Biology subjects

Marquardt, S.

Publications and source records attributed to Marquardt, S..

13 recordsLinked to original sources

bioRxiv2026

An integrative cardio-informatics approach identifies positionally conserved ancestors of human lncRNA genes transcribed across vertebrate hearts

The poor conservation of lncRNA genes limits their comprehensive functional studies, as genetic engineering of relevant animal models presupposes the presence of corresponding defined orthologs. This limitation is prominently evident in cardiovascular research, where heart-related lncRNAs are rarely conserved between humans and other vertebrates, despite the highly conserved nature of cardiac function. Because lncRNAs frequently regulate neighboring protein-coding genes essential for cardomyocyte function (herein termed cardiomyocyte indispensable, CMIs), we hypothesized that they are under evolutionary pressure to retain their genomic position and transcriptional activity, irrespective of sequence similarities to prototypical human lncRNA genes. By integrating mouse cardiac knockout phenotypes with human single-cell transcriptomics data, we systematically identified heart-expressed CMIs and their neighboring. lncRNA genes. Cross-species synteny analyses revealed regions flanking 109 CMIs with conserved relative positions and transcriptional orientations across vertebrate genomes. As most of these loci reside within poorly annotated non-coding regions, we developed VertLncRNAchecker, a neural network-based web interface, that predicts lncRNA-like genes within these regions, which we termed positional ancestors. Finally, we validated in situ that these positional ancestors express mature lncRNA transcripts in the hearts of mice, pigs, and frogs, mirroring the expression of their human lncRNA counterparts. We present an accurate and retrainable computational platform for cross-species lncRNA discovery that prioritizes conserved genomic position over sequence conservation or existing genome annotations. This pipeline revealed putative ancestors of human heart-related lncRNAs hidden within the vertebrate non-coding dark genome, providing novel insights into lncRNA biology and evolution.

evolutionary biology↗

bioRxiv2026

The long non-coding RNA ACHLYS modulates biomolecular condensates to regulate alternative splicing in root development

Alternative splicing (AS) enables eukaryotes to dynamically adjust RNA and protein isoforms encoded in one gene. Long non-coding RNAs (lncRNA) have emerged as novel regulators of AS through multiple modes of action, including interactions with splicing factor (SF) proteins. Here, we used Arabidopsis thaliana lateral root development to dissect the specificity of lncRNAs in AS regulation. Data mining and a transient expression screen allowed us to identify novel lncRNAs interacting in vivo with the well-characterized SFs Nuclear speckle RNA binding protein A (NSRa) and glycine-rich RNA-binding protein 7 (GRP7), that are differentially expressed during lateral root organogenesis. We identified 4 lncRNAs affecting more than 250 AS events in plant cells, whereby most AS events are unique for each lncRNA. Notably, 19% of the AS events linked to two NSRa-recognized lncRNAs are identical and positively correlated. One lncRNA was named ACHLYS and is highly conserved in several Brassicaceae whereas another was the recently characterized FLAIL lncRNA. ACHLYS knockdown (KD-ACHLYS) and overexpressing lines (OE-ACHLYS) modulate AS regulation in plants and affect root architecture. In parallel, we performed NSRa-iCLIP to determine in vivo genome-wide NSRa binding sites. Interestingly, NSRa binding sites are locally enriched in ACHLYS-dependent AS introns and ACHLYS itself. A specific ACHLYS-induced AS event requires NSRa function showing that ACHLYS defines AS targets through NSRa interaction on specific transcripts. In vitro assays indicate that direct interaction of NSRa with ACHLYS promotes NSRa phase separation. Furthermore, overexpression of ACHLYS in NSRa-GFP plants results in increased accumulation of NSRa in Nuclear speckles. Our data revealed that ACHLYS can modulate NSRa condensates in vivo and binds to NSRa for modifying AS patterns, suggesting a new mechanism where lncRNAs can fine tune SFs regulation and the transcriptome output in eukaryotic organogenesis.

molecular biology↗

bioRxiv2026

In situ vaccine effect of radiotherapy is associated with intratumoural ERV reactivation and RNA virus sensing

Radiotherapy (RT) transforms tumour tissues into in situ vaccines that trigger antitumor immunity. Immunogenicity depends on how RT is delivered, since heterogeneous RT (spatially fractionated RT, SFRT) elicits more prominent responses than the conventional homogenous one. However, this phenomenon cannot be clinically harnessed, unless the relevant pathways are identified. To gain insights, we developed a hybrid dry-lab/wet-lab approach that integrates systems-level immune phenotypes established by homogenous or heterogenous RT (SFRT) with the transcriptomic profiling of irradiated tumors. By further combining feature extraction with machine-learning, including multilayer perceptron modelling, we ranked predictors of immune infiltration and patient survivability for each RT type. We found that conventional RT induces coordinated upregulation of cytosolic sensors of RNA viruses (OASes and RIG I-like receptors) along with ERV RNAs predominately 400-800 base-pairs long, which might serve as their ligands. For schemes establishing abscopal effects, a coordinated upregulation of the OAS sensors and shared ERV transcripts was observed in both irradiated and distant tumours. Compared to homogenous RT, SFRT triggered earlier and stronger activation of OAS signaling along with NK cell responses. Overall, we show a co-involvement of tumour cell-intrinsic ERVs and their cytosolic RNA sensors in RT-induced antitumor immunity. This key finding could guide mechanistic studies and future precision oncology.

