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Integrated Molecular-Phenotypic Profiling Reveals Metabolic Control of Morphological Variation in Stembryos

Mammalian stem-cell-based models of embryo development (stembryos) hold great promise in basic and applied research. However, considerable phenotypic variation despite identical culture conditions limits their potential. The biological processes underlying this seemingly stochastic variation are poorly understood. Here, we investigate the roots of this phenotypic variation by intersecting transcriptomic states and morphological history of individual stembryos across stages modeling post-implantation and early organogenesis. Through machine learning and integration of time-resolved single-cell RNA-sequencing with imaging-based quantitative phenotypic profiling, we identify early features predictive of the phenotypic end-state. Leveraging this predictive power revealed that early imbalance of oxidative phosphorylation and glycolysis results in aberrant morphology and a neural lineage bias that can be corrected by metabolic interventions. Collectively, our work establishes divergent metabolic states as drivers of phenotypic variation, and offers a broadly applicable framework to chart and predict phenotypic variation in organoid systems. The strategy can be leveraged to identify and control underlying biological processes, ultimately increasing the reproducibility of in vitro systems. HighlightsO_LITime-resolved single-cell RNA-sequencing and imaging-based quantitative charting of hundreds of individual stembryos generates molecular and phenotypic fingerprints C_LIO_LIMachine learning and integration of molecular and phenotypic fingerprints identifies features and biological processes predictive of phenotypic end-state C_LIO_LIEarly imbalance of oxidative phosphorylation and glycolysis results in aberrant morphology and cellular composition C_LIO_LIMetabolic interventions tune stembryo end-state and can correct derailment of differentiation outcomes C_LI

developmental biology↗

MLL3/4 methyltransferases regulate the differentiation of pluripotent stem cells via cellular respiration

Enhancer-regulating epigenetic modifiers play critical roles in normal physiological processes and human pathogenesis. The major enhancer regulator paralogs MLL3 and MLL4 (MLL3/4) belong to the lysine methyltransferase 2 (KMT2) family, which catalyzes the methylation of lysine 4 on histone H3 (H3K4me). MLL3/4 are required for enhancer activation and are essential for mammalian development and stem cell differentiation. Although recent studies have linked MLL3/4 with different metabolic pathways in the regulation of stem cell self-renewal and cancer cell growth, the mechanisms connecting enhancer function to metabolic control remain elusive. Here, using respiration flux assays, stable isotope tracing, transcriptomics, and stem cell biology techniques, we show that the loss of MLL3/4 impairs glycolysis and mitochondrial respiration in murine embryonic stem cells. Mechanistically, MLL3/4 deficiency suppresses the expression of the rate-limiting glycolytic enzyme hexokinase 2 (HK2) and compromises the function of the oxoglutarate dehydrogenase (OGDH) complex, thereby coordinately impairing central carbon metabolism. Remarkably, combined restoration of HK2 and OGDH rescues the metabolic defects caused by MLL3/4 loss and reinstates differentiation capacity. Taken together, our study identifies a direct link between enhancer-regulating epigenetic machineries and metabolic control of cell fate transition, providing a mechanistic framework for understanding how enhancer malfunction contributes to developmental abnormalities and human diseases.

developmental biology↗

A protein phosphatase network controls temporal and spatial dynamics of differentiation commitment in human epidermis

Epidermal homeostasis depends on a balance between stem cell renewal and terminal differentiation. The transition between the two cell states, termed commitment, is poorly understood. Here we characterise commitment by integrating transcriptomic and proteomic data from disaggregated primary human keratinocytes held in suspension for up to 12h to induce differentiation. We find that cell detachment induces a network of protein phosphatases. The pro-commitment phosphatases - including DUSP6, PPTC7, PTPN1, PTPN13 and PPP3CA - promote differentiation by negatively regulating ERK MAPK and positively regulating AP1 transcription factors. Their activity is antagonised by concomitant upregulation of DUSP10. Boolean network modelling of phosphatase interactions identifies commitment as an inherently unstable biological switch between the stem and differentiated cell states. Furthermore, phosphatase expression is spatially regulated both in vivo and in vitro. We conclude that an auto-regulatory phosphatase network maintains epidermal homeostasis by controlling the onset and duration of commitment.

