Genome-Wide Association Study Identifies Risk Loci for Cluster Headache.

OBJECTIVE: This study was undertaken to identify susceptibility loci for cluster headache and obtain insights into relevant disease pathways. METHODS: We carried out a genome-wide association study, where 852 UK and 591 Swedish cluster headache cases were compared with 5,614 and 1,134 controls, respectively. Following quality control and imputation, single variant association testing was conducted using a logistic mixed model for each cohort. The 2 cohorts were subsequently combined in a merged analysis. Downstream analyses, such as gene-set enrichment, functional variant annotation, prediction and pathway analyses, were performed. RESULTS: Initial independent analysis identified 2 replicable cluster headache susceptibility loci on chromosome 2. A merged analysis identified an additional locus on chromosome 1 and confirmed a locus significant in the UK analysis on chromosome 6, which overlaps with a previously known migraine locus. The lead single nucleotide polymorphisms were rs113658130 (p = 1.92 × 10-17 , odds ratio [OR] = 1.51, 95% confidence interval [CI] = 1.37-1.66) and rs4519530 (p = 6.98 × 10-17 , OR = 1.47, 95% CI = 1.34-1.61) on chromosome 2, rs12121134 on chromosome 1 (p = 1.66 × 10-8 , OR = 1.36, 95% CI = 1.22-1.52), and rs11153082 (p = 1.85 × 10-8 , OR = 1.30, 95% CI = 1.19-1.42) on chromosome 6. Downstream analyses implicated immunological processes in the pathogenesis of cluster headache. INTERPRETATION: We identified and replicated several genome-wide significant associations supporting a genetic predisposition in cluster headache in a genome-wide association study involving 1,443 cases. Replication in larger independent cohorts combined with comprehensive phenotyping, in relation to, for example, treatment response and cluster headache subtypes, could provide unprecedented insights into genotype-phenotype correlations and the pathophysiological pathways underlying cluster headache. ANN NEUROL 2021;90:193-202.

Genetic Screening of Plasticity Regulating Nogo-Type Signaling Genes in Migraine.

Migraine is the sixth most prevalent disease in the world and a substantial number of experiments have been conducted to analyze potential differences between the migraine brain and the healthy brain. Results from these investigations point to the possibility that development and aggravation of migraine may include grey matter plasticity. Nogo-type signaling is a potent plasticity regulating system in the CNS and consists of ligands, receptors, co-receptors and modulators with a dynamic age- and activity-related expression in cortical and subcortical regions. Here we investigated a potential link between migraine and five key Nogo-type signaling genes: RTN4, OMGP, MAG, RTN4R and LINGO1, by screening 15 single nucleotide polymorphisms (SNPs) within these genes. In a large Swedish migraine cohort (749 migraine patients and 4032 controls), using a logistic regression with sex as covariate, we found that there was no such association. In addition, a haplotype analysis was performed which revealed three haplotype blocks. These blocks had no significant association with migraine. However, to robustly conclude that Nogo-type genotypes signaling do not influence the prevalence of migraine, further studies are encouraged.

Improved gene co-expression network quality through expression dataset down-sampling and network aggregation.

Large-scale gene co-expression networks are an effective methodology to analyze sets of co-expressed genes and discover new gene functions or associations. Distances between genes are estimated according to their expression profiles and are visualized in networks that may be further partitioned to reveal communities of co-expressed genes. Creating expression profiles is now eased by the large amounts of publicly available expression data (microarrays and RNA-seq). Although many distance calculation methods have been intensively compared and reviewed in the past, it is unclear how to proceed when many samples reflecting a wide range of different conditions are available. Should as many samples as possible be integrated into network construction or be partitioned into smaller sets of more related samples? Previous studies have indicated a saturation in network performances to capture known associations once a certain number of samples is included in distance calculations. Here, we examined the influence of sample size on co-expression network construction using microarray and RNA-seq expression data from three plant species. We tested different down-sampling methods and compared network performances in recovering known gene associations to networks obtained from full datasets. We further examined how aggregating networks may help increase this performance by testing six aggregation methods.

Anoctamin 3: A Possible Link between Cluster Headache and Ca2+ Signaling.

Cluster headache is a severe primary headache characterized by extremely painful attacks of unilateral headache. Verapamil is commonly used as a prophylactic treatment with good effect. In order to search for new pathways involved in the pathophysiology of cluster headache, we analyzed genetic variants that were previously linked to verapamil response in migraine in a Swedish cluster headache case-control sample. We used TaqMan qPCR for genetic screening and performed a gene expression analysis on associated genes in patient-derived fibroblasts, and further investigated which reference genes were suitable for analysis in fibroblasts from cluster headache patients. We discovered a significant association between anoctamin 3, a gene encoding a calcium-activated ion channel, and cluster headache. The association was not dependent on verapamil treatment since the associated variant, rs1531394, was also overrepresented in patients not using verapamil. No difference was found in the anoctamin 3 gene expression between controls and patients. Also, we determined that TBP, IPO8 and PDHB were suitable reference genes in cluster headache fibroblasts. This finding is the first report of an association between a variant in a gene encoding an ion-channel and cluster headache, and the first significant genetic evidence of calcium involvement in cluster headache pathophysiology.

Ranking genome-wide correlation measurements improves microarray and RNA-seq based global and targeted co-expression networks.

