Project description:There is increasing evidence on the role of circular RNAs (circRNAs) in neuronal and muscular processes. Accordingly, their dysregulation is associated with neurodegenerative diseases and myopathies. We investigated circRNA expression in the central nervous system (CNS) and skeletal muscle, the two main tissues affected in amyotrophic lateral sclerosis (ALS). Based on circRNA sequencing analysis in spinal cord from ALS mice (SOD1G93A) followed by a literature search, 30 circRNAs potentially involved in ALS were tested. All selected circRNAs were downregulated in the SOD1G93A spinal cord, whereas only half of these were quantifiable and were generally upregulated in quadriceps muscle of SOD1G93A mice. Such tissue-dependent expression pattern was observed in both sexes and circRNA abundance in the spinal cord was higher than in the muscle, both in wild type and in SOD1G93A mice. Finally, we assessed the 18 circRNAs with the largest expression differences and the highest degree of interspecies conservation in brain samples from sporadic ALS (sALS) patients and healthy controls. Similar to the mouse model, circRNA levels tended to decrease in the CNS of sALS patients. Expression of circRNAs may be systematically altered in the two tissues most affected by ALS in a progressive and opposed manner. Although more detailed studies are warranted, circRNAs are potentially related to ALS etiopathogenesis and could possibly serve as future biomarkers, therapeutic targets, or customized therapeutic tools to modulate the pathology.
Project description:Numerous genes mutated in amyotrophic lateral sclerosis (ALS) share a role in DNA damage and repair, emphasizing genome disintegration in ALS. DNA instability and repair mechanisms segregate extrachromosomal circular DNAs (ec/eccDNAs) that can modulate gene expression somatically. Here, circulome profiling in a hSOD1G93A genotoxicity model of ALS revealed a 6-fold enrichment of small-size eccDNAs relative to controls. DifCir-based differential analysis identified 189 genes with patterned segregation of differentially produced per gene circles (DPpGCs) from ALS but not from control samples, implicating an inter-sample recurrence rate of at least 89% for the top 6 DPpGCs. Mass spectrometry-based ALS circulome-proteome cross-referencing revealed 31 corresponding differentially expressed proteins (DEPs), with 12 DPpGC-DEP pairs being itemized in ALS risk GWAS databases. DPpGC-DEP hotspots mainly convey neuron-specific functions counteracting ALS detriments. This is unanticipated evidence for non-random, profiled eccDNA accumulation in ALS neurodegeneration, involving putative interactions with their gene products as well as biomarker perspectives.
Project description:Circular RNAs (circRNAs) are dynamically regulated during differentiation and show cell-type specific expression, which is altered in cancer and can have a direct impact on various hallmarks of cancer. In accordance, we hypothesized that circRNA expression is deregulated in acute myeloid leukemia (AML), and that circRNA candidates might contribute to the pathogenesis of the disease. To identify leukemia-specific and differentiation-independent changes in circRNA expression, we determined the whole circular RNAome of 61 AML patients and 16 healthy hematopoietic stem and progenitor cell (HSPC) samples using ribosomal RNA-depleted RNA sequencing. We found hundreds of circRNAs that were differentially expressed between AML and healthy HSPCs. Gene set analysis found that many of these circRNAs were transcribed from genes implicated in leukemia biology. We discovered a circRNA derived from the T cell transcription factor gene BCL11B, circBCL11B, which was exclusively expressed in AML patients and associated with a T cell-like gene expression signature. We were able to validate this finding in an independent cohort of 332 AML patients, and knockdown of circBCL11B had a negative effect on leukemic cell proliferation, thereby suggesting circBCL11B as a novel functionally relevant candidate in AML pathogenesis. In summary, our study enables comprehensive insights into circRNA expression changes upon leukemic transformation, and provides valuable information on the biology of leukemic cells and potential novel pathway dependencies relevant for AML therapy.
