Genetic lineage tracing of resident stem cells by DeaLT

Altered lipid metabolism promoting cardiac fibrosis is mediated by CD34+ cell-derived FABP4+ fibroblasts

Hyperlipidemia and hypertension might play a role in cardiac fibrosis, in which a heterogeneous population of fibroblasts seems important. However, it is unknown whether CD34+ progenitor cells are involved in the pathogenesis of heart fibrosis. This study aimed to explore the mechanism of CD34+ cell differentiation in cardiac fibrosis during hyperlipidemia. Through the analysis of transcriptomes from 50,870 single cells extracted from mouse hearts and 76,851 single cells from human hearts, we have effectively demonstrated the evolving cellular landscape throughout cardiac fibrosis. Disturbances in lipid metabolism can accelerate the development of fibrosis. Through the integration of bone marrow transplantation models and lineage tracing, our study showed that hyperlipidemia can expedite the differentiation of non-bone marrow-derived CD34+ cells into fibroblasts, particularly FABP4+ fibroblasts, in response to angiotensin II. Interestingly, the partial depletion of CD34+ cells led to a notable reduction in triglycerides in the heart, mitigated fibrosis, and improved cardiac function. Furthermore, immunostaining of human heart tissue revealed colocalization of CD34+ cells and fibroblasts. Mechanistically, our investigation of single-cell RNA sequencing data through pseudotime analysis combined with in vitro cellular studies revealed the crucial role of the PPARγ/Akt/Gsk3β pathway in orchestrating the differentiation of CD34+ cells into FABP4+ fibroblasts. Through our study, we generated valuable insights into the cellular landscape of CD34+ cell-derived cells in the hypertrophic heart with hyperlipidemia, indicating that the differentiation of non-bone marrow-derived CD34+ cells into FABP4+ fibroblasts during this process accelerates lipid accumulation and promotes heart failure via the PPARγ/Akt/Gsk3β pathway.

Skeletal stem cells in bone development, homeostasis, and disease

Tissue-resident stem cells are essential for development and repair, and in the skeleton, this function is fulfilled by recently identified skeletal stem cells (SSCs). However, recent work has identified that SSCs are not monolithic, with long bones, craniofacial sites, and the spine being formed by distinct stem cells. Recent studies have utilized techniques such as fluorescence-activated cell sorting, lineage tracing, and single-cell sequencing to investigate the involvement of SSCs in bone development, homeostasis, and disease. These investigations have allowed researchers to map the lineage commitment trajectory of SSCs in different parts of the body and at different time points. Furthermore, recent studies have shed light on the characteristics of SSCs in both physiological and pathological conditions. This review focuses on discussing the spatiotemporal distribution of SSCs and enhancing our understanding of the diversity and plasticity of SSCs by summarizing recent discoveries.

Synchronized lineage tracing of cell membranes and nuclei by dual recombinases and dual fluorescent

Genetic lineage tracing has been widely employed to investigate cell lineages and fate. However, conventional reporting systems often label the entire cytoplasm, making it challenging to discern cell boundaries. Additionally, single Cre-loxP recombination systems have limitations in tracing specific cell populations. This study proposes three reporting systems that utilizing Cre, Dre, and Dre + Cre mediated recombination. These systems incorporate tdTomato expression on the cell membrane and PhiYFP expression within the nucleus, allowing for clear observation of the nucleus and membrane. The efficacy of these systems is successfully demonstrated by labeling cardiomyocytes and hepatocytes. The potential for dynamic visualization of the cell membrane is showcased using intravital imaging microscopy or three-dimensional imaging. Furthermore, by combining this dual recombinase system with the ProTracer system, hepatocyte proliferation is traced with enhanced precision. This reporting system holds significant importance for advancing the understanding of cell fate studies in development, homeostasis, and diseases.

