Loss-of-Function Models of the Metabotropic Glutamate Receptor Genes Grm8a and Grm8b Display Distinct Behavioral Phenotypes in Zebrafish Larvae (Danio rerio)

Members of the family of metabotropic glutamate receptors are involved in the pathomechanism of several disorders of the nervous system. Besides the well-investigated function of dysfunctional glutamate receptor signaling in neurodegenerative diseases, neurodevelopmental disorders (NDD), like autism spectrum disorders (ASD) and attention-deficit and hyperactivity disorder (ADHD) might also be partly caused by disturbed glutamate signaling during development. However, the underlying mechanism of the type III metabotropic glutamate receptor 8 (mGluR8 or GRM8) involvement in neurodevelopment and disease mechanism is largely unknown. Here we show that the expression pattern of the two orthologs of human GRM8, grm8a and grm8b, have evolved partially distinct expression patterns in the brain of zebrafish (Danio rerio), especially at adult stages, suggesting sub-functionalization of these two genes during evolution. Using double in situ hybridization staining in the developing brain we demonstrate that grm8a is expressed in a subset of gad1a-positive cells, pointing towards glutamatergic modulation of GABAergic signaling. Building on this result we generated loss-of-function models of both genes using CRISPR/Cas9. Both mutant lines are viable and display no obvious gross morphological phenotypes making them suitable for further analysis. Initial behavioral characterization revealed distinct phenotypes in larvae. Whereas grm8a mutant animals display reduced swimming velocity, grm8b mutant animals show increased thigmotaxis behavior, suggesting an anxiety-like phenotype. We anticipate that our two novel metabotropic glutamate receptor 8 zebrafish models may contribute to a deeper understanding of its function in normal development and its role in the pathomechanism of disorders of the central nervous system.

Loss of full-length hnRNP R isoform impairs DNA damage response in motoneurons by inhibiting Yb1 recruitment to chromatin

Neurons critically rely on the functions of RNA-binding proteins to maintain their polarity and resistance to neurotoxic stress. HnRNP R has a diverse range of post-transcriptional regulatory functions and is important for neuronal development by regulating axon growth. Hnrnpr pre-mRNA undergoes alternative splicing giving rise to a full-length protein and a shorter isoform lacking its N-terminal acidic domain. To investigate functions selectively associated with the full-length hnRNP R isoform, we generated a Hnrnpr knockout mouse (Hnrnprtm1a/tm1a) in which expression of full-length hnRNP R was abolished while production of the truncated hnRNP R isoform was retained. Motoneurons cultured from Hnrnprtm1a/tm1a mice did not show any axonal growth defects but exhibited enhanced accumulation of double-strand breaks and an impaired DNA damage response upon exposure to genotoxic agents. Proteomic analysis of the hnRNP R interactome revealed the multifunctional protein Yb1 as a top interactor. Yb1-depleted motoneurons were defective in DNA damage repair. We show that Yb1 is recruited to chromatin upon DNA damage where it interacts with γ-H2AX, a mechanism that is dependent on full-length hnRNP R. Our findings thus suggest a novel role of hnRNP R in maintaining genomic integrity and highlight the function of its N-terminal acidic domain in this context.

Anxiety risk SNPs on chromosome 2 modulate arousal in children in a fear generalization paradigm

Alterations in fear learning/generalization are considered to be relevant mechanisms engendering the development of anxiety disorders being the most prevalent mental disorders. Although anxiety disorders almost exclusively have their first onset in childhood and adolescence, etiological research focuses on adult individuals. In this study, we evaluated findings of a recent meta-analysis of genome-wide association studies in adult anxiety disorders with significant associations of four single nucleotide polymorphisms (SNPs) in a large cohort of 347 healthy children (8-12 years) characterized for dimensional anxiety. We investigated the modulation of anxiety parameters by these SNPs in a discriminative fear conditioning and generalization paradigm in the to-date largest sample of children. Results extended findings of the meta-analysis showing a genomic locus on 2p21 to modulate anxious personality traits and arousal ratings. These SNPs might, thus, serve as susceptibility markers for a shared risk across pathological anxiety, presumably mediated by alterations in arousal.