Co-expression networks are essential tools to infer biological associations between gene products and predict gene annotation. Global networks can be analyzed at the transcriptome-wide scale or after querying them with a set of guide genes to capture the transcriptional landscape of a given pathway in a process named Pathway Level Coexpression (PLC). A critical step in network construction remains the definition of gene co-expression. In the present work, we compared how Pearson Correlation Coefficient (PCC), Spearman Correlation Coefficient (SCC), their respective ranked values (Highest Reciprocal Rank (HRR)), Mutual Information (MI) and Partial Correlations (PC) performed on global networks and PLCs. This evaluation was conducted on the model plant Arabidopsis thaliana using microarray and differently pre-processed RNA-seq datasets. We particularly evaluated how dataset × distance measurement combinations performed in 5 PLCs corresponding to 4 well described plant metabolic pathways (phenylpropanoid, carbohydrate, fatty acid and terpene metabolisms) and the cytokinin signaling pathway. Our present work highlights how PCC ranked with HRR is better suited for global network construction and PLC with microarray and RNA-seq data than other distance methods, especially to cluster genes in partitions similar to biological subpathways.

CHASE-Containing Histidine Kinase Receptors in Apple Tree: From a Common Receptor Structure to Divergent Cytokinin Binding Properties and Specific Functions.

Cytokinin signaling is a key regulatory pathway of many aspects in plant development and environmental stresses. Herein, we initiated the identification and functional characterization of the five CHASE-containing histidine kinases (CHK) in the economically important Malus domestica species. These cytokinin receptors named MdCHK2, MdCHK3a/MdCHK3b, and MdCHK4a/MdCHK4b by homology with Arabidopsis AHK clearly displayed three distinct profiles. The three groups exhibited architectural variations, especially in the N-terminal part including the cytokinin sensing domain. Using a yeast complementation assay, we showed that MdCHK2 perceives a broad spectrum of cytokinins with a substantial sensitivity whereas both MdCHK4 homologs exhibit a narrow spectrum. Both MdCHK3 homologs perceived some cytokinins but surprisingly they exhibited a basal constitutive activity. Interaction studies revealed that MdCHK2, MdCHK4a, and MdCHK4b homodimerized whereas MdCHK3a and MdCHK3b did not. Finally, qPCR analysis and bioinformatics approach pointed out contrasted expression patterns among the three MdCHK groups as well as distinct sets of co-expressed genes. Our study characterized for the first time the five cytokinin receptors in apple tree and provided a framework for their further functional studies.

Virus-induced gene silencing of the two squalene synthase isoforms of apple tree (Malus × domestica L.) negatively impacts phytosterol biosynthesis, plastid pigmentation and leaf growth.

MAIN CONCLUSION: The use of a VIGS approach to silence the newly characterized apple tree SQS isoforms points out the biological function of phytosterols in plastid pigmentation and leaf development. Triterpenoids are beneficial health compounds highly accumulated in apple; however, their metabolic regulation is poorly understood. Squalene synthase (SQS) is a key branch point enzyme involved in both phytosterol and triterpene biosynthesis. In this study, two SQS isoforms were identified in apple tree genome. Both isoforms are located at the endoplasmic reticulum surface and were demonstrated to be functional SQS enzymes using an in vitro activity assay. MdSQS1 and MdSQS2 display specificities in their expression profiles with respect to plant organs and environmental constraints. This indicates a possible preferential involvement of each isoform in phytosterol and/or triterpene metabolic pathways as further argued using RNAseq meta-transcriptomic analyses. Finally, a virus-induced gene silencing (VIGS) approach was used to silence MdSQS1 and MdSQS2. The concomitant down-regulation of both MdSQS isoforms strongly affected phytosterol synthesis without alteration in triterpene accumulation, since triterpene-specific oxidosqualene synthases were found to be up-regulated to compensate metabolic flux reduction. Phytosterol deficiencies in silenced plants clearly disturbed chloroplast pigmentation and led to abnormal development impacting leaf division rather than elongation or differentiation. In conclusion, beyond the characterization of two SQS isoforms in apple tree, this work brings clues for a specific involvement of each isoform in phytosterol and triterpene pathways and emphasizes the biological function of phytosterols in development and chloroplast integrity. Our report also opens the door to metabolism studies in Malus domestica using the apple latent spherical virus-based VIGS method.

Folivory elicits a strong defense reaction in Catharanthus roseus: metabolomic and transcriptomic analyses reveal distinct local and systemic responses.

Plants deploy distinct secondary metabolisms to cope with environment pressure and to face bio-aggressors notably through the production of biologically active alkaloids. This metabolism-type is particularly elaborated in Catharanthus roseus that synthesizes more than a hundred different monoterpene indole alkaloids (MIAs). While the characterization of their biosynthetic pathway now reaches completion, still little is known about the role of MIAs during biotic attacks. As a consequence, we developed a new plant/herbivore interaction system by challenging C. roseus leaves with Manduca sexta larvae. Transcriptomic and metabolic analyses demonstrated that C. roseus respond to folivory by both local and systemic processes relying on the activation of specific gene sets and biosynthesis of distinct MIAs following jasmonate production. While a huge local accumulation of strictosidine was monitored in attacked leaves that could repel caterpillars through its protein reticulation properties, newly developed leaves displayed an increased biosynthesis of the toxic strictosidine-derived MIAs, vindoline and catharanthine, produced by up-regulation of MIA biosynthetic genes. In this context, leaf consumption resulted in a rapid death of caterpillars that could be linked to the MIA dimerization observed in intestinal tracts. Furthermore, this study also highlights the overall transcriptomic control of the plant defense processes occurring during herbivory.