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Summary Delamination of neural progenitor cells (NPCs) from the ventricular surface is a crucial prerequisite to form the subventricular zone, the germinal layer linked to the expansion of the mammalian neocortex in development and evolution. Here, we dissect the molecular mechanism by which the transcription factor Insm1 promotes the generation of basal progenitors (BPs). Insm1 protein is most highly expressed in newborn BPs in mouse and human developing neocortex. Forced Insm1 expression in embryonic mouse neocortex causes NPC delamination, converting apical to basal radial glia. Insm1 represses the expression of the apical adherens junction belt-specific protein Plekha7. CRISPR/Cas9-mediated disruption of Plekha7 expression suffices to cause NPC delamination. Plekha7 overexpression impedes the intrinsic and counteracts the Insm1-induced, NPC delamination. Our findings uncover a novel molecular mechanism underlying NPC delamination in which a BP-genic transcription factor specifically targets the integrity of the apical adherens junction belt, rather than adherens junction components as such. [ABSTRACT FROM AUTHOR]

Summary Trained innate immunity fosters a sustained favorable response of myeloid cells to a secondary challenge, despite their short lifespan in circulation. We thus hypothesized that trained immunity acts via modulation of hematopoietic stem and progenitor cells (HSPCs). Administration of β-glucan (prototypical trained-immunity-inducing agonist) to mice induced expansion of progenitors of the myeloid lineage, which was associated with elevated signaling by innate immune mediators, such as IL-1β and granulocyte-macrophage colony-stimulating factor (GM-CSF), and with adaptations in glucose metabolism and cholesterol biosynthesis. The trained-immunity-related increase in myelopoiesis resulted in a beneficial response to secondary LPS challenge and protection from chemotherapy-induced myelosuppression in mice. Therefore, modulation of myeloid progenitors in the bone marrow is an integral component of trained immunity, which to date, was considered to involve functional changes of mature myeloid cells in the periphery. [ABSTRACT FROM AUTHOR]

Zebrafish regenerate their fins which involves a component of cell plasticity. It is currently unclear how regenerate cells divide labor to allow for appropriate growth and patterning. Here, we studied lineage relationships of fluorescence-activated cell sorting-enriched epidermal, bone-forming (osteoblast), and (non-osteoblast) blastemal fin regenerate cells by single-cell RNA sequencing, lineage tracing, targeted osteoblast ablation, and electron microscopy. Most osteoblasts in the outgrowing regenerate derive from osterix + osteoblasts, while mmp9 + cells reside at segment joints. Distal blastema cells contribute to distal osteoblast progenitors, suggesting compartmentalization of the regenerating appendage. Ablation of osterix + osteoblasts impairs segment joint and bone matrix formation and decreases regenerate length which is partially compensated for by distal regenerate cells. Our study characterizes expression patterns and lineage relationships of rare fin regenerate cell populations, indicates inherent detection and compensation of impaired regeneration, suggests variable dependence on growth factor signaling, and demonstrates zonation of the elongating fin regenerate., Competing Interests: The authors declare no competing interests., (© 2024 The Author(s).)