Distribution of transcripts of the GFOD gene family members gfod1 and gfod2 in the zebrafish central nervous system

The glucose-fructose oxidoreductase domain containing gene family (GFOD) is small and contains only two members in human (GFOD1 and GFOD2). Information about its function is scarce. As the name implies the proteins contain an enzyme-defining domain, however, if this is functional and has enzymatic activity remains to be shown. A single nucleotide polymorphism situated in an intron of GFOD1 was found to be associated with inattentive symptomology in patients with attention-deficit/hyperactivity disorder. Further, in a large schizophrenia genome-wide association study the GFOD2 locus was found to be associated with the psychiatric condition. Until now, however, it is unclear what specific functions are associated with the two GFOD-family members, if they might be involved in neurodevelopment and how this may relate to the development of psychiatric disorders. In order to gain first insights into the hypothesis that GFOD-family members are involved in brain development and/or function we performed RNA in situ hybridization on zebrafish (Danio rerio) tissues at different developmental stages. We found that both family members are expressed in the central nervous system at embryonic, larvae and adult stages. We were able to define subtle differences of expression of the two gfod genes and we showed that a subset of GABAergic neurons express gfod1. Taken together, we conclude that both gfod gene family members are expressed in overlapping as well as in distinct regions in the zebrafish central nervous system. Our data suggest that gfod1 and gfod2 are relevant both for the developing and adult zebrafish brain. This study paves the way for further functional analyses of this yet unexplored gene family.

Transcript Analysis of Zebrafish GLUT3 Genes, slc2a3a and slc2a3b, Define Overlapping as Well as Distinct Expression Domains in the Zebrafish (Danio rerio) Central Nervous System

The transport of glucose across the cell plasma membrane is vital to most mammalian cells. The glucose transporter (GLUT; also called SLC2A) family of transmembrane solute carriers is responsible for this function in vivo. GLUT proteins encompass 14 different isoforms in humans with different cell type-specific expression patterns and activities. Central to glucose utilization and delivery in the brain is the neuronally expressed GLUT3. Recent research has shown an involvement of GLUT3 genetic variation or altered expression in several different brain disorders, including Huntington's and Alzheimer's diseases. Furthermore, GLUT3 was identified as a potential risk gene for multiple psychiatric disorders. To study the role of GLUT3 in brain function and disease a more detailed knowledge of its expression in model organisms is needed. Zebrafish (Danio rerio) has in recent years gained popularity as a model organism for brain research and is now well-established for modeling psychiatric disorders. Here, we have analyzed the sequence of GLUT3 orthologs and identified two paralogous genes in the zebrafish, slc2a3a and slc2a3b. Interestingly, the Glut3b protein sequence contains a unique stretch of amino acids, which may be important for functional regulation. The slc2a3a transcript is detectable in the central nervous system including distinct cellular populations in telencephalon, diencephalon, mesencephalon and rhombencephalon at embryonic and larval stages. Conversely, the slc2a3b transcript shows a rather diffuse expression pattern at different embryonic stages and brain regions. Expression of slc2a3a is maintained in the adult brain and is found in the telencephalon, diencephalon, mesencephalon, cerebellum and medulla oblongata. The slc2a3b transcripts are present in overlapping as well as distinct regions compared to slc2a3a. Double in situ hybridizations were used to demonstrate that slc2a3a is expressed by some GABAergic neurons at embryonic stages. This detailed description of zebrafish slc2a3a and slc2a3b expression at developmental and adult stages paves the way for further investigations of normal GLUT3 function and its role in brain disorders.

Transcranial sonography in psychiatry as a potential tool in diagnosis and research

OBJECTIVES

During the last two decades transcranial sonography (TCS) of the brain parenchyma evolved from a pure research tool to a clinical relevant neuroimaging method especially in Parkinson's disease and related movement disorders. The aim of this systematic review is to update and summarise the published TCS findings in psychiatric disorders and critically address the question whether TCS may be a valuable tool for the diagnosis or differential diagnosis of psychiatric disorders similarly to the field of movement disorders.

METHODS

This paper provides detailed information about the perspectives and limitations of TCS, including guidelines for the scanning procedures, assessment of midbrain structures and discusses the potential causes of the ultrasound abnormalities in psychiatric disorders.

RESULTS

Changes in the echogenicity of subcortical brain structures were detected in different disorders, such as obsessive-compulsive disorder, autism spectrum disorder, schizophrenia, panic disorder, attention-deficit/hyperactivity (ADHD), bipolar disorder and depressive disorder. Although the physical properties of brain tissue underlying the echogenic features in TCS are largely unknown, no alternative technique provides the same insight into the specific central nervous structural characteristics.

CONCLUSIONS

Urgent research questions to further clarify the underlying pathophysiological and structural alterations are further outlined to bring this promising technique to the clinic.

