High-Resolution Studies of Proteins in Natural Membranes by Solid-State NMR.

Membrane proteins are vital for cell function and thus represent important drug targets. Solid-state Nuclear Magnetic Resonance (ssNMR) spectroscopy offers a unique access to probe the structure and dynamics of such proteins in biological membranes of increasing complexity. Here, we present modern solid-state NMR spectroscopy as a tool to study structure and dynamics of proteins in natural lipid membranes and at atomic scale. Such spectroscopic studies profit from the use of high-sensitivity ssNMR methods, i.e., proton-(1H)-detected ssNMR and DNP (Dynamic Nuclear Polarization) supported ssNMR. Using bacterial outer membrane beta-barrel protein BamA and the ion channel KcsA, we present methods to prepare isotope-labeled membrane proteins and to derive structural and motional information by ssNMR.

Detection of long repeat expansions from PCR-free whole-genome sequence data.

Identifying large expansions of short tandem repeats (STRs), such as those that cause amyotrophic lateral sclerosis (ALS) and fragile X syndrome, is challenging for short-read whole-genome sequencing (WGS) data. A solution to this problem is an important step toward integrating WGS into precision medicine. We developed a software tool called ExpansionHunter that, using PCR-free WGS short-read data, can genotype repeats at the locus of interest, even if the expanded repeat is larger than the read length. We applied our algorithm to WGS data from 3001 ALS patients who have been tested for the presence of the C9orf72 repeat expansion with repeat-primed PCR (RP-PCR). Compared against this truth data, ExpansionHunter correctly classified all (212/212, 95% CI [0.98, 1.00]) of the expanded samples as either expansions (208) or potential expansions (4). Additionally, 99.9% (2786/2789, 95% CI [0.997, 1.00]) of the wild-type samples were correctly classified as wild type by this method with the remaining three samples identified as possible expansions. We further applied our algorithm to a set of 152 samples in which every sample had one of eight different pathogenic repeat expansions, including those associated with fragile X syndrome, Friedreich's ataxia, and Huntington's disease, and correctly flagged all but one of the known repeat expansions. Thus, ExpansionHunter can be used to accurately detect known pathogenic repeat expansions and provides researchers with a tool that can be used to identify new pathogenic repeat expansions.

The role of de novo mutations in the development of amyotrophic lateral sclerosis.

The genetic basis combined with the sporadic occurrence of amyotrophic lateral sclerosis (ALS) suggests a role of de novo mutations in disease pathogenesis. Previous studies provided some evidence for this hypothesis; however, results were conflicting: no genes with recurrent occurring de novo mutations were identified and different pathways were postulated. In this study, we analyzed whole-exome data from 82 new patient-parents trios and combined it with the datasets of all previously published ALS trios (173 trios in total). The per patient de novo rate was not higher than expected based on the general population (P = 0.40). We showed that these mutations are not part of the previously postulated pathways, and gene-gene interaction analysis found no enrichment of interacting genes in this group (P = 0.57). Also, we were able to show that the de novo mutations in ALS patients are located in genes already prone for de novo mutations (P < 1 × 10-15 ). Although the individual effect of rare de novo mutations in specific genes could not be assessed, our results indicate that, in contrast to previous hypothesis, de novo mutations in general do not impose a major burden on ALS risk.

FoxO6 affects Plxna4-mediated neuronal migration during mouse cortical development.

The forkhead transcription factor FoxO6 is prominently expressed during development of the murine neocortex. However, its function in cortical development is as yet unknown. We now demonstrate that cortical development is altered in FoxO6+/- and FoxO6-/- mice, showing migrating neurons halted in the intermediate zone. Using a FoxO6-directed siRNA approach, we substantiate the requirement of FoxO6 for a correct radial migration in the developing neocortex. Subsequent genome-wide transcriptome analysis reveals altered expression of genes involved in cell adhesion, axon guidance, and gliogenesis upon silencing of FoxO6 We then show that FoxO6 binds to DAF-16-binding elements in the Plexin A4 (Plxna4) promoter region and affects Plxna4 expression. Finally, ectopic Plxna4 expression restores radial migration in FoxO6+/- and siRNA-mediated knockdown models. In conclusion, the presented data provide insights into the molecular mechanisms whereby transcriptional programs drive cortical development.

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.

C9orf72 ablation in mice does not cause motor neuron degeneration or motor deficits.

OBJECTIVE: How hexanucleotide (GGGGCC) repeat expansions in C9ORF72 cause amyotrophic lateral sclerosis (ALS) remains poorly understood. Both gain- and loss-of-function mechanisms have been proposed. Evidence supporting these mechanisms in vivo is, however, incomplete. Here we determined the effect of C9orf72 loss-of-function in mice. METHODS: We generated and analyzed a conditional C9orf72 knockout mouse model. C9orf72(fl/fl) mice were crossed with Nestin-Cre mice to selectively remove C9orf72 from neurons and glial cells. Immunohistochemistry was performed to study motor neurons and neuromuscular integrity, as well as several pathological hallmarks of ALS, such as gliosis and TDP-43 mislocalization. In addition, motor function and survival were assessed. RESULTS: Neural-specific ablation of C9orf72 in conditional C9orf72 knockout mice resulted in significantly reduced body weight but did not induce motor neuron degeneration, defects in motor function, or altered survival. INTERPRETATION: Our data suggest that C9orf72 loss-of-function, by itself, is insufficient to cause motor neuron disease. These results may have important implications for the development of therapeutic strategies for C9orf72-associated ALS.

