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CellCousin2: An Optimized System for Partial Ablation and Tracing of Regenerative Lineages

Regeneration can rely on multiple cellular sources, including stem cells, self-duplicating cells, and transdifferentiating cells. A central question in regenerative biology is how these distinct lineages contribute to repair and interact within a functional regenerate. We previously developed the CellCousin system to study hcellular plasticity using inducible recombination and nitroreductase-mediated ablation in zebrafish. Here, we present CellCousin2, which introduces two key improvements for long-term tracking of spared and regenerating cells. First, to reduce background recombination, we developed a Dihydrofolate Reductase (DHFR)-CreER system with dual control: DHFR- mediated degradation in the absence of trimethoprim, and tamoxifen-dependent activation. This combination minimizes leakiness while maintaining high recombination efficiency. Second, we replaced the original nitroreductase with NTR2.0, enabling effective ablation with tenfold lower metronidazole concentration, reducing off-target effects on the liver. Together, these enhancements make CellCousin2 a robust platform for dissecting the dynamics and interactions of regenerative lineages.

developmental biology↗

Identification of a Novel PP2A Regulator, WNK1, as Critical For Uterine Function

WNK1 is an atypical kinase protein ubiquitously expressed in humans and mice. A mutation in its encoding gene causes hypertension in humans which is associated with abnormal ion homeostasis. Our earlier findings demonstrated that WNK1 is critical for in vitro decidualization in human endometrial stromal cells – pointing towards an unrecognized role of WNK1 in female reproduction. Here, we employed a mouse model with conditional WNK1 ablation from the female reproductive tract to define its in vivo role in uterine biology. Loss of WNK1 altered uterine morphology, causing endometrial epithelial hyperplasia, adenomyosis and a delay in embryo implantation, ultimately resulting in compromised fertility. Combining transcriptomic, proteomic and interactomic analyses revealed a novel regulatory pathway whereby WNK1 represses AKT phosphorylation through the phosphatase PP2A in endometrial cells from both humans and mice. We show that WNK1 interacts with PPP2R1A, an isoform of the PP2A scaffold subunit. This interaction stabilizes the PP2A complex, which then dephosphorylates AKT. Therefore, loss of WNK1 reduced PP2A activity, causing AKT hypersignaling. Using FOXO1 as a readout of AKT activity, we demonstrate that there was escalated FOXO1 phosphorylation and nuclear exclusion, leading to a disruption in the regulation of genes that are crucial for embryo implantation.Competing Interest StatementThe authors have declared no competing interest.View Full Text

developmental biology↗

Human pluripotent stem cell-derived atrioventricular node-like pacemaker cells exhibit biological conduction bridge properties in vitro and in vivo

The atrioventricular node (AVN) ensures synchronized heart contractions by establishing the electrical connection between the atria and ventricles. Dysfunction of the pacemaker cells of the AVN leads to atrioventricular block (AV block), a life-threatening condition managed with electronic pacemakers (EPMs). EPMs have drawbacks that could be overcome by a human pluripotent stem cell (hPSC)-derived biological conduction bridge (BioCB). Recent studies demonstrated the differentiation of AVN-like cells from hPSCs, but their conduction properties upon engraftment in vivo remain unexplored. Here we report the generation of AVN-like pacemaker cells (AVNLPCs) from hPSCs using WNT and BMP signaling modulation. These AVNLPCs transcriptionally resemble fetal AVN pacemaker cells, exhibit pacemaker action potentials, and display unique AVN-like conduction properties. Notably, when transplanted into the guinea pig heart, AVNLPCs replicate the functional properties of the AVN. Our study highlights the potential of an AVNLPC-based BioCB as novel cell therapy to improve treatment for AV block patients.

developmental biology↗

Bayesian analysis of normal mouse cell lineage trees allowing intra-individual, cell population specific mutation rates

Individual cell lineage trees are of biological and clinical importance. The Sanger Mouse Pilot Study used clonal organoid lines of endodermal origin to extract somatic base substitutions from single cells of two healthy mice. Here we applied Bayesian phylogenetics analysis using the Pilots 35 somatic base substitutions in order to reconstruct the two cell trees and apply relaxed clock methods allowing intra-individual, cell lineage specific mutation rates. Detailed analysis provided support for the strict clock for mouse_1 and relaxed clock for mouse_2. Interestingly, a clade of two prostate organoid lines in mouse_2 presented one outlier branch mutation rate compared to the mean rates calculated. Based on this study unbiased clock analysis has the potential to add a new, useful layer to our understanding of normal and disturbed cell lineage trees. This study is the first to apply the popular Bayesian BEAST package to individual single cell resolution data.

