A novel reporter mouse strain that expresses enhanced green fluorescent protein upon Cre-mediated recombination

The Janus kinase 1 is critical for pancreatic cancer initiation and progression

Interleukin-6 (IL-6)-class inflammatory cytokines signal through the Janus tyrosine kinase (JAK)/signal transducer and activator of transcription (STAT) pathway and promote the development of pancreatic ductal adenocarcinoma (PDAC); however, the functions of specific intracellular signaling mediators in this process are less well defined. Using a ligand-controlled and pancreas-specific knockout in adult mice, we demonstrate in this study that JAK1 deficiency prevents the formation of KRASG12D-induced pancreatic tumors, and we establish that JAK1 is essential for the constitutive activation of STAT3, whose activation is a prominent characteristic of PDAC. We identify CCAAT/enhancer binding protein δ (C/EBPδ) as a biologically relevant downstream target of JAK1 signaling, which is upregulated in human PDAC. Reinstating the expression of C/EBPδ was sufficient to restore the growth of JAK1-deficient cancer cells as tumorspheres and in xenografted mice. Collectively, the findings of this study suggest that JAK1 executes important functions of inflammatory cytokines through C/EBPδ and may serve as a molecular target for PDAC prevention and treatment.

Incomplete accumulation of perilesional reactive astrocytes exacerbates wound healing after closed-head injury by increasing inflammation and BBB disruption

Wound healing after closed-head injury is a significant medical issue. However, conventional models of focal traumatic brain injury, such as fluid percussion injury and controlled cortical impact, employ mechanical impacts on the exposed cerebral cortex after craniotomy. These animal models are inappropriate for studying gliosis, as craniotomy itself induces gliosis. To address this, we developed a closed-head injury model and named "photo injury", which employs intense light illumination through a thinned-skull cranial window. Our prior work demonstrated that the gliosis of focal cerebral lesion after the photo injury does not encompass artificial gliosis and comprises two distinct reactive astrocyte subpopulations. The reactive astrocytes accumulated in the perilesional recovery area actively proliferate and express Nestin, a neural stem cell marker, while those in distal regions do not exhibit these traits. The present study investigated the role of perilesional reactive astrocytes (PRAs) in wound healing using the ablation of reactive astrocytes by the conditional knockout of Stat3. The extensive and non-selective ablation of reactive astrocytes in Nestin-Cre:Stat3f/f mice resulted in an exacerbation of injury, marked by increased inflammation and BBB disruption. On the other hand, GFAP-CreERT2:Stat3f/f mice exhibited the partial and selective ablation of the PRAs, while their exacerbation of injury was at the same extent as in Nestin-Cre:Stat3f/f mice. The comparison of these two mouse strains indicates that the PRAs are an essential astrocyte component for wound healing after closed-head injury, and their anti-inflammatory and regenerative functions are significantly affected even by incomplete accumulation. In addition, the reporter gene expression in the PRAs by GFAP-CreERT2 indicated a substantial elimination of these cells and an absence of differentiation into other cell types, despite Nestin expression, after wound healing. Thus, the accumulation and subsequent elimination of PRA are proposed as promising diagnostic and therapeutic avenues to bolster wound healing after closed-head injury.

Developmental conversion of thymocyte-attracting cells into self-antigen-displaying cells in embryonic thymus medulla epithelium

Thymus medulla epithelium establishes immune self-tolerance and comprises diverse cellular subsets. Functionally relevant medullary thymic epithelial cells (mTECs) include a self-antigen-displaying subset that exhibits genome-wide promiscuous gene expression promoted by the nuclear protein Aire and that resembles a mosaic of extrathymic cells including mucosal tuft cells. An additional mTEC subset produces the chemokine CCL21, thereby attracting positively selected thymocytes from the cortex to the medulla. Both self-antigen-displaying and thymocyte-attracting mTEC subsets are essential for self-tolerance. Here, we identify a developmental pathway by which mTECs gain their diversity in functionally distinct subsets. We show that CCL21-expressing mTECs arise early during thymus ontogeny in mice. Fate-mapping analysis reveals that self-antigen-displaying mTECs, including Aire-expressing mTECs and thymic tuft cells, are derived from CCL21-expressing cells. The differentiation capability of CCL21-expressing embryonic mTECs is verified in reaggregate thymus experiments. These results indicate that CCL21-expressing embryonic mTECs carry a developmental potential to give rise to self-antigen-displaying mTECs, revealing that the sequential conversion of thymocyte-attracting subset into self-antigen-displaying subset serves to assemble functional diversity in the thymus medulla epithelium.

FGF21 and autophagy coordinately counteract kidney disease progression during aging and obesity

Chronic kidney disease (CKD) has reached epidemic proportions worldwide, partly due to the increasing population of elderly and obesity. Macroautophagy/autophagy counteracts CKD progression, whereas autophagy is stagnated owing to lysosomal overburden during aging and obesity, which promotes CKD progression. Therefore, for preventing CKD progression during aging and obesity, it is important to elucidate the compensation mechanisms of autophagy stagnation. We recently showed that FGF21 (fibroblast growth factor 21), which is a prolongevity and metabolic hormone, is induced by autophagy deficiency in kidney proximal tubular epithelial cells (PTECs); however, its pathophysiological role remains uncertain. Here, we investigated the interplay between FGF21 and autophagy and the direct contribution of endogenous FGF21 in the kidney during aging and obesity using PTEC-specific fgf21- and/or atg5-deficient mice at 24 months (aged) or under high-fat diet (obese) conditions. PTEC-specific FGF21 deficiency in young mice increased autophagic flux due to increased demand of autophagy, whereas fgf21-deficient aged or obese mice exacerbated autophagy stagnation due to severer lysosomal overburden caused by aberrant autophagy. FGF21 was robustly induced by autophagy deficiency, and aged or obese PTEC-specific fgf21- and atg5-double deficient mice deteriorated renal histology compared with atg5-deficient mice. Mitochondrial function was severely disturbed concomitant with exacerbated oxidative stress and downregulated TFAM (transcription factor A, mitochondrial) in double-deficient mice. These results indicate that FGF21 is robustly induced by autophagy disturbance and protects against CKD progression during aging and obesity by alleviating autophagy stagnation and maintaining mitochondrial homeostasis, which will pave the way to a novel treatment for CKD.

Loss of Pax3 causes reduction of melanocytes in the developing mouse cochlea

Cochlear melanocytes are intermediate cells in the stria vascularis that generate endocochlear potentials required for auditory function. Human PAX3 mutations cause Waardenburg syndrome and abnormalities of skin and retinal melanocytes, manifested as congenital hearing loss (~ 70%) and hypopigmentation of skin, hair and eyes. However, the underlying mechanism of hearing loss remains unclear. Cochlear melanocytes in the stria vascularis originated from Pax3-traced melanoblasts and Plp1-traced Schwann cell precursors, both of which derive from neural crest cells. Here, using a Pax3-Cre knock-in mouse that allows lineage tracing of Pax3-expressing cells and disruption of Pax3, we found that Pax3 deficiency causes foreshortened cochlea, malformed vestibular apparatus, and neural tube defects. Lineage tracing and in situ hybridization show that Pax3+ derivatives contribute to S100+, Kir4.1+ and Dct+ melanocytes (intermediate cells) in the developing stria vascularis, all of which are significantly diminished in Pax3 mutant animals. Taken together, these results suggest that Pax3 is required for the development of neural crest cell-derived cochlear melanocytes, whose absence may contribute to congenital hearing loss of Waardenburg syndrome in humans.

Developmental conversion of thymocyte-attracting cells into self-antigen-displaying cells in embryonic thymus medulla epithelium

Thymus medulla epithelium establishes immune self-tolerance and comprises diverse cellular subsets. Functionally relevant medullary thymic epithelial cells (mTECs) include a self-antigen-displaying subset that exhibits genome-wide promiscuous gene expression promoted by the nuclear protein Aire and that resembles a mosaic of extrathymic cells including mucosal tuft cells. An additional mTEC subset produces the chemokine CCL21, thereby attracting positively selected thymocytes from the cortex to the medulla. Both self-antigen-displaying and thymocyte-attracting mTEC subsets are essential for self-tolerance. Here we identify a developmental pathway by which mTECs gain their diversity in functionally distinct subsets. We show that CCL21-expressing mTECs arise early during thymus ontogeny. Fate-mapping analysis reveals that self-antigen-displaying mTECs, including Aire-expressing mTECs and thymic tuft cells, are derived from CCL21-expressing cells. The differentiation capability of CCL21-expressing embryonic mTECs is verified in reaggregate thymus experiments. These results indicate that CCL21-expressing embryonic mTECs carry a developmental potential to give rise to self-antigen-displaying mTECs, revealing that the sequential conversion of thymocyte-attracting subset into self-antigen-displaying subset serves to assemble functional diversity in the thymus medulla epithelium.

