Biology subjects

Junker, J. P.

Publications and source records attributed to Junker, J. P..

14 recordsLinked to original sources

bioRxiv2026

Pre-existing chromatin accessibility primes δ-cells for injury-induced endocrine plasticity

Adult zebrafish rapidly recover glucose homeostasis after {beta}-cell loss, but the cellular basis and regulatory mechanisms that enable this response remain unclear. Here we combine single-cell transcriptomics, single-cell chromatin accessibility profiling, paired multiome analysis and functional perturbation to define early pancreatic recovery after {beta}-cell ablation. We show that, during the first month after injury, insulin production is restored predominantly by sst1.1+ {delta}1-cells rather than by rapid reconstitution of canonical {beta}-cells. Following ablation, {delta}1-cells adopt a bihormonal hybrid state and induce metabolic, secretory and {beta}-cell-associated gene programs. Systematic comparison of chromatin accessibility across endocrine cell types reveals that these {delta}1-cells are uniquely close to {beta}-cells and exhibit open chromatin at {beta}-cell enhancers in the steady state. Moreover, hybrid-cell formation occurs without major chromatin remodeling, with {beta}-cell associated loci being already accessible in {delta}1-cells before {beta}-cell injury. A comparable permissive state is present in medaka but not in human {delta}-cells, suggesting that restricted insulin accessibility may represent a barrier to endocrine plasticity in the human pancreas. In zebrafish, {delta}1-cells also show evidence of metabolic remodeling after {beta}-cell loss, including rapid accumulation of neutral lipids. Gene regulatory network analysis and perturbation identify meis1a/b as required regulators of {delta}1 hybrid-cell formation after {beta}-cell loss in zebrafish, whereas meis1a/b are not upregulated following {beta}-cell ablation in medaka. Together, our results define pre-existing chromatin accessibility, metabolic remodeling and instructive transcriptional regulation as key features of early functional recovery after {beta}-cell loss in the adult zebrafish pancreas.

developmental biology↗

bioRxiv2025

Lineage origin and microenvironment shape neuroblastoma transcriptional state and plasticity

Neuroblastoma, a neural-crest-derived malignancy of the peripheral nervous system, is a devastating pediatric disease characterized by high intra- and intertumoral heterogeneity. While several tumor expression programs correlate with patient outcome, the developmental and contextual determinants of their emergence remain incompletely understood. Here, we systematically dissected neuroblastoma transcriptional heterogeneity and measured how tumor expression programs are associated with lineage history and developmental context. To achieve this, we combined single-cell transcriptomics with high-throughput lineage tracing and tumor cell transplantation in zebrafish models of MYCN-driven neuroblastoma. We identified developmental cell-state-associated programs that align with sympathoadrenal development, as well as general cellular-process programs. Clonal analysis showed that developmental programs are preferentially clone-associated, whereas cellular-process programs are more context-responsive. Transplantation into an embryonic environment reshaped the activation of several initially clone-associated programs, consistent with developmentally determined state reconfiguration and/or selection of state-competent cells. Together, our results show that lineage history and developmental context jointly shape tumor-state architecture in vivo.

cancer biology↗

bioRxiv2023

Mapping lineage-traced cells across time points with moslin

Simultaneous profiling of single-cell gene expression and lineage history holds enormous potential for studying cellular decision-making beyond simpler pseudotime-based approaches. However, it is currently unclear how lineage and gene expression information across experimental time points can be combined in destructive experiments, which is particularly challenging for in-vivo systems. Here we present moslin, a Fused Gromov-Wasserstein-based model to couple matching cellular profiles across time points. In contrast to existing methods, moslin leverages both intra-individual lineage relations and inter-individual gene expression similarity. We demonstrate on simulated and real data that moslin outperforms state-of-the-art approaches that use either one or both data modalities, even when the lineage information is noisy. On C. elegans embryonic development, we show how moslin, combined with trajectory inference methods, predicts fate probabilities and putative decision driver genes. Finally, we use moslin to delineate lineage relationships among transiently activated fibroblast states during zebrafish heart regeneration. We anticipate moslin to play a crucial role in deciphering complex state change trajectories from lineage-traced single-cell data.