developmental biology↗

Computational modelling unveils how epiblast remodelling and positioning rely on trophectoderm morphogenesis during mouse implantation

Understanding the processes by which the mammalian embryo implants in the maternal uterus is a long-standing challenge in embryology. New insights into this morphogenetic event could be of great importance in helping, for example, to reduce human infertility. During implantation the blastocyst, composed of epiblast and trophectoderm, undergoes significant remodelling from an oval ball to an egg cylinder. A main feature of this transformation is symmetry breaking and reshaping of the epiblast into a “cup”. Based on previous studies, we hypothesise that this event is the result of mechanical constraints originating from the trophectoderm, which is also significantly transformed during this process. In order to investigate this hypothesis we propose MG#, an original computational model of biomechanics able to reproduce key cell shape changes and tissue level behaviours in silico. With this model, we simulate epiblast and trophectoderm morphogenesis during implantation. First, our results uphold experimental findings that repulsion at the apical surface of the epiblast is sufficient to drive lumenogenesis. Then, we provide new theoretical evidence that trophectoderm morphogenesis indeed dictates the cup shape of the epiblast and fosters its movement towards the uterine tissue. Together, these results offer mechanical insights into mouse implantation and highlight the usefulness of agent-based modelling methods in the study of embryogenesis.Author summary Computational modelling is increasingly used in the context of biological development. Here we propose a novel agent-based model of biological cell and tissue mechanics to investigate important morphological changes during mouse embryo implantation. Our model is able to replicate key biological cell shape changes and tissue-level behaviour. Simulating mouse implantation with this model, we bring theoretical support to previous experimental observations that lumenogenesis in the epiblast is driven by repulsion, and provide theoretical evidence that changes in epiblast shape during implantation are regulated by trophectoderm development.Competing Interest StatementThe authors have declared no competing interest.View Full Text

developmental biology↗

ANKRD5: a key component of the axoneme required for spermmotility and male fertility

Sperm motility is essential for male fertility and depends on the structural integrity of the sperm axoneme, which features a canonical "9+2" microtubule arrangement. This structure comprises nine outer doublet microtubules (DMTs) that are associated with various macromolecular complexes. Among them, the nexin-dynein regulatory complex (N-DRC) forms crossbridges between adjacent DMTs, contributing to their stabilization and enabling flagellar bending. In this study, we investigated Ankyrin repeat domain 5 (ANKRD5, also known as ANK5 or ANKEF1), a protein highly expressed in the sperm axoneme. We found that ANKRD5 interacts with DRC5/TCTE1 and DRC4/GAS8, two key components of the N-DRC, and these interactions occur independently of calcium regulation. Male Ankrd5-/- mice exhibited impaired sperm motility and infertility. Cryo-electron tomography revealed a typical "9+2" axoneme structure with intact DMTs in Ankrd5 null sperm; however, the DMTs showed pronounced morphological variability and increased structural heterogeneity. Notably, ANKRD5 deficiency did not alter ATP levels, reactive oxygen species (ROS) levels, or mitochondrial membrane potential. These findings suggest that ANKRD5 may attenuate the N-DRCs mechanical buffering-akin to a "car bumper"-between adjacent DMTs, thereby compromising axonemal stability under high mechanical stress during vigorous flagellar beating. Graphic Abstract O_FIG O_LINKSMALLFIG WIDTH=184 HEIGHT=200 SRC="FIGDIR/small/626701v3_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1ca36eforg.highwire.dtl.DTLVardef@dcafe3org.highwire.dtl.DTLVardef@9f6086org.highwire.dtl.DTLVardef@17a0a0b_HPS_FORMAT_FIGEXP M_FIG C_FIG Significance StatementMale infertility affects approximately 8%-12% of men globally, with defects in sperm motility accounting for over 80% of these cases. The axoneme, which functions as the motor apparatus of the sperm, adopts a canonical "9+2" microtubule arrangement, where the nexin-dynein regulatory complex (N-DRC) plays a critical role in providing structural support between adjacent outer microtubule doublets. Elucidating the interplay between the structural organization and protein composition of the N-DRC is essential for advancing the understanding of male reproductive biology. In this study, we identify ANKRD5 as a new component of N-DRC that is essential for maintaining normal sperm motility. These findings contribute to the molecular understanding of sperm motility and highlight ANKRD5 as a potential target for the development of novel male contraceptives.

