in VTA-projecting mPFC neurons after CVS. Finally, chemogenetic overactivation of the cortico-accumbal pathway triggered anxiety and behavioral despair in both sexes while its inhibition rescued the phenotype only in females.ConclusionsOur results suggest that by changing the activity of transcriptional programs controlling neuronal plasticity, CVS interferes with the morphological and synaptic properties of the cortico-accumbal and tegmental pathways differently in males and females contributing to the expression of anxiety and depressive-like behaviors distinctly in a sex-specific fashion.

Background The medial prefrontal cortex (mPFC) is part of a complex circuit controlling stress responses by sending projections to different limbic structures including the nucleus accumbens (NAc) and ventral tegmental area (VTA). However, the impact of chronic stress on NAc- and VTA-projecting mPFC neurons is still unknown, and the distinct contribution of these pathways to stress responses in males and females is unclear. Methods Behavioral stress responses were induced by 21 days of chronic variable stress in male and female C57BL/6NCrl mice. An intersectional viral approach was used to label both pathways and assess the functional, morphological, and transcriptional adaptations in NAc- and VTA-projecting mPFC neurons in stressed males and females. Using chemogenetic approaches, we modified neuronal activity of NAc-projecting mPFC neurons to decipher their contribution to stress phenotypes. Results Chronic variable stress induced depressive-like behaviors in males and females. NAc- and VTA-projecting mPFC neurons exhibited sex-specific functional, morphological, and transcriptional alterations. The functional changes were more severe in females in NAc-projecting mPFC neurons, while males exhibited more drastic reductions in dendritic complexity in VTA-projecting mPFC neurons after chronic variable stress. Finally, chemogenetic overactivation of the corticoaccumbal pathway triggered anxiety and behavioral despair in both sexes, while its inhibition rescued the phenotype only in females. Conclusions Our results suggest that stress responses in males and females result from pathway-specific changes in the activity of transcriptional programs controlling the morphological and synaptic properties of corticoaccumbal and corticotegmental pathways in a sex-specific fashion.

The RNA-binding protein TDP-43 is strongly linked to neurodegeneration. Not only are mutations in the gene encoding TDP-43 associated with ALS and FTLD, but this protein is also a major constituent of pathological intracellular inclusions in these diseases. Recent studies have significantly expanded our understanding of TDP-43 physiology. TDP-43 is now known to play important roles in neuronal RNA metabolism. It binds to and regulates the splicing and stability of numerous RNAs encoding proteins involved in neuronal development, synaptic function and neurodegeneration. Thus, a loss of these essential functions is an attractive hypothesis regarding the role of TDP-43 in neurodegeneration. Moreover, TDP-43 is an aggregation-prone protein and, given the role of toxic protein aggregates in neurodegeneration, a toxic gain-of-function mechanism is another rational hypothesis. Importantly, ALS related mutations modulate the propensity of TDP-43 to aggregate in cell culture. Several recent studies have documented that cytoplasmic TDP-43 aggregates co-localize with stress granule markers. Stress granules are cytoplasmic inclusions that repress translation of a subset of RNAs in times of cellular stress, and several proteins implicated in neurodegeneration (i.e. Ataxin-2 and SMN) interact with stress granules. Thus, understanding the interplay between TDP-43 aggregation, stress granules and the effect of ALS-associated TDP-43 mutations may be the key to understanding the role of TDP-43 in neurodegeneration. We propose two models of TDP-43 aggregate formation. The "independent model" stipulates that TDP-43 aggregation is independent of stress granule formation, in contrast to the "precursor model" which presents the idea that stress granule formation contributes to a TDP-43 aggregate "seed" and that chronic stress leads to concentration-dependent TDP-43 aggregation. This article is part of a Special Issue entitled: RNA-Binding Proteins.

