Skip to main content

Advertisement

Pathogenesis of FUS-associated ALS and FTD: insights from rodent models

Acta Neuropathologica Communicationsvolume 4, Article number: 99 (2016) | Download Citation

Abstract

Disruptions to genes linked to RNA processing and homeostasis are implicated in the pathogenesis of two pathologically related but clinically heterogeneous neurodegenerative diseases, amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Mutations in the Fused-in-Sarcoma (FUS) gene encoding a 526 amino-acid RNA-binding protein are found in a small subset of ALS cases, but FUS mutations do not appear to be a direct cause of FTD. Structural and functional similarities between FUS and another ALS-related RNA-binding protein, TDP-43, highlight the potential importance of aberrant RNA processing in ALS/FTD, and this pathway is now a major focus of interest. Recently, several research groups have reported transgenic vertebrate models of FUSopathy, with varying results. Here, we discuss the evidence for FUS pathogenicity in ALS/FTD, review the experimental approaches used and phenotypic features of FUS rodent models reported to date, and outline their contribution to our understanding of pathogenic mechanisms. Further refinement of vertebrate models will likely aid our understanding of the role of FUS in both diseases.

Introduction

Neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterised by the progressive destruction of neurons, associated with the aggregation and deposition of one or more types of proteinaceous inclusion. ALS is characterised by the degeneration of both upper (UMN) and lower (LMN) motor neurons, causing muscular atrophy and progressive paralysis [2], with death usually occurring within 3 years of symptom onset [1]. The majority of cases are classified as sporadic (sALS), with no obvious Mendelian inherited component. However, around 10 % of cases are caused by mutations in one or more known ALS genes [2] both in patients where there is a clear family history (familial ALS, fALS), but also in a minority of sALS cases, in which the mutation acts as a rare variant of significant disease determining effect. Treatment for ALS is mainly supportive, involving physical therapy, nutritional support and artificial ventilation in the later stages [10]. While widely prescribed, riluzole, the only pharmacological treatment available, produces only modest increases in survival in clinical trials [83].

FTD and its pathological presentation - Frontotemporal Lobar Degeneration (FTLD) – is the second most common form of young-onset dementia after Alzheimer’s disease [25]. FTLD is characterised by widespread degeneration of neurons in the frontal and temporal lobes, presenting clinically as significant behavioural or language abnormalities [7], with relative sparing of memory until late disease stages. FTD is clinically categorised as one of three subtypes: behavioural variant FTD (bvFTD), semantic dementia (SD) or progressive non-fluent aphasia (PNFA) [51, 64]. As for ALS, no disease modifying therapy is available. Symptomatic treatment includes selective serotonin re-uptake inhibitors (SSRI’s) to control compulsive behaviour [59] and general supportive care [7]. Diagnosis for both ALS and FTD is made primarily on clinical grounds in the context of an appropriate history and examination. Neurophysiological testing is useful in ALS, but other investigations such as imaging are essentially used to rule out mimic disorders [26, 72, 84]. While detectable cognitive dysfunction may be present in up to 50 % of ALS cases [58, 78], around 15 % of patients meet formal clinical criteria for both ALS and FTD (ALS-FTD) [56, 58, 68], the combination of which being associated with a worse prognosis and reduction in survival time of around one year [56].

Despite significant clinical heterogeneity, the overlap in genetics and pathology between ALS and FTD have led them to be widely considered as being part of a clinico-pathological disease continuum, with pure ALS and pure FTD representing spectral extremes [28, 89]. Cases with mutations in more than one ALS/FTD gene are being increasingly reported [14, 36, 87], suggesting that ‘oligogenic’ factors may be one element in a ‘multiple-hit’ model of disease [86]. In 2009, mutations to the Fused-in-Sarcoma (FUS) gene were identified as causative in a small number of ALS cases [39, 90]. This review summarises our understanding of the genetic and neuropathological features of FUS-related ALS/FTD, and critically appraises the progress that has been made in modelling FUS mutations in-vivo, with a particular focus on rodent models.

Fused-in-Sarcoma (FUS)

The most frequent genetic mutation linking ALS and FTD is a hexanucleotide (G4C2) repeat expansion within an intronic promoter region of the C9ORF72 gene [20, 66], accounting for around 35 % fALS cases [65] and around 25 % FTD cases [85]. Transactive DNA-binding protein 43 kDa (TDP-43) is the major component of inclusions in motor neurons of sALS and some cases of FTLD [4, 54], and mutations to its corresponding gene, TARDBP, are responsible for a small number of both fALS and sALS cases [27, 75], as well as FTD. Mutations to the Fused-in-Sarcoma (FUS) gene on chromosome 16 are responsible for a small, but important subset of both familial and sporadic ALS [39, 90] accounting for around 4 and 1 % of total cases respectively [21, 45]. Interestingly, variants have also been implicated in essential tremor [21].

FUS encodes a 526 amino acid, 15-exon RNA binding protein of the FET family, containing several distinct functional domains including a RNA-recognition motif and a highly-conserved C-terminal nuclear localization signal (NLS) [21] (Fig. 1), where many of the identified mutations occur. This domain architecture is shared with Ewing’s Sarcoma (EWS) protein and TATA-binding protein-associated factor 15 (TAF15), which together with FUS are referred to as the FET family of proteins that were initially characterised as part of fusion oncogenes in human malignancies [3]. The precise normal physiological function of FUS is unclear. However, known roles include transcriptional control [79], RNA processing through splicing regulation of pre-mRNA’s [40], and DNA repair [93, 46]. Recently, FUS mutations have been shown to significantly alter target gene expression by binding target gene mRNA within the aggregates of transfected human cells [16]. While there is still some debate on the nature of FUS toxicity, the range of functions involving FUS highlight its potential susceptibility to dysfunction and the consequences for the maintenance of cellular RNA homeostasis. Evidence to support both gain and loss-of-function mechanisms now exists, and it appears likely that both mechanisms are implicated, depending on the particular mutation and its functional connotations.

Fig. 1
figure1

Structure and functional domains of FUS. FUS is a member of the TET family of proteins, and contains several functional domains including a QGSY-rich region, multiple RNA binding regions, a C-terminal Zinc-finger motif and two putative ‘prion-like’ domains. The majority of mutations in ALS-FUS are located within the C-terminal nuclear localization signal domain in exon 15. Figure adapted by author from Vance et al. [91] and Deng et al. [21]

Full size image

Under normal physiological conditions FUS is predominantly localized in the nucleus in neurons, but is exclusively nuclear-based in glia [3]. However as an RNA-binding protein, it possesses the ability to move between both through its role in nucleocytoplasmic transport [13]. The characteristic presence of FUS-immunoreactive inclusions in the cytoplasm of ALS-FUS and FTLD-FUS has led to the suggestion that mislocalization of FUS to the cytoplasm contributes to neurodegeneration in these cases, by a gain-of-toxicity mechanism. This concept is closely tied to the formation of stress granules, which notably contain mutant FUS but not endogenous wild-type FUS [12]. The role of mutant FUS in stress-assembly dynamics is now well documented [11, 12, 18] and illustrates an obvious differential between normal and disease physiology. For example, one study has demonstrated how oxidative stress recruits mutant FUS into stress granules where it can sequester wild-type FUS to disrupt RNA processing and potentially initiate cell death [91]. Knock-down zebrafish models, however, display a subtle motor phenotype and hyper extended axonal branching that cannot be rescued with mutant FUS, suggesting loss-of-function [34], and a combination of both mechanisms remains possible.

ALS-FUS

Over 50 mutations in the FUS gene have now been reported in ALS – most of which are mis-sense – with a minority being in-frame deletions [21]. Many, including the most common FUS mutation in humans, R521C, occur within the highly conserved C-terminal nuclear localization signal [62]. Nearly all display an autosomal dominant pattern of inheritance, albeit with varying degrees of penetrance. Notably, some mutations such as P525L are associated with a more severe disease progression [31] and juvenile onset [8, 48], with apparently sporadic occurrence, presumably because the condition is frequently lethal before it can be transmitted [35].