developmental biology↗

R-loops orchestrate the maternal-to-zygotic transition by harnessing RNA polymerase II pause release

R-loops, ubiquitous three-stranded nucleic acid structures abundant in the mammalian genome, play pivotal roles in diverse biological processes1-3. However, the dynamics and functions of R-loops during mammalian preimplantation embryonic development remain poorly understood. Here we optimized an innovative, ultra-sensitive RIAN-seq method capable of mapping genome-wide R-loop landscape using ultra-low cell numbers to investigate R-loop dynamics in mouse gametes and early embryos. Our findings reveal the widespread presence of AT-rich R-loops during early mouse embryonic development and highlight their critical roles in orchestrating transcription machinery during zygotic genome activation (ZGA). We demonstrate that the stability and inheritance of R-loops through developmental stages are governed by their sequence composition, with GC-rich R-loops exhibiting greater stability. Notably, R-loops, particularly AT-rich R-loops, inhibit DDX21 helicase activity on the 7SK/HEXIM1 snRNP complex, thereby reducing CDK9 release. This, in turn, modulates the phosphorylation of Ser2 at C-terminal domain (CTD) of RNA polymerase II (RNAPIIS2p) at the promoters of major ZGA and maternal genes. Furthermore, R-loops promote RNAPII accumulation at major ZGA gene promoters, preventing RNAPII from premature release and ensuring timely activation of major ZGA genes. Conversely, R-loops enhance the retention of stalled RNAPII at maternal gene promoters, effectively repressing their expression and facilitating the maternal-to-zygotic transition. In summary, our study unveils a key role for R-loops in regulating the maternal-to-zygotic transcription transition and early embryonic development in mice.

developmental biology↗

In vivo dissection of Rhoa function in vascular development using zebrafish

RationaleThe small monomeric GTPase RHOA acts as a master regulator of signal transduction cascades by activating effectors of cellular signaling, including the Rho-associated protein kinases ROCK1/2. Previous in vitro cell culture studies suggest that RHOA can regulate many critical aspects of vascular endothelial cell (EC) biology, including focal adhesion, stress fiber formation, and angiogenesis. However, the specific in vivo roles of RHOA during vascular development and homeostasis are still not well understood. ObjectiveIn this study we examine the in vivo functions of RHOA in regulating vascular development and integrity in zebrafish. Methods and ResultsWe use zebrafish RHOA-ortholog (rhoaa) mutants, transgenic embryos expressing wild type, dominant-negative, or constitutively active forms of rhoaa in ECs, and a pharmacologic inhibitor of ROCK1/2 to study the in vivo consequences of RHOA gain- and loss-of-function in the vascular endothelium. Our findings document roles for RHOA in vascular integrity, developmental angiogenesis, and vascular morphogenesis. ConclusionsOur results indicate that either too much or too little RHOA activity leads to vascular dysfunction in vivo.

developmental biology↗

Effects of psychogenic stress on oxidative stress and antioxidant capacity at different growth stages.