Axolotl limb regeneration is accompanied by the transient induction of cellular senescence within the blastema, the structure that nucleates regeneration. The precise role of this blastemal senescent cell (bSC) population, however, remains unknown. Here, through a combination of gain- and loss-of-function assays, we elucidate the functions and molecular features of cellular senescence in vivo. We demonstrate that cellular senescence plays a positive role during axolotl regeneration by creating a pro-proliferative niche that supports progenitor cell expansion and blastema outgrowth. Senescent cells impact their microenvironment via Wnt pathway modulation. Further, we identify a link between Wnt signaling and senescence induction and propose that bSC-derived Wnt signals facilitate the proliferation of neighboring cells in part by preventing their induction into senescence. This work defines the roles of cellular senescence in the regeneration of complex structures., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Loss of limbs evolved many times in squamate reptiles. Here we investigated the genomic basis of convergent limb loss in reptiles. We sequenced the genomes of a closely related pair of limbless-limbed gymnophthalmid lizards and performed a comparative genomic analysis including five snakes and the limbless glass lizard. Our analysis of these three independent limbless lineages revealed that signatures of shared sequence or transcription factor binding site divergence in individual limb regulatory elements are generally rare. Instead, shared divergence occurs more often at the level of signaling pathways, involving different regulatory elements associated with the same limb genes (such as Hand2 or Hox) and/or patterning mechanisms (such as Shh signaling). Interestingly, although snakes are known to have mutations in the Shh ZRS limb enhancer, this enhancer lacks relevant mutations in limbless lizards. Thus, different mechanisms could contribute to limb loss, and there are likely multiple evolutionary paths to limblessness in reptiles., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Cellular redox states regulate the balance between stem cell maintenance and activation. Increased levels of intracellular reactive oxygen species (ROS) are linked to proliferation and lineage specification. In contrast to this general principle, we here show that in the hippocampus of adult mice, quiescent neural precursor cells (NPCs) maintain the highest ROS levels (hiROS). Classifying NPCs on the basis of cellular ROS content identified distinct functional states. Shifts in ROS content primed cells for a subsequent state transition, with lower ROS content marking proliferative activity and differentiation. Physical activity, a physiological activator of adult hippocampal neurogenesis, recruited hiROS NPCs into proliferation via a transient Nox2-dependent ROS surge. In the absence of Nox2, baseline neurogenesis was unaffected, but the activity-induced increase in proliferation disappeared. These results provide a metabolic classification of NPC functional states and describe a mechanism linking the modulation of cellular ROS by behavioral cues to the activation of adult NPCs., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Trained innate immunity, induced via modulation of mature myeloid cells or their bone marrow progenitors, mediates sustained increased responsiveness to secondary challenges. Here, we investigated whether anti-tumor immunity can be enhanced through induction of trained immunity. Pre-treatment of mice with β-glucan, a fungal-derived prototypical agonist of trained immunity, resulted in diminished tumor growth. The anti-tumor effect of β-glucan-induced trained immunity was associated with transcriptomic and epigenetic rewiring of granulopoiesis and neutrophil reprogramming toward an anti-tumor phenotype; this process required type I interferon signaling irrespective of adaptive immunity in the host. Adoptive transfer of neutrophils from β-glucan-trained mice to naive recipients suppressed tumor growth in the latter in a ROS-dependent manner. Moreover, the anti-tumor effect of β-glucan-induced trained granulopoiesis was transmissible by bone marrow transplantation to recipient naive mice. Our findings identify a novel and therapeutically relevant anti-tumor facet of trained immunity involving appropriate rewiring of granulopoiesis., Competing Interests: Declaration of interests M.G.N. is scientific founder of Trained Therapeutics and Discovery (TTxD)., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Large-scale RNAi screens are a powerful approach to identify functions of genes in a cell-type-specific manner. For model organisms, genetically identical (isogenic) cells from different cell types are readily available, making comparative studies meaningful. However, large-scale screens in isogenic human primary cells remain challenging. Here, we show that RNAi screens are possible in genetically identical human stem cells, using induced pluripotent stem cells as intermediates. The screens revealed SMARCA4 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily A member 4) as a stemness regulator, while balancing differentiation distinctively for each cell type. SMARCA4 knockdown in hematopoietic stem and progenitor cells caused impaired self-renewal in vitro and in vivo with skewed myeloid differentiation; whereas, in neural stem cells, it impaired self-renewal while biasing differentiation toward neural lineage, through combinatorial SWI/SNF subunit assembly. Our findings pose a powerful approach for deciphering human stem cell biology and attribute distinct roles to SMARCA4 in stem cell maintenance., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

The neural stem cell (NSC) reservoir can be harnessed for stem cell-based regenerative therapies. Zebrafish remarkably regenerate their brain by inducing NSC plasticity in a Amyloid-β-42 (Aβ42)-induced experimental Alzheimer's disease (AD) model. Interleukin-4 (IL-4) is also critical for AD-induced NSC proliferation. However, the mechanisms of this response have remained unknown. Using single-cell transcriptomics in the adult zebrafish brain, we identify distinct subtypes of NSCs and neurons and differentially regulated pathways and their gene ontologies and investigate how cell-cell communication is altered through ligand-receptor pairs in AD conditions. Our results propose the existence of heterogeneous and spatially organized stem cell populations that react distinctly to amyloid toxicity. This resource article provides an extensive database for the molecular basis of NSC plasticity in the AD model of the adult zebrafish brain. Further analyses of stem cell heterogeneity and neuro-regenerative ability at single-cell resolution could yield drug targets for mobilizing NSCs for endogenous neuro-regeneration in humans., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

Bone, cartilage, and marrow adipocytes are generated by skeletal progenitors, but the relationships between lineages and mechanisms controlling their differentiation are poorly understood. We established mouse clonal skeletal progenitors with distinct differentiation properties and analyzed their transcriptome. Unipotent osteogenic and adipogenic cells expressed specific transcriptional programs, whereas bipotent clones combined expression of those genes and did not show a unique signature. We tested potential regulators of lineage commitment and found that in the presence of interferon-γ (IFNγ) adipogenic clones can be induced to osteogenesis and that their adipogenic capacity is inhibited. Analysis of IFNγ-regulated genes showed that lineage signatures and fate commitment of skeletal progenitors were controlled by EGR1 and EGR2. Knockdown experiments revealed that EGR1 is a positive regulator of the adipogenic transcriptional program and differentiation capacity, whereas EGR2 inhibits the osteogenic program and potency. Therefore, our work revealed transcriptional signatures of osteogenic and adipogenic lineages and mechanism triggering cell fate., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