The neuropathology of ALS-FUS may be related to its specific genetic cause and subsequent disease course [42]. Predominantly a LMN disease with a younger average age of onset and an aggressive course, patients typically display severe neuronal loss in the spinal cord anterior horn with only low or moderate neuronal loss of Betz cells within layer V of the motor cortex [65] (Table 1). Neuronal and glial cytoplasmic inclusions (NCI) containing ubiquitinated FUS in the motor cortex, basal ganglia and spinal cord, as well as dystrophic neurites [2] are seen. TDP-43 pathology is entirely absent. Certain variants including P525L seemingly predispose the formation of basophilic inclusions (BI) [42], which can be readily viewed using haematoxylin and eosin (H&E) (Fig. 2). Clinical presentation is consistent with classical ALS, although three groups have reported similar clinical features in patients with the p.R521C variant, suggesting correlation between individual mutations and specific clinical abnormalities [17, 62, 81].

Table 1 Phenotype-pathology correlations summary of FUS-linked human ALS/FTD
Full size table
Fig. 2
figure2

Neuronal and glial cytoplasmic inclusions immunoreactive for FUS define the pathology of both ALS-FUS and FTLD-FUS. Basophilic inclusions are present in neurons in ALS-FUS (arrowed) and can be viewed using H&E stain, X400 (a). Discrete neuronal inclusion immunoreactive for FUS associated with the P525L mutation, X400 (b). ALS-FUS inclusions in the anterior horn of spinal cord, both X40 Obj (c, d). Well defined, compact inclusions (c) or intense diffuse cytoplasmic staining (d) are commonly seen, often with nuclear clearance

Full size image

FTLD-FUS

FUS mutations have only rarely been reported in FTD, and mostly co-exist with ALS, making their significance in its pathogenesis unclear [21, 45, 52, 74]. One study identified a unique variant within exon 4 (P106L) in a patient with pure bvFTD [32] (which could not be confirmed as co-segregating because of lack of DNA from other family members), and another reported a novel mis-sense variation (M254V) with predicted pathogenicity in an FTD patient without ALS [88], but neither case has been confirmed post-mortem. Indeed, there have been no reported cases of pure, clinical FTD that were both genetically and neuropathologically confirmed as FUS-related. Additionally, the largest genome-wide association study (GWAS) of clinical FTD to date involving exome sequencing of 3526 FTD patients and 9402 healthy controls found only weak association with variants at the FUS locus, with none being at a genome-wide significance level [25]. Genome-wide association studies, however, are only powered to detect an association between common variants and a disease. The picture emerging from ALS genetics, though as yet unconfirmed in FTD, is a genetic contribution mostly accounted for by rare variants.

Despite the absence of confirmed genetic cases, inclusions immunoreactive for FUS are present in a small proportion FTLD cases (FTLD-FUS) and can be neuropathologically sub-categorised as atypical FTLD-U, neuronal intermediate filament inclusion disease (NIFID), or basophilic inclusion body disease (BIBD) [44, 94] (Table 1) . All are defined by the presence of FUS-positive, tau/TDP-43 negative inclusions of varying formation, often co-localized with the other two FET proteins EWS and TAF15, alongside prominent degeneration of the frontal and temporal lobes. Atypical FTLD-U cases display uniform, round neuronal cytoplasmic inclusions (NCI) throughout the brain, but mainly within frontal and temporal neocortex, hippocampus and striatum [43]. NIFID is characterized by NCI’s that are immunoreactive for all class IV neurofilament chains - the form of which vary according to neuronal type and region [43] - with additional cytoplasmic granules of FUS aggregation [53]. BIBD cases show large, round basophilic neuronal inclusions on H&E staining that also show strong immunoreactivity for FUS, predominantly within subcortical regions [49]. Interestingly, basophilic inclusions have been noted in ALS-FUS without FTLD [8, 31, 80]. The considerable variation in neuropathology between patients with FTLD does not correlate clearly with differences in clinical features, compounding the difficulty in making assertions regarding neuropathological aetiology. However, there is some evidence that aFTLD-U cases show stereotypic clinical characteristics [74].

An ‘oligogenic’ hypothesis of disease

While there might be doubt about some FUS variants being directly causal, it may be speculated that they play a role as part of an oligogenic susceptibility profile, with mutations occuring in more than one ALS/FTD gene in a single patient at a higher rate than would be expected by chance. This hypothesis is exemplified in lineages containing inherited mutations that display incomplete penetrance in phenotypically normal family members, where affected individuals possess risk factor variants in multiple genes. Such oligogenic variants have the potential to influence the neuropathology or phenotype of a more dominant mutation in ALS/FTD, as has been evidenced in several cases [14, 15, 86, 87]. This effect is now recognised in the context of several other diseases [6, 60, 77, 95]. Investigating the relative contribution of these modifier variants to disease pathogenesis is often challenging, requiring extensive experimental as well as computational genomic and bioinformatic analysis, and further work is required to elucidate the influence of such genetic modifiers on the disease course of FUS-associated ALS/FTD.

Evidence for distinct pathogenesis of ALS-FUS and FTLD-FUS

Despite structural and functional similarities between FUS and TDP-43, they are differentially post-translationally modified (Table 2). TDP-43, for example is extensively phosphorylated and cleaved to produce toxic, aggregate-prone C-terminal fragments, while endogenous FUS is maintained at full length, even in disease [52]. The fact that neurodegeneration is induced through the presence of a single point mutation within the FUS gene in some cases of familial ALS, but FUS inclusions are the predominant pathological characteristic of a subset of FTLD cases despite lack of mutation to its corresponding gene, has led to the suggestion of each disease being driven by separate pathogenetic mechanisms. Post-translational modification of proteins can drastically alter their function; for example by changing their conformational shape through the addition of charged amino acids at certain residues. Recently, evidence has emerged involving specific post-translational modifications of FUS that suggest a possible explanation for the differences in pathogenesis between the two diseases, whilst simultaneously accounting for their shared FUS immunoreactivity.

Table 2 Pathogenetic differences between ALS-FUS and FTLD-FUS
Full size table

Arginine methylation is a common post-translational modification of RNA-binding proteins involving the addition of methyl groups either symmetrically or asymmetrically to nitrogen atoms in the arginine side chain [9]. At least 20 sites within the FUS protein, mainly located in the RGG3 domain, are arginine methylated [63], mediated primarily by protein N-arginine methyltransferase 1 (PRMT1) [24], inhibition of which limits the capacity of mutant FUS to localize to the cytoplasm to form inclusions [82]. The nuclear import karyopherin protein Transportin-1 strongly co-localizes with FUS in FTLD-FUS [13], however in FTLD-FUS all FET proteins co-localize with Transportin-1, whereas ALS-FUS inclusions contain exclusively FUS. In 2012, Dormann et al. [23] showed that arginine methylation impairs Transportin-1 dependent nuclear import of FUS by preventing Transportin-1 binding upstream of the NLS. Using a novel methyl-specific antibody, they also showed that inclusions in ALS-FUS are extensively asymmetrically methylated. The authors used this evidence to speculate that mislocalization of FUS in ALS is caused by mutations in the NLS that are then exacerbated by arginine methylation in the RGG3 domain, whereas mislocalization in FTLD-FUS may be caused more broadly by hypomethylation of all FET proteins, mediated by altered Transportin-1 binding. This concept has recently been elaborated through the development of monoclonal antibodies capable of distinguishing individually methylated forms of FUS protein - unmethylated arginine (UMA), monomethylated arginine (MMA) or asymmetrically arginine dimethylated (ADMA) [76]. Using these antibodies, it has been possible to show that FUS inclusions in FTLD-FUS contain UMA and MMA, whilst inclusions in ALS-FUS contain only ADMA. UMA and MMA show an increased binding capacity to Transportin-1, whilst arginine methylation decreases its binding capacity and thus reduces nuclear import. Together, these studies implicate a role for arginine methylation in FUSopathy, and for the first time provide substantive evidence of each disease being driven, at least in part, by distinct pathogenetic mechanisms.