cancer biology↗

bioRxiv2022

Histone chaperone ASF1 mediates H3.3-H4 deposition in Arabidopsis

Histone chaperones and chromatin remodelers control nucleosome dynamics, which are essential for transcription, replication, and DNA repair. The histone chaperone Anti-Silencing Factor 1 (ASF1) plays a central role in facilitating CAF-1-mediated replication-dependent H3.1 deposition and HIRA-mediated replication-independent H3.3 deposition in yeast and metazoans. Whether ASF1 function is evolutionarily conserved in plants is unknown. Here, we show that Arabidopsis ASF1 proteins display a preference for the HIRA complex. Simultaneous mutation of both Arabidopsis ASF1 genes caused a decrease in chromatin density and ectopic H3.1 occupancy at loci typically enriched with H3.3. Genetic, transcriptomic, and proteomic data indicate that ASF1 proteins strongly prefers the HIRA complex over CAF-1. asf1 mutants also displayed an increase in spurious Pol II transcriptional initiation and showed defects in the maintenance of gene body CG DNA methylation and in the distribution of histone modifications. Furthermore, ectopic targeting of ASF1 caused excessive histone deposition, less accessible chromatin, and gene silencing. These findings reveal the importance of ASF1-mediated histone deposition for proper epigenetic regulation of the genome.

plant biology↗

bioRxiv2021

A trans-acting long non-coding RNA represses flowering in Arabidopsis

Eukaryotic genomes give rise to thousands of long non-coding RNAs (lncRNAs), yet the purpose of lncRNAs remains largely enigmatic. Functional characterization of lncRNAs is challenging due to multiple orthogonal hypothesis for molecular activities of lncRNA loci. Here, we identified a flowering associated intergenic lncRNA (FLAIL) that represses flowering in Arabidopsis. An allelic series of flail loss-of-function mutants generated by CRISPR/Cas9 and T-DNA mutagenesis showed an early flowering phenotype. Gene expression analyses in flail mutants revealed differentially expressed genes linked to the regulation of flowering. A genomic rescue fragment of FLAIL introduced in flail mutants complemented gene expression defects and early flowering, consistent with trans-acting effects of the FLAIL RNA. Knock-down of FLAIL RNA levels using the artificial microRNA approach revealed an early flowering phenotype shared with genomic mutations, indicating a trans-acting role of FLAIL RNA in the repression of flowering time. Genome-wide detection of FLAIL-DNA interactions by ChIRP-seq suggested that FLAIL may directly bind genomic regions. FLAIL bound to genes involved in regulation of flowering that were differentially expressed in flail, consistent with the interpretation of FLAIL as a trans-acting lncRNA directly shaping gene expression. Our findings highlight FLAIL as a trans-acting lncRNA that affects flowering in Arabidopsis, likely through mediating transcriptional regulation of genes directly bound by FLAIL.

genomics↗

bioRxiv2021

R-loops between nascent pri-miRNAs and the encoding loci promote co-transcriptional processing of miRNAs in plants

In most organisms, the maturation of nascent RNAs is coupled to transcription, undergoing many processing steps co-transcriptionally. Unlike in animals, the RNA polymerase II (RNAPII) transcribes microRNAs (miRNAs) as long and structurally variable pri-miRNAs in plants. Current evidence suggests that the miRNA biogenesis complex assembly initiates early during the transcription of pri-miRNAs in plants. However, it is unknown whether miRNA processing occurs co-transcriptionally. Here, we show that plant miRNA biogenesis is coupled to transcription in a process that relies on the formation of DNA:RNA hybrids (R-loops) between the nascent transcript and the encoding loci. We used native elongating transcript sequencing data and imaging techniques to demonstrate that plant miRNA biogenesis occurs co-transcriptionally. We found that the entire biogenesis occurs coupled to transcription for pri-miRNAs processed from the loop but requires a second nucleoplasmic step for those processed from the base of the hairpin. Furthermore, we found that co- and post-transcriptional miRNA processing mechanisms co-exist for most miRNAs in a dynamic balance. Notably, we discovered that R-loops between the 5-end single-stranded arm of the pri-miRNAs and the encoding loci anchor the transcript, promoting co-transcriptional processing. Our data demonstrate the coupling of transcription and miRNA processing in plants and discovered an unexpected function for R-loops promoting RNA processing. Furthermore, our results suggest the neo-functionalization of co-transcriptionally processed miRNAs, boosting countless regulatory scenarios.