ALS-Associated Endoplasmic Reticulum Proteins in Denervated Skeletal Muscle: Implications for Motor Neuron Disease Pathology

Alpha-motoneurons and muscle fibres are structurally and functionally interdependent. Both cell types particularly rely on endoplasmic reticulum (ER/SR) functions. Mutations of the ER proteins VAPB, SigR1 and HSP27 lead to hereditary motor neuron diseases (MNDs). Here, we determined the expression profile and localization of these ER proteins/chaperons by immunohistochemistry and immunoblotting in biopsy and autopsy muscle tissue of patients with amyotrophic lateral sclerosis (ALS) and other neurogenic muscular atrophies (NMAs) and compared these patterns to mouse models of neurogenic muscular atrophy. Postsynaptic neuromuscular junction staining for VAPB was intense in normal human and mouse muscle and decreased in denervated Nmd^2J mouse muscle fibres. In contrast, VAPB levels together with other chaperones and autophagy markers were increased in extrasynaptic regions of denervated muscle fibres of patients with MNDs and other NMAs, especially at sites of focal myofibrillar disintegration (targets). These findings did not differ between NMAs due to ALS and other causes. G93A-SOD1 mouse muscle fibres showed a similar pattern of protein level increases in denervated muscle fibres. In addition, they showed globular VAPB-immunoreactive structures together with misfolded SOD1 protein accumulations, suggesting a primary myopathic change. Our findings indicate that altered expression and localization of these ER proteins and autophagy markers are part of the dynamic response of muscle fibres to denervation. The ER is particularly prominent and vulnerable in both muscle fibres and alpha-motoneurons. Thus, ER pathology could contribute to the selective build-up of degenerative changes in the neuromuscular axis in MNDs.

Serotonergic modulation of 'waiting impulsivity' is mediated by the impulsivity phenotype in humans

In rodents, the five-choice serial reaction time task (5-CSRTT) has been established as a reliable measure of waiting impulsivity being defined as the ability to regulate a response in anticipation of reinforcement. Key brain structures are the nucleus accumbens (NAcc) and prefrontal regions (for example, pre- and infralimbic cortex), which are, together with other transmitters, modulated by serotonin. In this functional magnetic resonance imaging study, we examined 103 healthy males while performing the 5-CSRTT measuring brain activation in humans by means of a paradigm that has been widely applied in rodents. Subjects were genotyped for the tryptophan hydroxylase-2 (TPH2; G-703T; rs4570625) variant, an enzyme specific for brain serotonin synthesis. We addressed neural activation patterns of waiting impulsivity and the interaction between the NAcc and the ventromedial prefrontal cortex (vmPFC) using dynamic causal modeling. Genetic influence was examined via interaction analyses between the TPH2 genotype (GG homozygotes vs T allele carriers) and the degree of impulsivity as measured by the 5-CSRTT. We found that the driving input of the vmPFC was reduced in highly impulsive T allele carriers (reflecting a reduced top-down control) in combination with an enhanced response in the NAcc after correct target processing (reflecting an augmented response to monetary reward). Taken together, we found a high overlap of our findings with reports from animal studies in regard to the underlying cognitive processes, the brain regions associated with waiting impulsivity and the neural interplay between the NAcc and vmPFC. Therefore, we conclude that the 5-CSRTT is a promising tool for translational studies.

C9ORF72 interaction with cofilin modulates actin dynamics in motor neurons

Intronic hexanucleotide expansions in C9ORF72 are common in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia, but it is unknown whether loss of function, toxicity by the expanded RNA or dipeptides from non-ATG-initiated translation are responsible for the pathophysiology. We determined the interactome of C9ORF72 in motor neurons and found that C9ORF72 was present in a complex with cofilin and other actin binding proteins. Phosphorylation of cofilin was enhanced in C9ORF72-depleted motor neurons, in patient-derived lymphoblastoid cells, induced pluripotent stem cell-derived motor neurons and post-mortem brain samples from ALS patients. C9ORF72 modulates the activity of the small GTPases Arf6 and Rac1, resulting in enhanced activity of LIM-kinases 1 and 2 (LIMK1/2). This results in reduced axonal actin dynamics in C9ORF72-depleted motor neurons. Dominant negative Arf6 rescues this defect, suggesting that C9ORF72 acts as a modulator of small GTPases in a pathway that regulates axonal actin dynamics.