Phosphorylation is another common post-translational modification involving the covalent addition of a phosphoryl group by a protein kinase. FUS is phosphorylated by DNA protein kinase (DNA-PK) in response to DNA damage, which leads to its cytoplasmic accumulation [22], and there is evidence of DNA damage in FTLD-FUS patients. Additionally, one group has shown that phosphorylation of a specific C-terminal tyrosine residue impairs Transportin binding and prevents nuclear import [19]. Given the multifactorial nature of FUSopathy (and indeed, ALS/FTD in general) it is likely that both types of post-translational modification contribute to disease pathogenesis. However, the actual pathological significance and contribution of each to human disease is still yet to be demonstrated.

Current rodent models of ALS-FUS

Significant progress has been made regarding modelling FUSopathies associated with FUS mutations in vivo; including the development of cellular, vertebrate and invertebrate models. While invertebrate models using Saccharomyces cerevisiae [33], Drosophila melanogaster [41], and Caenorhabditis elegans [50] have yielded various insights, vertebrate models in general provide more translatable results to human disease because of their increased genetic homology - at the notable expense of being considerably more complex and time consuming to generate. Recently several groups have characterised their own ALS-FUS rodent models created using a variety of transgenic and viral-mediated methods (Table 3).

Table 3 Rodent models of ALS-FUS
Full size table

Originally, FUS was identified for its role as a fusion oncoprotein in the development of round cell liposcarcomas and human myeloid leukaemias. Nine years before the recognition of its relevance to ALS/FTD, two groups created FUS knock out (KO) mouse models to investigate its functional role and effects of haploinsufficiency. Hicks et al. (2000) used insertional site mutagenesis to create a null mutation that effectively caused FUS transcriptional silencing. Mice failed to suckle, dying within 16 h of birth, and affected cells showed an increase in aneuploidy and chromosomal aberrations, which the authors used to highlight the importance of FUS in genomic maintenance and chromosomal stability. Another group used a similar non-functional insertional cassette technique to adequately disrupt FUS transcription, albeit resulting in low level expression of a severely truncated, non-functional protein [38]. Kuroda et al. analysed their model solely in terms of the reproductive system, and neither group investigated their model neuropathologically. The first neuropathological analysis of FUS KO mice was performed recently [37], utilising the same mice as Hicks but heterozygotes were outcrossed with ICR mice before inter-crossing the F1 progeny. FUS -/- mice displayed a reduced body weight but no motor phenotype, and numbers of choline-acetyltransferase positive neurons were normal. Mice did display non-progressive vacuolations, particularly in the hippocampus. The lack of both motor phenotype and neurodegeneration in KO mice suggests that FUS depletion alone is insufficient to cause ALS symptoms or pathology. Interestingly however, a reduction in motor activity has been reported in two zebrafish knock-down models using anti-sense morpholino oligonucleotides [5, 34]. This is perhaps surprising given that morpholinos are generally only capable of partially reducing target gene expression. The reason for this apparent phenotypic discrepancy between species is unclear, but the difficulties in identifying subtle motor impairments in embryonic zebrafish are noted. Alternatively, it may feasibly be due to a more significant functional role played by FUS in the developing zebrafish embryo than the adult mouse.

The effects of mutated FUS displaying a gain-of-function mechanism of toxicity have been described in various cell culture experiments, and the cellular toxicity of wild-type (WT) FUS overexpression has been documented in yeast [33]. The aggregation propensity of wild-type (WT) FUS was investigated by Mitchell et al. (2012) in mice, who overexpressed WT human FUS cDNA under the control of a mouse prion protein gene promoter. FUS+/+ mice developed a rapid decline in motor function from 4 weeks old, and displayed intense FUS perinuclear inclusions in Layer V motor cortex and striatum, with additional diffuse cytoplasmic staining throughout cortical neurons, despite total FUS expression being only 1.7 times higher than non-transgenic mice. Neuronal loss was seen in the spinal cord but not in the brain, with consequent impaired neuromuscular function. Aggregation of structurally normal (i.e. non-mutation affected) FUS is characteristic of FTLD, however the severe motor dysfunction seen in these mice supports the suggestion that aggregation of WT FUS is sufficient to induce neurodegeneration and the motor phenotype of ALS.

Normal FUS protein contains several distinct functional domains, including multiple RNA binding regions, a C-terminal Zinc-finger motif and a highly-conserved Nuclear Localization Signal (NLS). Recently, several groups have attempted to drive pathology by inducing mutations in the NLS. In perhaps the most extensive characterisation of a FUS rodent model to date, Qiu et al [61] used a prion promoter to drive expression of the human R521C mutation in transgenic mice, leading to severe motor deficits and death within 4-6 weeks of symptom onset. While there was significant and progressive neuronal loss, FUS expression was predominantly nuclear, demonstrating that neurodegeneration induced by the mutation was not caused by aggregation of cytoplasmic FUS. Expression analysis identified significant alterations in genes involved in transcription and RNA processing, which were predicted to be the cause of severe dendritic and synaptic defects in spinal and cortical motor neurons. In addition, the authors identified deficiencies in DNA repair caused by R251C mutant FUS being unable to interact with the chromatin re-modelling factor HDAC1. However, this study did not utilise mice expressing human WT FUS, so it is unknown whether these defects were the result of the mutation or overexpression of FUS protein itself.

Some groups have investigated more dramatic genetic FUS alterations. Shelkovnikova et al. [73] generated transgenic mice that lacked both the entire NLS and RNA binding motifs, while still retaining the N-terminal prion-like domain. This allowed the investigation of FUS pathogenicity independent of its ability to sequester RNA binding proteins and its effect on RNA processing, while still being highly aggregate prone. Mice showed degeneration of motor neurons, neuroinflammatory reactions with abrupt development of a severe motor phenotype, death within a few days of symptom onset, and distinct FUS inclusions within LMN cell bodies and in the motor cortex. Taken together, these results are significant because they suggest that FUS aggregation and inclusion formation caused by mutant FUS is sufficient to induce neurodegeneration independently of the role of FUS in RNA metabolism. Robinson et al. [67] combined approaches, and created a model that both lacked an RNA recognition motif and contained the R522G point mutation within the NLS. Mice exhibited pronounced tremor followed by early death, and widespread cytoplasmic FUS aggregation in the cortex, brainstem and cerebellum, suggesting that lack of RNA binding to FUS increases its inherent propensity for cytoplasmic aggregation. However, there was no evidence of neuronal loss or astrogliosis. While significant as proof-of-concept, the extent of genetic alteration required to induce pathology in both studies makes the relationship to human disease pathogenesis uncertain.

A different approach has been to use somatic brain transgenesis (SBT) to overexpress human mutant FUS cDNA [92]. Mice were intracerebally injected with an adeno-associated virus vector, incorporating either the R521C mutation or FUS lacking the nuclear localization signal entirely (∆14). The advantage of this method is its speed - mice can be generated within a few months as opposed to years when using traditional transgenic approaches. Affected mice however showed no phenotype when euthanized at 3 months. Neuropathologically, FUS R521C mice showed a large increase in cytoplasmic FUS without obvious NCI formation or neurodegeneration, while FUS ∆14 mice displayed FUS pathology more closely mimicking human disease including ubiquitin/p62 positive NCI. Additionally, the authors also used this method to overexpress wild-type (WT) human FUS. Unlike those reported previously [47], overexpression of WT FUS did not cause any abnormal pathology or neurodegeneration. Huang et al. [30] created two rat models; one expressing the R521C mutation, and one overexpressing WT human FUS at comparable levels. Similar to their mice counterparts, R521C rats developed a progressive paralysis resembling human ALS, and also displayed motor neuron axonopathy with motor neuron loss in both the hippocampus and the cortex. NCI were absent, but diffuse cytoplasmic FUS staining was noted in ventral horn motor neurons. Rats overexpressing WT FUS did not develop a significant motor phenotype, but did display deficits in spatial learning and memory, with moderate neuronal loss in the frontal cortex. Consistent with previous studies [47] this suggests that overexpression of WT FUS is sufficient to induce neuronal loss but that mutant FUS is more toxic than WT. The phenotypic differences between the Verbeeck model and other models involving the same mutations/WT-overexpression may be due to the transient expression of the adenovirus before it is cleared, the localized expression of AAV transgenes, or because mice were euthanized before the development of severe NCI formation/phenotype.