Developmental Biology↗

Evolutionary conservation of maternal RNA localization in fishes and amphibians revealed by TOMO-Seq

Asymmetrical localization of biomolecules inside the egg, results in uneven cell division and establishment of many biological processes, cell types and the body plan. However, our knowledge about evolutionary conservation of localized mRNAs is still limited to a few candidates. Our goal was to compare localization profiles along the animal-vegetal axis of mature eggs from four models, Xenopus laevis, Danio rerio, Ambystoma mexicanum and Acipenser ruthenus using the spatial expression method called TOMO-Seq. We revealed that RNAs of many known important genes such as germ layer determinants, germ plasm factors and members of key signalling pathways, are localized in completely different profiles among the models. There was also a poor correlation between vegetally localized genes but a relatively good correlation between animally localized genes. These findings indicate that the regulation of embryonic development within the animal kingdom is highly diverse and cannot be deduced based on a single model.

developmental biology↗

Simultaneously spatiotemporal gene expression and chromatin accessibility for mouse brain development

Brain are complex biological tissues which function relies on coordinated anatomical and molecular structure comprised by a large number of specialized cells. The spatial architecture of brain which is key to the understanding of its physiological and pathological significance is formed during embryo development. However, the molecular basis for discrete neuroanatomical domains particularly in the context of spatial organization of the brain is inadequate. Here, we introduced microfluidic indexing based spatial ATAC and RNA sequencing (MISAR-seq), a method for joint profiling of chromatin accessibility and gene expression with spatial information retained in the developing mouse brain. Our study has established a direct means to spatially determine the coordination between chromatin accessibility and transcriptome, identified the chromatin potential to define cell fate determination of brain organization, and uncovered spatiotemporal regulatory principles during mammalian brain development.

developmental biology↗

Temporal-spatial transcriptomics reveals key gene regulation for grain yield and quality in wheat

Cereal grain size and quality are important agronomic traits in crop production. The development of wheat grains is underpinned by complex regulatory networks. The precise spatial and temporal coordination of diverse cell types is essential for the formation of functional compartments. To provide comprehensive spatiotemporal information about biological processes in developing wheat grain, we performed a spatial transcriptomics study during the early grain development stage from 4 to 12 days after pollination. We defined a set of tissue-specific marker genes and discovered that certain genes or gene families exhibit specific spatial expression patterns over time. Weighted gene co-expression network and motif enrichment analyses identified specific groups of genes potentially regulating wheat grain development. The embryo and surrounding endosperm specifically expressed transcription factor TaABI3-3B negatively regulates embryo and grain size. In Chinese breeding programs, a haplotype associated with higher grain weight was identified, linked to altered expression levels of TaABI3-3B. Data and knowledge obtained from the proposed study will provide pivotal insights into yield improvement and serve as important genetic information for future wheat breeding.

developmental biology↗

Metabolic reprogramming regulates histone lactylation during zebrafish caudal fin regeneration

Tissue regeneration relies on precise molecular mechanisms controlling cell fate transitions, with cell metabolism emerging as a key regulator. Lactate-derived histone lactylation has recently been identified as an important epigenetic modification involved in the regulation of gene expression across various biological processes. In this study, we report an increase in global histone lactylation and H3K18Lac levels in the mesenchyme and osteoblasts of the zebrafish caudal fin, during the early stages of regeneration. Our findings demonstrate that this epigenetic modification is functionally regulated by increased lactate levels, while inhibition of glycolysis and lactate production significantly reduces histone lactylation. These results suggest that metabolic reprogramming, in response to caudal fin injury, regulates histone lactylation, potentially modulating gene expression essential for cell plasticity and proliferation. This study expands our understanding of how metabolic-epigenetic interactions influence regenerative processes, providing valuable insights for the development of novel therapeutic strategies to enhance tissue repair. Summary statementLactate-derived histone lactylation plays a role in the early stages of zebrafish caudal fin regeneration, coupling metabolic adaptation with tissue repair mechanisms, through epigenetic regulation.