Epicardial SMARCA4 deletion exacerbates cardiac injury in myocardial infarction and is related to the inhibition of epicardial epithelial-mesenchymal transition

The reactivated adult epicardium produces epicardium-derived cells (EPDCs) via epithelial-mesenchymal transition (EMT) to benefit the recovery of the heart after myocardial infarction (MI). SMARCA4 is the core catalytic subunit of the chromatin re-modeling complex, which has the potential to target some reactivated epicardial genes in MI. However, the effects of epicardial SMARCA4 on MI remain uncertain. This study found that SMARCA4 was activated over time in epicardial cells following MI, and some of activated cells belonged to downstream differentiation types of EPDCs. This study used tamoxifen to induce lineage tracing and SMARCA4 deletion from epicardial cells in Wt1-CreER;Smarca4fl/fl;Rosa26-RFP adult mice. Epicardial SMARCA4 deletion reduces the number of epicardial cells in adult mice, which was related to changes in the activation, proliferation, and apoptosis of epicardial cells. Epicardial SMARCA4 deletion reduced collagen deposition and angiogenesis in the infarcted area, exacerbated cardiac injury in MI. The exacerbation of cardiac injury was related to the inhibition of generation and differentiation of EPDCs. The alterations in EPDCs were associated with inhibited transition between E-CAD and N-CAD during the epicardial EMT, coupled with the down-regulation of WT1, SNAIL1, and PDGF signaling. In conclusion, this study suggests that Epicardial SMARCA4 plays a critical role in cardiac injury caused by MI, and its regulatory mechanism is related to epicardial EMT. Epicardial SMARCA4 holds potential as a novel molecular target for treating MI.

Continuous genetic monitoring of transient mesenchymal gene activities in distal tubule and collecting duct epithelial cells during renal fibrosis

Epithelial cells (ECs) have been proposed to contribute to myofibroblasts or fibroblasts through epithelial-mesenchymal transition (EMT) during renal fibrosis. However, since EMT may occur dynamically, transiently, and reversibly during kidney fibrosis, conventional lineage tracing based on Cre-loxP recombination in renal ECs could hardly capture the transient EMT activity, yielding inconsistent results. Moreover, previous EMT research has primarily focused on renal proximal tubule ECs, with few reports of distal tubules and collecting ducts. Here, we generated dual recombinases-mediated genetic lineage tracing systems for continuous monitoring of transient mesenchymal gene expression in E-cadherin+ and EpCAM+ ECs of distal tubules and collecting ducts during renal fibrosis. Activation of key EMT-inducing transcription factor (EMT-TF) Zeb1 and mesenchymal markers αSMA, vimentin, and N-cadherin, were investigated following unilateral ureteral obstruction (UUO). Our data revealed that E-cadherin+ and EpCAM+ ECs did not transdifferentiate into myofibroblasts, nor transiently expressed these mesenchymal genes during renal fibrosis. In contrast, in vitro a large amount of cultured renal ECs upregulated mesenchymal genes in response to TGF-β, a major inducer of EMT.

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.

A novel lineage of osteoprogenitor cells with dual epithelial and mesenchymal properties govern maxillofacial bone homeostasis and regeneration after MSFL

