A global double-fluorescent Cre reporter mouse

The age of bone marrow dictates the clonality of smooth muscle-derived cells in atherosclerotic plaques

Aging is the predominant risk factor for atherosclerosis, the leading cause of death. Rare smooth muscle cell (SMC) progenitors clonally expand giving rise to up to ~70% of atherosclerotic plaque cells; however, the effect of age on SMC clonality is not known. Our results indicate that aged bone marrow (BM)-derived cells non-cell autonomously induce SMC polyclonality and worsen atherosclerosis. Indeed, in myeloid cells from aged mice and humans, TET2 levels are reduced which epigenetically silences integrin β3 resulting in increased tumor necrosis factor [TNF]-α signaling. TNFα signals through TNF receptor 1 on SMCs to promote proliferation and induces recruitment and expansion of multiple SMC progenitors into the atherosclerotic plaque. Notably, integrin β3 overexpression in aged BM preserves dominance of the lineage of a single SMC progenitor and attenuates plaque burden. Our results demonstrate a molecular mechanism of aged macrophage-induced SMC polyclonality and atherogenesis and suggest novel therapeutic strategies.

Lineage Tracing of Spermatogonial Stem Cells Within the Male Germline

Spermatogonial stem cells (SSCs) are the fundamental units from which continuous spermatogenesis arises. Although our knowledge regarding the basic properties of SSCs has grown, driven primarily through the advancement of techniques and technologies to study SSCs, the mechanisms controlling their fate remain largely unknown. Among the modern strategies to evaluate SSCs, lineage tracing is among the few established approaches that allow for functional assessment of stem cell capacity. As a result, lineage tracing continues to forge new discoveries underlying the basic attributes of SSCs as well as the molecular factors that govern SSC function. Traditional approaches to lineage tracing with dyes or radioactive labels suffer from progressive loss after successive cell divisions or unintentional label transfer to neighboring cells. To address these limitations, genetic approaches primarily leveraging transgenic technologies have prevailed as the preferred avenue for modern lineage tracing. This chapter will discuss current protocols for effective genetic lineage tracing and address applications of this technology, considerations when designing lineage tracing experiments, and the methods involved in utilizing lineage tracing to study SSCs and other cell populations.

Development of an in-vitro high-throughput screening system to identify modulators of genitalia development

Sexually dimorphic outgrowth and differentiation of the embryonic genital tubercles (GTs) give rise to the penis in males and the clitoris in females. Defects in androgen production or in response to androgen signaling can lead to various congenital penile anomalies in both mice and humans. Due to lack of a high-throughput screening system, identification of crucial regulators of GT sexual differentiation has been slow. To overcome this research barrier, we isolated embryonic GT mesenchymal (GTme) cells to model genitalia growth and differentiation in vitro. Using either a mechanical or fluorescence-activated cell sorting-assisted purification method, GTme cells were isolated and assayed for their proliferation using a microscopy and image analysis system, on a single cell level over time. Male and female GTme cells inherently exhibit different cellular dynamics, consistent with their in-vivo behaviors. This system allows for the rapid quantitative analyses of numerous drug treatments, and enables the discovery of potential genetic modulators of GT morphogenesis on a large scale. Using this system, we completed a 438-compound library screen and identified 82 kinase inhibitor hits. In mice, in-utero exposure to one such candidate kinase inhibitor, Cediranib, resulted in embryos with severe genitalia defects, especially in males. Gene silencing by RNAi was optimized in this system, laying the foundation for future larger-scale genetic screenings. These findings demonstrate the power of this novel high-throughput system to rapidly and successfully identify modulators of genitalia growth and differentiation, expanding the toolbox for the study of functional genomics and environmental factors.

Intravital Microscopy for Hematopoietic Studies

The bone marrow (BM) is home to numerous cell types arising from hematopoietic stem cells (HSCs) and nonhematopoietic mesenchymal stem cells, as well as stromal cell components. Together they form the BM microenvironment or HSC niche. HSCs critically depend on signaling from these niches to function and survive in the long term. Significant advances in imaging technologies over the past decade have permitted the study of the BM microenvironment in mice, particularly with the development of intravital microscopy (IVM), which provides a powerful method to study these cells in vivo and in real time. Still, there is a lot to be learnt about the interactions of individual HSCs with their environment - at steady state and under various stresses - and whether specific niches exist for distinct developing hematopoietic lineages. Here, we describe our protocol and techniques used to visualize transplanted HSCs in the mouse calvarium, using combined confocal and two-photon IVM.

Live-Imaging Analysis of Epithelial Zippering During Mouse Neural Tube Closure

Zippering is a phenomenon of tissue morphogenesis whereby fusion between opposing epithelia progresses unidirectionally over significant distances, similar to the travel of a zip fastener, to ultimately ensure closure of an opening. A comparable process can be observed during Drosophila dorsal closure and mammalian wound healing, while zippering is employed by numerous organs such as the optic fissure, palatal shelves, tracheoesophageal foregut, and presumptive genitalia to mediate tissue sealing during normal embryonic development. Particularly striking is zippering propagation during neural tube morphogenesis, where the fusion point travels extensively along the embryonic axis to ensure closure of the neural tube. Advances in time-lapse microscopy and culture conditions have opened the opportunity for successful imaging of whole-mouse embryo development over time, providing insights into the precise cellular behavior underlying zippering propagation. Studies in mouse and the ascidian Ciona have revealed the fine-tuned cell shape changes and junction remodeling which occur at the site of zippering during neural tube morphogenesis. Here, we describe a step-by-step method for imaging at single-cell resolution the process of zippering and tissue remodeling which occurs during closure of the spinal neural tube in mouse. We also provide instructions and suggestions for quantitative morphometric analysis of cell behavior during zippering progression. This procedure can be further combined with genetic mutant models (e.g., knockouts), offering the possibility of studying the dynamics of tissue fusion and zippering propagation, which underlie a wide range of open neural tube defects.

Endothelial Caspase-8 prevents fatal necroptotic hemorrhage caused by commensal bacteria

Caspase-8 transduces signals from death receptor ligands, such as tumor necrosis factor, to drive potent responses including inflammation, cell proliferation or cell death. This is a developmentally essential function because in utero deletion of endothelial Caspase-8 causes systemic circulatory collapse during embryogenesis. Whether endothelial Caspase-8 is also required for cardiovascular patency during adulthood was unknown. To address this question, we used an inducible Cre recombinase system to delete endothelial Casp8 in 6-week-old conditionally gene-targeted mice. Extensive whole body vascular gene targeting was confirmed, yet the dominant phenotype was fatal hemorrhagic lesions exclusively within the small intestine. The emergence of these intestinal lesions was not a maladaptive immune response to endothelial Caspase-8-deficiency, but instead relied upon aberrant Toll-like receptor sensing of microbial commensals and tumor necrosis factor receptor signaling. This lethal phenotype was prevented in compound mutant mice that lacked the necroptotic cell death effector, MLKL. Thus, distinct from its systemic role during embryogenesis, our data show that dysregulated microbial- and death receptor-signaling uniquely culminate in the adult mouse small intestine to unleash MLKL-dependent necroptotic hemorrhage after loss of endothelial Caspase-8. These data support a critical role for Caspase-8 in preserving gut vascular integrity in the face of microbial commensals.