Fcγ receptor IIIA genotype is associated with rituximab response in antimyelin-associated glycoprotein neuropathy.

BACKGROUND: Treatment with anti-B cell antibody rituximab may ameliorate the disease course in a subgroup of patients with polyneuropathy associated with IgM monoclonal gammopathy. Polymorphisms of leukocyte IgG receptors (FcγR) that influence efficiency of antibody-dependent cell-mediated cytotoxicity determine rituximab efficacy in patients with lymphoma and autoimmune disease. OBJECTIVE: To investigate the association of FcγRIIA and FcγRIIIA polymorphisms with the response to rituximab treatment in a cohort of patients with polyneuropathy associated with IgM monoclonal gammopathy (PNP-IgM) with and without antimyelin-associated glycoprotein antibodies. METHODS: We determined FcγRIIA-R/H131 and FcγRIIIA-V/F158 genotypes in 27 patients with PNP-IgM using allele-specific PCR and Sanger sequencing. RESULTS: The FcγRIIIA-V/V158 genotype was associated with functional improvement (p=0.02) after 1 year. CONCLUSIONS: FcγRIIIA polymorphisms are potential biomarkers for response to rituximab treatment in polyneuropathy associated with IgM monoclonal gammopathy.

Lmx1a is an activator of Rgs4 and Grb10 and is responsible for the correct specification of rostral and medial mdDA neurons.

The LIM homeodomain transcription factor Lmx1a is a very potent inducer of stem cells towards dopaminergic neurons. Despite several studies on the function of this gene, the exact in vivo role of Lmx1a in mesodiencephalic dopamine (mdDA) neuronal specification is still not understood. To analyse the genes functioning downstream of Lmx1a, we performed expression microarray analysis of LMX1A-overexpressing MN9D dopaminergic cells. Several interesting regulated genes were identified, based on their regulation in other previously generated expression arrays and on their expression pattern in the developing mdDA neuronal field. Post analysis through in vivo expression analysis in Lmx1a mouse mutant (dr/dr) embryos demonstrated a clear decrease in expression of the genes Grb10 and Rgs4, in and adjacent to the rostral and dorsal mdDA neuronal field and within the Lmx1a expression domain. Interestingly, the DA marker Vmat2 was significantly up-regulated as a consequence of increased LMX1A dose, and subsequent analysis on Lmx1a-mutant E14.5 and adult tissue revealed a significant decrease in Vmat2 expression in mdDA neurons. Taken together, microarray analysis of an LMX1A-overexpression cell system resulted in the identification of novel direct or indirect downstream targets of Lmx1a in mdDA neurons: Grb10, Rgs4 and Vmat2.

Spatial and temporal lineage analysis of a Pitx3-driven Cre-recombinase knock-in mouse model.

Development and function of mesodiencephalic dopaminergic (mdDA) neurons has received a lot of scientific interest since these neurons are critically involved in neurological diseases as Parkinson and psychiatric diseases as schizophrenia, depression and attention deficit hyperactivity disorder (ADHD). The understanding of the molecular processes that lead to normal development and function of mdDA neurons has provided insight in the pathology and provided critical information on new treatment paradigms. In order to be able to study specific genetic ablation in mdDA neurons a new tools was developed that drives Cre-recombinase under the control of the Pitx3 locus. The Pitx3 gene is well known for its specific expression in mdDA neurons and is present at the onset of terminal differentiation. Analysis of newly generated Pitx3-Cre knock-in mice shows that Cre expression, measured through the activation of eYfp by removal of a "Stop" signal (LoxP-Stop-LoxP-eYfp reporter mouse), is present at the onset of terminal differentiation and mimics closely the native Pitx3 expression domain. In conclusion, we present here a new Cre-driver mouse model to be used in the restricted ablation of interesting genes in mdDA neurons in order to improve our understanding of the underlying molecular programming.

UBQLN2 in familial amyotrophic lateral sclerosis in The Netherlands.

Recently it was discovered that mutations in the UBQLN2 gene were a cause of an X-linked dominant type of familial amyotrophic lateral sclerosis (ALS). We investigated the frequency of mutations in this gene in a cohort of 92 families with ALS in the Netherlands. Eight families were excluded because of male-to-male transmission. In the remaining 84 familial ALS cases no mutations were discovered in UBQLN2. Hence, UBQLN2 was not found to be a cause of familial ALS in the Netherlands.