Biology subjects

Siebert, S.

Publications and source records attributed to Siebert, S..

14 recordsLinked to original sources

bioRxiv2025

RNAcare: Integrating Clinical Data with Transcriptomic Evidence using Rheumatoid Arthritis as a Case Study

BackgroundGene expression analysis is a crucial tool for uncovering the biological mechanisms that underlie differences between patient subgroups, offering insights that can inform clinical decisions. However, despite its potential, gene expression analysis remains challenging for clinicians due to the specialised skills required to access, integrate, and analyse large datasets. Existing tools primarily focus on RNA-Seq data analysis, providing user-friendly interfaces but often falling short in several critical areas: they typically do not integrate clinical data, lack support for patient-specific analyses, and offer limited flexibility in exploring relationships between gene expression and clinical outcomes in disease cohorts. Users, including clinicians with a general knowledge of transcriptomics, however, who may have limited programming experience, are increasingly seeking tools that go beyond traditional analysis. To overcome these issues, computational tools must incorporate advanced techniques, such as machine learning, to better understand how gene expression correlates with patient symptoms of interest. ResultsOur RNAcare platform, addresses these limitations by offering an interactive and reproducible solution specifically designed for analysing bulk RNA-Seq data from patient samples in a clinical context. This enables researchers to directly integrate gene expression data with clinical features, perform exploratory data analysis, and identify patterns among patients with similar diseases. By enabling users to integrate transcriptomic and clinical data, and customise the target label, the platform facilitates the analysis of the relationships between gene expression and clinical symptoms, like pain and fatigue. This allows users to generate hypotheses and illustrative visualisations/reports to support their research. As proof of concept, we use RNAcare to link inflammation-related genes to pain and fatigue in rheumatoid arthritis (RA) and detect signatures in the drug response group, confirming previous findings and generating new hypotheses. ConclusionWe present a novel computational platform allowing the interpretation of clinical and transcriptomics data in real-time. The platform can be used for data generated by the user, such as the patient data presented here or using published datasets. The platform is available at https://rna-care.mvls.gla.ac.uk/, with its source code at https://github.com/sii-scRNA-Seq/RNAcare/.

bioinformatics↗

bioRxiv2023

BCL7 proteins, metazoan-specific subunits of the mammalian SWI/SNF complex, bind the nucleosome core particle

BCL7 proteins are among the most recently identified subunits of the mammalian SWI/SNF (mSWI/SNF) chromatin remodeling complex and are absent from the unicellular version of the complex. Mutations in BCL7 proteins are associated with different kind of cancers including blood malignancies. The information on the molecular function and on the structure of BCL7 proteins is to date very limited. Here we report that BCL7 proteins directly bind the nucleosome core particle (NCP) and free DNA with high affinity. We demonstrate that BCL7 proteins form defined complexes with the NCP and we identify the conserved N-terminal part of BCL7 proteins as sufficient to nucleosome binding. We further characterize the impact of BCL7 protein mutations reported in cancer patients on NCP binding and show that the R11S driver mutation reduces the affinity for the nucleosome. Our findings clarify the molecular function of BCL7 proteins and help rationalize the impact of cancer-associated mutations.

biochemistry↗

bioRxiv2022

New Hydra Genomes Reveal Conserved Principles of Hydrozoan Transcriptional Regulation

The epithelial and interstitial stem cells of the freshwater polyp Hydra are the best characterized stem cell systems in any cnidarian, providing valuable insight into cell type evolution and the origin of stemness in animals. However, little is known about the transcriptional regulatory mechanisms that determine how these stem cells are maintained and how they give rise to their diverse differentiated progeny. To address such questions, a thorough understanding of transcriptional regulation in Hydra is needed. To this end, we generated extensive new resources for characterizing transcriptional regulation in Hydra, including new genome assemblies for Hydra oligactis and the AEP strain of Hydra vulgaris, an updated whole-animal single-cell RNA-seq atlas, and genome-wide maps of chromatin interactions, chromatin accessibility, sequence conservation, and histone modifications. These data revealed the existence of large chromatin interaction domains in the Hydra genome that likely influence transcriptional regulation in a manner distinct from topologically associating domains in bilaterians. We also uncovered the transcriptomic profiles of two previously molecularly uncharacterized cell types, isorhiza-containing nematocytes and somatic gonad ectoderm. We identified novel candidate regulators of cell-type-specific transcription, several of which have likely been conserved at least since the divergence of Hydra and the jellyfish Clytia hemisphaerica over 200 million years ago. The resources generated in this study, which collectively represent the most comprehensive characterization of transcriptional regulation in a cnidarian to date, are accessible through a newly created genome portal, available at research.nhgri.nih.gov/HydraAEP/.