Wnt activation disturbs cell competition and causes diffuse invasion of transformed cells through NF-κB-MMP21 pathway

Normal epithelial cells exert their competitive advantage over RasV12-transformed cells and eliminate them into the apical lumen via cell competition. However, the internal or external factors that compromise cell competition and provoke carcinogenesis remain elusive. In this study, we examine the effect of sequential accumulation of gene mutations, mimicking multi-sequential carcinogenesis on RasV12-induced cell competition in intestinal epithelial tissues. Consequently, we find that the directionality of RasV12-cell extrusion in Wnt-activated epithelia is reversed, and transformed cells are delaminated into the basal lamina via non-cell autonomous MMP21 upregulation. Subsequently, diffusively infiltrating, transformed cells develop into highly invasive carcinomas. The elevated production of MMP21 is elicited partly through NF-κB signaling, blockage of which restores apical elimination of RasV12 cells. We further demonstrate that the NF-κB-MMP21 axis is significantly bolstered in early colorectal carcinoma in humans. Collectively, this study shows that cells with high mutational burdens exploit cell competition for their benefit by behaving as unfit cells, endowing them with an invasion advantage.

Spatial heterogeneity of bone marrow endothelial cells unveils a distinct subtype in the epiphysis

Bone marrow endothelial cells (BMECs) play a key role in bone formation and haematopoiesis. Although recent studies uncovered the cellular taxonomy of stromal compartments in the bone marrow (BM), the complexity of BMECs is not fully characterized. In the present study, using single-cell RNA sequencing, we defined a spatial heterogeneity of BMECs and identified a capillary subtype, termed type S (secondary ossification) endothelial cells (ECs), exclusively existing in the epiphysis. Type S ECs possessed unique phenotypic characteristics in terms of structure, plasticity and gene expression profiles. Genetic experiments showed that type S ECs atypically contributed to the acquisition of bone strength by secreting type I collagen, the most abundant bone matrix component. Moreover, these cells formed a distinct reservoir for haematopoietic stem cells. These findings provide the landscape for the cellular architecture in the BM vasculature and underscore the importance of epiphyseal ECs during bone and haematopoietic development.

A Novel Long Noncoding RNA in Osteocytes Regulates Bone Formation through the Wnt/β-Catenin Signaling Pathway

The vast majority of transcribed RNAs are noncoding RNAs. Among noncoding RNAs, long noncoding RNAs (lncRNAs), which contain hundreds to thousands of bases, have received attention in many fields. The vast majority of the constituent cells in bone tissue are osteocytes, but their regulatory mechanisms are incompletely understood. Considering the wide range of potential contributions of lncRNAs to physiological processes and pathological conditions, we hypothesized that lncRNAs in osteocytes, which have not been reported, could be involved in bone metabolism. Here, we first isolated osteocytes from femurs of mice with osteocyte-specific GFP expression. Then, through RNA-sequencing, we identified osteocyte-specific lncRNAs and focused on a novel lncRNA, 9530026P05Rik (lncRNA953Rik), which strongly suppressed osteogenic differentiation. In the IDG-SW3 osteocyte line with lncRNA953Rik overexpression, the expression of Osterix and its downstream genes was reduced. RNA pull-down and subsequent LC-MS/MS analysis revealed that lncRNA953Rik bound the nuclear protein CCAR2. We demonstrated that CCAR2 promoted Wnt/β-catenin signaling and that lncRNA953Rik inhibited this pathway. lncRNA953Rik sequestered CCAR2 from HDAC1, leading to deacetylation of H3K27 in the Osterix promoter and consequent transcriptional downregulation of Osterix. This research is the first to clarify the role of a lncRNA in osteocytes. Our findings can pave the way for novel therapeutic options targeting lncRNAs in osteocytes to treat bone metabolic diseases such as osteoporosis.

Pax3 deficiency diminishes melanocytes in the developing mouse cochlea

Cochlear melanocytes are intermediate cells in the stria vascularis that generate endocochlear potentials required for auditory function. Human PAX3 mutations cause Waardenburg syndrome and abnormalities of melanocytes, manifested as congenital hearing loss and hypopigmentation of skin, hair and eyes. However, the underlying mechanism of hearing loss remains unclear. During development, cochlear melanocytes in the stria vascularis are dually derived from Pax3-Cre+ melanoblasts migrating from neuroepithelial cells including neural crest cells and Plp1+ Schwann cell precursors originated from also neural crest cells, differentiating in a basal-apical manner. Here, using a Pax3-Cre mouse line, we found that Pax3 deficiency causes foreshortened cochlea, malformed vestibular apparatus, and neural tube defects. Lineage tracing and in situ hybridization show that Pax3-Cre derivatives contribute to S100+ , Kir4.1+ and Dct+ melanocytes (intermediate cells) in the developing stria vascularis, all significantly diminished in Pax3 mutant animals. Taken together, these results suggest that Pax3 is required for the development of neural crest cell-derived cochlear melanocytes, whose absence may contribute to congenital hearing loss of Waardenburg syndrome in human.

Loss of Dead end1 induces testicular teratomas from primordial germ cells that failed to undergo sexual differentiation in embryonic testes

Spontaneous testicular teratomas (STTs) are tumours comprising a diverse array of cell and tissue types, which are derived from pluripotent stem-like cells called embryonal carcinoma cells (ECCs). Although mouse ECCs originate from primordial germ cells (PGCs) in embryonic testes, the molecular basis underlying ECC development remains unclear. This study shows that the conditional deletion of mouse Dead end1 (Dnd1) from migrating PGCs leads to STT development. In Dnd1-conditional knockout (Dnd1-cKO) embryos, PGCs colonise the embryonic testes but fail to undergo sexual differentiation; subsequently, ECCs develop from a portion of the PGCs. Transcriptomic analyses reveal that PGCs not only fail to undergo sexual differentiation but are also prone to transformation into ECCs by upregulating the expression of marker genes for primed pluripotency in the testes of Dnd1-cKO embryos. Thus, our results clarify the role of Dnd1 in developing STTs and developmental process of ECC from PGC, providing novel insights into pathogenic mechanisms of STTs.

Keratinocyte Growth Factor Stimulates Growth of p75+ Neural Crest Lineage Cells During Middle Ear Cholesteatoma Formation in Mice

During development, cranial neural crest (NC) cells display a striking transition from collective to single-cell migration and undergo a mesenchymal-to-epithelial transformation to form a part of the middle ear epithelial cells (MEECs). While MEECs derived from NC are known to control homeostasis of the epithelium and repair from otitis media, paracrine action of keratinocyte growth factor (KGF) promotes the growth of MEECs and induces middle ear cholesteatoma (cholesteatoma). The animal model of cholesteatoma was previously established by transfecting a human KGF-expression vector. Herein, KGF-inducing cholesteatoma was studied in Wnt1-Cre/Floxed-enhanced green fluorescent protein (EGFP) mice that conditionally express EGFP in the NC lineages. The cytokeratin 14-positive NC lineage expanded into the middle ear and formed cholesteatoma. Moreover, the green fluorescent protein-positive NC lineages comprising the cholesteatoma tissue expressed p75, an NC marker, with high proliferative activity. Similarly, a large number of p75-positive cells were observed in human cholesteatoma tissues. Injections of the immunotoxin murine p75-saporin induced depletion of the p75-positive NC lineages, resulting in the reduction of cholesteatoma in vivo. The p75 knockout in the MEECs had low proliferative activity with or without KGF protein in vitro. Controlling p75 signaling may reduce the proliferation of NC lineages and may represent a new therapeutic target for cholesteatoma.