Bone regeneration originates from proliferation and differentiation of osteoprogenitors via either endochondral or intramembranous ossification; and the regeneration capacities decline with age and estrogen loss. Maxillary sinus floor lifting (MSFL) is a commonly used surgical procedure for guiding bone regeneration in maxilla. Radiographic analysis of 1210 clinical cases of maxilla bone regeneration after MSFL revealed that the intrasinus osteogenic efficacy was independent of age and gender, however; and this might be related to the Schneiderian membrane that lines the sinus cavity. In view of the particularity of this biological process, our present study aimed to elucidate the underlying mechanism of MSFL-induced bone regeneration. We first established a murine model to simulate the clinical MSFL. By single-cell RNA-sequencing and flow cytometry-based bulk RNA-sequencing, we identified a novel Krt14⁺Ctsk⁺ subset of cells that display both epithelial and mesenchymal properties and the transcriptomic feature of osteoprogenitors. Dual recombinases-mediated lineage tracing and loss-of-function analyses showed that these Krt14⁺Ctsk⁺ progenitors contribute to both MSFL-induced osteogenesis and physiological bone homeostasis by differentiating into Krt14^-Ctsk⁺ descendants which show robust osteogenic capacity. In addition, we detected a similar population of Krt14⁺Ctsk⁺ cells in human samples of Schneiderian membrane, which show a highly similar osteogenic potential and transcriptomic feature to the corresponding cells in mice. The identification of this Krt14⁺Ctsk⁺ population, featured by osteoprogenitor characteristics and dual epithelial-mesenchymal properties, provides new insight into the understanding of bone regeneration and may open more possibilities for clinical applications.

Generation of an Ihh-mKate2-Dre knock-in mouse line

Indian hedgehog (Ihh), a member of the Hh family, plays important roles in vertebrate development and homeostasis. To improve our understanding of the function of Ihh-expressing cells and their progeny as well, we generate an Ihh-mKate2^tomm20 -Dre knock-in mouse line that can label Ihh-positive cells with a fluorescence protein mKate2 and trace Ihh-positive cells and their progeny via Dre-mediated recombination. Consistent with previous reports, we verified Ihh expression in hypertrophic chondrocytes of growth plate and granulosa cells of ovarian follicles by mKate2 immunostaining, and meanwhile confirmed Dre activity in these cells via a Dre reporter mouse line Rosa26-confetti2. We also found, for the first time, that Ihh can mark some cell types, including retinal ganglion cells, Purkinje cells, and gallbladder epithelial cells. Taken together, the Ihh-mKate2^tomm20 -Dre mouse is a genetic tool for examining the precise expression profile of Ihh and tracing Ihh-expressing cells and their progeny.

Dual Cre and Dre recombinases mediate synchronized lineage tracing and cell subset ablation in vivo

Genetic technology using site-specific recombinases (SSR), such as the Cre-loxP system, has been widely employed for labelling specific cell populations and for studying their functions in vivo. To enhance the precision of cell lineage tracing and functional study, a similar SSR system termed Dre-rox has been recently used in combination with Cre-loxP. To enable more specific cell lineage tracing and ablation through dual recombinase activity, we generated two mouse lines that render Dre- or Dre+Cre-mediated recombination to excise a stop codon sequence that prevents the expression of diphtheria toxin receptor (DTR) knocked into the ubiquitously expressed and safe Rosa26 locus. Using different Dre- and Cre-expressing mouse lines, we showed that the surrogate gene reporter tdTomato and DTR were simultaneously expressed in target cells and in their descendants, and observed efficient ablation of tdTomato⁺ cells after diphtheria toxin administration. These mouse lines were used to simultaneously trace and deplete target cells of interest through the inducible expression of a reporter and DTR using dual Cre and Dre recombinases, allowing more precise and efficient study of the role of specific cell subsets within a heterogeneous population in pathophysiological conditions in vivo.

The rise of developmental biology in China

Developmental biology research in China started from experimental embryology, in particular from studies on aquatic and reptile animals. The recent growth of the developmental biology community in China parallels the increased governmental funding support and the recruitment of overseas talents. This flourishing field in China embraces the activities of developmental biology-related societies, national meetings, key research initiatives and talented scientists. The first Development paper from China, published in 2000, marked the beginning of a new era. More recently, the second decade in the 21st century witnessed the blossoming of developmental biology research in China. Significant research spotlights, technical advances, and up-and-coming areas will be discussed in this overview.