Neural stem cells (NSCs) constitute an endogenous reservoir for neurons that could potentially be harnessed for regenerative therapies in disease contexts such as neurodegeneration. However, in Alzheimer's disease (AD), NSCs lose plasticity and thus possible regenerative capacity. We investigate how NSCs lose their plasticity in AD by using starPEG-heparin-based hydrogels to establish a reductionist 3D cell-instructive neuro-microenvironment that promotes the proliferative and neurogenic ability of primary and induced human NSCs. We find that administration of AD-associated Amyloid-β42 causes classical neuropathology and hampers NSC plasticity by inducing kynurenic acid (KYNA) production. Interleukin-4 restores NSC proliferative and neurogenic ability by suppressing the KYNA-producing enzyme Kynurenine aminotransferase (KAT2), which is upregulated in APP/PS1dE9 mouse model of AD and in postmortem human AD brains. Thus, our culture system enables a reductionist investigation of regulation of human NSC plasticity for the identification of potential therapeutic targets for intervention in AD., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The hematopoietic stem cell (HSC) compartment consists of a small pool of cells capable of replenishing all blood cells. Although it is established that the hematopoietic system is assembled as a hierarchical organization under steady-state conditions, emerging evidence suggests that distinct differentiation pathways may exist in response to acute stress. However, it remains unclear how different hematopoietic stem and progenitor cell subpopulations behave under sustained chronic stress. Here, by using adult transgenic mice overexpressing erythropoietin (EPO; Tg6) and a combination of in vivo, in vitro, and deep-sequencing approaches, we found that HSCs respond differentially to chronic erythroid stress compared with their closely related multipotent progenitors (MPPs). Specifically, HSCs exhibit a vastly committed erythroid progenitor profile with enhanced cell division, while MPPs display erythroid and myeloid cell signatures and an accumulation of uncommitted cells. Thus, our results identify HSCs as master regulators of chronic stress erythropoiesis, potentially circumventing the hierarchical differentiation-detour., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

High numbers of mast cells populate the stroma of many types of neoplasms, including human papilloma virus-induced benign and malignant tumors in man and mouse. Equipped with numerous pattern recognition receptors and capable of executing important pro-inflammatory responses, mast cells are considered innate sentinels that significantly impact tumor biology. Mast cells were reported to promote human papilloma virus (HPV)-induced epithelial hyperproliferation and neo-angiogenesis in an HPV-driven mouse model of skin cancer. We analyzed HPV-induced epithelial hyperplasia and squamous cell carcinoma formation, as well as growth of tumors inoculated into the dermis, in mice lacking skin mast cells. Unexpectedly, the absence of mast cells had no effect on HPV-induced epithelial growth or angiogenesis, on growth kinetics of inoculated tumors, or on the immunological tumor micro-milieu. Thus, the conspicuous recruitment of mast cells into tumor tissues cannot necessarily be equated with important mast cell functions in tumor growth., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Adenoviruses (Ads) are large human-pathogenic double-stranded DNA (dsDNA) viruses presenting an enormous natural diversity associated with a broad variety of diseases. However, only a small fraction of adenoviruses has been explored in basic virology and biomedical research, highlighting the need to develop robust and adaptable methodologies and resources. We developed a method for high-throughput direct cloning and engineering of adenoviral genomes from different sources utilizing advanced linear-linear homologous recombination (LLHR) and linear-circular homologous recombination (LCHR). We describe 34 cloned adenoviral genomes originating from clinical samples, which were characterized by next-generation sequencing (NGS). We anticipate that this recombineering strategy and the engineered adenovirus library will provide an approach to study basic and clinical virology. High-throughput screening (HTS) of the reporter-tagged Ad library in a panel of cell lines including osteosarcoma disease-specific cell lines revealed alternative virus types with enhanced transduction and oncolysis efficiencies. This highlights the usefulness of this resource., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Human brains are prone to neurodegeneration, given that endogenous neural stem/progenitor cells (NSPCs) fail to support neurogenesis. To investigate the molecular programs potentially mediating neurodegeneration-induced NSPC plasticity in regenerating organisms, we generated an Amyloid-β42 (Aβ42)-dependent neurotoxic model in adult zebrafish brain through cerebroventricular microinjection of cell-penetrating Aβ42 derivatives. Aβ42 deposits in neurons and causes phenotypes reminiscent of amyloid pathophysiology: apoptosis, microglial activation, synaptic degeneration, and learning deficits. Aβ42 also induces NSPC proliferation and enhanced neurogenesis. Interleukin-4 (IL4) is activated primarily in neurons and microglia/macrophages in response to Aβ42 and is sufficient to increase NSPC proliferation and neurogenesis via STAT6 phosphorylation through the IL4 receptor in NSPCs. Our results reveal a crosstalk between neurons and immune cells mediated by IL4/STAT6 signaling, which induces NSPC plasticity in zebrafish brains., (Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.)