A tamoxifen-inducible Cre knock-in mouse for lens-specific gene manipulation

Mouse models are valuable tools in studying lens biology and biochemistry, and the Cre-loxP system is the most used technology for gene targeting in the lens. However, numerous genes are indispensable in lens development. The conventional knockout method either prevents lens formation or causes simultaneous cataract formation, hindering the studies of their roles in lens structure, growth, metabolism, and cataractogenesis during lens aging. An inducible Cre-loxP mouse line is an excellent way to achieve such a purpose. We established a lens-specific Cre ERT2 knock-in mouse (LCEK), an inducible mouse model for lens-specific gene targeting in a spatiotemporal manner. LCEK mice were created by in-frame infusion of a P2A-CreERT2 at the C-terminus of the last coding exon of the gene alpha A crystallin (Cryaa). LCEK mice express tamoxifen-inducible Cre recombinase uniquely in the lens. Through ROSAmT/mG and two endogenous genes (Gclc and Rbpj) targeting, we found no Cre recombinase leakage in the lens epithelium, but 50-80% leakage was observed in the lens cortex and nucleus. Administration of tamoxifen almost completely abolished target gene expression in both lens epithelium and cortex but only mildly enhanced gene deletion in the lens nucleus. Notably, no overt leakage of Cre activity was detected in developing LCEK lens when bred with mice carrying loxP floxed genes that are essential for lens development. This newly generated LCEK line will be a powerful tool to target genes in the lens for gene functions study in lens aging, posterior capsule opacification (PCO), and other areas requiring precision gene targeting.

Tbc1d10c is a selective, constitutive suppressor of the CD8 T-cell anti-tumor response

Cancer immunotherapy approaches target signaling pathways that are highly synonymous between CD4 and CD8 T-cell subsets and, therefore, often stimulate nonspecific lymphocyte activation, resulting in cytotoxicity to otherwise healthy tissue. The goal of our study was to identify intrinsic modulators of basic T lymphocyte activation pathways that could discriminately bolster CD8 anti-tumor effector responses. Using a Tbc1d10c null mouse, we observed marked resistance to a range of tumor types conferred by Tbc1d10c deficiency. Moreover, tumor-bearing Tbc1d10c null mice receiving PD-1 or CTLA-4 monotherapy exhibited a 33% or 90% cure rate, respectively. While Tbc1d10c was not expressed in solid tumor cells, Tbc1d10c disruption selectively augmented CD8 T-cell activation and cytotoxic effector responses and adoptive transfer of CD8 T cells alone was sufficient to recapitulate Tbc1d10c null tumor resistance. Mechanistically, Tbc1d10c suppressed CD8 T-cell activation and anti-tumor function by intersecting canonical NF-κB pathway activation via regulation of Map3k3-mediated IKKβ phosphorylation. Strikingly, none of these cellular or molecular perturbations in the NF-κB pathway were featured in Tbc1d10c null CD4 T cells. Our findings identify a Tbc1d10c-Map3k3-NF-κB signaling axis as a viable therapeutic target to promote CD8 T-cell anti-tumor immunity while circumventing CD4 T cell-associated cytotoxicity and NF-κB activation in tumor cells.

Dissecting the fate of Foxl2-expressing cells in fetal ovary using lineage tracing and single-cell transcriptomics

Gonad somatic cells acquire sex-specific fates during sex determination. In XX gonad, a subset of somatic cells expresses Foxl2 after sex determination which is considered the progenitor of granulosa cells. However, whether these cells also contribute to other cell types at later developmental stages is unknown. In the present study, the cell fate of Foxl2-expressing cells in fetal ovaries was analyzed by lineage tracing and single-cell transcriptomics. We found that Foxl2-expressing cells gave rise to three cell types at later developmental stages, including granulosa cells, theca-interstitial cells, and stromal cells. Series single-cell RNA sequencing revealed FOXL2-positive cells were divided into two clusters at P0. One group further differentiated into granulosa cells and Theca-G (Theca-interstitial cells derived from granulosa) at P14. Another group was classified as stromal cell lineage, then a small portion of them further differentiated into 3β-HSD-positive Theca-S (Theca-interstitial cells derived from stroma). Cyp17a1 was expressed in Theca-S, but not in Theca-G. This study demonstrated that Folx2-expressing cells in XX gonad after sex determination are multipotent and theca-interstitial cells are derived from different progenitors. Our data provided an important resource, at single-cell resolution, for a better understanding of somatic cell differentiation in ovary development.

Hepatocyte-derived GDF15 suppresses feeding and improves insulin sensitivity in obese mice

Growth differentiation factor 15 (GDF15) is a stress-induced secreted protein whose circulating levels are increased in the context of obesity. Recombinant GDF15 reduces body weight and improves glycemia in obese models, which is largely attributed to the central action of GDF15 to suppress feeding and reduce body weight. Despite these advances in knowledge, the tissue-specific sites of GDF15 production during obesity are unknown, and the effects of modulating circulating GDF15 levels on insulin sensitivity have not been evaluated directly. Here, we demonstrate that hepatocyte Gdf15 expression is sufficient for changes in circulating levels of GDF15 during obesity and that restoring Gdf15 expression specifically in hepatocytes of Gdf15 knockout mice results in marked improvements in hyperinsulinemia, hepatic insulin sensitivity, and to a lesser extent peripheral insulin sensitivity. These data support that liver hepatocytes are the primary source of circulating GDF15 in obesity.

Kidney collecting duct cells make vasopressin in response to NaCl-induced hypertonicity

Vasopressin has traditionally been thought to be produced by the neurohypophyseal system and then released into the circulation where it regulates water homeostasis. The questions of whether vasopressin could be produced outside of the brain and if the kidney could be a source of vasopressin are raised by the syndrome of inappropriate antidiuretic hormone secretion (vasopressin). We found that mouse and human kidneys expressed vasopressin mRNA. Using an antibody that detects preprovasopressin, we found that immunoreactive preprovasopressin protein was found in mouse and human kidneys. Moreover, we found that murine collecting duct cells made biologically active vasopressin, which increased in response to NaCl-mediated hypertonicity, and that water restriction increased the abundance of kidney-derived vasopressin mRNA and protein expression in mouse kidneys. Thus, we provide evidence of biologically active production of kidney-derived vasopressin in kidney tubular epithelial cells.

Loss of SUMO-specific protease 2 causes isolated glucocorticoid deficiency by blocking adrenal cortex zonal transdifferentiation in mice

SUMOylation is a dynamic posttranslational modification, that provides fine-tuning of protein function involved in the cellular response to stress, differentiation, and tissue development. In the adrenal cortex, an emblematic endocrine organ that mediates adaptation to physiological demands, the SUMOylation gradient is inversely correlated with the gradient of cellular differentiation raising important questions about its role in functional zonation and the response to stress. Considering that SUMO-specific protease 2 (SENP2), a deSUMOylating enzyme, is upregulated by Adrenocorticotropic Hormone (ACTH)/cAMP-dependent Protein Kinase (PKA) signalling within the zona fasciculata, we generated mice with adrenal-specific Senp2 loss to address these questions. Disruption of SENP2 activity in steroidogenic cells leads to specific hypoplasia of the zona fasciculata, a blunted reponse to ACTH and isolated glucocorticoid deficiency. Mechanistically, overSUMOylation resulting from SENP2 loss shifts the balance between ACTH/PKA and WNT/β-catenin signalling leading to repression of PKA activity and ectopic activation of β-catenin. At the cellular level, this blocks transdifferentiation of β-catenin-positive zona glomerulosa cells into fasciculata cells and sensitises them to premature apoptosis. Our findings indicate that the SUMO pathway is critical for adrenal homeostasis and stress responsiveness.

SOX2 is essential for astrocyte maturation and its deletion leads to hyperactive behavior in mice

Children with SOX2 deficiency develop ocular disorders and extra-ocular CNS anomalies. Animal data show that SOX2 is essential for retinal and neural stem cell development. In the CNS parenchyma, SOX2 is primarily expressed in astroglial and oligodendroglial cells. Here, we report a crucial role of astroglial SOX2 in postnatal brain development. Astroglial Sox2-deficient mice develop hyperactivity in locomotion and increased neuronal excitability in the corticostriatal circuit. Sox2 deficiency inhibits postnatal astrocyte maturation molecularly, morphologically, and electrophysiologically without affecting astroglia proliferation. Mechanistically, SOX2 directly binds to a cohort of astrocytic signature and functional genes, the expression of which is significantly reduced in Sox2-deficient CNS and astrocytes. Consistently, Sox2 deficiency remarkably reduces glutamate transporter expression and compromised astrocyte function of glutamate uptake. Our study provides insights into the cellular mechanisms underlying brain defects in children with SOX2 mutations and suggests a link of astrocyte SOX2 with extra-ocular abnormalities in SOX2-mutant subjects.

