Kinetics of Xist-induced gene silencing can be predicted from combinations of epigenetic and genomic features.

To initiate X-Chromosome inactivation (XCI), the long noncoding RNA Xist mediates chromosome-wide gene silencing of one X Chromosome in female mammals to equalize gene dosage between the sexes. The efficiency of gene silencing is highly variable across genes, with some genes even escaping XCI in somatic cells. A gene's susceptibility to Xist-mediated silencing appears to be determined by a complex interplay of epigenetic and genomic features; however, the underlying rules remain poorly understood. We have quantified chromosome-wide gene silencing kinetics at the level of the nascent transcriptome using allele-specific Precision nuclear Run-On sequencing (PRO-seq). We have developed a Random Forest machine-learning model that can predict the measured silencing dynamics based on a large set of epigenetic and genomic features and tested its predictive power experimentally. The genomic distance to the Xist locus, followed by gene density and distance to LINE elements, are the prime determinants of the speed of gene silencing. Moreover, we find two distinct gene classes associated with different silencing pathways: a class that requires Xist-repeat A for silencing, which is known to activate the SPEN pathway, and a second class in which genes are premarked by Polycomb complexes and tend to rely on the B repeat in Xist for silencing, known to recruit Polycomb complexes during XCI. Moreover, a series of features associated with active transcriptional elongation and chromatin 3D structure are enriched at rapidly silenced genes. Our machine-learning approach can thus uncover the complex combinatorial rules underlying gene silencing during X inactivation.

Structural organization of the inactive X chromosome in the mouse.

X-chromosome inactivation (XCI) involves major reorganization of the X chromosome as it becomes silent and heterochromatic. During female mammalian development, XCI is triggered by upregulation of the non-coding Xist RNA from one of the two X chromosomes. Xist coats the chromosome in cis and induces silencing of almost all genes via its A-repeat region, although some genes (constitutive escapees) avoid silencing in most cell types, and others (facultative escapees) escape XCI only in specific contexts. A role for Xist in organizing the inactive X (Xi) chromosome has been proposed. Recent chromosome conformation capture approaches have revealed global loss of local structure on the Xi chromosome and formation of large mega-domains, separated by a region containing the DXZ4 macrosatellite. However, the molecular architecture of the Xi chromosome, in both the silent and expressed regions,remains unclear. Here we investigate the structure, chromatin accessibility and expression status of the mouse Xi chromosome in highly polymorphic clonal neural progenitors (NPCs) and embryonic stem cells. We demonstrate a crucial role for Xist and the DXZ4-containing boundary in shaping Xi chromosome structure using allele-specific genome-wide chromosome conformation capture (Hi-C) analysis, an assay for transposase-accessible chromatin with high throughput sequencing (ATAC-seq) and RNA sequencing. Deletion of the boundary disrupts mega-domain formation, and induction of Xist RNA initiates formation of the boundary and the loss of DNA accessibility. We also show that in NPCs, the Xi chromosome lacks active/inactive compartments and topologically associating domains (TADs), except around genes that escape XCI. Escapee gene clusters display TAD-like structures and retain DNA accessibility at promoter-proximal and CTCF-binding sites. Furthermore, altered patterns of facultative escape genes indifferent neural progenitor clones are associated with the presence of different TAD-like structures after XCI. These findings suggest a key role for transcription and CTCF in the formation of TADs in the context of the Xi chromosome in neural progenitors.

RNAi-dependent and independent control of LINE1 accumulation and mobility in mouse embryonic stem cells.

In most mouse tissues, long-interspersed elements-1 (L1s) are silenced via methylation of their 5'-untranslated regions (5'-UTR). A gradual loss-of-methylation in pre-implantation embryos coincides with L1 retrotransposition in blastocysts, generating potentially harmful mutations. Here, we show that Dicer- and Ago2-dependent RNAi restricts L1 accumulation and retrotransposition in undifferentiated mouse embryonic stem cells (mESCs), derived from blastocysts. RNAi correlates with production of Dicer-dependent 22-nt small RNAs mapping to overlapping sense/antisense transcripts produced from the L1 5'-UTR. However, RNA-surveillance pathways simultaneously degrade these transcripts and, consequently, confound the anti-L1 RNAi response. In Dicer(-/-) mESC complementation experiments involving ectopic Dicer expression, L1 silencing was rescued in cells in which microRNAs remained strongly depleted. Furthermore, these cells proliferated and differentiated normally, unlike their non-complemented counterparts. These results shed new light on L1 biology, uncover defensive, in addition to regulatory roles for RNAi, and raise questions on the differentiation defects of Dicer(-/-) mESCs.