This study examined the psychogenic stress (PS) effects on changes in oxidative stress and the antioxidant capacity of an organism at different growth stages. The experimental animals were male Wistar rats of five different ages from growth periods (GPs) to old age. The growth stages were randomly classified into control (C) and experimental (PS) groups. PS was performed using restraint and water immersion once daily for 3 h for 4 weeks. Reactive oxygen metabolites (d-ROMs) and the biological antioxidant potential (BAP) were measured before and after the experiment. In addition, the liver and adrenal glands were removed, and the wet weight was measured. The d-ROM and BAP of all growth stages given PS increased significantly. The d-ROM in the C group without PS increased significantly in GPs while decreased significantly in old-aged. In addition, the BAP of the C group in GP and early adulthood were all significantly elevated. There were significant differences in organ weights between the C and PS groups at all growth stages. Oxidative stress and antioxidant capacity differed depending on the organisms developmental status and growth stage, and PS also showed different effects. In particular, the variability in oxidative stress was remarkable, suggesting that the effect of PS was more significant in the organisms immature organs.

developmental biology↗

How to use online tools to generate new hypotheses for mammary gland biology research: a case study for Wnt7b

An increasing number of -omics datasets, generated by labs all across the world, are becoming available. They contain a wealth of data that are largely unexplored. Not every scientist, however, will have access to the required resources and expertise to analyze such data from scratch. Luckily, a growing number of investigators is dedicating their time and effort to the development of user friendly, online applications that allow researchers to use and investigate these datasets. Here, we will illustrate the usefulness of such an approach. Using regulation of Wnt7b as an example, we will highlight a selection of accessible tools and resources that are available to researchers in the area of mammary gland biology. We show how they can be used for in silico analyses of gene regulatory mechanisms, resulting in new hypotheses and providing leads for experimental follow up. We also call out to the mammary gland community to join forces in a coordinated effort to generate and share additional tissue-specific -omics datasets and thereby expand the in silico toolbox.

developmental biology↗

A nuclear role for the Argonaute protein AGO2 in mammalian gametogenesis

Argonaute 2 (AGO2) is a ubiquitously expressed protein critical for regulation of mRNA translation and vital to animal development. AGO2 protein is found in both cytoplasmic and nuclear compartments, and while its cytoplasmic role is well studied, the biological relevance of nuclear AGO2 is unclear. Here, we address this problem in vivo, using developing spermatogenic cells as a model. Remarkably, we find that AGO2 acts in the germ cell nucleus to positively regulate protein expression. We show that AGO2 dynamically binds both chromatin and nuclear mRNA transcripts of hundreds of genes required for sperm production, and germline conditional knockout (cKO) of Ago2 causes depletion of the corresponding proteins, along with defects in sperm number and morphology. Nuclear AGO2 partners with splicing, export, and chromatin factors to promote transcript export and protein expression. Together, our data reveal an unexpected role for nuclear AGO2 in enhancing expression of developmentally important genes.

developmental biology↗

Single-cell chromatin accessibility of developing murine pancreas identifies cell state-specific gene regulatory programs

Numerous studies have characterized the existence of cell subtypes, along with their corresponding transcriptional profiles, within the developing mouse pancreas. The upstream mechanisms that initiate and maintain gene expression programs across cell states, however, remain largely unknown. Here, we generate single-nucleus ATAC-Sequencing data of developing murine pancreas and perform an integrated, multi-omic analysis of both chromatin accessibility and RNA expression to describe the chromatin landscape of both the developing epithelium and mesenchyme at E14.5 at single-cell resolution. We identify candidate transcription factors regulating cell fate and construct gene regulatory networks of active transcription factor binding to regulatory regions of downstream target genes. This work serves as a valuable resource for the field of pancreatic biology in general and contributes to our understanding of lineage plasticity among endocrine cell types. In addition, these data identify which epigenetic states should be represented in the differentiation of stem cells to the pancreatic beta cell fate in order to best recapitulate in vitro the gene regulatory networks that are critical for progression along the beta cell lineage in vivo.

developmental biology↗

Topological data analysis of pattern formation of human induced pluripotent stem cell colonies

Understanding the multicellular organization of stem cells is vital for determining the mechanisms that coordinate cell fate decision-making during differentiation; these mechanisms range from neighbor-to-neighbor communication to tissue-level biochemical gradients. Current methods for quantifying multicellular patterning cannot capture the spatial properties of cell colonies across all scales and typically rely on human annotation or a priori selection of parameters. We present a computational pipeline that utilizes topological data analysis to generate quantitative, multiscale descriptors which capture the shape of data extracted from multichannel microscopy images. By applying our pipeline to certain stem cell colonies, we detected subtle differences in patterning that reflect distinct biological markers and progressive stages of differentiation. These results yield insight into directed cellular movement and morphogen-mediated, neighbor-to-neighbor signaling. Because of its broad applicability to immunofluorescence microscopy images, our pipeline is well-positioned to serve as a general-purpose tool for the quantitative study of multicellular pattern formation.