Finally, Sephton et al. [70] used a Cre-inducible transgenic approach to create two mice lines, expressing either human WT FUS (FUSWT) or the R521G (FUSR521G) mutation, both at comparably low levels. Nearly all mice developed a severe motor phenotype and early lethality, with some FUSR521G mice escaping this and exhibiting subtle motor impairments and altered sociability. This is in contrast to previous studies mentioned above, which concluded that expression of WT FUS is less pathogenic than mutant. While there was no evidence of FUS cytoplasmic mislocalization, aggregation or neuronal loss in either model, the authors suggested these features are end-stage pathological markers of human disease, precipitated by the denervation of neuromuscular junctions (NMJ) that caused the motor phenotype. Interestingly, differences in gene expression between models suggests that FUSWT exhibits a loss-of-function mechanism through its effects on gene expression, while FUSR521G exhibits gain-of-function toxicity through its disruption of synaptic homeostasis. This is consistent with the effects of the R521C mutation on the regulation of genes relating to synaptic function in the Qiu et al. model. Most recently in an elegant study, Sharma et al. [71] used Cre-LoxP to generate mice expressing a single copy of human WT FUS, (FUSWT), R521C (FUSR521C) or P525L (FUSP525L) at the MAPT locus, and an additional knock-out model. As in previous over-expression models [31, 47], they demonstrated that overexpression of WT FUS alone was sufficient to induce neurodegeneration, but that mutant FUS is more stable and pathogenic than WT. Pathogenicity in these models was mutation dependent, with FUSP525L mice showing motor neuron specific degeneration at a younger age and a greater degree of cytoplasmic FUS mislocalization than in the FUSR521C model, reflecting the mutation-dependent phenotype of human cases bearing these mutations [8, 48]. As in the previous Cre-LoxP model [70] there was also significant denervation of NMJ in both mutant models preceding neurodegeneration, adding weight to the suggestion that neuronal loss is a downstream consequence of NMJ denervation caused by these mutations. However, the survival time of these mice was normal, and there was no NCI formation in any line.

Conclusion

Given its significance in the pathophysiology of ALS/FTD, modelling FUSopathy in vivo has been a focus for several groups. However, reproducing both the motor dysfunction phenotype and the distinct neuropathological features of FUS-linked ALS has proven challenging in rodents. In particular, while the models discussed here provide clues as to the pathomechanistic role of FUS and its significance in the neurodegeneration of human disease, none of the above completely recapitulate the features of human ALS, and all current models compromise in at least one area of human pathophysiology. To our knowledge there is currently no vertebrate model that mimics the unique post-translational modifications associated with human FTLD-FUS, which are clearly distinct from FUSopathy with FUS mutations.

Several of the models described above were created using traditional plasmid-mediated transgenic methods, which have their own methodological limitations. Small cDNA-based transgenes lack the regulatory upstream sequences found as part of many complex mammalian genes. Also, several of the models described here use heterologous promoter sequences that cause expression of the transgene in excess of what would normally be expected in human disease. A Bacterial Artificial Chromosome (BAC) approach may somewhat ameliorate these issues, by allowing the integration of important regulatory sequences some distance upstream of FUS in addition to an endogenous mouse promoter, as well as being modifiable to direct cell-type specific gene expression. Unlike small cDNA-based transgenes, the expression of BAC clones also correlates closely with copy number. This approach has already been used in the context of ALS to generate two C9ORF72 mouse models [55, 57], and we are currently in the process of characterising our own FUS model that has been created in such a way. Additionally, the much publicised CRISPR-Cas9 genome editing tool is reaching stages of development that allows for the knock-in of specific point mutations, without extensive off target effects or the need for exogenous regulatory sequences, and it is anticipated that this tool will be used extensively in neurodegenerative disease modelling in the coming years. Finally, of note is that many of the aforementioned studies did not conduct significant transcriptional profiling of their models, which is perhaps surprising given the known role of FUS in the expression regulation of several target genes identified in cell culture experiments. Elucidating the precise normal physiological function of FUS and further refinement of vertebrate models will likely aid our understanding of its role in the pathogenesis of both ALS and FTD.

Abbreviations

ALS, Amyotrophic lateral sclerosis; bvFTD, Behavioural variant FTD; FTD, Frontotemporal dementia; FTLD, Frontotemporal lobar degeneration; FUS, Fused-in-sarcoma; LMN, Lower motor neuron; MND, Motor neurone disease; PNFA, Progressive non-fluent aphasia; SD, Semantic dementia; UMN, Upper motor neuron

References

  1. 1.

    Al-Chalabi A, Hardiman O. The epidemiology of ALS: a conspiracy of genes, environment and time. Nat Rev Neurol. 2013;9:617–28. doi:10.1038/nrneurol.2013.203.

  2. 2.

    Al-Chalabi A, Jones A, Troakes C, King A, Al-Sarraj S, van den Berg LH. The genetics and neuropathology of amyotrophic lateral sclerosis. Acta Neuropathol. 2012;124:339–52. doi:10.1007/s00401-012-1022-4.

  3. 3.

    Andersson MK, Stahlberg A, Arvidsson Y, Olofsson A, Semb H, Stenman G, Nilsson O, Aman P. The multifunctional FUS, EWS and TAF15 proto-oncoproteins show cell type-specific expression patterns and involvement in cell spreading and stress response. BMC Cell Biol. 2008;9:37. doi:10.1186/1471-2121-9-37.

  4. 4.

    Arai T, Hasegawa M, Akiyama H, Ikeda K, Nonaka T, Mori H, Mann D, Tsuchiya K, Yoshida M, Hashizume Y, et al. TDP-43 is a component of ubiquitin-positive tau-negative inclusions in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Biochem Biophys Res Commun. 2006;351:602–11. doi:10.1016/j.bbrc.2006.10.093.

  5. 5.

    Armstrong GA, Drapeau P. Loss and gain of FUS function impair neuromuscular synaptic transmission in a genetic model of ALS. Hum Mol Genet. 2013;22:4282–92. doi:10.1093/hmg/ddt278.

  6. 6.

    Aston CE, Ralph DA, Lalo DP, Manjeshwar S, Gramling BA, DeFreese DC, West AD, Branam DE, Thompson LF, Craft MA, et al. Oligogenic combinations associated with breast cancer risk in women under 53 years of age. Hum Genet. 2005;116:208–21. doi:10.1007/s00439-004-1206-7.

  7. 7.

    Bang J, Spina S, Miller BL. Frontotemporal dementia. Lancet. 2015;386:1672–82. doi:10.1016/S0140-6736(15)00461-4.

  8. 8.

    Baumer D, Hilton D, Paine SM, Turner MR, Lowe J, Talbot K, Ansorge O. Juvenile ALS with basophilic inclusions is a FUS proteinopathy with FUS mutations. Neurology. 2010;75:611–8. doi:10.1212/WNL.0b013e3181ed9cde.

  9. 9.

    Bedford MT, Clarke SG. Protein arginine methylation in mammals: who, what, and why. Mol Cell. 2009;33:1–13. doi:10.1016/j.molcel.2008.12.013.