NEK1 variants confer susceptibility to amyotrophic lateral sclerosis

To identify genetic factors contributing to amyotrophic lateral sclerosis (ALS), we conducted whole-exome analyses of 1,022 index familial ALS (FALS) cases and 7,315 controls. In a new screening strategy, we performed gene-burden analyses trained with established ALS genes and identified a significant association between loss-of-function (LOF) NEK1 variants and FALS risk. Independently, autozygosity mapping for an isolated community in the Netherlands identified a NEK1 p.Arg261His variant as a candidate risk factor. Replication analyses of sporadic ALS (SALS) cases and independent control cohorts confirmed significant disease association for both p.Arg261His (10,589 samples analyzed) and NEK1 LOF variants (3,362 samples analyzed). In total, we observed NEK1 risk variants in nearly 3% of ALS cases. NEK1 has been linked to several cellular functions, including cilia formation, DNA-damage response, microtubule stability, neuronal morphology and axonal polarity. Our results provide new and important insights into ALS etiopathogenesis and genetic etiology.

Genome-wide association analyses identify new risk variants and the genetic architecture of amyotrophic lateral sclerosis

To elucidate the genetic architecture of amyotrophic lateral sclerosis (ALS) and find associated loci, we assembled a custom imputation reference panel from whole-genome-sequenced patients with ALS and matched controls (n = 1,861). Through imputation and mixed-model association analysis in 12,577 cases and 23,475 controls, combined with 2,579 cases and 2,767 controls in an independent replication cohort, we fine-mapped a new risk locus on chromosome 21 and identified C21orf2 as a gene associated with ALS risk. In addition, we identified MOBP and SCFD1 as new associated risk loci. We established evidence of ALS being a complex genetic trait with a polygenic architecture. Furthermore, we estimated the SNP-based heritability at 8.5%, with a distinct and important role for low-frequency variants (frequency 1-10%). This study motivates the interrogation of larger samples with full genome coverage to identify rare causal variants that underpin ALS risk.

Developmental exposure to acetaminophen does not induce hyperactivity in zebrafish larvae

First line pain relief medication during pregnancy relies nearly entirely on the over-the-counter analgesic acetaminophen, which is generally considered safe to use during gestation. However, recent epidemiological studies suggest a risk of developing attention-deficit/hyperactivity disorder (ADHD)-like symptoms in children if mothers use acetaminophen during pregnancy. Currently, there are no experimental proofs that prenatal acetaminophen exposure causes developmental brain alterations of progeny. Exposure to high acetaminophen concentrations causes liver toxicity, which is well investigated in different model organisms. However, sub-liver-toxic concentrations have not been experimentally investigated with respect to ADHD endophenotypes such as hyperactivity. We used zebrafish to investigate the potential impact of acetaminophen exposure on locomotor activity levels, and compared it to the established zebrafish Latrophilin 3 (Lphn3) ADHD-model. We determined the sub-liver-toxic concentration of acetaminophen in zebrafish larvae and treated wild-type and lphn3.1 knockdown larvae with increasing concentrations of acetaminophen. We were able to confirm that lphn3.1 knockdown alone causes hyperactivity, strengthening the implication of Lphn3 dysfunction as an ADHD risk factor. Neither acute nor chronic exposure to acetaminophen at sub-liver-toxic concentrations in wild-type or lphn3.1 knock-downs increases locomotor activity levels. Together our findings show that embryonic to larval exposure to acetaminophen does not cause hyperactivity in zebrafish larvae. Furthermore, there are no additive and/or synergistic effects of acetaminophen exposure in a susceptible background induced by knock-down of lphn3.1. Our experimental study suggests that there is, at least in zebrafish larvae, no direct link between embryonic acetaminophen exposure and hyperactivity. Further work is necessary to clarify this issue in humans.

Deep proteomic evaluation of primary and cell line motoneuron disease models delineates major differences in neuronal characteristics

The fatal neurodegenerative disorders amyotrophic lateral sclerosis and spinal muscular atrophy are, respectively, the most common motoneuron disease and genetic cause of infant death. Various in vitro model systems have been established to investigate motoneuron disease mechanisms, in particular immortalized cell lines and primary neurons. Using quantitative mass-spectrometry-based proteomics, we compared the proteomes of primary motoneurons to motoneuron-like cell lines NSC-34 and N2a, as well as to non-neuronal control cells, at a depth of 10,000 proteins. We used this resource to evaluate the suitability of murine in vitro model systems for cell biological and biochemical analysis of motoneuron disease mechanisms. Individual protein and pathway analysis indicated substantial differences between motoneuron-like cell lines and primary motoneurons, especially for proteins involved in differentiation, cytoskeleton, and receptor signaling, whereas common metabolic pathways were more similar. The proteins associated with amyotrophic lateral sclerosis also showed distinct differences between cell lines and primary motoneurons, providing a molecular basis for understanding fundamental alterations between cell lines and neurons with respect to neuronal pathways with relevance for disease mechanisms. Our study provides a proteomics resource for motoneuron research and presents a paradigm of how mass-spectrometry-based proteomics can be used to evaluate disease model systems.