Langerhans cells are essential components of the angiogenic niche during murine skin repair

Angiogenesis, the growth of new blood vessels from pre-existing vessels, occurs during development, injury repair, and tumorigenesis to deliver oxygen, immune cells, and nutrients to tissues. Defects in angiogenesis occur in cardiovascular and inflammatory diseases, and chronic, non-healing wounds, yet treatment options are limited. Here, we provide a map of the early angiogenic niche by analyzing single-cell RNA sequencing of mouse skin wound healing. Our data implicate Langerhans cells (LCs), phagocytic, skin-resident immune cells, in driving angiogenesis during skin repair. Using lineage-driven reportersw, three-dimensional (3D) microscopy, and mouse genetics, we show that LCs are situated at the endothelial cell leading edge in mouse skin wounds and are necessary for angiogenesis during repair. These data provide additional future avenues for the control of angiogenesis to treat disease and chronic wounds and extend the function of LCs beyond their canonical role in antigen presentation and T cell immunity.

TRRAP-mediated acetylation on Sp1 regulates adult neurogenesis

The adult hippocampal neurogenesis plays a vital role in the function of the central nervous system (CNS), including memory consolidation, cognitive flexibility, emotional function, and social behavior. The deficiency of adult neural stem cells (aNSCs) in maintaining the quiescence and entering cell cycle, self-renewal and differentiation capacity is detrimental to the functional integrity of neurons and cognition of the adult brain. Histone acetyltransferase (HAT) and histone deacetylase (HDAC) have been shown to modulate brain functionality and are important for embryonic neurogenesis via regulation of gene transcription. We showed previously that Trrap, an adapter for several HAT complexes, is required for Sp1 transcriptional control of the microtubule dynamics in neuronal cells. Here, we find that Trrap deletion compromises self-renewal and differentiation of aNSCs in mice and in cultures. We find that the acetylation status of lysine residues K16, K19, K703 and K639 all fail to overcome Trrap-deficiency-incurred instability of Sp1, indicating a scaffold role of Trrap. Interestingly, the deacetylation of Sp1 at K639 and K703 greatly increases Sp1 binding to the promoter of target genes, which antagonizes Trrap binding, and thereby elevates Sp1 activity. However, only deacetylated K639 is refractory to Trrap deficiency and corrects the differentiation defects of Trrap-deleted aNSCs. We demonstrate that the acetylation pattern at K639 by HATs dictates the role of Sp1 in the regulation of adult neurogenesis.

Embryogenic stem cell-derived intestinal crypt fission directs de novo crypt genesis

Intestinal epithelial replenishment is fueled by continuously dividing intestinal stem cells (ISCs) resident at the crypt niche. However, the cell type(s) enabling replenishment upon damage and subsequent loss of whole crypts remain largely unclear. Using Set domain-containing protein 4 (Setd4), we identify a small population with reserve stem cell characteristics in the mouse intestine. Upon irradiation-induced injury, Setd4-expressing (Setd4⁺) cells survive radiation exposure and then activate to produce Sca-1-expressing cell types to restore the epithelial wall and regenerate crypts de novo via crypt fission. Setd4⁺ cells are confirmed to originate from the early fetal period, subsequently contributing to the development of embryonic gut and the establishment of postnatal crypts. Setd4⁺ cells are therefore represented as both originators and key regenerators of the intestine.

Efficient simultaneous double DNA knock-in in murine embryonic stem cells by CRISPR/Cas9 ribonucleoprotein-mediated circular plasmid targeting for generating gene-manipulated mice

Gene targeting of embryonic stem (ES) cells followed by chimera production has been conventionally used for developing gene-manipulated mice. Although direct knock-in (KI) using murine zygote via CRISPR/Cas9-mediated genome editing has been reported, ES cell targeting still has merits, e.g., high throughput work can be performed in vitro. In this study, we first compared the KI efficiency of mouse ES cells with CRISPR/Cas9 expression vector and ribonucleoprotein (RNP), and confirmed that KI efficiency was significantly increased by using RNP. Using CRISPR/Cas9 RNP and circular plasmid with homologous arms as a targeting vector, knock-in within ES cell clones could be obtained efficiently without drug selection, thus potentially shortening the vector construction or cell culture period. Moreover, by incorporating a drug-resistant cassette into the targeting vectors, double DNA KI can be simultaneously achieved at high efficiency by a single electroporation. This technique will help to facilitate the production of genetically modified mouse models that are fundamental for exploring topics related to human and mammalian biology.

Case report: Mafb promoter activity may define the alveolar macrophage dichotomy

Cre-LoxP system has been widely used to induce recombination of floxed genes of interest. Currently available macrophage promoter-specific Cre recombinase mice strains have various limitations that warrants the testing of additional Cre strains. V-maf musculoaponeurotic fibrosarcoma oncogene family, protein b -Cre (Mafb-Cre) mice label macrophages in most organs such as spleen, small intestine, lung, bone marrow, and peritoneal cavity. However, whether Mafb-Cre recombinase targets the gene recombination in alveolar macrophage remains untested. Here, we utilized Mafb^Cre/WTR26^mTmG/WT strain that expresses mTOM protein in all the cells of mouse body except for those that express Mafb-Cre-regulated mEGFP. We performed fluorescent microscopy and flow cytometry to analyze mTOM and mEGFP expression in alveolar macrophages from Mafb^Cre/WTR26^mTmG/WT mice. Our analyses revealed that the Mafb-Cre is active in only ~40% of the alveolar macrophages in an age-independent manner. While Mafb- (mTOM+/mEGFP-) and Mafb+ (mEGFP+) alveolar macrophages exhibit comparable expression of CD11b and CD11c surface markers, the surface expression of MHCII is elevated in the Mafb+ (mEGFP+) macrophages. The bone marrow-derived macrophages from Mafb^Cre/WTR26^mTmG/WT mice are highly amenable to Cre-LoxP recombination in vitro. The bone marrow depletion and reconstitution experiment revealed that ~98% of alveolar macrophages from Mafb^Cre/WTR26^mTmG/WT → WT chimera are amenable to the Mafb-Cre-mediated recombination. Finally, the Th2 stimulation and ozone exposure to the Mafb^Cre/WTR26^mTmG/WT mice promote the Mafb-Cre-mediated recombination in alveolar macrophages. In conclusion, while the Mafb-/Mafb+ dichotomy thwarts the use of Mafb-Cre for the induction of floxed alleles in the entire alveolar macrophage population, this strain provides a unique tool to induce gene deletion in alveolar macrophages that encounter Th2 microenvironment in the lung airspaces.

STAT3 suppression and β-cell ablation enhance α-to-β reprogramming mediated by Pdx1

As diabetes results from the absolute or relative deficiency of insulin secretion from pancreatic β cells, possible methods to efficiently generate surrogate β cells have attracted a lot of efforts. To date, insulin-producing cells have been generated from various differentiated cell types in the pancreas, such as acinar cells and α cells, by inducing defined transcription factors, such as PDX1 and MAFA, yet it is still challenging as to how surrogate β cells can be efficiently generated for establishing future regenerative therapies for diabetes. In this study, we demonstrated that the exogenous expression of PDX1 activated STAT3 in α cells in vitro, and STAT3-null PDX1-expressing α cells in vivo resulted in efficient induction of α-to-β reprogramming, accompanied by the emergence of α-cell-derived insulin-producing cells with silenced glucagon expression. Whereas β-cell ablation by alloxan administration significantly increased the number of α-cell-derived insulin-producing cells by PDX1, STAT3 suppression resulted in no further increase in β-cell neogenesis after β-cell ablation. Thus, STAT3 modulation and β-cell ablation nonadditively enhance α-to-β reprogramming induced by PDX1, which may lead to the establishment of cell therapies for curing diabetes.