developmental biology↗

Steller: a high-resolution platform for spatial clonal tracing of mammalian brain development

Resolving both lineage history and spatial position at single-cell resolution is essential for understanding how tissue assemble, yet simultaneously interrogation of both dimensions remains technically challenging. Here, we present Steller (Spatio-temporal cell lineage tracker), an integrated experimental and computational framework that overcomes the sensitivity bottleneck limiting lineage barcode detection in high-resolution spatial transcriptomics (ST). By co-depositing capture probes alongside conventional poly(T) oligonucleotides on high-density spatial arrays, Steller achieves targeted enrichment of lineage barcodes at spatial single cell resolution. Applied to clonally labeled embryonic day 12.5 (E12.5) mouse forebrain development harvested at postnatal day 4 (P4), Steller increased the proportion of barcode-detectable cells and recovered higher clonal diversity compared with poly(T) chip. Leveraging this enhanced sensitivity, we resolved distinct spatial clonal architectures across three forebrain regions: horizontal or radial-to-horizontal transitions in hippocampal pyramidal neurons, dorsoventrally restricted yet multi-nuclei spread in thalamus, and fate-restricted spiny projection neuron lineages. Steller establishes a generalizable strategy for lineage-enhanced spatial profiling compatible with existing high-resolution spatial transcriptomics platforms and adaptable to diverse biologic process, providing a framewrok for investigating lineage-dependent tissue organization. HighlightsO_LISteller integrates targeted lineage-barcode enrichment with high-resolution spatial transcriptomics C_LIO_LISteller substantially improves clonal detection sensitivity at single-cell resolution C_LIO_LISteller reveals region-specific spatial clonal architectures across the developing mouse forebrain C_LI

Developmental Biology↗

EWS-FLI1 Expression in Human Embryonic MSCs Leads to Transcriptional Reprograming, Defective DNA Damage Repair and Ewing Sarcoma

Ewing sarcoma (ES) is an aggressive bone and soft tissue neoplasm characterized by EWSR1/ETS rearrangements and whose cellular origin remains unclear. EWS-FLI1 expression in human pediatric mesenchymal stem cells (hpMSCs) induces a quantitatively and qualitatively different transcriptional response than its expression in human adult MSCs (haMSCs), but fails to form tumors in vivo. ES cells have early developmental lineage signatures distinct from postnatal MSCs. Here, we have generated MSCs from experimental teratomas out of human embryonic stem cells (heSCs). Transduction of these human embryonic mesenchymal stem cells (heMSCs) with EWS-FLI1 results in the acquisition of an ES transcriptome, although the oncogene does not preferentially bind to promoters, but to intronic and intergenic microsatellites with >10 CA dinucleotides and GGAA repeats, respectively. In heMSCs, EWS-FLI1 directly regulates BRCA1 expression, although EWS-FLI1-expressing cells show defects in DNA damage repair. Xenografting of EWS-FLI1-transduced heMSCs resulted in the formation of tumors expressing characteristic ES markers. In summary, EWS-FLI1 enforces an aberrant transcriptome and endows in vivo transforming capacity when expressed in an undifferentiated early heMSC. Our approach represents an innovative experimental method for understanding critical aspects of the biology of developmental tumors, from leukemia to sarcomas, in which few (even single) genetic alterations are able to transform a fetal stem cell.

cancer biology↗

Computational Transcriptomic and Comparative Genomic Analysis of dead box RNA Helicase gene AT2G45810 Expressed in Plants Arabidopsis thaliana