Mutations in the Matrin 3 gene cause familial amyotrophic lateral sclerosis

MATR3 is an RNA- and DNA-binding protein that interacts with TDP-43, a disease protein linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Using exome sequencing, we identified mutations in MATR3 in ALS kindreds. We also observed MATR3 pathology in ALS-affected spinal cords with and without MATR3 mutations. Our data provide more evidence supporting the role of aberrant RNA processing in motor neuron degeneration.

Clinical characteristics of patients with familial amyotrophic lateral sclerosis carrying the pathogenic GGGGCC hexanucleotide repeat expansion of C9ORF72

A large hexanucleotide (GGGGCC) repeat expansion in the first intron of C9ORF72, a gene located on chromosome 9p21, has been recently reported to be responsible for ~40% of familial amyotrophic lateral sclerosis cases of European ancestry. The aim of the current article was to describe the phenotype of amyotrophic lateral sclerosis cases carrying the expansion by providing a detailed clinical description of affected cases from representative multi-generational kindreds, and by analysing the age of onset, gender ratio and survival in a large cohort of patients with familial amyotrophic lateral sclerosis. We collected DNA and analysed phenotype data for 141 index Italian familial amyotrophic lateral sclerosis cases (21 of Sardinian ancestry) and 41 German index familial amyotrophic lateral sclerosis cases. Pathogenic repeat expansions were detected in 45 (37.5%) patients from mainland Italy, 12 (57.1%) patients of Sardinian ancestry and nine (22.0%) of the 41 German index familial amyotrophic lateral sclerosis cases. The disease was maternally transmitted in 27 (49.1%) pedigrees and paternally transmitted in 28 (50.9%) pedigrees (P = non-significant). On average, children developed disease 7.0 years earlier than their parents [children: 55.8 years (standard deviation 7.9), parents: 62.8 (standard deviation 10.9); P = 0.003]. Parental phenotype influenced the type of clinical symptoms manifested by the child: of the 13 cases where the affected parent had an amyotrophic lateral sclerosis-frontotemporal dementia or frontotemporal dementia, the affected child also developed amyotrophic lateral sclerosis-frontotemporal dementia in nine cases. When compared with patients carrying mutations of other amyotrophic lateral sclerosis-related genes, those with C9ORF72 expansion had commonly a bulbar onset (42.2% compared with 25.0% among non-C9ORF72 expansion cases, P = 0.03) and cognitive impairment (46.7% compared with 9.1% among non-C9ORF72 expansion cases, P = 0.0001). Median survival from symptom onset among cases carrying C9ORF72 repeat expansion was 3.2 years lower than that of patients carrying TARDBP mutations (5.0 years; 95% confidence interval: 3.6-7.2) and longer than those with FUS mutations (1.9 years; 95% confidence interval: 1.7-2.1). We conclude that C9ORF72 hexanucleotide repeat expansions were the most frequent mutation in our large cohort of patients with familial amyotrophic lateral sclerosis of Italian, Sardinian and German ancestry. Together with mutation of SOD1, TARDBP and FUS, mutations of C9ORF72 account for ~60% of familial amyotrophic lateral sclerosis in Italy. Patients with C9ORF72 hexanucleotide repeat expansions present some phenotypic differences compared with patients with mutations of other genes or with unknown mutations, namely a high incidence of bulbar-onset disease and comorbidity with frontotemporal dementia. Their pedigrees typically display a high frequency of cases with pure frontotemporal dementia, widening the concept of familial amyotrophic lateral sclerosis.

Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study

BACKGROUND

We aimed to accurately estimate the frequency of a hexanucleotide repeat expansion in C9orf72 that has been associated with a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).

METHODS

We screened 4448 patients diagnosed with ALS (El Escorial criteria) and 1425 patients with FTD (Lund-Manchester criteria) from 17 regions worldwide for the GGGGCC hexanucleotide expansion using a repeat-primed PCR assay. We assessed familial disease status on the basis of self-reported family history of similar neurodegenerative diseases at the time of sample collection. We compared haplotype data for 262 patients carrying the expansion with the known Finnish founder risk haplotype across the chromosomal locus. We calculated age-related penetrance using the Kaplan-Meier method with data for 603 individuals with the expansion.