developmental biology↗

Determining the age of single cells using scBayesAge

1Aging is a complex biological process marked by a gradual decline in physiological function that contributes to increased vulnerability to disease and mortality. Numerous studies have investigated the cellular and molecular aspects of aging at single-cell resolution, yet the heterogeneity of cellular aging in an individual remains poorly understood. To enhance our ability to study aging at the single cell level, we developed a statistical framework to predict the age of individual cells based on their transcriptomic profiles. Our Bayesian approach estimates the most likely age of a cell given its read counts. We applied the model to data from Tabula Muris Senis and examined organ- and cell-type-specific transcriptomic signatures of aging. Compared with standard regression-based methods, our framework achieved higher predictive accuracy. We show that scMLEAge is a powerful tool for dissecting the cellular heterogeneity of aging and age-related functional decline.

developmental biology↗

Heterogeneity of normal human breast stem and progenitor cells as revealed by transcriptional profiling

During development and pregnancy, the human mammary gland undergoes extensive remodeling in processes driven by populations of stem and progenitor cells. We recently reported that breast cancers are also hierarchically organized and driven by distinct populations of cancer stem cells characterized as CD44+CD24low/- or by expression of Aldehyde dehydrogenase (ALDH). These sets of markers identify largely non-overlapping mesenchymal and epithelial populations, each of which is capable of tumor initiation when transplanted into immunosuppressed mice. Less is known about these two populations, individually or their overlap, in the normal human mammary gland. The goal of this study was to understand the biology of the ALDH+ and CD44+CD24- populations in the normal human breast, using flow cytometry based sorting paired with functional ex vivo analyses, RNA-sequencing, and single cell RNA expression profiling. ALDH+ cells and ALDH-CD44+CD24- cells, generally, have epithelial-like and mesenchymal-like characteristics, respectively. Despite this, there are substantial similarities in the biological pathways activated in both populations when compared to differentiated cells. Additionally, we found a substantial proportion of cells that simultaneously express ALDH+ and CD44+CD24- whose abundance varies between individuals. At the single cell level, these cells have the greatest mammosphere forming capacity and express high levels of stemness and EMT-associated genes including ID1, SOX2, TWIST1, and ZEB2. Through unbiased analysis of individual ALDH+ cells, we find cells with either epithelial or mesenchymal expression phenotypes. We also identify a subpopulation of cells with a hybrid epithelial/mesenchymal expression phenotype that overexpress genes associated with aggressive triple negative breast cancers. These results highlight the utility of single cell analyses to characterize tissue heterogeneity, even in marker enriched cell populations, and further identifies the genes and pathways that define this heterogeneity.

developmental biology↗

Extracellular hyaluronate pressure shaped by cellular tethers drives tissue morphogenesis

How tissues acquire complex shapes is a fundamental question in biology and regenerative medicine. Zebrafish semicircular canals form from invaginations in the otic epithelium (buds) that extend and fuse to form the hubs of each canal. We find that conventional actomyosin-driven behaviors are not required. Instead, local secretion of hyaluronan, made by the enzymes ugdh and has3, drives canal morphogenesis. Charged hyaluronate polymers osmotically swell with water and generate isotropic extracellular pressure to deform the overlying epithelium into buds. The mechanical anisotropy needed to shape buds into tubes is conferred by a polarized distribution of cellular protrusions, linked between cells, that we term cytocinches. Most work on tissue morphogenesis ascribes actomyosin contractility as the driving force, while the extracellular matrix shapes tissues through differential stiffness. Our work inverts this expectation. Hyaluronate-pressure shaped by anisotropic tissue stiffness may be a widespread mechanism for powering morphological change in organogenesis and tissue engineering.

developmental biology↗

TFAP2C is a key regulator of intrauterine trophoblast cell invasion and deep hemochorial placentation

Transcription factor AP-2 gamma (TFAP2C) has been identified as a key regulator of the trophoblast cell lineage and hemochorial placentation. The rat possesses deep placentation characterized by extensive intrauterine trophoblast cell invasion, which resembles human placentation. Tfap2c is expressed in multiple trophoblast cell lineages, including invasive trophoblast cells situated within the uterine-placental interface of the rat placentation site. Global genome-editing was used to explore the biology of Tfap2c in rat placenta development. Homozygous global disruption of Tfap2c resulted in prenatal lethality. Heterozygous global disruption of Tfap2c was associated with diminished invasive trophoblast cell infiltration into the uterus. The role of TFAP2C in the invasive trophoblast cell lineage was explored using Cre-lox conditional mutagenesis. Invasive trophoblast cell-specific disruption of Tfap2c resulted in inhibition of intrauterine trophoblast cell invasion and intrauterine and postnatal growth restriction. The invasive trophoblast cell lineage was not impaired following conditional monoallelic disruption of Tfap2c. In summary, TFAP2C contributes to the progression of distinct stages of placental development. TFAP2C is a driver of early events in trophoblast cell development and reappears later in gestation as an essential regulator of the invasive trophoblast cell lineage. A subset of TFAP2C actions on trophoblast cells are dependent on gene dosage.