  10. 10.

    Beghi E, Chio A, Couratier P, Esteban J, Hardiman O, Logroscino G, Millul A, Mitchell D, Preux PM, Pupillo E, et al. The epidemiology and treatment of ALS: focus on the heterogeneity of the disease and critical appraisal of therapeutic trials. Amyotroph Lateral Scler. 2011;12:1–10. doi:10.3109/17482968.2010.502940.

  11. 11.

    Bentmann E, Neumann M, Tahirovic S, Rodde R, Dormann D, Haass C. Requirements for stress granule recruitment of fused in sarcoma (FUS) and TAR DNA-binding protein of 43 kDa (TDP-43). J Biol Chem. 2012;287:23079–94. doi:10.1074/jbc.M111.328757.

  12. 12.

    Bosco DA, Lemay N, Ko HK, Zhou H, Burke C, Kwiatkowski Jr TJ, Sapp P, McKenna-Yasek D, Brown Jr RH, Hayward LJ. Mutant FUS proteins that cause amyotrophic lateral sclerosis incorporate into stress granules. Hum Mol Genet. 2010;19:4160–75. doi:10.1093/hmg/ddq335.

  13. 13.

    Brelstaff J, Lashley T, Holton JL, Lees AJ, Rossor MN, Bandopadhyay R, Revesz T. Transportin1: a marker of FTLD-FUS. Acta Neuropathol. 2011;122:591–600. doi:10.1007/s00401-011-0863-6.

  14. 14.

    Bury JJ, Highley JR, Cooper-Knock J, Goodall EF, Higginbottom A, McDermott CJ, Ince PG, Shaw PJ, Kirby J. Oligogenic inheritance of optineurin (OPTN) and C9ORF72 mutations in ALS highlights localisation of OPTN in the TDP-43-negative inclusions of C9ORF72-ALS. Neuropathology. 2015. doi:10.1111/neup.12240.

  15. 15.

    Cady J, Allred P, Bali T, Pestronk A, Goate A, Miller TM, Mitra RD, Ravits J, Harms MB, Baloh RH. Amyotrophic lateral sclerosis onset is influenced by the burden of rare variants in known amyotrophic lateral sclerosis genes. Ann Neurol. 2015;77:100–13. doi:10.1002/ana.24306.

  16. 16.

    Coady TH, Manley JL. ALS mutations in TLS/FUS disrupt target gene expression. Genes Dev. 2015;29:1696–706. doi:10.1101/gad.267286.115.

  17. 17.

    Corrado L, Del Bo R, Castellotti B, Ratti A, Cereda C, Penco S, Soraru G, Carlomagno Y, Ghezzi S, Pensato V, et al. Mutations of FUS gene in sporadic amyotrophic lateral sclerosis. J Med Genet. 2010;47:190–4. doi:10.1136/jmg.2009.071027.

  18. 18.

    Daigle JG, Lanson Jr NA, Smith RB, Casci I, Maltare A, Monaghan J, Nichols CD, Kryndushkin D, Shewmaker F, Pandey UB. RNA-binding ability of FUS regulates neurodegeneration, cytoplasmic mislocalization and incorporation into stress granules associated with FUS carrying ALS-linked mutations. Hum Mol Genet. 2013;22:1193–205. doi:10.1093/hmg/dds526.

  19. 19.

    Darovic S, Prpar Mihevc S, Zupunski V, Guncar G, Stalekar M, Lee YB, Shaw CE, Rogelj B. Phosphorylation of C-terminal tyrosine residue 526 in FUS impairs its nuclear import. J Cell Sci. 2015;128:4151–9. doi:10.1242/jcs.176602.

  20. 20.

    DeJesus-Hernandez M, Mackenzie IR, Boeve BF, Boxer AL, Baker M, Rutherford NJ, Nicholson AM, Finch NA, Flynn H, Adamson J, et al. Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS. Neuron. 2011;72:245–56. doi:10.1016/j.neuron.2011.09.011.

  21. 21.

    Deng H, Gao K, Jankovic J. The role of FUS gene variants in neurodegenerative diseases. Nat Rev Neurol. 2014;10:337–48. doi:10.1038/nrneurol.2014.78.

  22. 22.

    Deng Q, Holler CJ, Taylor G, Hudson KF, Watkins W, Gearing M, Ito D, Murray ME, Dickson DW, Seyfried NT, et al. FUS is phosphorylated by DNA-PK and accumulates in the cytoplasm after DNA damage. J Neurosci. 2014;34:7802–13. doi:10.1523/JNEUROSCI.0172-14.2014.

  23. 23.

    Dormann D, Madl T, Valori CF, Bentmann E, Tahirovic S, Abou-Ajram C, Kremmer E, Ansorge O, Mackenzie IR, Neumann M, et al. Arginine methylation next to the PY-NLS modulates Transportin binding and nuclear import of FUS. EMBO J. 2012;31:4258–75. doi:10.1038/emboj.2012.261.

  24. 24.

    Du K, Arai S, Kawamura T, Matsushita A, Kurokawa R. TLS and PRMT1 synergistically coactivate transcription at the survivin promoter through TLS arginine methylation. Biochem Biophys Res Commun. 2011;404:991–6. doi:10.1016/j.bbrc.2010.12.097.

  25. 25.

    Ferrari R, Hernandez DG, Nalls MA, Rohrer JD, Ramasamy A, Kwok JB, Dobson-Stone C, Brooks WS, Schofield PR, Halliday GM, et al. Frontotemporal dementia and its subtypes: a genome-wide association study. Lancet Neurol. 2014;13:686–99. doi:10.1016/S1474-4422(14)70065-1.

  26. 26.

    Foerster BR, Welsh RC, Feldman EL. 25 years of neuroimaging in amyotrophic lateral sclerosis. Nat Rev Neurol. 2013;9:513–24. doi:10.1038/nrneurol.2013.153.

  27. 27.

    Gitcho MA, Baloh RH, Chakraverty S, Mayo K, Norton JB, Levitch D, Hatanpaa KJ, White 3rd CL, Bigio EH, Caselli R, et al. TDP-43 A315T mutation in familial motor neuron disease. Ann Neurol. 2008;63:535–8. doi:10.1002/ana.21344.

  28. 28.

    Guerreiro R, Bras J, Hardy J. SnapShot: Genetics of ALS and FTD. Cell. 2015;160(798):e791. doi:10.1016/j.cell.2015.01.052.

  29. 29.

    Huang C, Tong J, Bi F, Wu Q, Huang B, Zhou H, Xia XG. Entorhinal cortical neurons are the primary targets of FUS mislocalization and ubiquitin aggregation in FUS transgenic rats. Hum Mol Genet. 2012;21:4602–14. doi:10.1093/hmg/dds299.

  30. 30.

    Huang C, Zhou H, Tong J, Chen H, Liu YJ, Wang D, Wei X, Xia XG. FUS transgenic rats develop the phenotypes of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. PLoS Genet. 2011;7:e1002011. doi:10.1371/journal.pgen.1002011.

  31. 31.

    Huang EJ, Zhang J, Geser F, Trojanowski JQ, Strober JB, Dickson DW, Brown Jr RH, Shapiro BE, Lomen-Hoerth C. Extensive FUS-immunoreactive pathology in juvenile amyotrophic lateral sclerosis with basophilic inclusions. Brain Pathol. 2010;20:1069–76. doi:10.1111/j.1750-3639.2010.00413.x.

  32. 32.

    Huey ED, Ferrari R, Moreno JH, Jensen C, Morris CM, Potocnik F, Kalaria RN, Tierney M, Wassermann EM, Hardy J, et al. FUS and TDP43 genetic variability in FTD and CBS. Neurobiol Aging. 2012;33(1016):e1019–1017. doi:10.1016/j.neurobiolaging.2011.08.004.

  33. 33.