FINDINGS

In patients with sporadic ALS, we identified the repeat expansion in 236 (7·0%) of 3377 white individuals from the USA, Europe, and Australia, two (4·1%) of 49 black individuals from the USA, and six (8·3%) of 72 Hispanic individuals from the USA. The mutation was present in 217 (39·3%) of 552 white individuals with familial ALS from Europe and the USA. 59 (6·0%) of 981 white Europeans with sporadic FTD had the mutation, as did 99 (24·8%) of 400 white Europeans with familial FTD. Data for other ethnic groups were sparse, but we identified one Asian patient with familial ALS (from 20 assessed) and two with familial FTD (from three assessed) who carried the mutation. The mutation was not carried by the three Native Americans or 360 patients from Asia or the Pacific Islands with sporadic ALS who were tested, or by 41 Asian patients with sporadic FTD. All patients with the repeat expansion had (partly or fully) the founder haplotype, suggesting a one-off expansion occurring about 1500 years ago. The pathogenic expansion was non-penetrant in individuals younger than 35 years, 50% penetrant by 58 years, and almost fully penetrant by 80 years.

INTERPRETATION

A common Mendelian genetic lesion in C9orf72 is implicated in many cases of sporadic and familial ALS and FTD. Testing for this pathogenic expansion should be considered in the management and genetic counselling of patients with these fatal neurodegenerative diseases.

FUNDING

Full funding sources listed at end of paper (see Acknowledgments).

PTEN depletion rescues axonal growth defect and improves survival in SMN-deficient motor neurons

Phosphatase and tensin homolog (PTEN), a negative regulator of the mammalian target of rapamycin (mTOR) pathway, is widely involved in the regulation of protein synthesis. Here we show that the PTEN protein is enriched in cell bodies and axon terminals of purified motor neurons. We explored the role of the PTEN pathway by manipulating PTEN expression in healthy and diseased motor neurons. PTEN depletion led to an increase in growth cone size, promotion of axonal elongation and increased survival of these cells. These changes were associated with alterations of downstream signaling pathways for local protein synthesis as revealed by an increase in pAKT and p70S6. Most notably, this treatment also restores beta-actin protein levels in axonal growth cones of SMN-deficient motor neurons. Furthermore, we report here that a single injection of adeno-associated virus serotype 6 (AAV6) expressing siPTEN into hind limb muscles at postnatal day 1 in SMNDelta7 mice leads to a significant PTEN depletion and robust improvement in motor neuron survival. Taken together, these data indicate that PTEN-mediated regulation of protein synthesis in motor neurons could represent a target for therapy in spinal muscular atrophy.

A functional screen implicates microRNA-138-dependent regulation of the depalmitoylation enzyme APT1 in dendritic spine morphogenesis

The microRNA pathway has been implicated in the regulation of synaptic protein synthesis and ultimately in dendritic spine morphogenesis, a phenomenon associated with long-lasting forms of memory. However, the particular microRNAs (miRNAs) involved are largely unknown. Here we identify specific miRNAs that function at synapses to control dendritic spine structure by performing a functional screen. One of the identified miRNAs, miR-138, is highly enriched in the brain, localized within dendrites and negatively regulates the size of dendritic spines in rat hippocampal neurons. miR-138 controls the expression of acyl protein thioesterase 1 (APT1), an enzyme regulating the palmitoylation status of proteins that are known to function at the synapse, including the alpha(13) subunits of G proteins (Galpha(13)). RNA-interference-mediated knockdown of APT1 and the expression of membrane-localized Galpha(13) both suppress spine enlargement caused by inhibition of miR-138, suggesting that APT1-regulated depalmitoylation of Galpha(13) might be an important downstream event of miR-138 function. Our results uncover a previously unknown miRNA-dependent mechanism in neurons and demonstrate a previously unrecognized complexity of miRNA-dependent control of dendritic spine morphogenesis.

Mutation of Vps54 causes motor neuron disease and defective spermiogenesis in the wobbler mouse

Vacuolar-vesicular protein sorting (Vps) factors are involved in vesicular trafficking in eukaryotic cells. We identified the missense mutation L967Q in Vps54 in the wobbler mouse, an animal model of amyotrophic lateral sclerosis, and also characterized a lethal allele, Vps54(beta-geo). Motoneuron survival and spermiogenesis are severely compromised in the wobbler mouse, indicating that Vps54 has an essential role in these processes.