The ribosomal protein rpl26 promoter is required for its 3' sense terminus ncRNA transcription in Schizosaccharomyces pombe, implicating a new transcriptional mechanism for ncRNAs.

Transcriptome studies have revealed that many non-coding RNAs (ncRNAs) are located near the 3' sense terminus of protein-coding genes. However, the transcription and function of these RNAs remain elusive. Here, we identify a 3' sense termini-associated sRNA (TASR) downstream of rpl26 in Schizosaccharomyces pombe (S. pombe). Structure and function assays indicate that the TASR is an H/ACA box snoRNA required for 18S rRNA pseudouridylation at U121 and U305 sites and is therefore a cognate of snR49 from the budding yeast. Transcriptional studies show that pre-snR49 overlaps most of the coding sequence (CDS) of rpl26. Using scanning deletion analysis within promoter region, we show that the rpl26 promoter is required for the 3' TASR transcription. Interestingly, chromosomal synteny of rpl26-snR49 is found in the Schizosaccharomyces groups. Taken together, we have revealed a new transcriptional mechanism for 3' sense TASRs, which are transcribed by the same promoter as their upstream protein genes. These results further suggest that the origin and function of 3' sense ncRNAs are associated with upstream genes in higher eukaryotes.

Small RNAs derived from structural non-coding RNAs.

It has been shown in small RNA sequencing-based studies that some small RNA fragments are specifically processed from known structural non-coding RNAs, either through Dicer-dependent or Dicer-independent pathways. Although these small RNAs are often less abundant compared to microRNAs in normal mammalian tissues, they are always present in all sequenced libraries. In this paper, we use the ncPRO-seq pipeline, to describe different profiles of these small RNA fragments, and to discuss their potential processing pathways and functions. To assess whether more small RNA fragments can be detected in small RNA sequencing datasets, we decided to focus on small nuclear RNAs, abbreviated as snRNAs, which are associated with Sm ribonucleoproteins to form functional RNA-protein complexes. Here, we describe a group of small RNA fragments derived from snRNAs, which are typically highly enriched in regions bound by Sm proteins. Based on this, we propose the existence of a potential novel small RNA family associated with Sm proteins.

Plant noncoding RNA gene discovery by "single-genome comparative genomics".

Plant genomes have undergone multiple rounds of duplications that contributed massively to the growth of gene families. The structure of resulting families has been studied in depth for protein-coding genes. However, little is known about the impact of duplications on noncoding RNA (ncRNA) genes. Here we perform a systematic analysis of duplicated regions in the rice genome in search of such ncRNA repeats. We observe that, just like their protein counterparts, most ncRNA genes have undergone multiple duplications that left visible sequence conservation footprints. The extent of ncRNA gene duplication in plants is such that these sequence footprints can be exploited for the discovery of novel ncRNA gene families on a large scale. We developed an SVM model that is able to retrieve likely ncRNA candidates among the 100,000+ repeat families in the rice genome, with a reasonably low false-positive discovery rate. Among the nearly 4000 ncRNA families predicted by this means, only 90 correspond to putative snoRNA or miRNA families. About half of the remaining families are classified as structured RNAs. New candidate ncRNAs are particularly enriched in UTR and intronic regions. Interestingly, 89% of the putative ncRNA families do not produce a detectable signal when their sequences are compared to another grass genome such as maize. Our results show that a large fraction of rice ncRNA genes are present in multiple copies and are species-specific or of recent origin. Intragenome comparison is a unique and potent source for the computational annotation of this major class of ncRNA.

HiTC: exploration of high-throughput 'C' experiments.

SUMMARY: The R/Bioconductor package HiTC facilitates the exploration of high-throughput 3C-based data. It allows users to import and export 'C' data, to transform, normalize, annotate and visualize interaction maps. The package operates within the Bioconductor framework and thus offers new opportunities for future development in this field. AVAILABILITY AND IMPLEMENTATION: The R package HiTC is available from the Bioconductor website. A detailed vignette provides additional documentation and help for using the package.

ncPRO-seq: a tool for annotation and profiling of ncRNAs in sRNA-seq data.