bioinformatics↗

bioRxiv2022

Long-term imaging reveals behavioral plasticity during C. elegans dauer exit

During their lifetime, animals must adapt their behavior to survive in changing environments. This ability requires the nervous system to adjust through dynamic expression of neurotransmitters and receptors but also through growth, spatial reorganization and connectivity while integrating external stimuli. For instance, despite having a fixed neuronal cell lineage, the nematode Caenorhabditis elegans nervous system remains plastic throughout its development. Here, we focus on a specific example of nervous system plasticity, the C. elegans dauer exit decision. Under unfavorable conditions, larvae will enter the non-feeding and non-reproductive dauer stage and adapt their behavior to cope with a new environment. Upon improved conditions, this stress resistant developmental stage is actively reversed to resume reproductive development. However, how different environmental stimuli regulate the exit decision mechanism and thereby drive the larvas behavioral change is unknown. To fill this gap, we developed a new open hardware method for long-term imaging (12h) of C. elegans larvae. We identified dauer-specific behavioral motifs and characterized the behavioral trajectory of dauer exit in different environments to identify key decision points. Combining long-term behavioral imaging with transcriptomics, we find that bacterial ingestion triggers a change in neuropeptide gene expression to establish post-dauer behavior. Taken together, we show how a developing nervous system can robustly integrate environmental changes, activate a developmental switch and adapt the organisms behavior to a new environment.

animal behavior and cognition↗

bioRxiv2021

Transcription factor induction of vascular blood stem cell niches in vivo

The hematopoietic niche is a supportive microenvironment comprised of distinct cell types, including specialized vascular endothelial cells that directly interact with hematopoietic stem and progenitor cells (HSPCs). The molecular factors that specify niche endothelial cells and orchestrate HSPC homeostasis remain largely unknown. Using multi-dimensional gene expression and chromatin accessibility analyses, we define a conserved gene expression signature and cis-regulatory landscape unique to sinusoidal endothelial cells in the HSPC niche. Using enhancer mutagenesis and transcription factor overexpression, we elucidate a transcriptional code involving members of the Ets, Sox and Nuclear Hormone Receptor families that is sufficient to induce ectopic niche endothelial cells that associate with mesenchymal stromal cells and support the recruitment, maintenance and division of HSPCs in vivo. These studies set forth an approach for generating synthetic HSPC niches, in vitro or in vivo, and for effective therapies to modulate the endogenous niche.

developmental biology↗

bioRxiv2021

A single-cell atlas of de novo β-cell regeneration reveals the contribution of hybrid β/δ cells to diabetes recovery in zebrafish

Regeneration-competent species possess the ability to reverse the progression of severe diseases by restoring the function of the damaged tissue. However, the cellular dynamics underlying this capability remain unexplored. Here, we use single-cell transcriptomics to map de novo {beta}-cell regeneration during induction and recovery from diabetes in zebrafish. We show that the zebrafish has evolved two distinct types of somatostatin-producing {delta}-cells, which we term {delta}1- and {delta}2-cells. Moreover, we characterize a small population of glucose-responsive islet cells, which share the hormones and fate-determinants of both {beta}- and {delta}1-cells. The transcriptomic analysis of {beta}-cell regeneration reveals that {beta}/{delta} hybrid cells constitute a prominent source of insulin-expression during diabetes recovery. Using in vivo calcium imaging and cell tracking, we further show that the hybrid cells form de novo and acquire glucose-responsiveness in the course of regeneration. The overexpression of dkk3, a gene enriched in hybrid cells, increases their formation in the absence of {beta}-cell injury. Finally, interspecies comparison shows that plastic {delta}1-cells are partially related to PP-cells in the human pancreas. Our work provides an atlas of {beta}-cell regeneration and indicates that the rapid formation of glucose-responsive hybrid cells contributes to the resolution of diabetes in zebrafish

developmental biology↗

bioRxiv2021

Cellular drivers of injury response and regeneration in the adult zebrafish heart