Nestin is a marker of unipotent embryonic and adult progenitors differentiating into an epithelial cell lineage of the hair follicles

Nestin is an intermediate filament protein transiently expressed in neural stem/progenitor cells. We previously demonstrated that outer root sheath (ORS) keratinocytes of adult hair follicles (HFs) in mice descend from nestin-expressing cells, despite being an epithelial cell lineage. This study determined the exact stage when nestin-expressing ORS stem/precursor cells or their descendants appear during HF morphogenesis, and whether they are present in adult HFs. Using Nes-Cre/CAG-CAT-EGFP mice, in which enhanced green fluorescent protein (EGFP) is expressed following Cre-based recombination driven by the nestin promoter, we found that EGFP⁺ cells appeared in the epithelial layer of embryonic HFs as early as the peg stage. EGFP⁺ cells in hair pegs were positive for keratin 14 (K14) and K5, but not vimentin, SOX2, SOX10, or S100 alpha 6. Tracing of tamoxifen-induced EGFP⁺ cells in postnatal Nes-CreERT2/CAG-CAT-EGFP mice revealed labeling of some isthmus HF epithelial cells in the first anagen stage. EGFP⁺ cells in adult HFs were not immunolabeled for K15, an HF multipotent stem cell marker. However, when hairs were depilated in Nes-CreERT2/CAG-CAT-EGFP mice to induce the anagen stage after tamoxifen injection, the majority of ORS keratinocytes in depilation-induced anagen HFs were labeled for EGFP. Our findings indicate that nestin-expressing unipotent progenitor cells capable of differentiating into ORS keratinocytes are present in HF primordia and adult HFs.

Fluorescent transgenic mouse models for whole-brain imaging in health and disease

A paradigm shift is occurring in neuroscience and in general in life sciences converting biomedical research from a descriptive discipline into a quantitative, predictive, actionable science. Living systems are becoming amenable to quantitative description, with profound consequences for our ability to predict biological phenomena. New experimental tools such as tissue clearing, whole-brain imaging, and genetic engineering technologies have opened the opportunity to embrace this new paradigm, allowing to extract anatomical features such as cell number, their full morphology, and even their structural connectivity. These tools will also allow the exploration of new features such as their geometrical arrangement, within and across brain regions. This would be especially important to better characterize brain function and pathological alterations in neurological, neurodevelopmental, and neurodegenerative disorders. New animal models for mapping fluorescent protein-expressing neurons and axon pathways in adult mice are key to this aim. As a result of both developments, relevant cell populations with endogenous fluorescence signals can be comprehensively and quantitatively mapped to whole-brain images acquired at submicron resolution. However, they present intrinsic limitations: weak fluorescent signals, unequal signal strength across the same cell type, lack of specificity of fluorescent labels, overlapping signals in cell types with dense labeling, or undetectable signal at distal parts of the neurons, among others. In this review, we discuss the recent advances in the development of fluorescent transgenic mouse models that overcome to some extent the technical and conceptual limitations and tradeoffs between different strategies. We also discuss the potential use of these strains for understanding disease.

Dominant role of DNA methylation over H3K9me3 for IAP silencing in endoderm

Silencing of endogenous retroviruses (ERVs) is largely mediated by repressive chromatin modifications H3K9me3 and DNA methylation. On ERVs, these modifications are mainly deposited by the histone methyltransferase Setdb1 and by the maintenance DNA methyltransferase Dnmt1. Knock-out of either Setdb1 or Dnmt1 leads to ERV de-repression in various cell types. However, it is currently not known if H3K9me3 and DNA methylation depend on each other for ERV silencing. Here we show that conditional knock-out of Setdb1 in mouse embryonic endoderm results in ERV de-repression in visceral endoderm (VE) descendants and does not occur in definitive endoderm (DE). Deletion of Setdb1 in VE progenitors results in loss of H3K9me3 and reduced DNA methylation of Intracisternal A-particle (IAP) elements, consistent with up-regulation of this ERV family. In DE, loss of Setdb1 does not affect H3K9me3 nor DNA methylation, suggesting Setdb1-independent pathways for maintaining these modifications. Importantly, Dnmt1 knock-out results in IAP de-repression in both visceral and definitive endoderm cells, while H3K9me3 is unaltered. Thus, our data suggest a dominant role of DNA methylation over H3K9me3 for IAP silencing in endoderm cells. Our findings suggest that Setdb1-meditated H3K9me3 is not sufficient for IAP silencing, but rather critical for maintaining high DNA methylation.

Silencing of endogenous retroviruses is crucial for maintaining transcriptional and genomic integrity of cells and is maintained by histone H3K9 methylation and/or DNA methylation in various cell types. Here the authors show that loss of DNA methyltransferase DNMT1 in endoderm results in ERV derepression while H3K9me3 is unaltered.

Cre toxicity in mouse models of cardiovascular physiology and disease

The Cre-LoxP system provides a widely used method for studying gene requirements in the mouse as the main mammalian genetic model organism. To define the molecular and cellular mechanisms that underlie cardiovascular development, function and disease, various mouse strains have been engineered that allow Cre-LoxP-mediated gene targeting within specific cell types of the cardiovascular system. Despite the usefulness of this system, evidence is accumulating that Cre activity can have toxic effects in cells, independently of its ability to recombine pairs of engineered LoxP sites in target genes. Here, we have gathered published evidence for Cre toxicity in cells and tissues relevant to cardiovascular biology and provide an overview of mechanisms proposed to underlie Cre toxicity. Based on this knowledge, we propose that each study utilising the Cre-LoxP system to investigate gene function in the cardiovascular system should incorporate appropriate controls to account for Cre toxicity.

Non-degradable autophagic vacuoles are indispensable for cell competition

Cell competition is a process by which unwanted cells are eliminated from tissues. Apical extrusion is one mode whereby normal epithelial cells remove transformed cells, but it remains unclear how this process is mechanically effected. In this study, we show that autophagic and endocytic fluxes are attenuated in RasV12-transformed cells surrounded by normal cells due to lysosomal dysfunction, and that chemical manipulation of lysosomal activity compromises apical extrusion. We further find that RasV12 cells deficient in autophagy initiation machinery are resistant to elimination pressure exerted by normal cells, suggesting that non-degradable autophagic vacuoles are required for cell competition. Moreover, in vivo analysis revealed that autophagy-ablated RasV12 cells are less readily eliminated by cell competition, and remaining transformed cells destroy ductal integrity, leading to chronic pancreatitis. Collectively, our findings illuminate a positive role for autophagy in cell competition and reveal a homeostasis-preserving function of autophagy upon emergence of transformed cells.

Differing impact of phosphoglycerate mutase 1-deficiency on brown and white adipose tissue

Brown adipose tissue (BAT) is a metabolically active organ that contributes to the thermogenic response to cold exposure. In addition, other thermogenic cells termed beige adipocytes are generated in white adipose tissue (WAT) by cold exposure. Although activation of brown/beige adipose tissue is associated with mobilization of both glucose and lipids, few studies have focused on the role of glycolytic enzymes in regulating adipose tissue function. We generated mouse models with specific deletion of the glycolytic enzyme phosphoglycerate mutase 1 (PGAM1) from adipose tissue. Deletion of Pgam1 from both BAT and WAT promoted whitening of BAT with beiging of visceral WAT, whereas deletion of Pgam1 from BAT alone led to whitening of BAT without beiging of WAT. Our results demonstrate a potential role of glycolytic enzymes in beiging of visceral WAT and suggest that PGAM1 would be a novel therapeutic target in obesity and diabetes.

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Pgam1 deletion leads to whitening of brown adipose tissue

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Pgam1 deletion promotes beiging of visceral white adipose tissue (WAT)

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Pgam1 deletion-induced beiging is associated with increased levels of amino acids

Coupling of angiogenesis and odontogenesis orchestrates tooth mineralization in mice

The skeletal system consists of bones and teeth, both of which are hardened via mineralization to support daily physical activity and mastication. The precise mechanism for this process, especially how blood vessels contribute to tissue mineralization, remains incompletely understood. Here, we established an imaging technique to visualize the 3D structure of the tooth vasculature at a single-cell level. Using this technique combined with single-cell RNA sequencing, we identified a unique endothelial subtype specialized to dentinogenesis, a process of tooth mineralization, termed periodontal tip-like endothelial cells. These capillaries exhibit high angiogenic activity and plasticity under the control of odontoblasts; in turn, the capillaries trigger odontoblast maturation. Metabolomic analysis demonstrated that the capillaries perform the phosphate delivery required for dentinogenesis. Taken together, our data identified the fundamental cell-to-cell communications that orchestrate tooth formation, angiogenic–odontogenic coupling, a distinct mechanism compared to the angiogenic–osteogenic coupling in bones. This mechanism contributes to our understanding concerning the functional diversity of organotypic vasculature.

Generation of a BAC transgenic mouse strain that expresses CreERT and a fluorescent protein under the transcriptional control of the Fzd5 locus

BACKGROUND

The expression of FZD5 distinguishes immature human mesenchymal stem/stromal cells (MSC) in cultures, and the function of FZD5 is crucial for maintaining the proliferation and multilineage differentiation capacity of human MSC. We herein investigated whether Fzd5 expression also marks undifferentiated MSC in animals.