SUMMARY: Non-coding RNA (ncRNA) PROfiling in small RNA (sRNA)-seq (ncPRO-seq) is a stand-alone, comprehensive and flexible ncRNA analysis pipeline. It can interrogate and perform detailed profiling analysis on sRNAs derived from annotated non-coding regions in miRBase, Rfam and RepeatMasker, as well as specific regions defined by users. The ncPRO-seq pipeline performs both gene-based and family-based analyses of sRNAs. It also has a module to identify regions significantly enriched with short reads, which cannot be classified under known ncRNA families, thus enabling the discovery of previously unknown ncRNA- or small interfering RNA (siRNA)-producing regions. The ncPRO-seq pipeline supports input read sequences in fastq, fasta and color space format, as well as alignment results in BAM format, meaning that sRNA raw data from the three current major platforms (Roche-454, Illumina-Solexa and Life technologies-SOLiD) can be analyzed with this pipeline. The ncPRO-seq pipeline can be used to analyze read and alignment data, based on any sequenced genome, including mammals and plants. AVAILABILITY: Source code, annotation files, manual and online version are available at http://ncpro.curie.fr/. CONTACT: bioinfo.ncproseq@curie.fr or cciaudo@ethz.ch SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Genome-wide discovery and analysis of microRNAs and other small RNAs from rice embryogenic callus.

Small RNAs constitute a new and unanticipated layer of gene regulation present in the three domains of life. In plants, all organs are ultimately derived from a few pluripotent stem cells localized in specialized structures called apical meristems. The development of meristems involves a coordinated balance between undifferentiated growth and differentiation, a phenomenon requiring a tight regulation of gene expression. We used in vitro cultured embryogenic calli as a model to investigate the roles of meristem-associated small RNAs. Using high throughput sequencing, we sequenced 20 million short reads with size of 18-30 nt from rice undifferentiated and differentiated calli. We confirmed 50 known microRNA families, representing one third of annotated rice microRNAs. Using a specific computational pipeline for plant microRNA identification, we identified 24 novel microRNA families. Among them, 53 microRNA or microRNA* sequences appear to vary in expression between differentiated and undifferentiated calli, suggesting a role in meristem development. Our analysis also revealed a new class of plant small RNAs derived from 5' or 3' ends of mature tRNA analogous to the tRFs in human cancer cell. We independently verified the expression of these small RNAs from 5' end of mature tRNA using qRT-PCR.

Characteristics and prognostic significance of genetic mutations in acute myeloid leukemia based on a targeted next-generation sequencing technique.

To explore the characteristics and prognostic significance of genetic mutations in acute myeloid leukemia (AML), we screened the gene mutation profile of 171 previously untreated AML patients using a next-generation sequencing technique targeting 127 genes with potential prognostic significance. A total of 390 genetic alterations were identified in 149 patients with a frequency of 87.1%. Younger age and high sensitivity to induction chemotherapy were associated with a lower number of mutations. NPM1 mutation was closely related to DNMT3A and FLT3-internal tandem duplication (FLT3-ITD) mutations, but mutually exclusive with ASXL1 mutation and CEBPAdouble mutation . In univariate analysis, ASXL1 or TET2 mutation predicted shorter overall survival (OS) or relapse-free survival (RFS), DNMT3A, FLT3-ITD, or RUNX1 mutation predicted a higher likelihood of remission-induction failure, whereas NRAS mutation or CEBPAdouble mutation predicted longer OS. Concurrent DNMT3A, FLT3-ITD, and NPM1 mutations predicted shorter OS. Hypomethylation agents could improve the OS in patients with DNA methylation-related mutations. According to multivariate analysis, TET2 mutation was recognized as an independent prognostic factors for RFS. In summary, our study provided a detailed pattern of gene mutations and their prognostic relevance in Chinese AML patients based on targeted next-generation sequencing screening.

Genomewide analysis of box C/D and box H/ACA snoRNAs in Chlamydomonas reinhardtii reveals an extensive organization into intronic gene clusters.