Myocardial infarction is a leading cause of death worldwide, as the adult human heart does not have the ability to regenerate efficiently after insults. In contrast, the adult zebrafish heart has a high capacity for regeneration, and understanding the mechanisms of regenerative processes in fish allows identification of novel therapeutic strategies. While several pro-regenerative factors have been described, the cell types orchestrating heart regeneration remain largely elusive. To overcome this conceptual limitation, we dissected cell type diversity in the regenerating zebrafish heart based on single cell transcriptomics and spatiotemporal analysis. We discovered a dramatic induction of several pro-regenerative cell types with fibroblast characteristics. To understand the cascade of events leading to heart regeneration, we determined the origin of these cell types by high-throughput lineage tracing. We found that pro-regenerative fibroblasts are derived from two separate sources, the epicardium and the endocardium. Mechanistically, we identified Wnt signaling as a key regulator of the endocardial regenerative response. In summary, our results uncover specialized fibroblast cell types as major drivers of heart regeneration, thereby opening up new possibilities to interfere with the regenerative capacity of the vertebrate heart.

systems biology↗

bioRxiv2020

Spatio-temporal mRNA dynamics in the early zebrafish embryo

Early stages of embryogenesis depend heavily on subcellular localization and transport of maternally deposited mRNA. However, systematic analysis of these processes is currently hindered by a lack of spatio-temporal information in single-cell RNA sequencing. Here, we combined spatially-resolved transcriptomics and single-cell RNA labeling to study the spatio-temporal dynamics of the transcriptome during the first few hours of zebrafish development. We measured spatial localization of mRNA molecules with sub-single-cell resolution at the one-cell stage, which allowed us to identify a class of mRNAs that are specifically localized at an extraembryonic position, the vegetal pole. Furthermore, we established a method for high-throughput single-cell RNA labeling in early zebrafish embryos, which enabled us to follow the fate of individual maternal transcripts until gastrulation. This approach revealed that many localized transcripts are specifically transported to the primordial germ cells. Finally, we acquired spatial transcriptomes of two xenopus species, and we compared evolutionary conservation of localized genes as well as enriched sequence motifs. In summary, we established sub-single-cell spatial transcriptomics and single-cell RNA labeling to reveal principles of mRNA localization in early vertebrate development.

systems biology↗

bioRxiv2020

Morphine alleviates pain after heart cryoinjury in zebrafish without impeding regeneration

Nociceptive response belongs to a basic animal behavior facilitating adaptability and survival upon external or internal stimuli. Fish, similarly to higher vertebrates, also possess nociceptive machinery. Current protocols involving procedures performed on adult zebrafish including heart cryoinjury do not, however, take into account the adverse effects including pain that may potentially arise from these methodologies. Here, we assess the effect of two analgesics, lidocaine and morphine, followed after heart cryoinjury in zebrafish. Monitoring swimming behavior together with histology and gene expression analysis at the single cell level using scRNA sequencing and RNAscope fluorescent in situ hybridization technology, we show morphine, but not lidocaine, significantly improves animal welfare 6 hours post-cryoinjury, without impairing the heart regeneration process. Altogether, we propose morphine to be considered as the analgesic of choice to reduce post-surgical pain in adult zebrafish. HighlightsO_LICryoinury could be considered as a potential noxious stimulus in adult zebrafish. C_LIO_LIMorphine but not lidocaine treatment effectively alleviates noxious effects post-cryoinjury. C_LIO_LILidocaine treatment delays heart repair and regeneration. C_LIO_LI6 hours Morphine treatment after cryoinjury does not impede heart regeneration. C_LI

developmental biology↗

bioRxiv2020

Variability of an early developmental cell population underlies stochastic laterality defects

Embryonic development seemingly proceeds with almost perfect precision. However, it is largely unknown how much underlying microscopic variability is compatible with normal development. Here, we quantified embryo-to-embryo variability in vertebrate development, by studying cell number variation in the zebrafish endoderm. We noticed that the size of a sub-population of the endoderm, the dorsal forerunner cells (which later form the left-right organizer), exhibits significantly more embryo-to-embryo variation than the rest of the endoderm. We found that, when incubated at elevated temperature, the frequency of left-right laterality defects is increased drastically in embryos with a low number of dorsal forerunner cells. Furthermore, we observed that these fluctuations have a large stochastic component among fish of the same genetic background. Hence, a stochastic variation in early development leads to a remarkably strong macroscopic phenotype. These fluctuations appear to be associated with maternal effects in the specification of the dorsal forerunner cells.