plant biology↗

bioRxiv2021

Hda1C restricts the transcription initiation frequency to limit divergent non-coding RNA transcription

Nucleosome-depleted regions (NDRs) at gene promoters support initiation of RNA Polymerase II transcription. Interestingly, transcription often initiates in both directions, resulting in an mRNA, and a divergent non-coding (DNC) transcript with an unclear purpose. Here, we characterized the genetic architecture and molecular mechanism of DNC transcription in budding yeast. We identified the Hda1 histone deacetylase complex (Hda1C) as a repressor of DNC in high-throughput reverse genetic screens based on quantitative single-cell fluorescence measurements. Nascent transcription profiling showed a genome-wide role of Hda1C in DNC repression. Live-cell imaging of transcription revealed that Hda1C reduced the frequency of DNC transcription. Hda1C contributed to decreased acetylation of histone H3 in DNC regions, supporting DNC repression by histone deacetylation. Our data support the interpretation that DNC results as a consequence of the NDR-based architecture of eukaryotic promoters, but that it is governed by locus-specific repression to maintain genome fidelity.

genomics↗

bioRxiv2020

TrancriptomeReconstructoR: data-driven annotation of complex transcriptomes

BackgroundThe quality of gene annotation determines the interpretation of results obtained in transcriptomic studies. The growing number of genome sequence information calls for experimental and computational pipelines for de novo transcriptome annotation. Ideally, gene and transcript models should be called from a limited set of key experimental data. ResultsWe developed TranscriptomeReconstructoR, an R package which implements a pipeline for automated transcriptome annotation. It relies on integrating features from independent and complementary datasets: i) full-length RNA-seq for detection of splicing patterns and ii) high-throughput 5 and 3 tag sequencing data for accurate definition of gene borders. The pipeline can also take a nascent RNA-seq dataset to supplement the called gene model with transient transcripts. We reconstructed de novo the transcriptional landscape of wild type Arabidopsis thaliana seedlings as a proof-of-principle. A comparison to the existing transcriptome annotations revealed that our gene model is more accurate and comprehensive than the two most commonly used community gene models, TAIR10 and Araport11. In particular, we identify thousands of transient transcripts missing from the existing annotations. Our new annotation promises to improve the quality of A.thaliana genome research. ConclusionsOur proof-of-concept data suggest a cost-efficient strategy for rapid and accurate annotation of complex eukaryotic transcriptomes. We combine the choice of library preparation methods and sequencing platforms with the dedicated computational pipeline implemented in the TranscriptomeReconstructoR package. The pipeline only requires prior knowledge on the reference genomic DNA sequence, but not the transcriptome. The package seamlessly integrates with Bioconductor packages for downstream analysis.

bioinformatics↗

bioRxiv2020

Light-dependent translation change of Arabidopsis psbA correlates with RNA structure alterations at the translation initiation region

mRNA secondary structure influences translation. Proteins that modulate the mRNA secondary structure around the translation initiation region may regulate translation in plastids. To test this hypothesis, we exposed Arabidopsis thaliana to high light, which induces translation of psbA mRNA encoding the D1 subunit of photosystem II. We assayed translation by ribosome profiling and applied two complementary methods to analyze in vivo RNA secondary structure: DMS-MaPseq and SHAPE-seq. We detected increased accessibility of the translation initiation region of psbA after high light treatment, likely contributing to the observed increase in translation by facilitating translation initiation. Furthermore, we identified the footprint of a putative regulatory protein in the 5 UTR of psbA at a position where occlusion of the nucleotide sequence would cause the structure of the translation initiation region to open up, thereby facilitating ribosome access. Moreover, we show that other plastid genes with weak Shine-Dalgarno sequences (SD) are likely to exhibit psbA-like regulation, while those with strong SDs do not. This supports the idea that changes in mRNA secondary structure might represent a general mechanism for translational regulation of psbA and other plastid genes. SIGNIFICANCERNA structure changes in the translation initiation region, most likely as a result of protein binding, affect the translation of psbA and possibly other plastid genes with weak Shine-Dalgarno sequences.

plant biology↗

bioRxiv2019

Native Elongation Transcript sequencing reveals temperature dependent dynamics of nascent RNAPII transcription in Arabidopsis