TBX2 specifies and maintains inner hair and supporting cell fate in the Organ of Corti

The auditory function of the mammalian cochlea relies on two types of mechanosensory hair cells and various non-sensory supporting cells. Recent studies identified the transcription factors INSM1 and IKZF2 as regulators of outer hair cell (OHC) fate. However, the transcriptional regulation of the differentiation of inner hair cells (IHCs) and their associated inner supporting cells (ISCs) has remained enigmatic. Here, we show that the expression of the transcription factor TBX2 is restricted to IHCs and ISCs from the onset of differentiation until adulthood and examine its function using conditional deletion and misexpression approaches in the mouse. We demonstrate that TBX2 acts in prosensory progenitors as a patterning factor by specifying the inner compartment of the sensory epithelium that subsequently gives rise to IHCs and ISCs. Hair cell-specific inactivation or misexpression causes transdifferentiation of hair cells indicating a cell-autonomous function of TBX2 in inducing and maintaining IHC fate.

PIK3CA gain-of-function mutation in adipose tissue induces metabolic reprogramming with Warburg-like effect and severe endocrine disruption

PIK3CA-related overgrowth syndrome (PROS) is a genetic disorder caused by somatic mosaic gain-of-function mutations of PIK3CA. Clinical presentation of patients is diverse and associated with endocrine disruption. Adipose tissue is frequently involved, but its role in disease development and progression has not been elucidated. Here, we created a mouse model of PIK3CA-related adipose tissue overgrowth that recapitulates patient phenotype. We demonstrate that PIK3CA mutation leads to GLUT4 membrane accumulation with a negative feedback loop on insulin secretion, a burst of liver IGFBP1 synthesis with IGF-1 sequestration, and low circulating levels. Mouse phenotype was mainly driven through AKT2. We also observed that PIK3CA mutation induces metabolic reprogramming with Warburg-like effect and protein and lipid synthesis, hallmarks of cancer cells, in vitro, in vivo, and in patients. We lastly show that alpelisib is efficient at preventing and improving PIK3CA-adipose tissue overgrowth and reversing metabolomic anomalies in both animal models and patients.

Induction of whole-body gene deletion via R26-regulated tamoxifen-inducible Cre recombinase activity

Germline deletion of certain genes causes embryonic lethality, therefore, understanding the effect of deletion of such genes on mammalian pathophysiology remains challenging. Tamoxifen (TAM)-inducible Cre recombinase is widely used for tissue-specific and temporal induction of gene deletion in mice. However, the tamoxifen treatment regimen for the generation of whole-body deletion of a gene is not yet fully standardized for the majority of organs/tissues. Accordingly, we employed GtROSA26 (R26) promoter-regulated Cre and a reporter gene expression strategy. GtROSA26 (R26) is an ubiquitous promoter and mice carrying the R26^Cre-ERT2 transgene express Cre-ERT2 in all the cells. Similarly, mice carrying the R26^mTOM-mEGFP transgene express mTOM (membrane-targeted tdTomato), in the absence of Cre or mEGFP (membrane-targeted enhanced green fluorescent protein), in the presence of Cre, in all the cells. The progeny carrying one allele of both transgenes were subjected to different TAM regimens, i.e., IP injections (4 injections; 1.35 mg/injection), diet (400 mg TAM-citrate/kg food), or diet (400 mg TAM-citrate/kg food) combined with either TAM-oral gavage (4 gavages; 1.35 mg/gavage) or TAM IP injections (4 injections; 1.35 mg/injection) for 2-weeks beginning at postnatal day (PND) 21 and the extent of Cre recombination in different tissues was determined at PND35. Tamoxifen administration resulted in a transient loss of body weight in all the treatment regimens with a relatively slower rate of weight gain in the TAM-diet plus TAM-oral gavage group compared to other groups. While the efficiency of Cre recombination, as determined by the expression of mEGFP protein, was variable among tissues, major tissues such as the liver, heart, lungs, spleen, and thymus-showed almost complete recombination. No recombination was evident in any of the tissues examined from the control mice. In general, the efficiency of Cre recombination was better with a combined regimen of TAM-diet with either TAM-injections or TAM-oral gavage compared to TAM-diet alone or TAM-injections alone. Our results demonstrate that a combination of TAM-diet with either TAM-injections or TAM-oral gavage can be employed for the efficient deletion of a gene in the whole body. Our findings will provide technical expertise to the researchers employing TAM-inducible Cre for the deletion of floxed genes in varied tissues.

In situ cell-type-specific cell-surface proteomic profiling in mice

Cell-surface proteins (CSPs) mediate intercellular communication throughout the lives of multicellular organisms. However, there are no generalizable methods for quantitative CSP profiling in specific cell types in vertebrate tissues. Here, we present in situ cell-surface proteome extraction by extracellular labeling (iPEEL), a proximity labeling method in mice that enables spatiotemporally precise labeling of cell-surface proteomes in a cell-type-specific environment in native tissues for discovery proteomics. Applying iPEEL to developing and mature cerebellar Purkinje cells revealed differential enrichment in CSPs with post-translational protein processing and synaptic functions in the developing and mature cell-surface proteomes, respectively. A proteome-instructed in vivo loss-of-function screen identified a critical, multifaceted role for Armh4 in Purkinje cell dendrite morphogenesis. Armh4 overexpression also disrupts dendrite morphogenesis; this effect requires its conserved cytoplasmic domain and is augmented by disrupting its endocytosis. Our results highlight the utility of CSP profiling in native mammalian tissues for identifying regulators of cell-surface signaling.

Chemical induction of gut β-like-cells by combined FoxO1/Notch inhibition as a glucose-lowering treatment for diabetes

OBJECTIVE

Lifelong insulin replacement remains the mainstay of type 1 diabetes treatment. Genetic FoxO1 ablation promotes enteroendocrine cell (EECs) conversion into glucose-responsive β-like cells. Here, we tested whether chemical FoxO1 inhibitors can generate β-like gut cells.

METHODS

We used Ngn3-or Villin-driven FoxO1 ablation to capture the distinctive developmental effects of FoxO1 on EEC pool. We combined FoxO1 ablation with Notch inhibition to enhance the expansion of EEC pool. We tested the ability of an orally available small molecule of FoxO1 inhibitor, Cpd10, to phenocopy genetic ablation of FoxO1. We evaluated the therapeutic impact of genetic ablation or chemical inhibition of FoxO1 on insulin-deficient diabetes in Ins2^Akita/+ mice.

RESULTS

Pan-intestinal epithelial FoxO1 ablation expanded the EEC pool, induced β-like cells, and improved glucose tolerance in Ins2^Akita/+ mice. This genetic effect was phenocopied by Cpd10. Cpd10 induced β-like cells that released insulin in response to glucose in gut organoids, and this effect was enhanced by the Notch inhibitor, DBZ. In Ins2^Akita/+ mice, a five-day course of either Cpd10 or DBZ induced intestinal insulin-immunoreactive β-like cells, lowered glycemia, and increased plasma insulin levels without apparent adverse effects.

CONCLUSION

These results provide proof of principle of gut cell conversion into β-like cells by a small molecule FoxO1 inhibitor, paving the way for clinical applications.

VEGFR3 modulates brain microvessel branching in a mouse model of 22q11.2 deletion syndrome

The loss of a single copy of TBX1 accounts for most of the clinical signs and symptoms of 22q11.2 deletion syndrome, a common genetic disorder that is characterized by multiple congenital anomalies and brain-related clinical problems, some of which likely have vascular origins. Tbx1 mutant mice have brain vascular anomalies, thus making them a useful model to gain insights into the human disease. Here, we found that the main morphogenetic function of TBX1 in the mouse brain is to suppress vessel branching morphogenesis through regulation of Vegfr3 We demonstrate that inactivating Vegfr3 in the Tbx1 expression domain on a Tbx1 mutant background enhances brain vessel branching and filopodia formation, whereas increasing Vegfr3 expression in this domain fully rescued these phenotypes. Similar results were obtained using an in vitro model of endothelial tubulogenesis. Overall, the results of this study provide genetic evidence that VEGFR3 is a regulator of early vessel branching and filopodia formation in the mouse brain and is a likely mediator of the brain vascular phenotype caused by Tbx1 loss of function.