    Ju S, Tardiff DF, Han H, Divya K, Zhong Q, Maquat LE, Bosco DA, Hayward LJ, Brown Jr RH, Lindquist S, et al. A yeast model of FUS/TLS-dependent cytotoxicity. PLoS Biol. 2011;9:e1001052. doi:10.1371/journal.pbio.1001052.

  34. 34.

    Kabashi E, Bercier V, Lissouba A, Liao M, Brustein E, Rouleau GA, Drapeau P. FUS and TARDBP but not SOD1 interact in genetic models of amyotrophic lateral sclerosis. PLoS Genet. 2011;7:e1002214. doi:10.1371/journal.pgen.1002214.

  35. 35.

    Kent L, Vizard TN, Smith BN, Topp SD, Vance C, Gkazi A, Miller J, Shaw CE, Talbot K. Autosomal dominant inheritance of rapidly progressive amyotrophic lateral sclerosis due to a truncation mutation in the fused in sarcoma (FUS) gene. Amyotroph Lateral Scler Frontotemporal Degener. 2014;15:557–62. doi:10.3109/21678421.2014.920033.

  36. 36.

    King A, Troakes C, Smith B, Nolan M, Curran O, Vance C, Shaw CE, Al-Sarraj S. ALS-FUS pathology revisited: singleton FUS mutations and an unusual case with both a FUS and TARDBP mutation. Acta Neuropathol Commun. 2015;3:62. doi:10.1186/s40478-015-0235-x.

  37. 37.

    Kino Y, Washizu C, Kurosawa M, Yamada M, Miyazaki H, Akagi T, Hashikawa T, Doi H, Takumi T, Hicks GG, et al. FUS/TLS deficiency causes behavioral and pathological abnormalities distinct from amyotrophic lateral sclerosis. Acta Neuropathol Commun. 2015;3:24. doi:10.1186/s40478-015-0202-6.

  38. 38.

    Kuroda M, Sok J, Webb L, Baechtold H, Urano F, Yin Y, Chung P, de Rooij DG, Akhmedov A, Ashley T, et al. Male sterility and enhanced radiation sensitivity in TLS(-/-) mice. EMBO J. 2000;19:453–62. doi:10.1093/emboj/19.3.453.

  39. 39.

    Kwiatkowski Jr TJ, Bosco DA, Leclerc AL, Tamrazian E, Vanderburg CR, Russ C, Davis A, Gilchrist J, Kasarskis EJ, Munsat T, et al. Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis. Science. 2009;323:1205–8. doi:10.1126/science.1166066.

  40. 40.

    Lagier-Tourenne C, Polymenidou M, Hutt KR, Vu AQ, Baughn M, Huelga SC, Clutario KM, Ling SC, Liang TY, Mazur C, et al. Divergent roles of ALS-linked proteins FUS/TLS and TDP-43 intersect in processing long pre-mRNAs. Nat Neurosci. 2012;15:1488–97. doi:10.1038/nn.3230.

  41. 41.

    Lanson Jr NA, Maltare A, King H, Smith R, Kim JH, Taylor JP, Lloyd TE, Pandey UB. A Drosophila model of FUS-related neurodegeneration reveals genetic interaction between FUS and TDP-43. Hum Mol Genet. 2011;20:2510–23. doi:10.1093/hmg/ddr150.

  42. 42.

    Mackenzie IR, Ansorge O, Strong M, Bilbao J, Zinman L, Ang LC, Baker M, Stewart H, Eisen A, Rademakers R, et al. Pathological heterogeneity in amyotrophic lateral sclerosis with FUS mutations: two distinct patterns correlating with disease severity and mutation. Acta Neuropathol. 2011;122:87–98. doi:10.1007/s00401-011-0838-7.

  43. 43.

    Mackenzie IR, Munoz DG, Kusaka H, Yokota O, Ishihara K, Roeber S, Kretzschmar HA, Cairns NJ, Neumann M. Distinct pathological subtypes of FTLD-FUS. Acta Neuropathol. 2011;121:207–18. doi:10.1007/s00401-010-0764-0.

  44. 44.

    Mackenzie IR, Neumann M, Bigio EH, Cairns NJ, Alafuzoff I, Kril J, Kovacs GG, Ghetti B, Halliday G, Holm IE, et al. Nomenclature and nosology for neuropathologic subtypes of frontotemporal lobar degeneration: an update. Acta Neuropathol. 2010;119:1–4. doi:10.1007/s00401-009-0612-2.

  45. 45.

    Mackenzie IR, Rademakers R, Neumann M. TDP-43 and FUS in amyotrophic lateral sclerosis and frontotemporal dementia. Lancet Neurol. 2010;9:995–1007. doi:10.1016/S1474-4422(10)70195-2.

  46. 46.

    Mastrocola AS, Kim SH, Trinh AT, Rodenkirch LA, Tibbetts RS. The RNA-binding protein fused in sarcoma (FUS) functions downstream of poly(ADP-ribose) polymerase (PARP) in response to DNA damage. J Biol Chem. 2013;288:24731–41. doi:10.1074/jbc.M113.497974.

  47. 47.

    Mitchell JC, McGoldrick P, Vance C, Hortobagyi T, Sreedharan J, Rogelj B, Tudor EL, Smith BN, Klasen C, Miller CC, et al. Overexpression of human wild-type FUS causes progressive motor neuron degeneration in an age- and dose-dependent fashion. Acta Neuropathol. 2013;125:273–88. doi:10.1007/s00401-012-1043-z.

  48. 48.

    Mochizuki Y, Isozaki E, Takao M, Hashimoto T, Shibuya M, Arai M, Hosokawa M, Kawata A, Oyanagi K, Mihara B, et al. Familial ALS with FUS P525L mutation: two Japanese sisters with multiple systems involvement. J Neurol Sci. 2012;323:85–92. doi:10.1016/j.jns.2012.08.016.

  49. 49.

    Munoz DG, Neumann M, Kusaka H, Yokota O, Ishihara K, Terada S, Kuroda S, Mackenzie IR. FUS pathology in basophilic inclusion body disease. Acta Neuropathol. 2009;118:617–27. doi:10.1007/s00401-009-0598-9.

  50. 50.

    Murakami T, Yang SP, Xie L, Kawano T, Fu D, Mukai A, Bohm C, Chen F, Robertson J, Suzuki H, et al. ALS mutations in FUS cause neuronal dysfunction and death in Caenorhabditis elegans by a dominant gain-of-function mechanism. Hum Mol Genet. 2012;21:1–9. doi:10.1093/hmg/ddr417.

  51. 51.

    Neary D, Snowden JS, Gustafson L, Passant U, Stuss D, Black S, Freedman M, Kertesz A, Robert PH, Albert M, et al. Frontotemporal lobar degeneration: a consensus on clinical diagnostic criteria. Neurology. 1998;51:1546–54.

  52. 52.

    Neumann M, Rademakers R, Roeber S, Baker M, Kretzschmar HA, Mackenzie IR. A new subtype of frontotemporal lobar degeneration with FUS pathology. Brain. 2009;132:2922–31. doi:10.1093/brain/awp214.

  53. 53.

    Neumann M, Roeber S, Kretzschmar HA, Rademakers R, Baker M, Mackenzie IR. Abundant FUS-immunoreactive pathology in neuronal intermediate filament inclusion disease. Acta Neuropathol. 2009;118:605–16. doi:10.1007/s00401-009-0581-5.

  54. 54.

    Neumann M, Sampathu DM, Kwong LK, Truax AC, Micsenyi MC, Chou TT, Bruce J, Schuck T, Grossman M, Clark CM, et al. Ubiquitinated TDP-43 in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Science. 2006;314:130–3. doi:10.1126/science.1134108.

  55. 55.

    O’Rourke JG, Bogdanik L, Muhammad AK, Gendron TF, Kim KJ, Austin A, Cady J, Liu EY, Zarrow J, Grant S, et al. C9orf72 BAC Transgenic Mice Display Typical Pathologic Features of ALS/FTD. Neuron. 2015;88:892–901. doi:10.1016/j.neuron.2015.10.027.