METHODS

We generated a transgenic mouse strain (Fzd5-CreERT-tFP635) that expresses CreERT and the fluorescent protein, TurboFP635 (tFP635), under the transcriptional control of the Fzd5 gene using the BAC transgenic technique, and identified cells expressing tFP635 by flow cytometry. We also conducted lineage tracing with this strain.

RESULTS

In the bone marrow of transgenic mice, tFP635 was preferentially expressed in MSC, Leptin receptor-expressing MSC (LepR⁺MSCs), and some Pdgfrα⁺ Sca1⁺ MSC (PαS). Inducible lineage tracing using the Fzd5-CreERT-tFP635; CAG-CAT-EGFP strain at the adult stage showed that Fzd5-expressing cells and their descendants labeled with GFP were progressively dominant in LepR⁺MSC and PαS, and GFP⁺ cells persisted for 1 year after the activation of CreERT. Adipocyte progenitor cells (APCs), osteoblast progenitor cells (OPCs), and Cd51⁺ stromal cells were also labeled with GFP.

CONCLUSIONS

Our transgenic mouse marks two different types of MSC, LepR⁺MSC and PαS.

Tumor-specific inter-endothelial adhesion mediated by FLRT2 facilitates cancer aggressiveness

Blood vessel abnormalization alters cancer cell metabolism and promotes cancer dissemination and metastasis. However, the biological features of the abnormalized blood vessels that facilitate cancer progression and whether they can be targeted therapeutically have not been fully investigated. Here, we found that an axon guidance molecule, fibronectin leucine-rich transmembrane protein 2 (FLRT2), is expressed preferentially in abnormalized vessels of advanced colorectal cancers in humans, and that its expression correlates negatively with long-term survival. Endothelial-specific deletion of Flrt2 in mice selectively pruned abnormalized vessels, resulting in a unique metabolic state termed "oxygen-glucose uncoupling", which suppresses tumor metastasis. Moreover, Flrt2 deletion caused an increase in the number of mature vessels, resulting in a significant increase in the anti-tumor effects of immune checkpoint blockers. Mechanistically, we found that FLRT2 forms non-canonical inter-endothelial adhesions that safeguard against oxidative stress through homophilic binding. Together, our results demonstrate the existence of tumor-specific inter-endothelial adhesions that enable abnormalized vessels to facilitate cancer aggressiveness. Targeting this type of adhesion complex could be a safe and effective therapeutic option to suppress cancer progression.

Genetic Deletion of Vascular Endothelial Growth Factor Receptor 2 in Endothelial Cells Leads to Immediate Disruption of Tumor Vessels and Aggravation of Hypoxia

Vascular endothelial growth factor (VEGF) blockers are used widely in clinics to target various types of human cancer. Although VEGF blockers exert marked tumor suppressive effects, the therapeutic effects can be limited. Moreover, accumulating evidence shows that VEGF acts not just on endothelial cells but also on various nonendothelial cells, including tumor and immune cells, suggesting a need to revisit the bona fide action of VEGF on endothelial cells using specific genetic mouse models. Herein, tamoxifen-inducible endothelial-specific knockout mice lacking VEGF receptor 2 (Vegfr2), the major signal transducer for VEGF, were used. The initial event resulting from cessation of endothelial Vegfr2 signaling was vascular truncation and fragmentation, rather than maturation of abnormalized vessels. Although deletion of endothelial Vegfr2 suppressed intratumor hemorrhage, it enhanced hypoxia in tumor cells and reduced the number of infiltrating cytotoxic T cells, suggesting a profound reduction in intratumor blood flow. In various tissues, deletion of endothelial Vegfr2 induced regression of healthy capillaries in intestinal villi, substantiating intestinal perforation, which is one of the most common adverse effects of VEGF blockade in humans. Overall, the data suggest that some of the known effects of VEGF blockers on tumor vessels are caused by partial cessation of VEGF signaling, or by actions on nonendothelial cells. The results increase the understanding of the mechanisms underlying anti-angiogenic therapy.

GLI3 Is Required for OLIG2+ Progeny Production in Adult Dorsal Neural Stem Cells

The ventricular-subventricular zone (V-SVZ) is a postnatal germinal niche. It holds a large population of neural stem cells (NSCs) that generate neurons and oligodendrocytes for the olfactory bulb and (primarily) the corpus callosum, respectively. These NSCs are heterogeneous and generate different types of neurons depending on their location. Positional identity among NSCs is thought to be controlled in part by intrinsic pathways. However, extrinsic cell signaling through the secreted ligand Sonic hedgehog (Shh) is essential for neurogenesis in both the dorsal and ventral V-SVZ. Here we used a genetic approach to investigate the role of the transcription factors GLI2 and GLI3 in the proliferation and cell fate of dorsal and ventral V-SVZ NSCs. We find that while GLI3 is expressed in stem cell cultures from both dorsal and ventral V-SVZ, the repressor form of GLI3 is more abundant in dorsal V-SVZ. Despite this high dorsal expression and the requirement for other Shh pathway members, GLI3 loss affects the generation of ventrally-, but not dorsally-derived olfactory interneurons in vivo and does not affect trilineage differentiation in vitro. However, loss of GLI3 in the adult dorsal V-SVZ in vivo results in decreased numbers of OLIG2-expressing progeny, indicating a role in gliogenesis.

The concurrent stimulation of Wnt and FGF8 signaling induce differentiation of dental mesenchymal cells into odontoblast-like cells

Fibroblast growth factor 8 (FGF8) is known to be a potent stimulator of canonical Wnt/β-catenin activity, an essential factor for tooth development. In this study, we analyzed the effects of co-administration of FGF8 and a CHIR99021 (GSK3β inhibitor) on differentiation of dental mesenchymal cells into odontoblasts. Utilizing Cre-mediated EGFP reporter mice, dentin matrix protein 1 (Dmp1) expression was examined in mouse neonatal molar tooth germs. At birth, expression of Dmp1-EGFP was not found in mesenchymal cells but rather epithelial cells, after which Dmp1-positive cells gradually emerged in the mesenchymal area along with disappearance in the epithelial area. Primary cultured mesenchymal cells from neonatal tooth germ specimens showed loss of Dmp1-EGFP positive signals, whereas addition of Wnt3a or the CHIR99021 significantly regained Dmp1 positivity within approximately 2 weeks. Other odontoblast markers such as dentin sialophosphoprotein (Dspp) could not be clearly detected. Concurrent stimulation of primary cultured mesenchymal cells with the CHIR99021 and FGF8 resulted in significant upregulation of odonto/osteoblast proteins. Furthermore, increased expression levels of runt-related transcription factor 2 (Runx2), osterix, and osteocalcin were also observed. The present findings indicate that coordinated action of canonical Wnt/β-catenin and FGF8 signals is essential for odontoblast differentiation of tooth germs in mice.

Dual recombinase action in the normal and neoplastic mammary gland epithelium

We developed a transgenic mouse line that expresses the codon-optimized Flp recombinase under the control of the MMTV promoter in luminal epithelial cells of the mammary gland. In this report, we demonstrate the versatile applicability of the new MMTV-Flp strain to manipulate genes in a temporally and spatially controlled manner in the normal mammary gland, in luminal-type mammary tumors that overexpress ERBB2, and in a new KRAS-associated mammary cancer model. Although the MMTV-Flp is expressed in a mosaic pattern in the luminal epithelium, the Flp-mediated activation of a mutant Kras^G12D allele resulted in basal-like mammary tumors that progressively acquired mesenchymal features. Besides its applicability as a tool for gene activation and cell lineage tracing to validate the cellular origin of primary and metastatic tumor cells, we employed the MMTV-Flp transgene together with the tamoxifen-inducible Cre recombinase to demonstrate that the combinatorial action of both recombinases can be used to delete or to activate genes in established tumors. In a proof-of-principle experiment, we conditionally deleted the JAK1 tyrosine kinase in KRAS-transformed mammary cancer cells using the dual recombinase approach and found that lack of JAK1 was sufficient to block the constitutive activation of STAT3. The collective results from the various lines of investigation showed that it is, in principle, feasible to manipulate genes in a ligand-controlled manner in neoplastic mammary epithelial cells, even when cancer cells acquire a state of cellular plasticity that may no longer support the expression of the MMTV-Flp transgene.