Arginase-1 Deletion in Erythrocytes Promotes Vascular Calcification via Enhanced GSNOR (S-Nitrosoglutathione Reductase) Expression and NO Signaling in Smooth Muscle Cells

BACKGROUND

Erythrocytes (red blood cells) participate in the control of vascular NO bioavailability. The purpose of this study was to determine whether and how genetic deletion of ARG1 (arginase-1) affects vascular smooth muscle cell NO signaling, osteoblastic differentiation, and atherosclerotic lesion calcification.

METHODS

Atherosclerosis-prone mice with conditional, erythrocyte-restricted deletion of ARG1 (apoE^-/- red blood cell.ARG1 knockout) were generated and vascular calcification studied using molecular imaging of the osteogenic activity agent OsteoSense, Alizarin staining or immunohistochemistry, qPCR of osteogenic markers and ex vivo assays.

RESULTS

Atherosclerotic lesion size at the aortic root did not differ, but calcification was significantly more pronounced in apoE^-/- mice lacking erythrocyte ARG1. Incubation of murine and human VSMCs with lysed erythrocyte membranes from apoE^-/- red blood cell. ARG1-knockout mice accelerated their osteogenic differentiation, and mRNA transcripts of osteogenic markers decreased following NO scavenging. In addition to NO signaling via sGC (soluble guanylyl cyclase), overexpression of GSNOR (S-nitrosoglutathione reductase) enhanced degradation of S-nitrosoglutathione to glutathione and reduced protein S-nitrosation of HSP (heat shock protein)-70 were identified as potential mechanisms of vascular smooth muscle cell calcification in mice lacking ARG1 in erythrocytes, and calcium phosphate deposition was enhanced by heat shock and prevented by GSNOR inhibition. Messenger RNA levels of enzymes metabolizing the arginase products L-ornithine and L-proline also were elevated in VSMCs, paralleled by increased proliferation, myofibroblast marker and collagen type 1 expression.

CONCLUSIONS

Our findings support an important role of erythrocyte ARG1 for NO bioavailability and L-arginine metabolism in VSMCs, which controls atherosclerotic lesion composition and calcification.

Autophagic degradation of CNS myelin maintains axon integrity

(Macro)autophagy is a major lysosome-dependent degradation mechanism which engulfs, removes and recycles unwanted cytoplasmic material, including damaged organelles and toxic protein aggregates. Although a few studies implicate autophagy in CNS demyelinating pathologies, its role, particularly in mature oligodendrocytes and CNS myelin, remains poorly studied. Here, using both pharmacological and genetic inhibition of the autophagic machinery, we provide evidence that autophagy is an essential mechanism for oligodendrocyte maturation in vitro. Our study reveals that two core myelin proteins, namely proteolipid protein (PLP) and myelin basic protein (MBP) are incorporated into autophagosomes in oligodendrocytes, resulting in their degradation. Furthermore, we ablated atg5, a core gene of the autophagic machinery, specifically in myelinating glial cells in vivo by tamoxifen administration (plp-Cre ERT2 ; atg5 f/f ) and showed that myelin maintenance is perturbed, leading to PLP accumulation. Significant morphological defects in myelin membrane such as decompaction accompanied with increased axonal degeneration are observed. As a result, the mice exhibit behavioral deficits. In summary, our data highlight that the maintenance of adult myelin homeostasis in the CNS requires the involvement of a fully functional autophagic machinery.

Maf family transcription factors are required for nutrient uptake in the mouse neonatal gut

There are fundamental differences in how neonatal and adult intestines absorb nutrients. In adults, macromolecules are broken down into simpler molecular components in the lumen of the small intestine, then absorbed. In contrast, neonates are thought to rely on internalization of whole macromolecules and subsequent degradation in the lysosome. Here, we identify the Maf family transcription factors MAFB and c-MAF as markers of terminally differentiated intestinal enterocytes throughout life. The expression of these factors is regulated by HNF4α and HNF4γ, master regulators of enterocyte cell fate. Loss of Maf factors results in a neonatal-specific failure to thrive and loss of macromolecular nutrient uptake. RNA-Seq and CUT&RUN analyses defined an endo-lysosomal program as being downstream of these transcription factors. We demonstrate major transcriptional changes in metabolic pathways, including fatty acid oxidation and increases in peroxisome number, in response to loss of Maf proteins. Finally, we show that loss of BLIMP1, a repressor of adult enterocyte genes, shows highly overlapping changes in gene expression and similar defects in macromolecular uptake. This work defines transcriptional regulators that are necessary for nutrient uptake in neonatal enterocytes.

Prenatal inflammation perturbs murine fetal hematopoietic development and causes persistent changes to postnatal immunity

Adult hematopoietic stem and progenitor cells (HSPCs) respond directly to inflammation and infection, causing both acute and persistent changes to quiescence, mobilization, and differentiation. Here we show that murine fetal HSPCs respond to prenatal inflammation in utero and that the fetal response shapes postnatal hematopoiesis and immune cell function. Heterogeneous fetal HSPCs show divergent responses to maternal immune activation (MIA), including changes in quiescence, expansion, and lineage-biased output. Single-cell transcriptomic analysis of fetal HSPCs in response to MIA reveals specific upregulation of inflammatory gene profiles in discrete, transient hematopoietic stem cell (HSC) populations that propagate expansion of lymphoid-biased progenitors. Beyond fetal development, MIA causes the inappropriate expansion and persistence of fetal lymphoid-biased progenitors postnatally, concomitant with increased cellularity and hyperresponsiveness of fetal-derived innate-like lymphocytes. Our investigation demonstrates how inflammation in utero can direct the output and function of fetal-derived immune cells by reshaping fetal HSC establishment.

Croix B. Cancer cell survival depends on collagen uptake into tumor-associated stroma

Collagen I, the most abundant protein in humans, is ubiquitous in solid tumors where it provides a rich source of exploitable metabolic fuel for cancer cells. While tumor cells were unable to exploit collagen directly, here we show they can usurp metabolic byproducts of collagen-consuming tumor-associated stroma. Using genetically engineered mouse models, we discovered that solid tumor growth depends upon collagen binding and uptake mediated by the TEM8/ANTXR1 cell surface protein in tumor-associated stroma. Tumor-associated stromal cells processed collagen into glutamine, which was then released and internalized by cancer cells. Under chronic nutrient starvation, a condition driven by the high metabolic demand of tumors, cancer cells exploited glutamine to survive, an effect that could be reversed by blocking collagen uptake with TEM8 neutralizing antibodies. These studies reveal that cancer cells exploit collagen-consuming stromal cells for survival, exposing an important vulnerability across solid tumors with implications for developing improved anticancer therapy.

Cbln1 regulates axon growth and guidance in multiple neural regions

The accurate construction of neural circuits requires the precise control of axon growth and guidance, which is regulated by multiple growth and guidance cues during early nervous system development. It is generally thought that the growth and guidance cues that control the major steps of axon development have been defined. Here, we describe cerebellin-1 (Cbln1) as a novel cue that controls diverse aspects of axon growth and guidance throughout the central nervous system (CNS) by experiments using mouse and chick embryos. Cbln1 has previously been shown to function in late neural development to influence synapse organization. Here, we find that Cbln1 has an essential role in early neural development. Cbln1 is expressed on the axons and growth cones of developing commissural neurons and functions in an autocrine manner to promote axon growth. Cbln1 is also expressed in intermediate target tissues and functions as an attractive guidance cue. We find that these functions of Cbln1 are mediated by neurexin-2 (Nrxn2), which functions as the Cbln1 receptor for axon growth and guidance. In addition to the developing spinal cord, we further show that Cbln1 functions in diverse parts of the CNS with major roles in cerebellar parallel fiber growth and retinal ganglion cell axon guidance. Despite the prevailing role of Cbln1 as a synaptic organizer, our study discovers a new and unexpected function for Cbln1 as a general axon growth and guidance cue throughout the nervous system.