TAR DNA-binding protein 43 (TDP-43) is a highly conserved, ubiquitously expressed RNA-binding protein of the heterogeneous nuclear ribonucleoprotein (hnRNP) family (11, 47, 73). TDP-43 and other hnRNPs are multifunctional proteins that regulate gene expression in both the nucleus and the cytoplasm (47, 75). In the nucleus, TDP-43 binds single-stranded DNA and RNA (10, 11, 19, 20, 49, 62) and can function as both a transcriptional repressor (1, 2, 62) and a splicing modulator (15, 17, 20, 55). Specifically, TDP-43 regulates pre-mRNA splicing by binding mRNA with (UG)6-12 sequences (19) and by recruiting other hnRNP proteins into repressive splicing complexes (10, 18, 55). However, as a nucleocytoplasmic shuttling protein (12), TDP-43 also has distinct cytoplasmic functions, including mRNA stabilization (74). Recent studies indicate that TDP-43 localizes to stress granules (SGs) in response to heat shock, oxidative stress, and chemical inducers of stress (23, 33). SGs are dynamic cytoplasmic structures that are believed to act as sorting stations for mRNAs (5). SG composition and morphology differ according to stress and cell type (5, 39), but some core components are conserved. These core components include the RNA-binding protein TIAR (TIA-1 cytotoxic granule-associated RNA-binding protein-like 1) and the stalled translation initiation complex components eIF3 and eIF4G (44, 45). In contrast, the incorporation of the RNA-binding proteins HuR and hnRNP A1 into SGs differs with the cell type and stress (5, 39). The physiological stressors that cause TDP-43 aggregates and SGs to form—and the cells in which this occurs—remain unresolved. Moreover, very little is known about the function of cytoplasmic TDP-43, a pressing issue, since TDP-43 has been linked to multiple neurodegenerative diseases. “TDP-43 proteinopathies” encompass a spectrum of neurodegenerative diseases with ubiquitinated aggregates composed primarily of TDP-43 (21, 35). Ubiquitinated TDP-43 is especially prevalent in patients with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U). In these diseases, many mutations have been identified within the glycine-rich region (GRR) of TDP-43 (∼30 mutations in ALS [37, 48, 51, 63, 66, 69, 72] and 2 in FTLD-U [14, 21, 38, 46]). How TDP-43 contributes to neurodegeneration is not known, but other pathological alterations to TDP-43 implicate aberrant proteolysis, hyperphosphorylation, and misaccumulation in the cytoplasm (7, 16, 21, 35, 59). It is not clear how genetic mutations in TDP-43 contribute to neurodegeneration at the molecular and cellular levels. Existing evidence is compatible with the hypothesis that TDP-43 proteinopathies arise from a gain of TDP-43 function in the cytoplasm due to its misaccumulation in the cytoplasm. This may indirectly or directly impact its nuclear function, since cytoplasmic misaccumulation would reduce the amount of functional TDP-43 in the nuclear compartment. In this study, as a first step toward testing this hypothesis, we build a robust, quantitative, and physiologically relevant cellular model that allows us to establish the conditions under which TDP-43 accumulates in the cytoplasm, such as those seen in TDP-43 proteinopathies. We show that elevated levels of the sugar sorbitol, an intermediate in the polyol pathway (an ATP-independent metabolic route that generates fructose from glucose) (22), result in TDP-43 localization to SGs in Hek293T cells and, similarly, in primary cultured glia. Furthermore, we use this new cellular model to examine the dynamic assembly of TDP-43+ SGs, including the control of SG size and the molecular determinants within TDP-43 necessary for its assembly into SGs. Finally, we use this model to distinguish between the responses of wild-type TDP-43 and pathological mutant TDP-43 to stress. Mutant TDP-43 variants are incorporated into stress granules earlier than wild-type TDP-43, and these mutants form significantly larger stress granules. In striking contrast, wild-type TDP-43 forms more cytoplasmic granules over time, but the granule size remains relatively unchanged. Thus, we establish in this study a simple yet rigorous quantitative, physiologically relevant measurement of TDP-43 aggregate formation in vivo, and we use our novel assay to identify the regions of TDP-43 that contribute to this pathological phenomenon.