A multistate stem cell dynamics maintains homeostasis in mouse spermatogenesis

In mouse testis, a heterogeneous population of undifferentiated spermatogonia (Aundiff) harbors spermatogenic stem cell (SSC) potential. Although GFRα1+ Aundiff maintains the self-renewing pool in homeostasis, the functional basis of heterogeneity and the implications for their dynamics remain unresolved. Here, through quantitative lineage tracing of SSC subpopulations, we show that an ensemble of heterogeneous states of SSCs supports homeostatic, persistent spermatogenesis. Such heterogeneity is maintained robustly through stochastic interconversion of SSCs between a renewal-biased Plvap+/GFRα1+ state and a differentiation-primed Sox3+/GFRα1+ state. In this framework, stem cell commitment occurs not directly but gradually through entry into licensed but uncommitted states. Further, Plvap+/GFRα1+ cells divide slowly, in synchrony with the seminiferous epithelial cycle, while Sox3+/GFRα1+ cells divide much faster. Such differential cell-cycle dynamics reduces mitotic load, and thereby the potential to acquire harmful de novo mutations of the self-renewing pool, while keeping the SSC density high over the testicular open niche.

Suppression of MyoD induces spontaneous adipogenesis in skeletal muscle progenitor cell culture

The degree of intramuscular adipose tissue accumulation is one of the factors affecting meat quality. Accumulation of adipocytes is also observed under the pathological condition of skeletal muscle such as muscular dystrophy and sarcopenia. The origin of adipocytes seen in skeletal muscle is mesenchymal progenitor cells that can give rise to both adipocytes and fibroblasts. In the present study, we demonstrated that siRNA-mediated suppression of MyoD expression in rat skeletal muscle progenitor cell culture, which comprises both myogenic satellite cells and mesenchymal progenitor cells, resulted in diminished myotube formation and an unexpected spontaneous appearance of white adipocytes. Suppressing myomaker expression also resulted in complete absence of myotube formation without reducing MyoD expression, but no adipogenesis was seen in this scenario, indicating that decline in MyoD expression rather than decreased myotube formation is necessary to induce adipogenesis. In addition, spontaneous adipogenesis induced by suppressing MyoD expression in culture was inhibited by the conditioned medium from control culture, indicating that anti-adipogenic factor(s) are secreted from MyoD-positive myogenic cells. These results indicate the presence of regulatory mechanism on adipogenesis by myogenic cells.

Highly metastatic claudin-low mammary cancers can originate from luminal epithelial cells

Claudin-low breast cancer represents an aggressive molecular subtype that is comprised of mostly triple-negative mammary tumor cells that possess stem cell-like and mesenchymal features. Little is known about the cellular origin and oncogenic drivers that promote claudin-low breast cancer. In this study, we show that persistent oncogenic RAS signaling causes highly metastatic triple-negative mammary tumors in mice. More importantly, the activation of endogenous mutant KRAS and expression of exogenous KRAS specifically in luminal epithelial cells in a continuous and differentiation stage-independent manner induces preneoplastic lesions that evolve into basal-like and claudin-low mammary cancers. Further investigations demonstrate that the continuous signaling of oncogenic RAS, as well as regulators of EMT, play a crucial role in the cellular plasticity and maintenance of the mesenchymal and stem cell characteristics of claudin-low mammary cancer cells.

Effects of leptin on proliferation of astrocyte- and tanycyte-like neural stem cells in the adult mouse medulla oblongata

Astrocyte- and tanycyte-like neural stem cells (NSCs) were recently detected in the area postrema (AP) and central canal (CC) of the adult medulla oblongata, respectively. The present study aimed to examine dynamical behaviors of the astrocyte- and tanycyte-like NSCs of the mouse medulla oblongata to leptin. The neurosphere assay identified astrocytes in the AP and tanycytes in the CC as NSCs based on their self-renewing neurospherogenic potential. Both NSCs in neurosphere cultures were multipotent cells that generate astrocytes, oligodendrocytes, and neurons. Astrocyte-like NSCs actively proliferated and tanycyte-like NSCs were quiescent under physiologically-relevant in vivo conditions. Chronic leptin treatment promoted proliferation of astrocyte-like NSCs in the AP both in vitro and in vivo. Leptin receptors were expressed in astrocyte-like, but not tanycyte-like NSCs. Food deprivation significantly diminished proliferation of astrocyte-like NSCs. Therefore, the present study indicates that proliferation of astrocyte-like, but not tanycyte-like NSCs is regulated by nutritional conditions.

Transient suppression of transplanted spermatogonial stem cell differentiation restores fertility in mice

A remarkable feature of tissue stem cells is their ability to regenerate the structure and function of host tissue following transplantation. However, the dynamics of donor stem cells during regeneration remains largely unknown. Here we conducted quantitative clonal fate studies of transplanted mouse spermatogonial stem cells in host seminiferous tubules. We found that, after a large population of donor spermatogonia settle in host testes, through stochastic fate choice, only a small fraction persist and regenerate over the long term, and the rest are lost through differentiation and cell death. Further, based on these insights, we showed how repopulation efficiency can be increased to a level where the fertility of infertile hosts is restored by transiently suppressing differentiation using a chemical inhibitor of retinoic acid synthesis. These findings unlock a range of potential applications of spermatogonial transplantation, from fertility restoration in individuals with cancer to conservation of biological diversity.

Indispensable role of Galectin-3 in promoting quiescence of hematopoietic stem cells

Hematopoietic stem cells (HSCs) in adult bone marrow (BM) are usually maintained in a state of quiescence. The cellular mechanism coordinating the balance between HSC quiescence and differentiation is not fully understood. Here, we report that galactose-binding lectin-3 (galectin-3; Gal-3) is upregulated by Tie2 or Mpl activation to maintain quiescence. Conditional overexpression of Gal-3 in mouse HSCs under the transcriptional control of Tie2 or Vav1 promoters (Gal-3 Tg) causes cell cycle retardation via induction of p21. Conversely, the cell cycle of long-term repopulating HSCs (LT-HSCs) in Gal-3-deficient (Gal-3^-/-) mice is accelerated, resulting in their exhaustion. Mechanistically, Gal-3 regulates p21 transcription by forming a complex with Sp1, thus blocking cell cycle entry. These results demonstrate that Gal-3 is a negative regulator of cell-cycling in HSCs and plays a crucial role in adult hematopoiesis to prevent HSC exhaustion.

Long term haematopoitic stem cells (LT-HSCs) are in a quiescent state during homeostasis, which is critical for their maintenance. Here, the authors show that Gal-3 expression in LT-HSCs is induced in response to Tie2 and Mpl and is both necessary and sufficient for LT-HSC quiescence through regulation of p21.

Neural crest-derived cells in nasal conchae of adult mice contribute to bone regeneration

Neural crest-derived cells (NCDCs), a class of adult stem cells not restricted to embryonic tissues, are attractive tissue regenerative therapy candidates because of their ease of isolation, self-renewing properties, and multipotency. Although adult NCDCs can undergo osteogenic differentiation in vitro, whether they induce bone formation in vivo remains unclear. Previously, our group reported findings showing high amounts of NCDCs scattered throughout nasal concha tissues of adult mice. In the present study, NCDCs in nasal conchae labeled with enhanced green fluorescent protein (EGFP) were collected from adult P0-Cre/CAG-CAT-EGFP double transgenic mice, then cultured in serum-free medium to increase the number. Subsequently, NCDCs were harvested and suspended in type I atelocollagen gel, then an atelocollagen sponge was used as a scaffold for the cell suspension. Atelocollagen scaffolds with NCDCs were placed on bone defects created in a mouse calvarial bone defect model. Over the ensuing 12 weeks, micro-CT and histological analysis findings showed that mice with scaffolds containing NCDCs had slightly greater bone formation as compared to those with a scaffold alone. Furthermore, Raman spectroscopy revealed spectral properties of bone in mice that received scaffolds with NCDCs similar to those of native calvarial bone. Bone regeneration is important not only for gaining bone mass but also chemical properties. These results are the first to show the validity of biomolecule-free adult nasal concha-derived NCDCs for bone regeneration, including the chemical properties of regenerated bone tissue.

Umbilical artery tissue contains p75 neurotrophin receptor-positive pericyte-like cells that possess neurosphere formation capacity and neurogenic differentiation potential

INTRODUCTION

The p75 neurotrophin receptor (p75NTR) is known as an efficient marker for the prospective isolation of mesenchymal stem cells (MSCs) and neural crest-derived stem cells (NCSCs). To date, there is quite limited information concerning p75NTR-expressing cells in umbilical cord (UC), although UC is known as a rich source of MSCs. We show for the first time the localization, phenotype, and functional properties of p75NTR+ cells in UC.