E-Cadherin Expression Distinguishes Mouse from Human Hematopoiesis in the Basophil and Erythroid Lineages

E-cadherin is a key regulator of epithelial cell-cell adhesion, the loss of which accelerates tumor growth and invasion. E-cadherin is also expressed in hematopoietic cells as well as epithelia. The function of hematopoietic E-cadherin is, however, mostly elusive. In this study, we explored the validity of mouse models to functionally investigate the role of hematopoietic E-cadherin in human hematopoiesis. We generated a hematopoietic-specific E-cadherin knockout mouse model. In mice, hematopoietic E-cadherin is predominantly expressed within the basophil lineage, the expression of which is dispensable for the generation of basophils. However, neither E-cadherin mRNA nor protein were detected in human basophils. In contrast, human hematopoietic E-cadherin marks the erythroid lineage. E-cadherin expression in hematopoiesis thereby revealed striking evolutionary differences between the basophil and erythroid cell lineage in humans and mice. This is remarkable as E-cadherin expression in epithelia is highly conserved among vertebrates including humans and mice. Our study therefore revealed that the mouse does not represent a suitable model to study the function of E-cadherin in human hematopoiesis and an alternative means to study the role of E-cadherin in human erythropoiesis needs to be developed.

CHD7 regulates otic lineage specification and hair cell differentiation in human inner ear organoids

Mutations in CHD7 cause CHARGE syndrome, affecting multiple organs including the inner ear in humans. We investigate how CHD7 mutations affect inner ear development using human pluripotent stem cell-derived organoids as a model system. We find that loss of CHD7 or its chromatin remodeling activity leads to complete absence of hair cells and supporting cells, which can be explained by dysregulation of key otic development-associated genes in mutant otic progenitors. Further analysis of the mutant otic progenitors suggests that CHD7 can regulate otic genes through a chromatin remodeling-independent mechanism. Results from transcriptome profiling of hair cells reveal disruption of deafness gene expression as a potential underlying mechanism of CHARGE-associated sensorineural hearing loss. Notably, co-differentiating CHD7 knockout and wild-type cells in chimeric organoids partially rescues mutant phenotypes by restoring otherwise severely dysregulated otic genes. Taken together, our results suggest that CHD7 plays a critical role in regulating human otic lineage specification and hair cell differentiation.

Chimeric 3D gastruloids - a versatile tool for studies of mammalian peri-gastrulation development

Stem cell-derived three-dimensional (3D) gastruloids show a remarkable capacity of self-organisation and recapitulate many aspects of gastrulation stage mammalian development. Gastruloids can be rapidly generated and offer several experimental advantages, such as scalability, observability and accessibility for manipulation. Here, we present approaches to further expand the experimental potency of murine 3D gastruloids by using functional genetics in mouse embryonic stem cells (mESCs) to generate chimeric gastruloids. In chimeric gastruloids, fluorescently labelled cells of different genotypes harbouring inducible gene expression or loss-of-function alleles are combined with wild-type cells. We showcase this experimental approach in chimeric gastruloids of mESCs carrying homozygous deletions of the Tbx transcription factor brachyury or inducible expression of Eomes. Resulting chimeric gastruloids recapitulate reported Eomes and brachyury functions, such as instructing cardiac fate and promoting posterior axial extension, respectively. Additionally, chimeric gastruloids revealed previously unrecognised phenotypes, such as the tissue sorting preference of brachyury deficient cells to endoderm and the cell non-autonomous effects of brachyury deficiency on Wnt3a patterning along the embryonic axis, demonstrating some of the advantages of chimeric gastruloids as an efficient tool for studies of mammalian gastrulation.

Impaired mitochondrial oxidative metabolism in skeletal progenitor cells leads to musculoskeletal disintegration

Although skeletal progenitors provide a reservoir for bone-forming osteoblasts, the major energy source for their osteogenesis remains unclear. Here, we demonstrate a requirement for mitochondrial oxidative phosphorylation in the osteogenic commitment and differentiation of skeletal progenitors. Deletion of Evolutionarily Conserved Signaling Intermediate in Toll pathways (ECSIT) in skeletal progenitors hinders bone formation and regeneration, resulting in skeletal deformity, defects in the bone marrow niche and spontaneous fractures followed by persistent nonunion. Upon skeletal fracture, Ecsit-deficient skeletal progenitors migrate to adjacent skeletal muscle causing muscle atrophy. These phenotypes are intrinsic to ECSIT function in skeletal progenitors, as little skeletal abnormalities were observed in mice lacking Ecsit in committed osteoprogenitors or mature osteoblasts. Mechanistically, Ecsit deletion in skeletal progenitors impairs mitochondrial complex assembly and mitochondrial oxidative phosphorylation and elevates glycolysis. ECSIT-associated skeletal phenotypes were reversed by in vivo reconstitution with wild-type ECSIT expression, but not a mutant displaying defective mitochondrial localization. Collectively, these findings identify mitochondrial oxidative phosphorylation as the prominent energy-driving force for osteogenesis of skeletal progenitors, governing musculoskeletal integrity.

GATA4 Regulates Developing Endocardium Through Interaction With ETS1

BACKGROUND

The pioneer transcription factor (TF) GATA4 (GATA Binding Protein 4) is expressed in multiple cardiovascular lineages and is essential for heart development. GATA4 lineage-specific occupancy in the developing heart underlies its lineage specific activities. Here, we characterized GATA4 chromatin occupancy in cardiomyocyte and endocardial lineages, dissected mechanisms that control lineage specific occupancy, and analyzed GATA4 regulation of endocardial gene expression.

METHODS

We mapped GATA4 chromatin occupancy in cardiomyocyte and endocardial cells of embryonic day 12.5 (E12.5) mouse heart using lineage specific, Cre-activated biotinylation of GATA4. Regulation of GATA4 pioneering activity was studied in cell lines stably overexpressing GATA4. GATA4 regulation of endocardial gene expression was analyzed using single cell RNA sequencing and luciferase reporter assays.

RESULTS

Cardiomyocyte-selective and endothelial-selective GATA4 occupied genomic regions had features of lineage specific enhancers. Footprints within cardiomyocyte- and endothelial-selective GATA4 regions were enriched for NKX2-5 (NK2 homeobox 5) and ETS1 (ETS Proto-Oncogene 1) motifs, respectively, and both of these TFs interacted with GATA4 in co-immunoprecipitation assays. In stable NIH3T3 cell lines expressing GATA4 with or without NKX2-5 or ETS1, the partner TFs re-directed GATA4 pioneer binding and augmented its ability to open previously inaccessible regions, with ETS1 displaying greater potency as a pioneer partner than NKX2-5. Single-cell RNA sequencing of embryonic hearts with endothelial cell-specific Gata4 inactivation identified Gata4-regulated endocardial genes, which were adjacent to GATA4-bound, endothelial regions enriched for both GATA4 and ETS1 motifs. In reporter assays, GATA4 and ETS1 cooperatively stimulated endothelial cell enhancer activity.

CONCLUSIONS

Lineage selective non-pioneer TFs NKX2-5 and ETS1 guide the activity of pioneer TF GATA4 to bind and open chromatin and create active enhancers and mechanistically link ETS1 interaction to GATA4 regulation of endocardial development.

