Amyotrophic lateral sclerosis (ALS) is a devastating neurological disease with no effective treatment. Here we report the results of a moderate-scale sequencing study aimed at identifying new genes contributing to predisposition for ALS. We performed whole exome sequencing of 2,874 ALS patients and compared them to 6,405 controls. Several known ALS genes were found to be associated, and the non-canonical IκB kinase family TANK-Binding Kinase 1 (TBK1) was identified as an ALS gene. TBK1 is known to bind to and phosphorylate a number of proteins involved in innate immunity and autophagy, including optineurin (OPTN) and p62 (SQSTM1/sequestosome), both of which have also been implicated in ALS. These observations reveal a key role of the autophagic pathway in ALS and suggest specific targets for therapeutic intervention.

Amyotrophic lateral sclerosis (ALS) is a fatal, late-onset neurodegenerative disease primarily impacting motor neurons. A unifying feature of many proteins associated with ALS, including TDP-43 and Ataxin-2, is that they localize to stress granules. Unexpectedly, we found that genes that modulate stress granules are striking modifiers of TDP-43 toxicity in Saccharomyces cerevisiae and Drosophila melanogaster, eIF2α phosphorylation is upregulated by TDP-43 toxicity in flies, and TDP-43 interacts with a central stress granule component polyA binding protein (PABP). In human ALS spinal cord neurons, PABP accumulates abnormally, suggesting that prolonged stress granule dysfunction may contribute to pathogenesis. We investigated the efficacy of a small molecule inhibitor of eIF2α-phosphorylation in ALS models. This treatment mitigated TDP-43 toxicity in flies and mammalian neurons. These findings indicate that dysfunction induced by prolonged stress granule formation may contribute directly to ALS and that compounds that mitigate this process may represent a novel therapeutic approach.

To identify novel genes associated with ALS, we undertook two lines of investigation. We carried out a genome-wide association study comparing 20,806 ALS cases and 59,804 controls. Independently, we performed a rare variant burden analysis comparing 1,138 index familial ALS cases and 19,494 controls. Through both approaches, we identified kinesin family member 5A (KIF5A) as a novel gene associated with ALS. Interestingly, mutations predominantly in the N-terminal motor domain of KIF5A are causative for two neurodegenerative diseases: hereditary spastic paraplegia (SPG10) and Charcot-Marie-Tooth type 2 (CMT2). In contrast, ALS-associated mutations are primarily located at the C-terminal cargo-binding tail domain and patients harboring loss-of-function mutations displayed an extended survival relative to typical ALS cases. Taken together, these results broaden the phenotype spectrum resulting from mutations in KIF5A and strengthen the role of cytoskeletal defects in the pathogenesis of ALS.

ALS is a devastating neurodegenerative disease whose causes are still poorly understood. To identify additional genetic risk factors, here we assess the role of de novo mutations in ALS by sequencing the exomes of 47 ALS patients and both of their unaffected parents (n=141 exomes). We found that amino acid-altering de novo mutations are enriched in genes encoding chromatin regulators, including the neuronal chromatin remodeling complex component SS18L1/CREST. CREST mutations inhibit activity-dependent neurite outgrowth in primary neurons, and CREST associates with the ALS protein FUS. These findings expand our understanding of the ALS genetic landscape and provide a resource for future studies into the pathogenic mechanisms contributing to sporadic ALS.

In the peripheral nervous system, Schwann cells make myelin, a specialized sheath that is essential for rapid axonal conduction of action potentials. Immature Schwann cells initially interact with many axons, but, through a process termed radial sorting, eventually interact with one segment of a single axon as promyelinating Schwann cells. Previous studies have identified genes that are required for Schwann cell process extension and proliferation during radial sorting. Previous analyses also show that ErbB signaling is required for Schwann cell proliferation, myelination, radial sorting, and the proper formation of unmyelinated Remak bundles. Because ErbB signaling and Schwann cell proliferation are both required during radial sorting, we sought to determine if the primary function of ErbB signaling in this process is to regulate Schwann cell proliferation or if ErbB signaling also controls other aspects of radial sorting. To address this question, we applied small molecule inhibitors in vivo in zebrafish to independently block ErbB signaling and proliferation. Ultrastructural analysis of treated animals revealed that both ErbB signaling and Schwann cell proliferation are required for radial sorting in vivo. ErbB signaling, however, is required for Schwann cell process extension, while Schwann cell proliferation is not. These results provide in vivo evidence that ErbB signaling plays a direct role in process extension during radial sorting, in addition to its role in regulating Schwann cell proliferation.