developmental biology↗

bioRxiv2021

Single-cell transcriptome reveals insights into the development and function of the zebrafish ovary

Zebrafish are an established research organism that has made many contributions to our understanding of vertebrate tissue and organ development, yet there are still significant gaps in our understanding of the genes that regulate gonad development, sex, and reproduction. Unlike the development of many organs, such as the brain and heart that form during the first few days of development, zebrafish gonads do not begin to form until the larval stage ([≥]5 dpf). Thus, forward genetic screens have identified very few genes required for gonad development. In addition, bulk RNA sequencing studies which identify genes expressed in the gonads do not have the resolution necessary to define minor cell populations that may play significant roles in development and function of these organs. To overcome these limitations, we have used single-cell RNA sequencing to determine the transcriptomes of cells isolated from juvenile zebrafish ovaries. This resulted in the profiles of 10,658 germ cells and 14,431 somatic cells. Our germ cell data represents all developmental stages from germline stem cells to early meiotic oocytes. Our somatic cell data represents all known somatic cell types, including follicle cells, theca cells and interstitial stromal cells. Further analysis revealed an unexpected number of cell subpopulations within these broadly defined cell types. To further define their functional significance, we determined the location of these cell subpopulations within the ovary. Finally, for select examples, we used gene knockout experiments to determine the role of newly identified genes. Our results reveal novel insights into ovarian development and function and the sequencing information will provide a valuable resource for future studies.

developmental biology↗

bioRxiv2021

Evolution of gene expression across species and specialized zooids in Siphonophora

BackgroundSiphonophores are complex colonial animals, consisting of asexually-produced bodies (called zooids) that are functionally specialized for specific tasks, including feeding, swimming, and sexual reproduction. Though this extreme functional specialization has captivated biologists for generations, its genomic underpinnings remain unknown. We use RNA-seq to investigate gene expression patterns in five zooids and one specialized tissue (pneumatophore) across seven siphonophore species. Analyses of gene expression across species present several challenges, including identification of comparable expression changes on gene trees with complex histories of speciation, duplication, and loss. Here, we conduct three analyses of expression. First, we examine gene expression within species. Then, we conduct classical analyses examining expression patterns between species. Lastly, we introduce Speciation Branch Filtering, which allows us to examine the evolution of expression in a phylogenetic framework. ResultsWithin and across species, we identified hundreds of zooid-specific and species-specific genes, as well as a number of putative transcription factors showing differential expression in particular zooids and developmental stages. We found that gene expression patterns tended to be largely consistent in zooids with the same function across species, but also some large lineage-specific shifts in gene expression. ConclusionsOur findings show that patterns of gene expression have the potential to define zooids in colonial organisms. We also show that traditional analyses of the evolution of gene expression focus on the tips of gene phylogenies, identifying large-scale expression patterns that are zooid or species variable. The new explicit phylogenetic approach we propose here focuses on branches (not tips) offering a deeper evolutionary perspective into specific changes in gene expression within zooids along all branches of the gene (and species) trees.

evolutionary biology↗

bioRxiv2021

Self-organized yolk sac-like organoids allow for scalable generation of multipotent hematopoietic progenitor cells from human induced pluripotent stem cells

The human definitive yolk sac is an important organ supporting the early developing embryo through nutrient supply and by facilitating the establishment of the embryonic circulatory system. However, the molecular and cellular biology of the human yolk sac remains largely obscure due to the lack of suitable in vitro models. Here, we show that human induced pluripotent stem cells (hiPSCs) co-cultured with various types of stromal cells as spheroids self-organize into yolk sac-like organoids without the addition of exogenous factors. Yolk sac-like organoids recapitulated a yolk sac specific cellular complement and structures as well as the functional ability to generate definitive hematopoietic progenitor cells (HPCs). Furthermore, sequential hemato-vascular ontogenesis could be observed during organoid formation. Notably, our organoid system can be performed in a scalable, autologous, and xeno-free condition, thereby providing an important model of human definitive yolk sac development and allows for efficient bulk generation of hiPSC-derived HPCs.

cell biology↗

bioRxiv2021

Differential gene regulation in DAPT-treated Hydra reveals molecular pathways dependent on Notch signalling during interstitial cell differentiation and formation of the oral-aboral axis in Hydra.