When form meets function: the cells and signals that shape the lymphatic vasculature during development

The lymphatic vasculature is an integral component of the cardiovascular system. It is essential to maintain tissue fluid homeostasis, direct immune cell trafficking and absorb dietary lipids from the digestive tract. Major advances in our understanding of the genetic and cellular events important for constructing the lymphatic vasculature during development have recently been made. These include the identification of novel sources of lymphatic endothelial progenitor cells, the recognition of lymphatic endothelial cell specialisation and heterogeneity, and discovery of novel genes and signalling pathways underpinning developmental lymphangiogenesis. Here, we review these advances and discuss how they inform our understanding of lymphatic network formation, function and dysfunction.

Genetic fate-mapping reveals surface accumulation but not deep organ invasion of pleural and peritoneal cavity macrophages following injury

During injury, monocytes are recruited from the circulation to inflamed tissues and differentiate locally into mature macrophages, with prior reports showing that cavity macrophages of the peritoneum and pericardium invade deeply into the respective organs to promote repair. Here we report a dual recombinase-mediated genetic system designed to trace cavity macrophages in vivo by intersectional detection of two characteristic markers. Lineage tracing with this method shows accumulation of cavity macrophages during lung and liver injury on the surface of visceral organs without penetration into the parenchyma. Additional data suggest that these peritoneal or pleural cavity macrophages do not contribute to tissue repair and regeneration. Our in vivo genetic targeting approach thus provides a reliable method to identify and characterize cavity macrophages during their development and in tissue repair and regeneration, and distinguishes these cells from other lineages.

New Insights into Development of Female Reproductive Tract-Hedgehog-Signal Response in Wolffian Tissues Directly Contributes to Uterus Development

The reproductive tract in mammals emerges from two ductal systems during embryogenesis: Wolffian ducts (WDs) and Mullerian ducts (MDs). Most of the female reproductive tract (FRT) including the oviducts, uterine horn and cervix, originate from MDs. It is widely accepted that the formation of MDs depends on the preformed WDs within the urogenital primordia. Here, we found that the WD mesenchyme under the regulation of Hedgehog (Hh) signaling is closely related to the developmental processes of the FRT during embryonic and postnatal periods. Deficiency of Sonic hedgehog (Shh), the only Hh ligand expressed exclusively in WDs, prevents the MD mesenchyme from affecting uterine growth along the radial axis. The in vivo cell tracking approach revealed that after WD regression, distinct cells responding to WD-derived Hh signal continue to exist in the developing FRT and gradually contribute to the formation of various tissues such as smooth muscle, endometrial stroma and vascular vessel, in the mouse uterus. Our study thus provides a novel developmental mechanism of FRT relying on WD.

Cellular Plasticity during Metastasis: New Insights Provided by Intravital Microscopy

Metastasis is a highly dynamic process during which cancer and microenvironmental cells undergo a cascade of events required for efficient dissemination throughout the body. During the metastatic cascade, tumor cells can change their state and behavior, a phenomenon commonly defined as cellular plasticity. To monitor cellular plasticity during metastasis, high-resolution intravital microscopy (IVM) techniques have been developed and allow us to visualize individual cells by repeated imaging in animal models. In this review, we summarize the latest technological advancements in the field of IVM and how they have been applied to monitor metastatic events. In particular, we highlight how longitudinal imaging in native tissues can provide new insights into the plastic physiological and developmental processes that are hijacked by cancer cells during metastasis.

Hematopoietic Stem Cell Transcription Factors in Cardiovascular Pathology

Transcription factors as multifaceted modulators of gene expression that play a central role in cell proliferation, differentiation, lineage commitment, and disease progression. They interact among themselves and create complex spatiotemporal gene regulatory networks that modulate hematopoiesis, cardiogenesis, and conditional differentiation of hematopoietic stem cells into cells of cardiovascular lineage. Additionally, bone marrow-derived stem cells potentially contribute to the cardiovascular cell population and have shown potential as a therapeutic approach to treat cardiovascular diseases. However, the underlying regulatory mechanisms are currently debatable. This review focuses on some key transcription factors and associated epigenetic modifications that modulate the maintenance and differentiation of hematopoietic stem cells and cardiac progenitor cells. In addition to this, we aim to summarize different potential clinical therapeutic approaches in cardiac regeneration therapy and recent discoveries in stem cell-based transplantation.