developmental biology↗

bioRxiv2020

Single-cell-resolved dynamics of chromatin architecture delineate cell and regulatory states in wildtype and cloche/npas4l mutant zebrafish embryos

DNA accessibility of cis regulatory elements (CREs) dictates transcriptional activity and drives cell differentiation during development. While many of the genes that regulate embryonic development have been described, the underlying CRE dynamics controlling their expression remain largely unknown. To address this, we applied single-cell combinatorial indexing ATAC-seq (sci-ATAC-seq) to whole 24 hours post fertilization (hpf) stage zebrafish embryos and developed a new computational tool, ScregSeg, that selects informative genome segments and classifies complex accessibility dynamics. We integrated the ScregSeg output with bulk measurements for histone post-translational modifications and 3D genome organization, expanding knowledge of regulatory principles between chromatin modalities. Sci-ATAC-seq profiling of npas4l/cloche mutant embryos revealed novel cellular roles for this hemato-vascular transcriptional master regulator and suggests an intricate mechanism regulating its expression. Our work constitutes a valuable resource for future studies in developmental, molecular, and computational biology.

genomics↗

bioRxiv2019

The transcriptome dynamics of single cells during the cell cycle

Despite advances in single-cell data analysis, the dynamics and topology of the cell cycle in high-dimensional gene expression space remains largely unknown. Here, we use a linear analysis of transcriptome data to reveal that cells move along a circular trajectory in transcriptome space during the cell cycle. This movement occurs largely independently from other cellular processes. Non-cycling gene expression (changes in environment or epigenetic state) adds a third dimension and causes helical motion on a hollow cylinder. The circular trajectory shape indicates minimal acceleration of transcription, i.e. the cell cycle has evolved to minimize changes of transcriptional activity and its entailing regulatory effort. Thus, we uncover a general design principle of the cell cycle that may be of relevance to many other cellular differentiation processes. One Sentence SummaryCells traverse high-dimensional gene expression space in a 2D circular motion, thus minimizing changes of expression changes ("Acceleration").

systems biology↗

bioRxiv2018

Spatial transcriptomics of C. elegans males and hermaphrodites identifies novel fertility genes

To advance our understanding of the genetic programs that drive cell and tissue specialization, it is necessary to obtain a comprehensive overview of gene expression patterns. Here, we have used RNA tomography to generate the first high-resolution, anteroposterior gene expression maps of C. elegans males and hermaphrodites. To explore these maps, we have developed computational methods for discovering region and tissue-specific genes. Moreover, by combining pattern-based analysis with differential gene expression analysis, we have found extensive sex-specific gene expression differences in the germline and sperm. We have also identified genes that are specifically expressed in the male reproductive tract, including a group of uncharacterized genes that encode small secreted proteins that are required for male fertility. We conclude that spatial gene expression maps provide a powerful resource for identifying novel tissue-specific gene functions in C. elegans. Importantly, we found that expression maps from different animals can be precisely aligned, which opens up new possibilities for transcriptome-wide comparisons of gene expression patterns.

genomics↗

bioRxiv2017

Massively parallel single cell lineage tracing using CRISPR/Cas9 induced genetic scars

A key goal of developmental biology is to understand how a single cell transforms into a full-grown organism consisting of many different cell types. Single-cell RNA-sequencing (scRNA-seq) has become a widely-used method due to its ability to identify all cell types in a tissue or organ in a systematic manner 1-3. However, a major challenge is to organize the resulting taxonomy of cell types into lineage trees revealing the developmental origin of cells. Here, we present a strategy for simultaneous lineage tracing and transcriptome profiling in thousands of single cells. By combining scRNA-seq with computational analysis of lineage barcodes generated by genome editing of transgenic reporter genes, we reconstruct developmental lineage trees in zebrafish larvae and adult fish. In future analyses, LINNAEUS (LINeage tracing by Nuclease-Activated Editing of Ubiquitous Sequences) can be used as a systematic approach for identifying the lineage origin of novel cell types, or of known cell types under different conditions.

systems biology↗