  56. 56.

    Olney RK, Murphy J, Forshew D, Garwood E, Miller BL, Langmore S, Kohn MA, Lomen-Hoerth C. The effects of executive and behavioral dysfunction on the course of ALS. Neurology. 2005;65:1774–7. doi:10.1212/01.wnl.0000188759.87240.8b.

  57. 57.

    Peters OM, Cabrera GT, Tran H, Gendron TF, McKeon JE, Metterville J, Weiss A, Wightman N, Salameh J, Kim J, et al. Human C9ORF72 Hexanucleotide Expansion Reproduces RNA Foci and Dipeptide Repeat Proteins but Not Neurodegeneration in BAC Transgenic Mice. Neuron. 2015;88:902–9. doi:10.1016/j.neuron.2015.11.018.

  58. 58.

    Phukan J, Pender NP, Hardiman O. Cognitive impairment in amyotrophic lateral sclerosis. Lancet Neurol. 2007;6:994–1003. doi:10.1016/S1474-4422(07)70265-X.

  59. 59.

    Pressman PS, Miller BL. Diagnosis and management of behavioral variant frontotemporal dementia. Biol Psychiatry. 2014;75:574–81. doi:10.1016/j.biopsych.2013.11.006.

  60. 60.

    Priest JR, Osoegawa K, Mohammed N, Nanda V, Kundu R, Schultz K, Lammer EJ, Girirajan S, Scheetz T, Waggott D, et al. De Novo and Rare Variants at Multiple Loci Support the Oligogenic Origins of Atrioventricular Septal Heart Defects. PLoS Genet. 2016;12:e1005963. doi:10.1371/journal.pgen.1005963.

  61. 61.

    Qiu H, Lee S, Shang Y, Wang WY, Au KF, Kamiya S, Barmada SJ, Finkbeiner S, Lui H, Carlton CE, et al. ALS-associated mutation FUS-R521C causes DNA damage and RNA splicing defects. J Clin Invest. 2014;124:981–99. doi:10.1172/JCI72723.

  62. 62.

    Rademakers R, Stewart H, Dejesus-Hernandez M, Krieger C, Graff-Radford N, Fabros M, Briemberg H, Cashman N, Eisen A, Mackenzie IR. Fus gene mutations in familial and sporadic amyotrophic lateral sclerosis. Muscle Nerve. 2010;42:170–6. doi:10.1002/mus.21665.

  63. 63.

    Rappsilber J, Friesen WJ, Paushkin S, Dreyfuss G, Mann M. Detection of arginine dimethylated peptides by parallel precursor ion scanning mass spectrometry in positive ion mode. Anal Chem. 2003;75:3107–14.

  64. 64.

    Rascovsky K, Hodges JR, Knopman D, Mendez MF, Kramer JH, Neuhaus J, van Swieten JC, Seelaar H, Dopper EG, Onyike CU, et al. Sensitivity of revised diagnostic criteria for the behavioural variant of frontotemporal dementia. Brain. 2011;134:2456–77. doi:10.1093/brain/awr179.

  65. 65.

    Ravits J, Appel S, Baloh RH, Barohn R, Brooks BR, Elman L, Floeter MK, Henderson C, Lomen-Hoerth C, Macklis JD, et al. Deciphering amyotrophic lateral sclerosis: what phenotype, neuropathology and genetics are telling us about pathogenesis. Amyotroph Lateral Scler Frontotemporal Degener. 2013;14 Suppl 1:5–18. doi:10.3109/21678421.2013.778548.

  66. 66.

    Renton AE, Majounie E, Waite A, Simon-Sanchez J, Rollinson S, Gibbs JR, Schymick JC, Laaksovirta H, van Swieten JC, Myllykangas L, et al. A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD. Neuron. 2011;72:257–68. doi:10.1016/j.neuron.2011.09.010.

  67. 67.

    Robinson HK, Deykin AV, Bronovitsky EV, Ovchinnikov RK, Ustyugov AA, Shelkovnikova TA, Kukharsky MS, Ermolkevich TG, Goldman IL, Sadchikova ER, et al. Early lethality and neuronal proteinopathy in mice expressing cytoplasm-targeted FUS that lacks the RNA recognition motif. Amyotroph Lateral Scler Frontotemporal Degener. 2015;16:402–9. doi:10.3109/21678421.2015.1040994.

  68. 68.

    Rodriguez de Rivera FJ, Rambold HA, Diez-Tejedor E. Assessment of cognitive impairment in amyotrophic lateral sclerosis. J Neurol Sci. 2014;337:1–2. doi:10.1016/j.jns.2013.11.030.

  69. 69.

    Scekic-Zahirovic J, Sendscheid O, El Oussini H, Jambeau M, Sun Y, Mersmann S, Wagner M, Dieterle S, Sinniger J, Dirrig-Grosch S, et al. Toxic gain of function from mutant FUS protein is crucial to trigger cell autonomous motor neuron loss. EMBO J. 2016. doi:10.15252/embj.201592559.

  70. 70.

    Sephton CF, Tang AA, Kulkarni A, West J, Brooks M, Stubblefield JJ, Liu Y, Zhang MQ, Green CB, Huber KM, et al. Activity-dependent FUS dysregulation disrupts synaptic homeostasis. Proc Natl Acad Sci U S A. 2014;111:E4769–78. doi:10.1073/pnas.1406162111.

  71. 71.

    Sharma A, Lyashchenko AK, Lu L, Nasrabady SE, Elmaleh M, Mendelsohn M, Nemes A, Tapia JC, Mentis GZ, Shneider NA. ALS-associated mutant FUS induces selective motor neuron degeneration through toxic gain of function. Nat Commun. 2016;7:10465. doi:10.1038/ncomms10465.

  72. 72.

    Shaw PJ, Williams R. Serum and cerebrospinal fluid biochemical markers of ALS. Amyotroph Lateral Scler Other Motor Neuron Disord. 2000;1 Suppl 2:S61–7.

  73. 73.

    Shelkovnikova TA, Peters OM, Deykin AV, Connor-Robson N, Robinson H, Ustyugov AA, Bachurin SO, Ermolkevich TG, Goldman IL, Sadchikova ER, et al. Fused in sarcoma (FUS) protein lacking nuclear localization signal (NLS) and major RNA binding motifs triggers proteinopathy and severe motor phenotype in transgenic mice. J Biol Chem. 2013;288:25266–74. doi:10.1074/jbc.M113.492017.

  74. 74.

    Snowden JS, Hu Q, Rollinson S, Halliwell N, Robinson A, Davidson YS, Momeni P, Baborie A, Griffiths TD, Jaros E, Perry RH, Richardson A, Pickering-Brown SM, Neary D, Mann DM. The most common type of FTLD-FUS (aFTLD-U) is associated with a distinct clinical form of frontotemporal dementia but is not related to mutations in the FUS gene. Acta Neuropathol. 2011;122:99–110.

  75. 75.

    Sreedharan J, Blair IP, Tripathi VB, Hu X, Vance C, Rogelj B, Ackerley S, Durnall JC, Williams KL, Buratti E, et al. TDP-43 mutations in familial and sporadic amyotrophic lateral sclerosis. Science. 2008;319:1668–72. doi:10.1126/science.1154584.

  76. 76.

    Suarez-Calvet M, Neumann M, Arzberger T, Abou-Ajram C, Funk E, Hartmann H, Edbauer D, Kremmer E, Gobl C, Resch M, et al. Monomethylated and unmethylated FUS exhibit increased binding to Transportin and distinguish FTLD-FUS from ALS-FUS. Acta Neuropathol: Doi. 2016. doi:10.1007/s00401-016-1544-2.

  77. 77.