Project description:The pervasive expression of circular RNA from protein coding loci is a recently discovered feature of many eukaryotic gene expression programs. Computational methods to discover and quantify circular RNA are essential to the study of the mechanisms of circular RNA biogenesis and potential functional roles they may play. In this paper, we present a new statistical algorithm that increases the sensitivity and specificity of circular RNA detection.by discovering and quantifying circular and linear RNA splicing events at both annotated exon boundaries and in un-annotated regions of the genome Unlike previous approaches which rely on heuristics like read count and homology between exons predicted to be circularized to determine confidence in prediction of circular RNA expression, our algorithm is a statistical approach. We have used this algorithm to discover general induction of circular RNAs in many tissues during human fetal development. We find that some regions of the brain show marked enrichment for genes where circular RNA is the dominant isoform. Beyond this global trend, specific circular RNAs are tissue specifically induced during fetal development, including a circular isoform of NCX1 in the developing fetal heart that, by 20 weeks, is more highly expressed than the linear isoform as well as beta-actin. In addition, while the vast majority of circular RNA production occurs at canonical U2 (major spliceosome) splice sites, we find the first examples of developmentally induced circular RNAs processed by the U12 (minor) spliceosome, and an enriched propensity of U12 donors to splice into circular RNA at un-annotated, rather than annotated, exons. Together, our algorithm and its results suggest a potentially significant role for circular RNA in human development. 35 human fetal samples from 6 tissues (3 - 7 replicates per tissue) collected between 10 and 20 weeks gestational time were sequenced using Illumina TruSeq Stranded Total RNA with Ribo-Zero Gold sample prep kit.
Project description:Mutations causing amyotrophic lateral sclerosis (ALS) strongly implicate regulators of RNA-processing that are ubiquitously expressed throughout development. To understand the molecular impact of ALS-causing mutations on early neuronal development and disease, we performed transcriptomic analysis of differentiated human control and VCP-mutant induced pluripotent stem cells (iPSCs) during motor neurogenesis. We identify intron retention (IR) as the predominant splicing change affecting early stages of wild-type neural differentiation, targeting key genes involved in the splicing machinery. Importantly, IR occurs prematurely in VCP-mutant cultures compared with control counterparts; these events are also observed in independent RNAseq datasets from SOD1- and FUS-mutant motor neurons (MNs). Together with related effects on 3’UTR length variation, these findings implicate alternative RNA-processing in regulating distinct stages of lineage restriction from iPSCs to MNs, and reveal a temporal deregulation of such processing by ALS mutations. Thus, ALS-causing mutations perturb the same post-transcriptional mechanisms that underlie human motor neurogenesis.
Project description:Circular RNAs are abundant, covalently closed transcripts that arise in cells through back-splicing and display distinct expression patterns across cells and developmental stages. While their functions are largely unknown, their intrinsic stability has made them valuable biomarkers in diseases like cancer. Here, we set out to examine circRNA patterns in amyotrophic lateral sclerosis (ALS). By RNA-sequencing analysis, we first identified circRNAs and linear RNAs that were differentially abundant in skeletal muscle biopsies from ALS and normal individuals. Among these, 8 circRNAs were significantly elevated and 10 significantly reduced in ALS, while the linear counterparts, arising from shared precursor RNAs, did not change. Several of these circRNAs were also differentially abundant in motor neurons derived from human induced pluripotent stem cells (iPSCs) bearing ALS mutations, and across different disease stages in skeletal muscle from a mouse model of ALS (SOD1G93A). Interestingly, several of the circRNAs significantly elevated in muscle were significantly reduced in the spinal cord from ALS patients and ALS (SOD1G93A) mice. In sum, we have identified differentially abundant circRNAs in ALS-relevant tissues (muscle and spinal cord) that could inform about neuromuscular molecular programs in ALS and guide the development of therapies.
Project description:Circular RNAs are abundant, covalently closed transcripts that arise in cells through back-splicing and display distinct expression patterns across cells and developmental stages. While their functions are largely unknown, their intrinsic stability has made them valuable biomarkers in diseases like cancer. Here, we set out to examine circRNA patterns in amyotrophic lateral sclerosis (ALS). By RNA-sequencing analysis, we first identified circRNAs and linear RNAs that were differentially abundant in skeletal muscle biopsies from ALS and normal individuals. Among these, 8 circRNAs were significantly elevated and 10 significantly reduced in ALS, while the linear counterparts, arising from shared precursor RNAs, did not change. Several of these circRNAs were also differentially abundant in motor neurons derived from human induced pluripotent stem cells (iPSCs) bearing ALS mutations, and across different disease stages in skeletal muscle from a mouse model of ALS (SOD1G93A). Interestingly, several of the circRNAs significantly elevated in muscle were significantly reduced in the spinal cord from ALS patients and ALS (SOD1G93A) mice. In sum, we have identified differentially abundant circRNAs in ALS-relevant tissues (muscle and spinal cord) that could inform about neuromuscular molecular programs in ALS and guide the development of therapies.