Arabidopsis thaliana is a short life cycle, small genome, and Brassicaceae family winter annual small flowering plants. It is popularly used as a model organism in genetics and plant biology research, and it is essential to understanding the molecular biology of many plant features, including light sensing and flower formation. It also plays a key role in the science of agronomy, and plant transcriptomics as well as genomics. When it comes to the development of multicellular creatures, transcriptional programs are crucial. The constantly active growth of different organ systems is supported by transcriptional programs. Arabidopsis embryos possess remarkable transcriptomes compared to other plant tissues comprising somatic embryo differentiation circumstances operating during plant embryogenesis. Here we show that the transcriptomic analysis of the genome dead box RNA helicase gene AT2G45810 of Arabidopsis thaliana Araport11 species which revealed the specific gene expression patterns of Arabidopsis tissue-specific information of developmental map, embryo, single cell, DNA damage, cellular interactions, pathway analysis, etc., through In Silico or computational approaches. In this particular study, we used the TAIR, Phytozome, and plant comparative genomics portal for retrieving and identification of specific genes of interest. Next, we used web-based Bar utoronto tools to visualize other data, including functional genomics. Their protein and gene expression tools facilitate the exploration of promoters, the identification of protein-protein interactions, the viewing of expression patterns as electronic fluorescent pictographs or heatmaps, and more.

developmental biology↗

A screen of mutants generated and imaged by the International Mouse Phenotyping Consortium identifies 39 novel genes regulating the development of the secondary palate.

The International Mouse Phenotyping Consortium (IMPC) has generated thousands of knockout mouse lines, many of which exhibit embryonic or perinatal lethality. Using micro-computed tomography (micro-CT), the IMPC has created and publicly released 3D image datasets of embryos from these lethal and subviable lines. In this study, we leveraged this dataset to screen homozygous null mutants for anomalies in secondary palate development. We analyzed optical sections from 2,987 embryos at embryonic days E15.5 and E18.5, representing 484 homozygous mutant lines. Our analysis identified 45 novel genes implicated in palatogenesis. Gene set enrichment analysis highlighted biological processes and pathways relevant to palate development and uncovered 18 genes jointly regulating the development of the eye and the palate. These findings present a valuable resource for further research, offer novel insights into the molecular mechanisms underlying palatogenesis, and provide important context for understanding the etiology of rare human congenital disorders involving simultaneous malformations of the palate and other organs, including the eyes, ears, kidneys, and lungs.

developmental biology↗

A chemically inducible muscle ablation system for zebrafish

An effective method for tissue specific ablation in zebrafish is the nitroreductase/metronidazole system. Expressing bacterial nitroreductase (ntr) in the presence of nitroimidazole compounds causes apoptotic cell death, which can be useful for understanding many biological processes. However, this requires tissue specific expression of the ntr enzyme, and many tissues have yet to be targeted with transgenic lines that express ntr. We generated a transgenic zebrafish line expressing ntr in differentiated skeletal muscle. Treatment of embryos with metronidazole caused muscle specific cell ablation. We demonstrate this line can be used to monitor muscle regeneration in whole embryos and in transplanted transgenic cells. Summary statement

developmental biology↗

Thymic epithelial organoids mediate T cell development

Although the advent of organoids opened unprecedented perspectives for basic and translational research, immune system-related organoids remain largely underdeveloped. Here we established organoids from the thymus, the lymphoid organ responsible for T cell development. We identified conditions enabling thymic epithelial progenitor cell proliferation and development into organoids with in vivo-like transcriptional profiles and diverse cell populations. Contrary to two-dimensional cultures, thymic epithelial organoids maintained thymus functionality in vitro and mediated physiological T cell development upon reaggregation with T cell progenitors. The reaggregates showed in vivo-like epithelial diversity and ability to attract T cell progenitors. Thymic epithelial organoids provide new opportunities to study TEC biology and T cell development in vitro, pave the way for future thymic regeneration strategies and are the first organoids originating from the stromal compartment of a lymphoid organ. Summary statementEstablishment of organoids from the epithelial cells of the thymus which resemble their in vivo counterpart and have thymopoietic ability in reaggregate culture.

developmental biology↗