Transplantation of GABAergic interneurons (INs) can provide long-term functional benefits in animal models of epilepsy and other neurological disorders. Whereas GABAergic INs can be differentiated from embryonic stem cells, alternative sources of GABAergic INs may be more tractable for disease modeling and transplantation. We identified five factors (Foxg1, Sox2, Ascl1, Dlx5, and Lhx6) that convert mouse fibroblasts into induced GABAergic INs (iGABA-INs) possessing molecular signatures of telencephalic INs. Factor overexpression activates transcriptional networks required for GABAergic fate specification. iGABA-INs display progressively maturing firing patterns comparable to cortical INs, form functional synapses, and release GABA. Importantly, iGABA-INs survive and mature upon being grafted into mouse hippocampus. Optogenetic stimulation demonstrated functional integration of grafted iGABA-INs into host circuitry, triggering inhibition of host granule neuron activity. These five factors also converted human cells into functional GABAergic INs. These properties suggest that iGABA-INs have potential for disease modeling and cell-based therapeutic approaches to neurological disorders., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The liver maintains glucose and lipid homeostasis by adapting its metabolic activity to the energy needs of the organism. Communication between hepatocytes and extracellular environment via endocytosis is key to such homeostasis. Here, we addressed the question of whether endosomes are required for gluconeogenic gene expression. We took advantage of the loss of endosomes in the mouse liver upon Rab5 silencing. Strikingly, we found hepatomegaly and severe metabolic defects such as hypoglycemia, hypercholesterolemia, hyperlipidemia, and glycogen accumulation that phenocopied those found in von Gierke's disease, a glucose-6-phosphatase (G6Pase) deficiency. G6Pase deficiency alone can account for the reduction in hepatic glucose output and glycogen accumulation as determined by mathematical modeling. Interestingly, we uncovered functional alterations in the transcription factors, which regulate G6Pase expression. Our data highlight a requirement of Rab5 and the endosomal system for the regulation of gluconeogenic gene expression that has important implications for metabolic diseases., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

The transition from maternal to zygotic control is fundamental to the life cycle of all multicellular organisms. It is widely believed that genomes are transcriptionally inactive from fertilization until zygotic genome activation (ZGA). Thus, the earliest genes expressed probably support the rapid cell divisions that precede morphogenesis and, if so, might be evolutionarily conserved. Here, we identify the earliest zygotic transcripts in the zebrafish, Danio rerio, through metabolic labeling and purification of RNA from staged embryos. Surprisingly, the mitochondrial genome was highly active from the one-cell stage onwards, showing that significant transcriptional activity exists at fertilization. We show that 592 nuclear genes become active when cell cycles are still only 15 min long, confining expression to relatively short genes. Furthermore, these zygotic genes are evolutionarily younger than those expressed at other developmental stages. Comparison of fish, fly, and mouse data revealed different sets of genes expressed at ZGA. This species specificity uncovers an evolutionary plasticity in early embryogenesis that probably confers substantial adaptive potential., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)

Aicardi-Goutières syndrome (AGS), a hereditary autoimmune disease, clinically and biochemically overlaps with systemic lupus erythematosus (SLE) and, like SLE, is characterized by spontaneous type I interferon (IFN) production. The finding that defects of intracellular nucleases cause AGS led to the concept that intracellular accumulation of nucleic acids triggers inappropriate production of type I IFN and autoimmunity. AGS can also be caused by defects of SAMHD1, a 3' exonuclease and deoxynucleotide (dNTP) triphosphohydrolase. Human SAMHD1 is an HIV-1 restriction factor that hydrolyzes dNTPs and decreases their concentration below the levels required for retroviral reverse transcription. We show in gene-targeted mice that also mouse SAMHD1 reduces cellular dNTP concentrations and restricts retroviral replication in lymphocytes, macrophages, and dendritic cells. Importantly, the absence of SAMHD1 triggered IFN-β-dependent transcriptional upregulation of type I IFN-inducible genes in various cell types indicative of spontaneous IFN production. SAMHD1-deficient mice may be instrumental for elucidating the mechanisms that trigger pathogenic type I IFN responses in AGS and SLE., (Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.)