The Notch pathway is highly conserved and essential for animal development. We investigated the function of Notch-signalling in Hydra by using the presenilin inhibitor DAPT, which efficiently blocks propagation of Notch-signals. In Hydra, DAPT treatment prevents differentiation of proliferating nematocyte progenitor cells into mature nematocytes. Moreover, it causes defects in the Hydra head by compromising the head organizer. In order to understand the molecular mechanisms by which the Notch pathway regulates these processes we performed RNAseq to identify genes that are differentially regulated in response to 48 hours of DAPT-exposure. This revealed downregulation of 624 genes and upregulation of 207 genes. To identify candidate direct regulators of Notch-signalling, we also profiled gene expression changes that occur during restoration of Notch-activity 3 and 6 hours after DAPT-removal. We then analysed gene expression patterns of these Notch-responsive genes in untreated animals by interrogating the available single cell sequencing data set for untreated animals and found that almost half of the Notch responsive genes were specifically expressed in nematocytes and nematocyte progenitors. This confirms the critical role for Notch-signalling in nematocyte development. Promoter analyses and gene expression profiling after DAPT-removal suggested an indirect role for Notch in regulating a POU-transcription factor, which is critical for nematogenesis. In support of a role for Notch-signalling in head organizer formation, we identified several head organizer genes in the Notch regulated gene data set, including Cngsc, a homologue of goosecoid, a gene associated with the Spemann organizer, and the Wnt pathway genes Sp5, Tcf and Wnt-7. Finally, the expression levels of the tentacle patterning genes HyAlx and Sp5 rapidly recovered after DAPT removal. Given that these genes possess Notch-responsive RBPJ transcription factor binding sites in their regulatory regions, these genes are likely directly targeted by Notch signalling. In summary, our data provide a comprehensive picture of the molecular pathways regulated by Notch signalling in interstitial cell differentiation and formation of the oral-aboral axis in Hydra.

developmental biology↗

bioRxiv2019

PIWI-piRNA pathway-mediated transposable element repression in Hydra somatic stem cells

Transposable elements (TEs) can damage genomes, thus organisms employ a variety of mechanisms to repress TE expression. However, these mechanisms often fail over time leading to de-repression of TEs in aging tissues. The PIWI-piRNA pathway is a small RNA pathway that represses TE expression in the germline of animals. Here we explore the function of the pathway in the epithelial stem cells of Hydra, a long-lived freshwater cnidarian. Hydra have three stem cell populations; endodermal and ectodermal epithelial stem cells are strictly somatic, whereas the interstitial stem cells retain germline competence. In our previous study, we found that the PIWI proteins are expressed in all three Hydra stem cell types. In this study, we focus on the ectodermal and endodermal epithelial stem cells to understand the somatic function of the pathway. We isolated piRNAs from Hydra that lack the interstitial lineage and found that these somatic piRNAs map predominantly to TE transcripts and display the conserved sequence signatures typical of germline piRNAs. Three lines of evidence suggest that the PIWI-piRNA pathway represses TEs in Hydra epithelial stem cells. First, epithelial knockdown of the Hydra PIWI protein hywi resulted in upregulation of TE expression. Second, degradome sequencing revealed evidence of PIWI-mediated cleavage of TE RNAs in epithelial cells using the ping-pong mechanism. Finally, we demonstrated a direct association between Hywi protein and TE transcripts in epithelial cells using RNA immunoprecipitation. Interestingly, we found that RNAi knockdown of hywi leads to an upregulation of genes involved in innate immunity, which may be in response to TE upregulation; this is consistent with recent studies on TE expression in mammalian cells. Altogether, this study suggests a function for the PIWI-piRNA pathway in maintaining the long-lived somatic cell lineages of Hydra and may point to a broader role for this pathway in protecting somatic tissue from TE-induced damage.