Constitutive bone marrow adipocytes suppress local bone formation

BM adipocytes (BMAd) are a unique cell population derived from BM mesenchymal progenitors and marrow adipogenic lineage precursors. Although they have long been considered to be a space filler within bone cavities, recent studies have revealed important physiological roles in hematopoiesis and bone metabolism. To date, the approaches used to study BMAd function have been confounded by contributions by nonmarrow adipocytes or by BM stromal cells. To address this gap in the field, we have developed a BMAd-specific Cre mouse model to deplete BMAds by expression of diphtheria toxin A (DTA) or by deletion of peroxisome proliferator-activated receptor gamma (Pparg). We found that DTA-induced loss of BMAds results in decreased hematopoietic stem and progenitor cell numbers and increased bone mass in BMAd-enriched locations, including the distal tibiae and caudal vertebrae. Elevated bone mass appears to be secondary to enhanced endosteal bone formation, suggesting a local effect caused by depletion of BMAd. Augmented bone formation with BMAd depletion protects mice from bone loss induced by caloric restriction or ovariectomy, and it facilitates the bone-healing process after fracture. Finally, ablation of Pparg also reduces BMAd numbers and largely recapitulates high-bone mass phenotypes observed with DTA-induced BMAd depletion.

Early developmental plasticity enables the induction of an intermediate extraembryonic cell state

Two fundamental elements of pre-implantation embryogenesis are cells' intrinsic self-organization program and their developmental plasticity, which allows embryos to compensate for alterations in cell position and number; yet, these elements are still poorly understood. To be able to decipher these features, we established culture conditions that enable the two fates of blastocysts' extraembryonic lineages-the primitive endoderm and the trophectoderm-to coexist. This plasticity emerges following the mechanisms of the first lineage segregation in the mouse embryo, and it manifests as an extended potential for extraembryonic chimerism during the pre-implantation embryogenesis. Moreover, this shared state enables robust assembly into higher-order blastocyst-like structures, thus combining both the cell fate plasticity and self-organization features of the early extraembryonic lineages.

Only Acute but Not Chronic Thrombocytopenia Protects Mice against Left Ventricular Dysfunction after Acute Myocardial Infarction

BACKGROUND

Platelets are major players of thrombosis and inflammation after acute myocardial infarction (AMI). The impact of thrombocytopenia on platelet-induced cellular processes post AMI is not well defined.

METHODS

The left anterior descending artery was ligated in C57/Bl6 mice and in two thrombocytopenic mouse models to induce AMI.

RESULTS

Platelets from STEMI patients and from C57/Bl6 mice displayed enhanced platelet activation after AMI. This allows platelets to migrate into the infarct but not into the remote zone of the left ventricle. Acute thrombocytopenia by antibody-induced platelet depletion resulted in reduced infarct size and improved cardiac function 24 h and 21 days post AMI. This was due to reduced platelet-mediated inflammation after 24 h and reduced scar formation after 21 days post AMI. The collagen composition and interstitial collagen content in the left ventricle were altered due to platelet interaction with cardiac fibroblasts. Acute inflammation was also significantly reduced in Mpl-/- mice with chronic thrombocytopenia, but cardiac remodeling was unaltered. Consequently, left ventricular function, infarct size and scar formation in Mpl-/- mice were comparable to controls.

CONCLUSION

This study discovers a novel role for platelets in cardiac remodeling and reveals that acute but not chronic thrombocytopenia protects left ventricular function post AMI.

Stromal androgen signaling acts as tumor niches to drive prostatic basal epithelial progenitor-initiated oncogenesis

The androgen receptor (AR)-signaling pathways are essential for prostate tumorigenesis. Although significant effort has been devoted to directly targeting AR-expressing tumor cells, these therapies failed in most prostate cancer patients. Here, we demonstrate that loss of AR in stromal sonic-hedgehog Gli1-lineage cells diminishes prostate epithelial oncogenesis and tumor development using in vivo assays and mouse models. Single-cell RNA sequencing and other analyses identified a robust increase of insulin-like growth factor (IGF) binding protein 3 expression in AR-deficient stroma through attenuation of AR suppression on Sp1-regulated transcription, which further inhibits IGF1-induced Wnt/β-catenin activation in adjacent basal epithelial cells and represses their oncogenic growth and tumor development. Epithelial organoids from stromal AR-deficient mice can regain IGF1-induced oncogenic growth. Loss of human prostate tumor basal cell signatures reveals in basal cells of stromal AR-deficient mice. These data demonstrate a distinct mechanism for prostate tumorigenesis and implicate co-targeting stromal and epithelial AR-signaling for prostate cancer.

FGF8 induces chemokinesis and regulates condensation of mouse nephron progenitor cells

Kidneys develop via iterative branching of the ureteric epithelial tree and subsequent nephrogenesis at the branch points. Nephrons form in the cap mesenchyme as the metanephric mesenchyme (MM) condenses around the epithelial ureteric buds (UBs). Previous work has demonstrated that FGF8 is important for the survival of nephron progenitor cells (NPCs), and early deletion of Fgf8 leads to the cessation of nephron formation, which results in post-natal lethality. We now reveal a previously unreported function of FGF8. By combining transgenic mouse models, quantitative imaging assays and data-driven computational modelling, we show that FGF8 has a strong chemokinetic effect and that this chemokinetic effect is important for the condensation of NPCs to the UB. The computational model shows that the motility must be lower close to the UB to achieve NPC attachment. We conclude that the FGF8 signalling pathway is crucial for the coordination of NPC condensation at the UB. Chemokinetic effects have also been described for other FGFs and may be generally important for the formation of mesenchymal condensates.

The transcription factors Foxf1 and Foxf2 integrate the SHH, HGF and TGFβ signaling pathways to drive tongue organogenesis

The tongue is a highly specialized muscular organ with diverse cellular origins, which provides an excellent model for understanding mechanisms controlling tissue-tissue interactions during organogenesis. Previous studies showed that SHH signaling is required for tongue morphogenesis and tongue muscle organization, but little is known about the underlying mechanisms. Here we demonstrate that the Foxf1/Foxf2 transcription factors act in the cranial neural crest cell (CNCC)-derived mandibular mesenchyme to control myoblast migration into the tongue primordium during tongue initiation, and thereafter continue to regulate intrinsic tongue muscle assembly and lingual tendon formation. We performed chromatin immunoprecipitation sequencing analysis and identified Hgf, Tgfb2 and Tgfb3 among the target genes of Foxf2 in the embryonic tongue. Through genetic analyses of mice with CNCC-specific inactivation of Smo or both Foxf1 and Foxf2, we show that Foxf1 and Foxf2 mediate hedgehog signaling-mediated regulation of myoblast migration during tongue initiation and intrinsic tongue muscle formation by regulating the activation of the HGF and TGFβ signaling pathways. These data uncover the molecular network integrating the SHH, HGF and TGFβ signaling pathways in regulating tongue organogenesis.

CNS Pericytes Modulate Local T Cell Infiltration in EAE

Pericytes at the blood–brain barrier (BBB) are located between the tight endothelial cell layer of the blood vessels and astrocytic endfeet. They contribute to central nervous system (CNS) homeostasis by regulating BBB development and maintenance. Loss of pericytes results in increased numbers of infiltrating immune cells in the CNS in experimental autoimmune encephalomyelitis (EAE), the mouse model for multiple sclerosis (MS). However, little is known about their competence to modulate immune cell activation or function in CNS autoimmunity. To evaluate the capacity of pericytes to directly interact with T cells in an antigen-specific fashion and potentially (re)shape their function, we depleted major histocompatibility complex (MHC) class II from pericytes in a cell type-specific fashion and performed T cell-pericyte cocultures and EAE experiments. We found that pericytes present antigen in vitro to induce T cell activation and proliferation. In an adoptive transfer EAE experiment, pericyte-specific MHC II KO resulted in locally enhanced T cell infiltration in the CNS; even though, overall disease course of mice was not affected. Thus, pericytes may serve as non-professional antigen-presenting cells affecting states of T cell activation, thereby locally shaping lesion formation in CNS inflammation but without modulating disease severity.