TAR DNA-binding protein 43 (TDP-43) is associated with a spectrum of neurodegenerative diseases. Although TDP-43 resembles heterogeneous nuclear ribonucleoproteins, its RNA targets and physiological protein partners remain unknown. Here we identify RNA targets of TDP-43 from cortical neurons by RNA immunoprecipitation followed by deep sequencing (RIP-seq). The canonical TDP-43 binding site (TG)(n) is 55.1-fold enriched, and moreover, a variant with adenine in the middle, (TG)(n)TA(TG)(m), is highly abundant among reads in our TDP-43 RIP-seq library. TDP-43 RNA targets can be divided into three different groups: those primarily binding in introns, in exons, and across both introns and exons. TDP-43 RNA targets are particularly enriched for Gene Ontology terms related to synaptic function, RNA metabolism, and neuronal development. Furthermore, TDP-43 binds to a number of RNAs encoding for proteins implicated in neurodegeneration, including TDP-43 itself, FUS/TLS, progranulin, Tau, and ataxin 1 and -2. We also identify 25 proteins that co-purify with TDP-43 from rodent brain nuclear extracts. Prominent among them are nuclear proteins involved in pre-mRNA splicing and RNA stability and transport. Also notable are two neuron-enriched proteins, methyl CpG-binding protein 2 and polypyrimidine tract-binding protein 2 (PTBP2). A PTBP2 consensus RNA binding motif is enriched in the TDP-43 RIP-seq library, suggesting that PTBP2 may co-regulate TDP-43 RNA targets. This work thus reveals the protein and RNA components of the TDP-43-containing ribonucleoprotein complexes and provides a framework for understanding how dysregulation of TDP-43 in RNA metabolism contributes to neurodegeneration.

3'-Phosphoinositide-dependent protein kinase-1 (PDK1), the direct upstream kinase of Akt, can localize to the nucleus during specific signalling events. The mechanism used for its import into the nucleus, however, remains unresolved as it lacks a canonical nuclear localization signal (NLS). Expression of activated Src kinase in C6 glioblastoma cells promotes the association of tyrosylphosphorylated PDK1 with the NLS-containing tyrosine phosphatase SHP-1 as well as the nuclear localization of both proteins. A constitutive nucleo-cytoplasmic SHP-1:PDK1 shuttling complex is supported by several lines of evidence including (i) the distribution of both proteins to similar subcellular compartments following manipulation of the nuclear pore complex, (ii) the nuclear retention of SHP-1 upon overexpression of a PDK1 protein bearing a disrupted nuclear export signal (NES), and (iii) the exclusion of PDK1 from the nucleus upon overexpression of SHP-1 lacking the NLS or following siRNA-mediated knock-down of SHP-1. The latter case results in a perinuclear distribution of PDK1 that corresponds with the distribution of PIP3 (phosphatidylinositol 3,4,5-triphosphate), while a PDK1 protein bearing a mutated PH domain that abrogates PIP3-binding is excluded from the nucleus. Our data suggest that the SHP-1:PDK1 complex is recruited to the nuclear membrane by binding to perinuclear PIP3, whereupon SHP-1 (and its NLS) facilitates active import. Export from the nucleus relies on PDK1 (and its NES). The intact complex contributes to Src kinase-induced, Akt-sensitive podial formation in C6 cells.

The RNA-binding protein fused-in-sarcoma (FUS) has been associated with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), two neurodegenerative disorders that share similar clinical and pathological features. Both missense mutations and overexpression of wild-type FUS protein can be pathogenic in human patients. To study the molecular and cellular basis by which FUS mutations and overexpression cause disease, we generated novel transgenic mice globally expressing low levels of human wild-type protein (FUS(WT)) and a pathological mutation (FUS(R521G)). FUS(WT) and FUS(R521G) mice that develop severe motor deficits also show neuroinflammation, denervated neuromuscular junctions, and premature death, phenocopying the human diseases. A portion of FUS(R521G) mice escape early lethality; these escapers have modest motor impairments and altered sociability, which correspond with a reduction of dendritic arbors and mature spines. Remarkably, only FUS(R521G) mice show dendritic defects; FUS(WT) mice do not. Activation of metabotropic glutamate receptors 1/5 in neocortical slices and isolated synaptoneurosomes increases endogenous mouse FUS and FUS(WT) protein levels but decreases the FUS(R521G) protein, providing a potential biochemical basis for the dendritic spine differences between FUS(WT) and FUS(R521G) mice.