METHODS

Human UC tissue sections were subjected to immunohistochemistry for MSC markers including p75NTR. Enzymatically isolated umbilical artery (UA) cells containing p75NTR+ cells were assessed for immunophenotype, clonogenic capacity, and differentiation potential. To identify the presence of neural crest-derived cells in the UA, P0-Cre/Floxed-EGFP reporter mouse embryos were used, and immunohistochemical analysis of UC tissue was performed.

RESULTS

Immunohistochemical analysis revealed that p75NTR+ cells were specifically localized to the subendothelial area of the UA and umbilical vein. The p75NTR+ cells co-expressed PDGFRβ, CD90, CD146, and NG2, phenotypic markers of MSCs and pericytes. Isolated UA cells possessed the potential to form neurospheres that further differentiated into neuronal and glial cell lineages. Genetic lineage tracing analysis showed that EGFP+ neural crest-derived cells were detected in the subendothelial area of UA with p75NTR immunoreactivity.

CONCLUSIONS

These results show that UA tissue harbors p75NTR+ pericyte-like cells in the subendothelial area that have the capacity to form neurospheres and the potential for neurogenic differentiation. The lineage tracing data suggests the p75NTR+ cells are putatively derived from the neural crest.

Distinct types of stem cell divisions determine organ regeneration and aging in hair follicles

Hair follicles, mammalian mini-organs that grow hair, miniaturize during aging, leading to hair thinning and loss. Here we report that hair follicle stem cells (HFSCs) lose their regenerative capabilities during aging owing to the adoption of an atypical cell division program. Cell fate tracing and cell division axis analyses revealed that while HFSCs in young mice undergo typical symmetric and asymmetric cell divisions to regenerate hair follicles, upon aging or stress, they adopt an atypical 'stress-responsive' type of asymmetric cell division. This type of division is accompanied by the destabilization of hemidesmosomal protein COL17A1 and cell polarity protein aPKCλ and generates terminally differentiating epidermal cells instead of regenerating the hair follicle niche. With the repetition of these atypical divisions, HFSCs detach from the basal membrane causing their exhaustion, elimination and organ aging. The experimentally induced stabilization of COL17A1 rescued organ homeostasis through aPKCλ stabilization. These results demonstrate that distinct stem cell division programs may govern tissue and organ aging.

Notch1 and Notch2 collaboratively maintain radial glial cells in mouse neurogenesis

During mammalian corticogenesis, Notch signaling is essential to maintain neural stem cells called radial glial cells (RGCs) and the cortical architecture. Because the conventional knockout of either Notch1 or Notch2 causes a neuroepithelial loss prior to neurogenesis, their functional relationship in RGCs remain elusive. Here, we investigated the impacts of single knockout of Notch1 and Notch2 genes, and their conditional double knockout (DKO) on mouse corticogenesis. We demonstrated that Notch1 single knockout affected RGC maintenance in early to mid-neurogenesis whereas Notch2 knockout caused no apparent defect. In contrast, Notch2 plays a role in the RGC maintenance as Notch1 does at the late stage. Notch1 and Notch2 DKO resulted in the complete loss of RGCs, suggesting their cooperative function. We found that Notch activity in RGCs depends on the Notch gene dosage irrespective of Notch1 or Notch2 at late neurogenic stage, and that Notch1 and Notch2 have a similar activity, most likely due to a drastic increase in Notch2 transcription. Our results revealed that Notch1 has an essential role in establishing the RGC pool during the early stage, whereas Notch1 and Notch2 subsequently exhibit a comparable function for RGC maintenance and neurogenesis in the late neurogenic period in the mouse telencephalon.

Blood and lymphatic systems are segregated by the FLCN tumor suppressor

Blood and lymphatic vessels structurally bear a strong resemblance but never share a lumen, thus maintaining their distinct functions. Although lymphatic vessels initially arise from embryonic veins, the molecular mechanism that maintains separation of these two systems has not been elucidated. Here, we show that genetic deficiency of Folliculin, a tumor suppressor, leads to misconnection of blood and lymphatic vessels in mice and humans. Absence of Folliculin results in the appearance of lymphatic-biased venous endothelial cells caused by ectopic expression of Prox1, a master transcription factor for lymphatic specification. Mechanistically, this phenotype is ascribed to nuclear translocation of the basic helix-loop-helix transcription factor Transcription Factor E3 (TFE3), binding to a regulatory element of Prox1, thereby enhancing its venous expression. Overall, these data demonstrate that Folliculin acts as a gatekeeper that maintains separation of blood and lymphatic vessels by limiting the plasticity of committed endothelial cells.

Blood and lymphatic vessels bear a strong resemblance but do not share a lumen, thus maintaining their distinct functions. Here, the authors describe that Folliculin, a tumor suppressor, prevents the fusion of these vessels during development by limiting the plasticity of venous and lymphatic endothelial cells.

RasV12 Expression in Microglia Initiates Retinal Inflammation and Induces Photoreceptor Degeneration

Purpose

The role of activated retinal microglia in driving retinal degeneration has been implicated in a number of in vivo disease models. Here, we investigated the primary consequences of microglial activation by the specific expression of constitutively active Ras in microglia in a transgenic mouse model before the onset of any degenerative changes in the retina.

Methods

The double transgenic lines CAG-LSL-RasV12-IRES-EGFP; Cx3cr1CreER/+ (Cx3cr1-RasV12 mice) and CAG-LSL-EGFP; Cx3cr1CreER_+ (control mice) were generated. The expression of RasV12 was induced in microglia by tamoxifen administration, and the retinas were examined by immunohistochemistry of frozen sections, RT-qPCR, and live imaging.

Results

RasV12 expression in retinal microglial cells promoted cell proliferation, cytokine expression, and phagocytosis. RasV12-expressing microglia migrated toward the inner and outer layers of the retina. Examination of glial fibrillary acidic protein (GFAP) expression revealed activation of Müller glia in the retina. We also observed loss of the photoreceptors in the outer nuclear layer in close proximity to microglial cells. However, no significant neurodegeneration was detected in the inner nuclear layer (INL) or ganglion cell layer (GCL). The morphology of RasV12-expressing microglia in the GCL and INL retained more ramified features compared with the predominantly-ameboid morphology found in outer retinal microglia.

Conclusions

The expression of RasV12 is sufficient to activate microglia and lead to photoreceptor degeneration. Neurons in the inner side of the retina were not damaged by the RasV12-activated microglia, suggesting that microenvironment cues may modulate the microglial phenotypic features and effects of microglial activation.

Tracing the cellular basis of islet specification in mouse pancreas

Pancreatic islets play an essential role in regulating blood glucose level. Although the molecular pathways underlying islet cell differentiation are beginning to be resolved, the cellular basis of islet morphogenesis and fate allocation remain unclear. By combining unbiased and targeted lineage tracing, we address the events leading to islet formation in the mouse. From the statistical analysis of clones induced at multiple embryonic timepoints, here we show that, during the secondary transition, islet formation involves the aggregation of multiple equipotent endocrine progenitors that transition from a phase of stochastic amplification by cell division into a phase of sublineage restriction and limited islet fission. Together, these results explain quantitatively the heterogeneous size distribution and degree of polyclonality of maturing islets, as well as dispersion of progenitors within and between islets. Further, our results show that, during the secondary transition, α- and β-cells are generated in a contemporary manner. Together, these findings provide insight into the cellular basis of islet development.

The cellular basis of islet morphogenesis and fate allocation remain unclear. Here, the authors use a R26-CreER-R26R-Confetti mouse line to follow quantitatively the clonal dynamics of islet formation showing how, during the secondary transition, islet progenitors amplify through rounds of stochastic cell division before becoming restricted to α and β cell sublineages.

Fibroblasts as a source of self-antigens for central immune tolerance

Fibroblasts are one of the most common but also neglected types of stromal cells, the heterogeneity of which underlies the specific function of tissue microenvironments in development and regeneration. In the thymus, autoreactive T cells are thought to be negatively selected by reference to the self-antigens expressed in medullary epithelial cells, but the contribution of other stromal cells to tolerance induction has been poorly examined. In the present study, we report a PDGFR⁺ gp38⁺ DPP4^- thymic fibroblast subset that is required for T cell tolerance induction. The deletion of the lymphotoxin β-receptor in thymic fibroblasts caused an autoimmune phenotype with decreased expression of tissue-restricted and fibroblast-specific antigens, offering insight into the long-sought target of lymphotoxin signaling in the context of the regulation of autoimmunity. Thus, thymic medullary fibroblasts play an essential role in the establishment of central tolerance by producing a diverse array of self-antigens.