Chlamydomonas reinhardtii is a unicellular green alga, the lineage of which diverged from that of land plants >1 billion years ago. Using the powerful small nucleolar RNA (snoRNA) mining platform to screen the C. reinhardtii genome, we identified 322 snoRNA genes grouped into 118 families. The 74 box C/D families can potentially guide methylation at 96 sites of ribosomal RNAs (rRNAs) and snRNAs, and the 44 box H/ACA families can potentially guide pseudouridylation at 62 sites. Remarkably, 242 of the snoRNA genes are arranged into 76 clusters, of which 77% consist of homologous genes produced by small local tandem duplications. At least 70 snoRNA gene clusters are found within introns of protein-coding genes. Although not exhaustive, this analysis reveals that C. reinhardtii has the highest number of intronic snoRNA gene clusters among eukaryotes. The prevalence of intronic snoRNA gene clusters in C. reinhardtii is similar to that of rice but in contrast with the one-snoRNA-per-intron organization of vertebrates and fungi and with that of Arabidopsis thaliana in which only a few intronic snoRNA gene clusters were identified. This analysis of C. reinhardtii snoRNA gene organization shows the functional importance of introns in a single-celled organism and provides evolutionary insight into the origin of intron-encoded RNAs in the plant lineage.

Association of Gene Mutations with Response to Arsenic-Containing Compound Qinghuang Powder () in Patients with Myelodysplastic Syndromes.

OBJECTIVES: To investigate the relationship between gene mutations and response to Compound Qinghuang Powder (, CQHP) in patients with myelodysplastic syndrome (MDS). METHODS: Forty-three MDS patients were genotyped by ultra-deep targeted sequencing and the clinical data of patients were collected and the relationship between them was analyzed. RESULTS: Up to 41.86% of patients harbored genet mutations, in most cases with more than one mutation. The most common mutations were in SF3B1, U2AF1, ASXL1, and DNMT3A. After treatment with CQHP, about 88.00% of patients no longer required blood transfusion, or needed half of prior transfusions. CONCLUSIONS: CQHP is an effective treatment for patients with MDS, especially those with gene mutations in SF3B1, DNMT3A, U2AF1, and/or ASXL1.

High resolution global chromosomal aberrations from spontaneous miscarriages revealed by low coverage whole genome sequencing.

OBJECTIVE: Chromosome aberrations are generally considered as one of the most substantial causative factors contributing to spontaneous miscarriages. Cytogenetic analyses like G-banded karyotype and chromosomal microarray analyses are often performed to further investigate the chromosome status of a miscarried fetus. STUDY DESIGN: Here, we describe a novel method, AnnoCNV, to detect DNA copy number variations (CNVs) using low coverage whole genome sequencing (WGS). We investigated the overall frequency of chromosomal abnormalities in 149 miscarriage specimens using AnnoCNV. RESULTS: Among 149 fetal miscarriage samples, more than two fifths of them (42.95%, 64) carried at least one chromosomal abnormality, and a subset (40) was identified as autosomal trisomy which account for 26.84% of all samples. We have also developed a robust algorithm in AnnoCNV, which is able to differentiate specifically karyotype 69,XXY from sex chromosomal aneuploidy 45,X, and to identify 45,X/46,XX mosaicism. Lastly, across the whole genome AnnoCNV identifies CNVs, which are associated with both reported symptoms and unknown clinical conditions. CONCLUSION: This cost-effective strategy reveals genome wide discovery of chromosome aberrations at higher resolution, which are consistent with parallel investigation conducted by SNP based assay.

Contribution of epigenetic landscapes and transcription factors to X-chromosome reactivation in the inner cell mass.

X-chromosome inactivation is established during early development. In mice, transcriptional repression of the paternal X-chromosome (Xp) and enrichment in epigenetic marks such as H3K27me3 is achieved by the early blastocyst stage. X-chromosome inactivation is then reversed in the inner cell mass. The mechanisms underlying Xp reactivation remain enigmatic. Using in vivo single-cell approaches (allele-specific RNAseq, nascent RNA-fluorescent in situ hybridization and immunofluorescence), we show here that different genes are reactivated at different stages, with more slowly reactivated genes tending to be enriched in H3meK27. We further show that in UTX H3K27 histone demethylase mutant embryos, these genes are even more slowly reactivated, suggesting that these genes carry an epigenetic memory that may be actively lost. On the other hand, expression of rapidly reactivated genes may be driven by transcription factors. Thus, some X-linked genes have minimal epigenetic memory in the inner cell mass, whereas others may require active erasure of chromatin marks.

Xist-dependent imprinted X inactivation and the early developmental consequences of its failure.