developmental biology↗

Epidermal turnover in the planarian Schmidtea mediterranea involves basal cell extrusion and intestinal digestion.

Planarian flatworms undergo continuous internal turnover, wherein old cells are replaced by the division progeny of adult pluripotent stem cells known as neoblasts. How dynamic cell turnover is executed at the organismal scale remains an intriguing question in planarians and biological systems in general. While previous studies have predominantly focused on neoblast proliferation, little is known about the processes that mediate cell loss during tissue homeostasis. Here, we use the planarian epidermis as a model to study the mechanisms of cell removal in Schmidtea mediterranea. We established a covalent dye-labeling assay and image analysis pipeline to quantify the cell turnover rate in the planarian epidermis. Our findings indicate that the ventral epidermis is highly dynamic, with a half-life of the constituent cells of approximately 4.5 days. Using live-imaging and pulse-chase assays, we find that epidermal cells undergo internalization via basal extrusion, followed by a migration towards the intestine and ultimately digestion by intestinal phagocytes. Overall, our studies reveal an intricate homeostatic cell clearance process that may reduce the metabolic costs of high turnover tissues in planarians.

developmental biology↗

Sulfatase modifying factors control the timing of zebrafish gastrulation morphogenesis

To shape the emerging body plan, morphogenetic cell movements must be coordinated not only in space, but also in time. Convergence and Extension (C&E) movements that elongate the anteroposterior axis initiate with precise timing during vertebrate gastrulation, but the mechanisms controlling their onset remain unknown. We examined this question using zebrafish embryonic explants that faithfully recapitulate C&E cell movements and their precise timing in culture, in isolation from other gastrulation movements. We determined that new transcription is required at gastrulation onset for C&E in explants and identified sulfatase modifying factor 2 (sumf2) as a candidate trigger gene expressed at this time. sumf2 and its paralog sumf1 encode negative and positive regulators, respectively, of all sulfatase enzymes, which remove sulfate groups from their substrates, altering their biological activity. In zebrafish embryos and explants, sumf1 and sumf2 expression levels invert at gastrulation onset, predicting a reduction in sulfatase activity and consequent increase of substrate sulfation. We found that overexpressing sumf1 and sumf2 causes delayed or precocious C&E onset, respectively, whereas loss of sumf1 and sumf2 function shifts C&E timing in the opposite direction. We further identified Sulf1, an extracellular sulfatase that modifies heparan sulfate proteoglycans (HSPGs), as the key effector by which sumf1 and sumf2 control C&E timing. Accordingly, reduced or increased levels of sulfated heparan sulfate similarly shift C&E onset and suppress sumf1 and sumf2 mutant phenotypes. Together, our work supports a model in which sumf2 expression at zebrafish gastrulation onset reduces sulfatase activity, rewriting HSPG sulfation patterns to promote and/or permit C&E morphogenesis.

developmental biology↗

E-cadherin bridges cell polarity and spindle orientation to ensure prostate epithelial integrity and prevent carcinogenesis in vivo

Cell polarity and correct mitotic spindle positioning are essential for the maintenance of a proper prostate epithelial architecture, and disruption of the two biological features occurs at early stages in prostate tumorigenesis. However, whether and how these two epithelial attributes are connected in vivo is largely unknown. We herein report that conditional genetic deletion of E-cadherin, a key component of adherens junctions, in a mouse model results in loss of prostate luminal cell polarity and randomization of spindle orientations. Critically, E-cadherin ablation causes prostatic hyperplasia which progresses to invasive adenocarcinoma. Mechanistically, E-cadherin and the spindle positioning determinant LGN interacts with the PDZ domain of cell polarity protein SCRIB and form a ternary protein complex to bridge cell polarity and cell division orientation. These findings provide a novel mechanism by which E-cadherin acts an anchor to maintain prostate epithelial integrity and to prevent carcinogenesis in vivo.