Visualization and isolation of zone-specific murine hepatocytes that maintain distinct cytochrome P450 oxidase expression in primary culture

Parenchymal hepatocytes are responsible for most of the metabolic functions of the liver, but exhibit distinct functional properties depending on their localization within the hepatic lobule. Cytochrome P450 oxidases represent a family of drug-metabolizing enzymes, which are expressed predominantly in hepatocytes localized in the centrilobular area (zone 3). The present study describes a unique transgenic mouse strain that distinguishes zone 3 hepatocytes from periportal zone 1 hepatocytes by the intensity of EGFP fluorescence. Both zone 1 and zone 3 hepatocytes isolated from these mice showed the same zone-specific gene expression patterns as in liver tissue in vivo. Experiments using primary cultures of hepatocytes indicated that a combination of low oxygen concentration and activation of Wnt/β-catenin signaling maintained the expression of zone 3-specific P450 drug-metabolizing enzymes, which was characterized by their susceptibility to acetaminophen-induced mitochondrial dysfunction. These zone-specific hepatocytes provide a useful system in the research area of liver pathophysiology and drug development.

Neural Stem Cells Direct Axon Guidance via Their Radial Fiber Scaffold

Neural stem cells directly or indirectly generate all neurons and macroglial cells and guide migrating neurons by using a palisade-like scaffold made of their radial fibers. Here, we describe an unexpected role for the radial fiber scaffold in directing corticospinal and other axons at the junction between the striatum and globus pallidus. The maintenance of this scaffold, and consequently axon pathfinding, is dependent on the expression of an atypical RHO-GTPase, RND3/RHOE, together with its binding partner ARHGAP35/P190A, a RHO GTPase-activating protein, in the radial glia-like neural stem cells within the ventricular zone of the medial ganglionic eminence. This role is independent of RND3 and ARHGAP35 expression in corticospinal neurons, where they regulate dendritic spine formation, axon elongation, and pontine midline crossing in a FEZF2-dependent manner. The prevalence of neural stem cell scaffolds and their expression of RND3 and ARHGAP35 suggests that these observations might be broadly relevant for axon guidance and neural circuit formation.

Isolation and characterization of neural crest-like progenitor cells in human umbilical cord blood

Introduction

Neural crest (NC)-like stem/progenitor cells provide an attractive cell source for regenerative medicine because of their multipotent property and ease of isolation from adult tissue. Although human umbilical cord blood (HUCB) is known to be a rich source of stem cells, the presence of the NC-like stem/progenitor cells in HUCB remains to be elucidated. In this study, we have isolated NC-like progenitor cells using an antibody to p75 neurotrophin receptor (p75NTR) and examined their phenotype and stem cell function in vitro.

Methods

To confirm whether p75NTR⁺ NC-derived cells are present in cord blood, flow cytometric analysis of cord blood derived from P0-Cre/Floxed-EGFP reporter mouse embryos was performed. Freshly isolated HUCB mononuclear cells was subjected to flow cytometry to detect p75NTR⁺ cells and determined their immunophenotype. HUCB p75NTR⁺ cells were then collected by immunomagnetic separation and their immunophenotype, clonogenic potential, gene expression profile, and multilineage differentiation potential were examined.

Results

NC-derived EGFP⁺ cells co-expressing p75NTR was detected in cord blood of P0-Cre/Floxed-EGFP reporter mice. We found that freshly isolated HUCB mononuclear cells contained 0.23% of p75NTR⁺ cells. Isolated p75NTR⁺ cells from HUCB efficiently formed neurospheres and could differentiate into neuronal and glial cell lineages. The p75NTR⁺ cells expressed a set of NC-associated genes and undifferentiated neural cell marker genes before and after the culture.

Conclusions

These findings revealed that HUCB contained the p75NTR⁺ NC-like progenitor cell population which have the self-renewal capacity and the potential to differentiate into both neuronal and glial cell lineages.

GPR30-Expressing Gastric Chief Cells Do Not Dedifferentiate But Are Eliminated via PDK-Dependent Cell Competition During Development of Metaplasia

BACKGROUND & AIMS

Gastric chief cells, a mature cell type that secretes digestive enzymes, have been proposed to be the origin of metaplasia and cancer through dedifferentiation or transdifferentiation. However, studies supporting this claim have had technical limitations, including issues with the specificity of chief cell markers and the toxicity of drugs used. We therefore sought to identify genes expressed specifically in chief cells and establish a model to trace these cells.

METHODS

We performed transcriptome analysis of Mist1-CreERT-traced cells, with or without chief cell depletion. Gpr30-rtTA mice were generated and crossed to TetO-Cre mice, and lineage tracing was performed after crosses to R26-TdTomato mice. Additional lineage tracing experiments were performed using Mist1-CreERT, Kitl-CreERT, Tff1-Cre, and Tff2-Cre mice crossed to reporter mice. Mice were given high-dose tamoxifen or DMP-777 or were infected with Helicobacter pylori to induce gastric metaplasia. We studied mice that expressed mutant forms of Ras in gastric cells, using TetO-Kras^G12D, LSL-Kras^G12D, and LSL-Hras^G12V mice. We analyzed stomach tissues from GPR30-knockout mice. Mice were given dichloroacetate to inhibit pyruvate dehydrogenase kinase (PDK)-dependent cell competition.

RESULTS

We identified GPR30, the G-protein-coupled form of the estrogen receptor, as a cell-specific marker of chief cells in gastric epithelium of mice. Gpr30-rtTA mice crossed to TetO-Cre;R26-TdTomato mice had specific expression of GPR30 in chief cells, with no expression noted in isthmus stem cells or lineage tracing of glands. Expression of mutant Kras in GPR30⁺ chief cells did not lead to the development of metaplasia or dysplasia but, instead, led to a reduction in labeled numbers of chief cells and a compensatory expansion of neck lineage, which was derived from upper Kitl⁺ clones. Administration of high-dose tamoxifen, DMP-777, or H pylori decreased the number of labeled chief cells. Chief cells were eliminated from epithelia via GPR30- and PDK-dependent cell competition after metaplastic stimuli, whereas loss of GRP30 or inhibition of PDK activity preserved chief cell numbers and attenuated neck lineage cell expansion.

CONCLUSIONS

In tracing studies of mice, we found that most chief cells are lost during metaplasia and therefore are unlikely to contribute to gastric carcinogenesis. Expansion of cells that coexpress neck and chief lineage markers, known as spasmolytic polypeptide-expressing metaplasia, does not occur via dedifferentiation from chief cells but, rather, through a compensatory response from neck progenitors to replace the eliminated chief cells.

GPC1 specific CAR-T cells eradicate established solid tumor without adverse effects and synergize with anti-PD-1 Ab

Current xenogeneic mouse models cannot evaluate on-target off-tumor adverse effect, hindering the development of chimeric antigen receptor (CAR) T cell therapies for solid tumors, due to limited human/mouse cross-reactivity of antibodies used in CAR and sever graft-versus-host disease induced by administered human T cells. We have evaluated safety and antitumor efficacy of CAR-T cells targeting glypican-1 (GPC1) overexpressed in various solid tumors. GPC1-specific human and murine CAR-T cells generated from our original anti-human/mouse GPC1 antibody showed strong antitumor effects in xenogeneic and syngeneic mouse models, respectively. Importantly, the murine CAR-T cells enhanced endogenous T cell responses against a non-GPC1 tumor antigen through the mechanism of antigen-spreading and showed synergistic antitumor effects with anti-PD-1 antibody without any adverse effects in syngeneic models. Our study shows the potential of GPC1 as a CAR-T cell target for solid tumors and the importance of syngeneic and xenogeneic models for evaluating their safety and efficacy.

Neuron-derived VEGF contributes to cortical and hippocampal development independently of VEGFR1/2-mediated neurotrophism

Vascular endothelial growth factor (VEGF) is a potent mitogen critical for angiogenesis and organogenesis. Deletion or inhibition of VEGF during development not only profoundly suppresses vascular outgrowth, but significantly affects the development and function of various organs. In the brain, VEGF is thought to not only promote vascular growth, but also directly act on neurons as a neurotrophic factor by activating VEGF receptors. In the present study, we demonstrated that deletion of VEGF using hGfap-Cre line, which recombines genes specifically in cortical and hippocampal neurons, severely impaired brain organization and vascularization of these regions. The mutant mice had motor deficits, with lethality around the time of weaning. Multiple reporter lines indicated that VEGF was highly expressed in neurons, but that its cognate receptors, VEGFR1 and 2 were exclusive to endothelial cells in the brain. In accordance, mice lacking neuronal VEGFR1 and VEGFR2 did not exhibit neuronal deformities or lethality. Taken together, our data suggest that neuron-derived VEGF contributes to cortical and hippocampal development likely through angiogenesis independently of direct neurotrophic effects mediated by VEGFR1 and 2.