During peripheral nerve development, Schwann cells ensheathe axons and form myelin to enable rapid and efficient action potential propagation. Although myelination requires profound changes in Schwann cell shape, how neuron-glia interactions converge on the Schwann cell cytoskeleton to induce these changes is unknown. Here, we demonstrate that the submembranous cytoskeletal proteins αII and βII spectrin are polarized in Schwann cells and colocalize with signaling molecules known to modulate myelination in vitro. Silencing expression of these spectrins inhibited myelination in vitro, and remyelination in vivo. Furthermore, myelination was disrupted in motor nerves of zebrafish lacking αII spectrin. Finally, we demonstrate that loss of spectrin significantly reduces both F-actin in the Schwann cell cytoskeleton and the Nectin-like protein, Necl4, at the contact site between Schwann cells and axons. Therefore, we propose αII and βII spectrin in Schwann cells integrate the neuron-glia interactions mediated by membrane proteins into the actin-dependent cytoskeletal rearrangements necessary for myelination.R apid and efficient action potential propagation in vertebrates depends on axon ensheathement by a multilammelar membrane sheath called myelin. Myelin is made by Schwann cells in the peripheral nervous system (PNS). During development, neuron-glia interactions induce reciprocal differentiation such that axons regulate Schwann cell differentiation, migration, and myelination, and Schwann cells regulate the organization of axonal membrane domains (1-3). The mechanisms regulating PNS myelination still remain poorly understood. In particular, myelination requires dramatic and dynamic changes in the Schwann cell cytoskeleton, leading to the profound changes in cell shape that accompany axonal ensheathement and wrapping. However, how axon-Schwann cell interactions converge on the Schwann cell cytoskeleton to induce these changes is unknown.A recent study suggests that submembranous cytoskeletal proteins, called spectrins, may contribute to myelination: a dominantnegative human mutation in αII spectrin causes severe cerebral hypomyelination (4). Spectrins are a family of extended, flexible cytoskeletal molecules consisting of α and β subunits (5). β-Spectrins interact with both the actin cytoskeleton and various membrane proteins via scaffolding proteins, such as ankyrins or 4.1 proteins. Spectrins are thought to (i) stabilize membrane protein complexes, (ii) provide mechanical support for cell membrane integrity, and (iii) serve as a multifunctional regulatory platform for cell signaling (6). Spectrins are abundantly expressed in the nervous system, but have traditionally been assumed to be mostly neuronal. For example, spectrins contribute to stabilization of axonal membrane domains including the node of Ranvier (7). Although spectrins were previously reported in myelinating Schwann cells, their specific isoforms and functions are not known (8).Here, we demonstrate that the submembranous cytoskeletal proteins in Schwann...

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive degeneration of motor neurons, ultimately leading to paralysis and death. Approximately 10% of ALS cases are familial, with the remaining 90% of cases being sporadic. Genetic studies in familial cases of ALS have been extremely informative in determining the causative mutations behind ALS, especially as the same mutations identified in familial ALS can also cause sporadic disease. However, the cause of ALS in approximately 30% of familial cases and in the majority of sporadic cases remains unknown. Sporadic ALS cases represent an underutilized resource for genetic information about ALS; therefore, we undertook a targeted sequencing approach of 169 known and candidate ALS disease genes in 242 sporadic ALS cases and 129 matched controls to try to identify novel variants linked to ALS. We found a significant enrichment in novel and rare variants in cases versus controls, indicating that we are likely identifying disease associated mutations. This study highlights the utility of next generation sequencing techniques combined with functional studies and rare variant analysis tools to provide insight into the genetic etiology of a heterogeneous sporadic disease.

The alpha-dystroglycanopathies are genetically heterogeneous muscular dystrophies that result from hypoglycosylation of alpha-dystroglycan (α-DG). Alpha-dystroglycan is an essential link between the extracellular matrix and the muscle fiber sarcolemma, and proper glycosylation is critical for its ability to bind to ligands in the extracellular matrix. We sought to identify the genetic basis of alpha-dystroglycanopathy in a family wherein the affected individuals presented with congenital muscular dystrophy, brain abnormalities and generalized epilepsy. We performed whole exome sequencing and identified compound heterozygous GMPPB mutations in the affected children. GMPPB is an enzyme in the glycosylation pathway, and GMPPB mutation were recently linked to eight cases of alpha-dystroglycanopathy with a range of symptoms. We identified a novel mutation in GMPPB (p.I219T) as well as a previously published mutation (p.R287Q). Thus, our work further confirms a role for GMPPB defects in alpha-dystroglycanopathy, and suggests that glycosylation may play a role in the neuronal membrane channels or networks involved in the physiology of generalized epilepsy syndromes.