Yap and Taz promote osteogenesis and prevent chondrogenesis in neural crest cells in vitro and in vivo

Neural crest cells (NCCs) are multipotent stem cells that can differentiate into multiple cell types, including the osteoblasts and chondrocytes, and constitute most of the craniofacial skeleton. Here, we show through in vitro and in vivo studies that the transcriptional regulators Yap and Taz have redundant functions as key determinants of the specification and differentiation of NCCs into osteoblasts or chondrocytes. Primary and cultured NCCs deficient in Yap and Taz switched from osteogenesis to chondrogenesis, and NCC-specific deficiency for Yap and Taz resulted in bone loss and ectopic cartilage in mice. Yap bound to the regulatory elements of key genes that govern osteogenesis and chondrogenesis in NCCs and directly regulated the expression of these genes, some of which also contained binding sites for the TCF/LEF transcription factors that interact with the Wnt effector β-catenin. During differentiation of NCCs in vitro and NCC-derived osteogenesis in vivo, Yap and Taz promoted the expression of osteogenic genes such as Runx2 and Sp7 but repressed the expression of chondrogenic genes such as Sox9 and Col2a1. Furthermore, Yap and Taz interacted with β-catenin in NCCs to coordinately promote osteoblast differentiation and repress chondrogenesis. Together, our data indicate that Yap and Taz promote osteogenesis in NCCs and prevent chondrogenesis, partly through interactions with the Wnt-β-catenin pathway.

Wnt4 is heterogeneously activated in maturing β-cells to control calcium signaling, metabolism and function

Diabetes is a multifactorial disorder characterized by loss or dysfunction of pancreatic β-cells. β-cells are heterogeneous, exhibiting different glucose sensing, insulin secretion and gene expression. They communicate with other endocrine cell types via paracrine signals and between β-cells via gap junctions. Here, we identify the importance of signaling between β-cells via the extracellular signal WNT4. We show heterogeneity in Wnt4 expression, most strikingly in the postnatal maturation period, Wnt4-positive cells, being more mature while Wnt4-negative cells are more proliferative. Knock-out in adult β-cells shows that WNT4 controls the activation of calcium signaling in response to a glucose challenge, as well as metabolic pathways converging to lower ATP/ADP ratios, thereby reducing insulin secretion. These results reveal that paracrine signaling between β-cells is important in addition to gap junctions in controling insulin secretion. Together with previous reports of WNT4 up-regulation in obesity our observations suggest an adaptive insulin response coordinating β-cells.

Insights into skeletal stem cells

The tissue-resident skeletal stem cells (SSCs), which are self-renewal and multipotent, continuously provide cells (including chondrocytes, bone cells, marrow adipocytes, and stromal cells) for the development and homeostasis of the skeletal system. In recent decade, utilizing fluorescence-activated cell sorting, lineage tracing, and single-cell sequencing, studies have identified various types of SSCs, plotted the lineage commitment trajectory, and partially revealed their properties under physiological and pathological conditions. In this review, we retrospect to SSCs identification and functional studies. We discuss the principles and approaches to identify bona fide SSCs, highlighting pioneering findings that plot the lineage atlas of SSCs. The roles of SSCs and progenitors in long bone, craniofacial tissues, and periosteum are systematically discussed. We further focus on disputes and challenges in SSC research.

Sexually dimorphic activation of innate antitumor immunity prevents adrenocortical carcinoma development

Unlike most cancers, adrenocortical carcinomas (ACCs) are more frequent in women than in men, but the underlying mechanisms of this sexual dimorphism remain elusive. Here, we show that inactivation of Znrf3 in the mouse adrenal cortex, recapitulating the most frequent alteration in ACC patients, is associated with sexually dimorphic tumor progression. Although female knockouts develop metastatic carcinomas at 18 months, adrenal hyperplasia regresses in male knockouts. This male-specific phenotype is associated with androgen-dependent induction of senescence, recruitment, and differentiation of highly phagocytic macrophages that clear out senescent cells. In contrast, in females, macrophage recruitment is delayed and dampened, which allows for aggressive tumor progression. Consistently, analysis of TCGA-ACC data shows that phagocytic macrophages are more prominent in men and are associated with better prognosis. Together, these data show that phagocytic macrophages are key players in the sexual dimorphism of ACC that could be previously unidentified allies in the fight against this devastating cancer.

Cellular shape reinforces niche to stem cell signaling in the small intestine

Niche-derived factors regulate tissue stem cells, but apart from the mechanosensory pathways, the effect of niche geometry is not well understood. We used organoids and bioengineered tissue culture platforms to demonstrate that the conical shape of Lgr5+ small intestinal stem cells (ISCs) facilitate their self-renewal and function. Inhibition of non-muscle myosin II (NM II)-driven apical constriction altered ISC shape and reduced niche curvature and stem cell capacity. Niche curvature is decreased in aged mice, suggesting that suboptimal interactions between old ISCs and their niche develop with age. We show that activation of NM IIC or physical restriction to young topology improves in vitro regeneration by old epithelium. We propose that the increase in lateral surface area of ISCs induced by apical constriction promotes interactions between neighboring cells, and the curved topology of the intestinal niche has evolved to maximize signaling between ISCs and neighboring cells.

Osteopontin promotes infarct repair

Understanding how macrophages promote myocardial repair can help create new therapies for infarct repair. We aimed to determine what mechanisms underlie the reparative properties of macrophages. Cytokine arrays revealed that neonatal cardiac macrophages from the injured neonatal heart secreted high amounts of osteopontin (OPN). In vitro, recombinant OPN stimulated cardiac cell outgrowth, cardiomyocyte (CM) cell-cycle re-entry, and CM migration. In addition, OPN induced nuclear translocation of the cytoplasmatic yes-associated protein 1 (YAP1) and upregulated transcriptional factors and cell-cycle genes. Significantly, by blocking the OPN receptor CD44, we eliminated the effects of OPN on CMs. OPN also activated the proliferation and migration of non-CM cells: endothelial cells and cardiac mesenchymal stromal cells in vitro. Notably, the significant role of OPN in myocardial healing was demonstrated by impaired healing in OPN-deficient neonatal hearts. Finally, in the adult mice, a single injection of OPN into the border of the ischemic zone induced CM cell-cycle re-entry, improved scar formation, local and global cardiac function, and LV remodelling 30 days after MI. In summary, we have shown, for the first time, that recombinant OPN activates cell-cycle re-entry in CMs. In addition, recombinant OPN stimulates multiple cardiac cells and improves scar formation, LV remodelling, and regional and global function after MI. Therefore, we propose OPN as a new cell-free therapy to optimize infarct repair.

Phosphatase protector alpha4 (α4) is involved in adipocyte maintenance and mitochondrial homeostasis through regulation of insulin signaling

Insulin signaling is mediated via a network of protein phosphorylation. Dysregulation of this network is central to obesity, type 2 diabetes and metabolic syndrome. Here we investigate the role of phosphatase binding protein Alpha4 (α4) that is essential for the serine/threonine protein phosphatase 2A (PP2A) in insulin action/resistance in adipocytes. Unexpectedly, adipocyte-specific inactivation of α4 impairs insulin-induced Akt-mediated serine/threonine phosphorylation despite a decrease in the protein phosphatase 2A (PP2A) levels. Interestingly, loss of α4 also reduces insulin-induced insulin receptor tyrosine phosphorylation. This occurs through decreased association of α4 with Y-box protein 1, resulting in the enhancement of the tyrosine phosphatase protein tyrosine phosphatase 1B (PTP1B) expression. Moreover, adipocyte-specific knockout of α4 in male mice results in impaired adipogenesis and altered mitochondrial oxidation leading to increased inflammation, systemic insulin resistance, hepatosteatosis, islet hyperplasia, and impaired thermogenesis. Thus, the α4 /Y-box protein 1(YBX1)-mediated pathway of insulin receptor signaling is involved in maintaining insulin sensitivity, normal adipose tissue homeostasis and systemic metabolism.