Neural stem cell phenotype of tanycyte-like ependymal cells in the circumventricular organs and central canal of adult mouse brain

Tanycyte is a subtype of ependymal cells which extend long radial processes to brain parenchyma. The present study showed that tanycyte-like ependymal cells in the organum vasculosum of the lamina terminalis, subfornical organ and central canal (CC) expressed neural stem cell (NSC) marker nestin, glial fibrillar acidic protein and sex determining region Y. Proliferation of these tanycyte-like ependymal cells was promoted by continuous intracerebroventricular infusion of fibroblast growth factor-2 and epidermal growth factor. Tanycytes-like ependymal cells in the CC are able to form self-renewing neurospheres and give rise mostly to new astrocytes and oligodendrocytes. Collagenase-induced small medullary hemorrhage increased proliferation of tanycyte-like ependymal cells in the CC. These results demonstrate that these tanycyte-like ependymal cells of the adult mouse brain are NSCs and suggest that they serve as a source for providing new neuronal lineage cells upon brain damage in the medulla oblongata.

Possible application of muscle specific conditional mouse-derived induced pluripotent stem cells for muscle research

The Cre-driver mouse line, which allows for in vivo regulation of target gene(s) in specific cells, is an indispensable tool for recent muscle research. In this study, I aimed to explore new applications of muscle specific Cre-driver mouse line in muscle research. For this purpose, I generated an iPS cells from a myofiber specific conditional mouse with tamoxifen inducible GFP expression, and then I checked whether homologous recombination was induced in the iPS-derived myogenic cells by tamoxifen administration. Fibroblasts were isolated from the tails of Myf6^CE/wt::CAG-EGFP mice, which expressed GFP specifically in Myf6 lineages by tamoxifen injection, and then iPS cells was generated by transfection with a vector based on sendai-virus and containing OSKM genes. Muscle specific conditional mouse-derived iPS cells (mCM-iPSCs) were successfully differentiated to myogenic cells, such as Pax7⁺ muscle progenitors, MyoD⁺ myoblasts, and MHC⁺ myotubes, under myogenic differentiation conditions. Using this model, I examined whether homologous recombination was induced in mCM-iPSC-derived myotubes by 4-hydroxytamoxifen (4OH-TAM) administration. As a result, multinucleated myotubes showed GFP expression, while no GFP signals were detected in both Pax7⁺ muscle progenitor and non-myogenic cells. These results indicated that homologous recombination could be induced in mCM-iPSC–derived myotubes by tamoxifen administration, and that this system operated normally even in reprogrammed cells. Also, I evidenced that GFP reporter was expressed in myoblasts in addition to multinucleated myotubes when tamoxifen-pulse was applied at an early phase of myogenesis. Taken together, Myf6^CE/wt::CAG-EGFP mouse-derived iPS cells reproduced at least in part Myf6 expression during mouse myogenesis. This study demonstrated a novel application of muscle specific conditional mouse in addition to in vivo application, and mCM-iPSCs could also be used in in vitro investigations with muscle specific conditional knock-out mouse.

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iPS cells can be generated from muscle specific conditional mouse line.

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mCM-iPS cells reproduce early muscle development in vitro.

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mCM-iPS cells are available for lineage tracing of Myf6⁺ muscle progenitors.

Metabolic effects of RUBCN/Rubicon deficiency in kidney proximal tubular epithelial cells

Macroautophagy/autophagy is a lysosomal degradation system which plays a protective role against kidney injury. RUBCN/Rubicon (RUN domain and cysteine-rich domain containing, Beclin 1-interacting protein) inhibits the fusion of autophagosomes and lysosomes. However, its physiological role in kidney proximal tubular epithelial cells (PTECs) remains uncertain. In the current study, we analyzed the phenotype of newly generated PTEC-specific rubcn-deficient (KO) mice. Additionally, we investigated the role of RUBCN in lipid metabolism using isolated rubcn-deficient PTECs. Although KO mice exhibited sustained high autophagic flux in PTECs, they were not protected from acute ischemic kidney injury. Unexpectedly, KO mice exhibited hallmark features of metabolic syndrome accompanied by expanded lysosomes containing multi-layered phospholipids in PTECs. RUBCN deficiency in cultured PTECs promoted the mobilization of phospholipids from cellular membranes to lysosomes via enhanced autophagy. Treatment of KO PTECs with oleic acid accelerated fatty acids transfer to mitochondria. Furthermore, KO PTECs promoted massive triglyceride accumulation in hepatocytes (BNL-CL2 cells) co-cultured in transwell, suggesting accelerated fatty acids efflux from the PTECs contributes to the metabolic syndrome in KO mice. This study shows that sustained high autophagic flux by RUBCN deficiency in PTECs leads to metabolic syndrome concomitantly with an accelerated mobilization of phospholipids from cellular membranes to lysosomes. Abbreviations: ABC: ATP binding cassette; ACADM: acyl-CoA dehydrogenase medium chain; ACTB: actin, beta; ATG: autophagy related; AUC: area under the curve; Baf: bafilomycin A₁; BAT: brown adipose tissue; BODIPY: boron-dipyrromethene; BSA: bovine serum albumin; BW: body weight; CAT: chloramphenicol acetyltransferase; CM: complete medium; CPT1A: carnitine palmitoyltransferase 1a, liver; CQ: chloroquine; CTRL: control; EGFP: enhanced green fluorescent protein; CTSD: cathepsin D; EAT: epididymal adipose tissue; EGFR: epidermal growth factor receptor; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; FA: fatty acid; FBS: fetal bovine serum; GTT: glucose tolerance test; HE: hematoxylin and eosin; HFD: high-fat diet; I/R: ischemia-reperfusion; ITT: insulin tolerance test; KAP: kidney androgen regulated protein; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LD: lipid droplet; LRP2: low density lipoprotein receptor related protein 2; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MAT: mesenteric adipose tissue; MS: mass spectrometry; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; NDRG1: N-myc downstream regulated 1; NDUFB5: NADH:ubiquinone oxidoreductase subunit B5; NEFA: non-esterified fatty acid; OA: oleic acid; OCT: optimal cutting temperature; ORO: Oil Red O; PAS: Periodic-acid Schiff; PFA: paraformaldehyde; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PPARA: peroxisome proliferator activated receptor alpha; PPARGC1A: PPARG coactivator 1 alpha; PTEC: proximal tubular epithelial cell; RAB7A: RAB7A, member RAS oncogene family; RPS6: ribosomal protein S6; RPS6KB1: ribosomal protein S6 kinase B1; RT: reverse transcription; RUBCN: rubicon autophagy regulator; SAT: subcutaneous adipose tissue; SFC: supercritical fluid chromatography; SQSTM1: sequestosome 1; SREBF1: sterol regulatory element binding transcription factor 1; SV-40: simian virus-40; TFEB: transcription factor EB; TG: triglyceride; TS: tissue specific; TUNEL: terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling; UN: urea nitrogen; UQCRB: ubiquinol-cytochrome c reductase binding protein; UVRAG: UV radiation resistance associated; VPS: vacuolar protein sorting; WAT: white adipose tissue.

Efficient tissue-type specific expression of target genes in a tetracycline-controlled manner from the ubiquitously active Eef1a1 locus

Using an efficient gene targeting approach, we developed a novel mouse line that expresses the tetracycline-controlled transactivator (tTA) from the constitutively active Eef1a1 locus in a Cre recombinase-inducible manner. The temporally and spatially controlled expression of the EF1-LSL-tTA knockin and activation of tTA-driven responder transgenes was tested using four transgenic lines that express Cre under tissue-specific promoters of the pancreas, mammary gland and other secretory tissues, as well as an interferon-inducible promoter. In all models, the endogenous Eef1a1 promoter facilitated a cell-type-specific activation of target genes at high levels without exogenous enhancer elements. The applicability of the EF1-LSL-tTA strain for biological experiments was tested in two studies related to mammary gland development and tumorigenesis. First, we validated the crucial role of active STAT5 as a survival factor for functionally differentiated epithelial cells by expressing a hyperactive STAT5 mutant in the mammary gland during postlactational remodeling. In a second experiment, we assessed the ability of the EF1-tTA to initiate tumor formation through upregulation of mutant KRAS. The collective results show that the EF1-LSL-tTA knockin line is a versatile genetic tool that can be applied to constitutively express transgenes in specific cell types to examine their biological functions at defined developmental stages.