    Sykiotis GP, Plummer L, Hughes VA, Au M, Durrani S, Nayak-Young S, Dwyer AA, Quinton R, Hall JE, Gusella JF, et al. Oligogenic basis of isolated gonadotropin-releasing hormone deficiency. Proc Natl Acad Sci U S A. 2010;107:15140–4. doi:10.1073/pnas.1009622107.

  78. 78.

    Talbot K, Ansorge O. Recent advances in the genetics of amyotrophic lateral sclerosis and frontotemporal dementia: common pathways in neurodegenerative disease. Hum Mol Genet 2006; 15 Spec No 2: R182-187 Doi 10.1093/hmg/ddl202.

  79. 79.

    Tan AY, Riley TR, Coady T, Bussemaker HJ, Manley JL. TLS/FUS (translocated in liposarcoma/fused in sarcoma) regulates target gene transcription via single-stranded DNA response elements. Proc Natl Acad Sci U S A. 2012;109:6030–5. doi:10.1073/pnas.1203028109.

  80. 80.

    Tateishi T, Hokonohara T, Yamasaki R, Miura S, Kikuchi H, Iwaki A, Tashiro H, Furuya H, Nagara Y, Ohyagi Y, et al. Multiple system degeneration with basophilic inclusions in Japanese ALS patients with FUS mutation. Acta Neuropathol. 2010;119:355–64. doi:10.1007/s00401-009-0621-1.

  81. 81.

    Ticozzi N, Silani V, LeClerc AL, Keagle P, Gellera C, Ratti A, Taroni F, Kwiatkowski Jr TJ, McKenna-Yasek DM, Sapp PC, et al. Analysis of FUS gene mutation in familial amyotrophic lateral sclerosis within an Italian cohort. Neurology. 2009;73:1180–5. doi:10.1212/WNL.0b013e3181bbff05.

  82. 82.

    Tradewell ML, Yu Z, Tibshirani M, Boulanger MC, Durham HD, Richard S. Arginine methylation by PRMT1 regulates nuclear-cytoplasmic localization and toxicity of FUS/TLS harbouring ALS-linked mutations. Hum Mol Genet. 2012;21:136–49. doi:10.1093/hmg/ddr448.

  83. 83.

    Turner MR, Parton MJ, Leigh PN. Clinical trials in ALS: an overview. Semin Neurol. 2001;21:167–75. doi:10.1055/s-2001-15262.

  84. 84.

    Turner MR, Talbot K. Mimics and chameleons in motor neurone disease. Pract Neurol. 2013;13:153–64. doi:10.1136/practneurol-2013-000557.

  85. 85.

    van Blitterswijk M, De-Jesus-Hernandez M, Rademakers R. How do C9ORF72 repeat expansions cause ALS and FTD: can we learn from other non-coding repeat expansion disorders? Curr Opin Neurology. 2012;25:689–700.

  86. 86.

    van Blitterswijk M, van Es MA, Hennekam EA, Dooijes D, van Rheenen W, Medic J, Bourque PR, Schelhaas HJ, van der Kooi AJ, de Visser M, et al. Evidence for an oligogenic basis of amyotrophic lateral sclerosis. Hum Mol Genet. 2012;21:3776–84. doi:10.1093/hmg/dds199.

  87. 87.

    van Blitterswijk M, van Es MA, Koppers M, van Rheenen W, Medic J, Schelhaas HJ, van der Kooi AJ, de Visser M, Veldink JH, van den Berg LH. VAPB and C9orf72 mutations in 1 familial amyotrophic lateral sclerosis patient. Neurobiol Aging. 2012;33(2950):e2951–4. doi:10.1016/j.neurobiolaging.2012.07.004.

  88. 88.

    Van Langenhove T, van der Zee J, Sleegers K, Engelborghs S, Vandenberghe R, Gijselinck I, Van den Broeck M, Mattheijssens M, Peeters K, De Deyn PP, et al. Genetic contribution of FUS to frontotemporal lobar degeneration. Neurology. 2010;74:366–71. doi:10.1212/WNL.0b013e3181ccc732.

  89. 89.

    Van Langenhove T, van der Zee J, Van Broeckhoven C. The molecular basis of the frontotemporal lobar degeneration-amyotrophic lateral sclerosis spectrum. Ann Med. 2012;44:817–28. doi:10.3109/07853890.2012.665471.

  90. 90.

    Vance C, Rogelj B, Hortobagyi T, De Vos KJ, Nishimura AL, Sreedharan J, Hu X, Smith B, Ruddy D, Wright P, et al. Mutations in FUS, an RNA processing protein, cause familial amyotrophic lateral sclerosis type 6. Science. 2009;323:1208–11. doi:10.1126/science.1165942.

  91. 91.

    Vance C, Scotter EL, Nishimura AL, Troakes C, Mitchell JC, Kathe C, Urwin H, Manser C, Miller CC, Hortobagyi T, et al. ALS mutant FUS disrupts nuclear localization and sequesters wild-type FUS within cytoplasmic stress granules. Hum Mol Genet. 2013;22:2676–88. doi:10.1093/hmg/ddt117.

  92. 92.

    Verbeeck C, Deng Q, Dejesus-Hernandez M, Taylor G, Ceballos-Diaz C, Kocerha J, Golde T, Das P, Rademakers R, Dickson DW, et al. Expression of Fused in sarcoma mutations in mice recapitulates the neuropathology of FUS proteinopathies and provides insight into disease pathogenesis. Mol Neurodegener. 2012;7:53. doi:10.1186/1750-1326-7-53.

  93. 93.

    Wang WY, Pan L, Su SC, Quinn EJ, Sasaki M, Jimenez JC, Mackenzie IR, Huang EJ, Tsai LH. Interaction of FUS and HDAC1 regulates DNA damage response and repair in neurons. Nat Neurosci. 2013;16:1383–91. doi:10.1038/nn.3514.

  94. 94.

    Yokota O, Tsuchiya K, Terada S, Ishizu H, Uchikado H, Ikeda M, Oyanagi K, Nakano I, Murayama S, Kuroda S, et al. Basophilic inclusion body disease and neuronal intermediate filament inclusion disease: a comparative clinicopathological study. Acta Neuropathol. 2008;115:561–75. doi:10.1007/s00401-007-0329-z.

  95. 95.

    Zaghloul NA, Liu Y, Gerdes JM, Gascue C, Oh EC, Leitch CC, Bromberg Y, Binkley J, Leibel RL, Sidow A, et al. Functional analyses of variants reveal a significant role for dominant negative and common alleles in oligogenic Bardet-Biedl syndrome. Proc Natl Acad Sci U S A. 2010;107:10602–7. doi:10.1073/pnas.1000219107.

Download references

Funding

MN is funded by a PhD studentship from the Motor Neuron Disease Association. KT receives funding from the Motor Neuron Disease Association, SMA Trust and Medical Research Council. OA gratefully acknowledges support by the Motor Neurone Disease Association, the Medical Research Council (MRC), Brains for Dementia Research (BDR) (Alzheimer Society and Alzheimer Research UK) and the NIHR Oxford Biomedical Research Centre.

Authors’ contributions

MN wrote the manuscript. OA conceived the review. All authors contributed to and approved the final manuscript.

Competing interests

The authors declare that they have no competing interests.

Author information

Affiliations

  1. Neuropathology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK

    • Matthew Nolan
    •  & Olaf Ansorge

  2. Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK

    • Kevin Talbot

Authors

  1. Search for Matthew Nolan in:

  2. Search for Kevin Talbot in:

  3. Search for Olaf Ansorge in:

Corresponding author

Correspondence to Olaf Ansorge.

Rights and permissions

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Keywords

  • Amyotrophic lateral sclerosis
  • Frontotemporal dementia
  • MND
  • Frontotemporal lobar degeneration
  • FUS
  • FUSopathy
  • TDP-43

Acta Neuropathologica Communications

ISSN: 2051-5960

Contact us