Temperature profoundly affects the kinetics of biochemical reactions, yet how large molecular complexes such as the transcription machinery accommodate changing temperatures to maintain cellular function is poorly understood. Here, we developed plant native elongating transcripts sequencing (plaNET-seq) to profile genome-wide nascent RNA polymerase II (RNAPII) transcription during the cold-response of Arabidopsis thaliana with single-nucleotide resolution. Combined with temporal resolution, these data revealed transient genome-wide reprogramming of nascent RNAPII transcription during cold, including characteristics of RNAPII elongation and thousands of non-coding transcripts connected to gene expression. Our results suggest a role for promoter-proximal RNAPII stalling in predisposing genes for transcriptional activation during plant-environment interactions. At gene 3-ends, cold initially facilitated transcriptional termination by limiting the distance of read-through transcription. Within gene bodies, cold reduced the kinetics of co-transcriptional splicing leading to increased intragenic stalling. Our data resolved multiple distinct mechanisms by which temperature transiently altered the dynamics of nascent RNAPII transcription and associated RNA processing, illustrating potential biotechnological solutions and future focus areas to promote food security in the context of a changing climate.

genomics↗

bioRxiv2019

Transcript isoform sequencing reveals widespread promoter-proximal transcriptional termination

Higher organisms achieve optimal gene expression by tightly regulating the transcriptional activity of RNA Polymerase II (RNAPII) along DNA sequences of genes1. RNAPII density across genomes is typically highest where two key choices for transcription occur: near transcription start sites (TSSs) and polyadenylation sites (PASs) at the beginning and end of genes, respectively2,3. Alternative TSSs and PASs amplify the number of transcript isoforms from genes4, but how alternative TSSs connect to variable PASs is unresolved from common transcriptomics methods. Here, we define TSS/PAS pairs for individual transcripts in Arabidopsis thaliana using an improved Transcript Isoform sequencing (TIF-seq) protocol and find on average over four different isoforms corresponding to variable TSS/PAS pairs per expressed gene. While intragenic initiation represents a large source of regulated isoform diversity, we discover that [~] 14% of expressed genes generate relatively unstable short promoter-proximal RNAs (sppRNAs) from nascent transcript cleavage and polyadenylation shortly after initiation. The location of sppRNAs coincides with increased RNAPII density, indicating these large pools of promoter-stalled RNAPII across genomes are often engaged in transcriptional termination. RNAPII elongation factors progress transcription beyond sites of sppRNA formation, demonstrating RNAPII density near promoters represents a checkpoint for early transcriptional termination that governs full-length gene isoform expression.

genomics↗

bioRxiv2018

Transcriptional read-through of the long non-coding RNA SVALKA governs plant cold acclimation

Most DNA in the genomes of higher organisms does not encode proteins, but is transcribed by RNA polymerase II (RNAPII) into long non-coding RNA (lncRNA). The biological significance of most lncRNA is largely unclear. Here, we identify a lncRNA (SVALKA) in a cold-sensitive region of the Arabidopsis genome. Mutations in SVALKA affect the timing of maximal CBF1 expression and freezing tolerance. RNAPII read-through transcription of SVALKA results in a cryptic lncRNA overlapping CBF1 on the antisense strand, termed asCBF1. asCBF1 transcription is anti-correlated with CBF1 expression. Our molecular dissection reveals that CBF1 is suppressed by RNAPII collision stemming from the SVALKA-asCBF1 lncRNA cascade. The SVK-asCBF1 cascade provides a mechanism to tightly control CBF1 expression and timing that could be exploited to maximize freezing tolerance with mitigated fitness costs. Inversion of the transcriptional direction of a lncRNA cascade relative to the genes in a co-regulated cluster provides an elegant inbuilt negative feedback for cluster expression. Our results provide a compelling example of local gene regulation by lncRNA transcription having a profound impact on the ability of plants to appropriately acclimate to suboptimal environmental conditions.

genomics↗

bioRxiv2018

Transcription-driven Chromatin Repression of Intragenic Promoters

Progression of RNA polymerase II (RNAPII) transcription relies on the appropriately positioned activities of elongation factors. The resulting profile of factors and chromatin signatures along transcription units provides a \"positional information system\" for transcribing RNAPII. Here, we investigate a chromatin-based mechanism that suppresses intragenic initiation of RNAPII transcription. We demonstrate that RNAPII transcription across gene promoters represses their function in plants. This repression is characterized by reduced promoter-specific molecular signatures and increased molecular signatures associated with RNAPII elongation. The FACT histone chaperone complex is required for this repression mechanism. Genome-wide mapping of Transcription Start Sites (TSSs) reveals thousands of discrete intragenic TSS positions in FACT mutants. Histone 3 lysine 4 mono-methylation poises exonic sites to initiate RNAPII transcription in FACT mutants. Uncovering the mechanism for intragenic TSS repression through the act of RNAPII elongation has important implications for understanding pervasive RNAPII transcription and the regulation of transcript isoform diversity.

genomics↗