Ward et al. report retinal thinning in humans with progranulin mutations that precedes dementia onset, and an age-dependent retinal neurodegenerative phenotype in progranulin null mice. Nuclear depletion of TDP-43 precedes retinal neuronal loss and is accompanied by reduced GTPase Ran, with overexpression of Ran restoring nuclear TDP-43 and neuronal survival., Frontotemporal dementia (FTD) is the most common cause of dementia in people under 60 yr of age and is pathologically associated with mislocalization of TAR DNA/RNA binding protein 43 (TDP-43) in approximately half of cases (FLTD-TDP). Mutations in the gene encoding progranulin (GRN), which lead to reduced progranulin levels, are a significant cause of familial FTLD-TDP. Grn-KO mice were developed as an FTLD model, but lack cortical TDP-43 mislocalization and neurodegeneration. Here, we report retinal thinning as an early disease phenotype in humans with GRN mutations that precedes dementia onset and an age-dependent retinal neurodegenerative phenotype in Grn-KO mice. Retinal neuron loss in Grn-KO mice is preceded by nuclear depletion of TDP-43 and accompanied by reduced expression of the small GTPase Ran, which is a master regulator of nuclear import required for nuclear localization of TDP-43. In addition, TDP-43 regulates Ran expression, likely via binding to its 3′-UTR. Augmented expression of Ran in progranulin-deficient neurons restores nuclear TDP-43 levels and improves their survival. Our findings establish retinal neurodegeneration as a new phenotype in progranulin-deficient FTLD, and suggest a pathological loop involving reciprocal loss of Ran and nuclear TDP-43 as an underlying mechanism.

GRN mutations cause frontotemporal lobar degeneration with TDP-43-positive inclusions. The mechanism of pathogenesis is haploinsufficiency. Recently, homozygous GRN mutations were detected in two patients with neuronal ceroid lipofuscinosis, a lysosomal storage disease. It is unknown whether the pathogenesis of these two conditions is related. Progranulin is cleaved into smaller peptides called granulins. Progranulin and granulins are attributed with roles in cancer, inflammation, and neuronal physiology. Cell surface receptors for progranulin, but not granulin peptides, have been reported. Revealing the cell surface receptors and the intracellular functions of granulins and progranulin is crucial for understanding their contributions to neurodegeneration.

Notch is a transmembrane receptor that controls a diverse array of cellular processes including cell proliferation, differentiation, survival, and migration. The cellular outcome of Notch signaling is dependent on extracellular and intracellular signals, but the complexities of its regulation are not well understood. Canonical Notch signaling involves ligand association that triggers sequential and regulated proteolysis of Notch at several sites. Ligand-dependent proteolysis at the S2 site removes the bulk of the extracellular domain of Notch. Subsequent γ-secretase-mediated intramembrane proteolysis of the remaining membrane-tethered Notch fragment at the S3 site produces a nuclear-destined Notch intracellular domain (NICD). Here we show that following γ-secretase cleavage, Notch is proteolyzed at a novel S5 site. We have identified this S5 site to be eight amino acids downstream of the S3 site. Biochemical fractionation and purification resulted in the identification of the S5 site protease as the mitochondrial intermediate peptidase (MIPEP). Expression of the MIPEP-cleaved NICD (ΔNICD) results in a decrease in cell viability and mitochondria membrane potential. The sequential and regulated proteolysis by γ-secretase and MIPEP suggests a new means by which Notch function can be modulated.

TDP-43 is a DNA/RNA-binding protein implicated in multiple steps of transcriptional and post-transcriptional regulation of gene expression. Alteration of this multifunctional protein is associated with a number of neurodegenerative diseases including amyotrophic lateral sclerosis and frontotemporal lobar degeneration with ubiquitin positive inclusions. Whereas a pathological link to neurodegenerative disorders has been established, the cellular and physiological functions of TDP-43 remain unknown. In this study, we show that TDP-43 is a nuclear protein with persistent high-level expression during embryonic development and with progressively decreased protein levels during postnatal development. In mice where the TDP-43 gene (Tardbp) was disrupted using a gene trap that carries a beta-galactosidase marker gene, heterozygous (Tardbp(+/-)) mice are fertile and healthy, but intercrosses of Tardbp(+/-) mice yielded no viable homozygotic null (Tardbp(-/-)) mice. Indeed, Tardbp(-/-) embryos die between 3.5 and 8.5 days of development. Tardbp(-/-) blastocysts grown in cell culture display abnormal expansion of their inner cell mass. The pattern of beta-galactosidase staining at E9.5 Tardbp(+/-) embryos is predominantly restricted to the neuroepithelium and remains prominent in neural progenitors at E10.5-12.5. TDP-43 is detected in spinal cord progenitors and in differentiated motor neurons as well as in the dorsal root ganglia at E12.5. Beta-galactosidase staining of tissues from adult Tardbp(+/-) mice shows widespread expression of TDP-43, including prominent levels in various regions of the central nervous system afflicted in neurodegenerative disorders. These results indicate that TDP-43 is developmentally regulated and indispensible for early embryonic development.