developmental biology↗

Active and Passive Mechanical Deficits Precede Spinal Curvature in a Zebrafish Model of Idiopathic Scoliosis

Idiopathic scoliosis is a common spinal disorder characterized by progressive three-dimensional curvature of unknown cause. Although biomechanical imbalance has long been proposed to contribute to scoliosis, the early physiological states that precede curvature onset remain poorly understood. Here, we investigated this problem using zebrafish uts2r3 mutants, which develop fully penetrant juvenile-onset spinal curvature following disruption of urotensin signaling. Transcriptomic analysis before curvature revealed altered expression of muscle-associated genes, suggesting that Uts2r3 influences axial muscle development or function. However, immunofluorescence, birefringence imaging, and quantitative analysis of myotome morphology showed that mutants lack overt muscle architectural defects or dystrophic pathology. By contrast, direct measurements of isolated larval trunks revealed pre-curvature biomechanical abnormalities: namely, uts2r3 mutants generated reduced active force following electrical stimulation while also exhibiting increased passive resistance to stretch. These findings identify urotensin signaling as a regulator of axial tissue biomechanics during growth and suggest that scoliosis-like curvature can arise from an early imbalance between active force generation and passive tissue stiffness. SignificanceSpinal curvature is common, but the biological events that cause the spine to bend during growth remain poorly understood. Animal models, especially zebrafish, make it possible to study these events before curvature begins. Zebrafish lacking urotensin signaling develop spinal curves that arise during juvenile growth, similar to idiopathic scoliosis in humans. Here, we demonstrate that zebrafish lacking the urotensin pathway receptor Uts2r3 develop an abnormal biomechanical state prior to curve onset. Their axial tissues generate less active force when contracting and, at the same time, show increased passive resistance to stretch--an unexpected combination that reveals a distinct pre-curvature biomechanical state. These findings suggest that spinal curvature can arise from an early imbalance in tissue mechanics during growth and identify urotensin signaling as a pathway that helps preserve spinal morphology through a biomechanical mechanism.

developmental biology↗

WUSCHEL-Related Homeobox Genes Cooperate with Cytokinin Signalling to Promote Bulbil Formation in Lilium lancifolium

The bulbil is an important vegetative reproductive organ in triploid Lilium lancifolium. Based on our previously obtained transcriptome data, we screened two WUSCHCEL-related homeobox (WOX) genes closely related to bulbil formation, LlWOX9 and LlWOX11. However, the biological functions and regulatory mechanisms of LlWOX9 and LlWOX11 are unclear. In this study, we cloned the full-length coding sequences of LlWOX9 and LlWOX11. Transgenic Arabidopsis showed increased branch numbers, and the overexpression of LlWOX9 and LlWOX11 in stem segments promoted bulbil formation, while the silencing of LlWOX9 and LlWOX11 inhibited bulbil formation, indicating that LlWOX9 and LlWOX11 are positive regulators of bulbil formation. Cytokinins acting through type-B response regulators (type-B RRs) could bind to the promoters of LlWOX9 and LlWOX11 and promote their transcription. LlWOX11 could enhance cytokinin pathway signalling by inhibiting the transcription of type-A LlRR9. Our study enriches the understanding of the regulation of plant development by the WOX gene family and lays a foundation for further research on the molecular mechanism of bulbil formation in lily.

developmental biology↗

Initiating mammalian reproduction from a single male genome

Sex in mammals is unidirectionally determined by the configuration of sex chromosomes. In contrast, several species, including fishes, can switch sexes in response to environmental cues, illustrating the reproductive advantages of sexual plasticity. Thus, technologies that can bypass the unidirectional nature of mammalian sex determination could open new avenues in reproductive biology. Here, by establishing a method that enables robust Y-chromosome elimination in embryos, we provide a strategy to regulate sex in mice. We show that this approach efficiently induces male-to-female sex reversal by releasing the Y chromosome as micronuclei during early development. When integrated with optimized somatic cell nuclear transfer, it enabled the parallel production of both male and sex-reversed female mice from a single male genome source. Offspring were successfully obtained from crosses between these male and sex-reversed female clones, demonstrating that this "dual-sex cloning" strategy can initiate sexual reproduction solely from a male somatic genome. These findings highlight dual-sex cloning as a valuable platform for securing mammalian reproduction and biodiversity from limited genetic resources.

developmental biology↗