Lineage tracing: technology tool for exploring the development, regeneration, and disease of the digestive system

Lineage tracing is the most widely used technique to track the migration, proliferation, and differentiation of specific cells in vivo. The currently available gene-targeting technologies have been developing for decades to study organogenesis, tissue injury repairing, and tumor progression by tracing the fates of individual cells. Recently, lineage tracing has expanded the platforms available for disease model establishment, drug screening, cell plasticity research, and personalized medicine development in a molecular and cellular biology perspective. Lineage tracing provides new views for exploring digestive organ development and regeneration and techniques for digestive disease causes and progression. This review focuses on the lineage tracing technology and its application in digestive diseases.

New insights on the reparative cells in bone regeneration and repair

Bone possesses a remarkable repair capacity to regenerate completely without scar tissue formation. This unique characteristic, expressed during bone development, maintenance and injury (fracture) healing, is performed by the reparative cells including skeletal stem cells (SSCs) and their descendants. However, the identity and functional roles of SSCs remain controversial due to technological difficulties and the heterogeneity and plasticity of SSCs. Moreover, for many years, there has been a biased view that bone marrow is the main cell source for bone repair. Together, these limitations have greatly hampered our understanding of these important cell populations and their potential applications in the treatment of fractures and skeletal diseases. Here, we reanalyse and summarize current understanding of the reparative cells in bone regeneration and repair and outline recent progress in this area, with a particular emphasis on the temporal and spatial process of fracture healing, the sources of reparative cells, an updated definition of SSCs, and markers of skeletal stem/progenitor cells contributing to the repair of craniofacial and long bones, as well as the debate between SSCs and pericytes. Finally, we also discuss the existing problems, emerging novel technologies and future research directions in this field.

Optimization of Timing and Times for Administration of Atorvastatin-Pretreated Mesenchymal Stem Cells in a Preclinical Model of Acute Myocardial Infarction

Our previous studies showed that the combination of atorvastatin (ATV) and single injection of ATV-pretreated mesenchymal stem cells (MSCs) (ATV -MSCs) at 1 week post-acute myocardial infarction (AMI) promoted MSC recruitment and survival. This study aimed to investigate whether the combinatorial therapy of intensive ATV with multiple injections of ATV -MSCs has greater efficacy at different stages to better define the optimal strategy for MSC therapy in AMI. In order to determine the optimal time window for MSC treatment, we first assessed stromal cell-derived factor-1 (SDF-1) dynamic expression and inflammation. Next, we compared MSC recruitment and differentiation, cardiac function, infarct size, and angiogenesis among animal groups with single, dual, and triple injections of ATV -MSCs at early (Early1, Early2, Early3), mid-term (Mid1, Mid2, Mid3), and late (Late1, Late2, Late3) stages. Compared with AMI control, intensive ATV significantly augmented SDF-1 expression 1.5∼2.6-fold in peri-infarcted region with inhibited inflammation. ATV -MSCs implantation with ATV administration further enhanced MSC recruitment rate by 3.9%∼24.0%, improved left ventricular ejection fraction (LVEF) by 2.0%∼16.2%, and reduced infarct size in all groups 6 weeks post-AMI with most prominent improvement in mid groups and still effective in late groups. Mechanistically, ATV -MSCs remarkably suppressed inflammation and apoptosis while increasing angiogenesis. Furthermore, triple injections of ATV -MSCs were much more effective than single administration during early and mid-term stages of AMI with the best effects in Mid3 group. We conclude that the optimal strategy is multiple injections of ATV -MSCs combined with intensive ATV administration at mid-term stage of AMI. The translational potential of this strategy is clinically promising. Stem Cells Translational Medicine 2019;8:1068-1083.