molecular biology↗

bioRxiv2019

Molecular Mechanisms Driving Bistable Switch Behavior in Xylem Cell Differentiation

Plant xylem cells conduct water and mineral nutrients. Although most plant cells are totipotent, xylem cells are unusual and undergo terminal differentiation. Many genes regulating this process are well characterized, including the VASCULAR-RELATED NAC DOMAIN7 (VND7), MYB46 and MYB83 transcription factors which are proposed to act in interconnected feed-forward loops. Much less is known regarding the dynamic behavior underlying the terminal transition to xylem cell differentiation. Here we utilize whole root and single cell data to mathematically model this relationship. These provide evidence for VND7 regulating bistable switching of cells in the root to a xylem cell identity, with additional features of hysteresis. We further determine that although MYB46 responds to VND7 induction, it is not inherently involved in executing the binary switch. A novel regulatory architecture is proposed that involves four downstream targets of VND7 that act in a cycle. These data provide an important model to study the emergent properties that may give rise to totipotency relative to terminal differentiation and reveal novel xylem cell subtypes.

plant biology↗

bioRxiv2018

Systems-level properties of EGFR/Ras/ERK signalling amplify local signals to generate gene expressionplasticity

The EGFR/Ras/ERK signalling pathway is a driver of cancer cell proliferation and metastasis in tumours that exhibit high cell-to-cell heterogeneity. While the signalling activity of this pathway is frequently amplified in tumours, it is not understood how the kinetic aspects of its activation in tumours differ from normal cellular signalling. Using live-cell reporters of ERK signalling in the breast cancer progression series HMT-3522, we found that ERK activity in invasive cells is similar in amplitude to isogenic non-malignant cells but is highly dynamic and more disordered, leading to more heterogeneous expression of ERK target genes. Our analysis reveals that this diversification arises from systems-level functions of the pathway, including intracellular amplification of amphiregulin-mediated paracrine signalling and differential kinetic filtering by genes including Fra-1, c-Myc, and Egr1. Our findings establish a mechanism for the generation of non-genetic tumour cell plasticity arising from the specific quantitative properties of a signal transduction pathway.

cancer biology↗

bioRxiv2018

Stem cell differentiation trajectories in Hydra resolved at single-cell resolution

The adult Hydra polyp continuously renews all of its cells using three separate stem cell populations, but the genetic pathways enabling homeostatic tissue maintenance are not well understood. We used Drop-seq to sequence transcriptomes of 24,985 single Hydra cells and identified the molecular signatures of a broad spectrum of cell states, from stem cells to terminally differentiated cells. We constructed differentiation trajectories for each cell lineage and identified the transcription factors expressed along these trajectories, thus creating a comprehensive molecular map of all developmental lineages in the adult animal. We unexpectedly found that neuron and gland cell differentiation transits through a common progenitor state, suggesting a shared evolutionary history for these secretory cell types. Finally, we have built the first gene expression map of the Hydra nervous system. By producing a comprehensive molecular description of the adult Hydra polyp, we have generated a resource for addressing fundamental questions regarding the evolution of developmental processes and nervous system function.

developmental biology↗

bioRxiv2018

Evidence of a common causal relationship between body mass index and inflammatory skin disease: a Mendelian Randomization study