Withdrawal of serum from cell cultures constitutes a useful model for the study of mechanisms involved in the regulation of Akt function in vitro. However, there have been several reports of changes in Akt activity that are not fully explained by the current model of phosphatidylinositol 3'-kinase (PI3K)/Akt signaling. We demonstrate the expected loss of Akt phosphorylation in C6 glioma cells cultured in serum-free conditions, yet we also observed a paradoxical increase in PI3K-lipid kinase activity in the same cultures. These events corresponded with relocalization of p85, the regulatory subunit of PI3K, to the perinuclear region and a local increase in PI3K-lipid kinase products. Treatment with platelet-derived growth factor (PDGF) maintained the association between p85 and the PDGF receptor during serum withdrawal and restored PI3K-lipid production at the plasma membrane. Although this protected Akt from dephosphorylation, it only slightly reversed cell-cycle arrest. These effects were not sensitive to treatment with epidermal growth factor, thus precluding a generalized role for growth factors. Our data suggest that loss of growth factor signaling, including PDGF signaling, may disrupt recruitment and/or anchoring of an active p85(PI3K) complex at the plasma membrane during serum withdrawal, which could account for the concurrent loss of Akt function.

The antipsychotic drug haloperidol (HAL) has been linked to apoptosis and to inhibition of prosurvival Akt signalling in pheochromocytoma (PC12) and neuronal cell cultures. However, the mechanism involved is unclear.We used HAL to induce cytotoxicity in preneuronal PC12 cells. The expression and the subcellular localization of selected components of the PI3K-Akt survival cascade were monitored with standard biochemical approaches, such as subcellular fractionation, western blot analysis, gene transfer and fluorescence microscopy.PC12 cell stimulation with the epidermal growth factor (used as a control) results in normal processing of phosphatidylinositol 3'-kinase (PI3K)-Akt signalling (e.g., localization of PI3K to the plasma membrane and phosphorylation of Akt (Ser473). Surprisingly, HAL induces PI3K-generated phosphoinositol [phosphatidylinositol-3,4,5-triphosphate (PIP3), which conflicts with its ability to inhibit Akt. In fact, the production of PIP3s is nuclear, as assessed by the localized concentration of a fluorophore-tagged PIP3-targeting pleckstrin homology protein and a fluorophore-tagged substrate-trapping mutant of the phosphoinositide phosphatase, phosphatase and tensin homologue deleted on chromosome 10 (PTEN). However, phosphoinositide-dependent protein kinase 1 (PDK1, the activating kinase of Akt) does not colocalize to the nucleus with the PI3K complex. This effectively inactivates both cytoplasmic and nuclear pools of Akt.The differential compartmentalization of effectors of the PI3K-PDK1-Akt pathway is a unique means by which HAL disrupts Akt functioning in PC12 cells.

The loss of synapses is a central event in neurodegenerative diseases. Synaptic proteins are often associated with disease neuropathology, but their role in synaptic loss is not fully understood. Of the many processes involved in sustaining the integrity of synapses, local protein translation can directly impact synaptic formation, communication, and maintenance. RNA-binding proteins and their association with RNA granules serve to regulate mRNA transportation and translation at synapses and in turn regulate the synapse. Genetic mutations in RNA-binding proteins FUS and TDP-43 have been linked with causing neurodegenerative diseases: amyotrophic lateral sclerosis and frontotemporal dementia. The observation that mutations in FUS and TDP-43 coincide with changes in RNA granules provides evidence that dysfunction of RNA metabolism may underlie the mechanism of synaptic loss in these diseases. However, we do not know how mutations in RNA-binding proteins would affect RNA granule dynamics and local translation, or if these alterations would cause neurodegeneration. Further investigation into this area will lead to important insights into how disruption of RNA metabolism and local translation at synapses can cause neurodegenerative diseases.