The long noncoding RNA Xist is expressed from only the paternal X chromosome in mouse preimplantation female embryos and mediates transcriptional silencing of that chromosome. In females, absence of Xist leads to postimplantation lethality. Here, through single-cell RNA sequencing of early preimplantation mouse embryos, we found that the initiation of imprinted X-chromosome inactivation absolutely requires Xist. Lack of paternal Xist leads to genome-wide transcriptional misregulation in the early blastocyst and to failure to activate the extraembryonic pathway that is essential for postimplantation development. We also demonstrate that the expression dynamics of X-linked genes depends on the strain and parent of origin as well as on the location along the X chromosome, particularly at the first 'entry' sites of Xist. This study demonstrates that dosage-compensation failure has an effect as early as the blastocyst stage and reveals genetic and epigenetic contributions to orchestrating transcriptional silencing of the X chromosome during early embryogenesis.

Maternal LSD1/KDM1A is an essential regulator of chromatin and transcription landscapes during zygotic genome activation.

Upon fertilization, the highly specialised sperm and oocyte genomes are remodelled to confer totipotency. The mechanisms of the dramatic reprogramming events that occur have remained unknown, and presumed roles of histone modifying enzymes are just starting to be elucidated. Here, we explore the function of the oocyte-inherited pool of a histone H3K4 and K9 demethylase, LSD1/KDM1A during early mouse development. KDM1A deficiency results in developmental arrest by the two-cell stage, accompanied by dramatic and stepwise alterations in H3K9 and H3K4 methylation patterns. At the transcriptional level, the switch of the maternal-to-zygotic transition fails to be induced properly and LINE-1 retrotransposons are not properly silenced. We propose that KDM1A plays critical roles in establishing the correct epigenetic landscape of the zygote upon fertilization, in preserving genome integrity and in initiating new patterns of genome expression that drive early mouse development.

HiC-Pro: an optimized and flexible pipeline for Hi-C data processing.

HiC-Pro is an optimized and flexible pipeline for processing Hi-C data from raw reads to normalized contact maps. HiC-Pro maps reads, detects valid ligation products, performs quality controls and generates intra- and inter-chromosomal contact maps. It includes a fast implementation of the iterative correction method and is based on a memory-efficient data format for Hi-C contact maps. In addition, HiC-Pro can use phased genotype data to build allele-specific contact maps. We applied HiC-Pro to different Hi-C datasets, demonstrating its ability to easily process large data in a reasonable time. Source code and documentation are available at http://github.com/nservant/HiC-Pro .

Statistical Approach to Decreasing the Error Rate of Noninvasive Prenatal Aneuploid Detection caused by Maternal Copy Number Variation.

Analyses of cell-free fetal DNA (cff-DNA) from maternal plasma using massively parallel sequencing enable the noninvasive detection of feto-placental chromosome aneuploidy; this technique has been widely used in clinics worldwide. Noninvasive prenatal tests (NIPT) based on cff-DNA have achieved very high accuracy; however, they suffer from maternal copy-number variations (CNV) that may cause false positives and false negatives. In this study, we developed an algorithm to exclude the effect of maternal CNV and refined the Z-score that is used to determine fetal aneuploidy. The simulation results showed that the algorithm is robust against variations of fetal concentration and maternal CNV size. We also introduced a method based on the discrepancy between feto-placental concentrations to help reduce the false-positive ratio. A total of 6615 pregnant women were enrolled in a prospective study to validate the accuracy of our method. All 106 fetuses with T21, 20 with T18, and three with T13 were tested using our method, with sensitivity of 100% and specificity of 99.97%. In the results, two cases with maternal duplications in chromosome 21, which were falsely predicted as T21 by the previous NIPT method, were correctly classified as normal by our algorithm, which demonstrated the effectiveness of our approach.

Developmental dynamics and disease potential of random monoallelic gene expression.

X chromosome inactivation (XCI) and allelic exclusion of olfactory receptors or immunoglobulin loci represent classic examples of random monoallelic expression (RME). RME of some single copy genes has also been reported, but the in vivo relevance of this remains unclear. Here we identify several hundred RME genes in clonal neural progenitor cell lines derived from embryonic stem cells. RME occurs during differentiation, and, once established, the monoallelic state can be highly stable. We show that monoallelic expression also occurs in vivo, in the absence of DNA sequence polymorphism. Several of the RME genes identified play important roles in development and have been implicated in human autosomal-dominant disorders. We propose that monoallelic expression of such genes contributes to the fine-tuning of the developmental regulatory pathways they control, and, in the context of a mutation, RME can predispose to loss of function in a proportion of cells and thus contribute to disease.