ObjectivePsoriasis and eczema are common inflammatory skin diseases that have been reported to be associated with obesity. However, causality has not yet been established. We aimed to investigate the possible causal relationship between body mass index (BMI) and psoriasis or eczema.\n\nMethodsFollowing a review of published epidemiological evidence of the association between obesity and either psoriasis or eczema, Mendelian Randomization (MR) was used to test for a causal relationship between BMI and these inflammatory skin conditions. We used a genetic instrument comprising 97 single nucleotide polymorphisms (SNPs) associated with BMI. One-sample MR was conducted using individual-level data (401,508 individuals) from the UK Biobank and the Nord-Trondelag Health Study (HUNT), Norway. Two-sample MR was performed with summary-level data (731,021 individuals) from published BMI, psoriasis and eczema GWAS. The one-sample and two-sample MR estimates were meta-analysed using a fixed effect model. To explore the reverse causal direction, MR analysis with genetic instruments comprising variants from recent genome-wide analyses for psoriasis and eczema were used to test if inflammatory skin disease has a causal effect on BMI.\n\nResultsPublished observational data show an association of greater BMI with both psoriasis and eczema case status. The observational associations were confirmed in UK Biobank and HUNT datasets. MR analyses provide evidence that higher BMI causally increases the odds of psoriasis (by 53% per 5 units higher BMI; OR= 1.09 (1.06 to 1.12) per 1 kg/m2; P=4.67x10-9) and eczema (by 8% per 5 units higher BMI; OR=1.02 (1.00 to 1.03) per 1 kg/m2; P=0.09). When investigating causality in the opposite direction, MR estimates provide little evidence for an effect of either psoriasis or eczema influencing BMI.\n\nConclusionOur study, using genetic variants as instrumental variables for BMI, shows that higher BMI leads to a higher risk of inflammatory skin disease. The causal relationship was stronger for psoriasis than eczema. Therapies and life-style interventions aimed at controlling BMI or targeting the mechanisms linking obesity with skin inflammation may offer an opportunity for the prevention or treatment of these common skin diseases.

genetics↗

bioRxiv2018

Improved phylogenetic resolution within Siphonophora (Cnidaria) with implications for trait evolution

Siphonophores are a diverse group of hydrozoans (Cnidaria) that are found at all depths of the ocean - from the surface, like the familiar Portuguese man of war, to the deep sea. Siphonophores play an important role in ocean ecosystems, and are among the most abundant gelatinous predators. A previous phylogenetic study based on two ribosomal RNA genes provided insight into the internal relationships between major siphonophore groups, however there was little support for many deep relationships within the clade Codonophora. Here, we present a new siphonophore phylogeny based on new transcriptome data from 30 siphonophore species analyzed in combination with 13 publicly available genomic and transcriptomic datasets. We use this new phylogeny to reconstruct several traits that are central to siphonophore biology, including sexual system (monoecy vs. dioecy), gain and loss of zooid types, life history traits, and habitat. The phylogenetic relationships in this study are largely consistent with the previous phylogeny, but we find strong support for new clades within Codonophora that were previously unresolved. These results have important implications for trait evolution within Siphonophora, including favoring the hypothesis that monoecy arose twice.

evolutionary biology↗

bioRxiv2017

Pairwise comparisons are problematic when analyzing functional genomic data across species

AbstractThere is considerable interest in comparing functional genomic data across species. One goal of such work is to provide an integrated understanding of genome and phenotype evolution. Most comparative functional genomic studies have relied on multiple pairwise comparisons between species, an approach that does not incorporate information about the evolutionary relationships among species. The statistical problems that arise from not considering these relationships can lead pairwise approaches to the wrong conclusions, and are a missed opportunity to learn about biology that can only be understood in an explicit phylogenetic context. Here we examine two recently published studies that compare gene expression across species with pairwise methods, and find reason to question the original conclusions of both. One study interpreted pairwise comparisons of gene expression as support for the ortholog conjecture, the hypothesis that orthologs tend to be more similar than paralogs. The other study interpreted pairwise comparisons of embryonic gene expression across distantly related animals as evidence for a distinct evolutionary process that gave rise to phyla. In each study, distinct patterns of pairwise similarity among species were originally interpreted as evidence of particular evolutionary processes, but instead we find they reflect species relationships. These reanalyses concretely demonstrate the inadequacy of pairwise comparisons for analyzing functional genomic data across species. It will be critical to adopt phylogenetic comparative methods in future functional genomic work. Fortunately, phylogenetic comparative biology is also a rapidly advancing field with many methods that can be directly applied to functional genomic data.\n\nSignificanceComparisons of genome function between species are providing important insight into the evolutionary origins of diversity. Here we demonstrate that comparative functional genomics studies can come to the wrong conclusions if they do not take the relationships of species into account and instead rely on pairwise comparisons between species, as is common practice. We re-examined two previously published studies and found problems with pairwise comparisons that draw both their original conclusions into question. One study had found support for the ortholog conjecture and the other had concluded that the evolution of gene expression was different between animal phyla than within them. Our results demonstrate that to answer evolutionary questions about genome function, it is critical to consider evolutionary relationships.

genomics↗