Prostaglandin E2 regulates vertebrate haematopoietic stem cell homeostasis

A Jasmonate Signaling Network Activates Root Stem Cells and Promotes Regeneration

Plants are sessile and have to cope with environmentally induced damage through modification of growth and defense pathways. How tissue regeneration is triggered in such responses and whether this involves stem cell activation is an open question. The stress hormone jasmonate (JA) plays well-established roles in wounding and defense responses. JA also affects growth, which is hitherto interpreted as a trade-off between growth and defense. Here, we describe a molecular network triggered by wound-induced JA that promotes stem cell activation and regeneration. JA regulates organizer cell activity in the root stem cell niche through the RBR-SCR network and stress response protein ERF115. Moreover, JA-induced ERF109 transcription stimulates CYCD6;1 expression, functions upstream of ERF115, and promotes regeneration. Soil penetration and response to nematode herbivory induce and require this JA-mediated regeneration response. Therefore, the JA tissue damage response pathway induces stem cell activation and regeneration and activates growth after environmental stress.

Prostaglandin signaling regulates renal multiciliated cell specification and maturation

Multiciliated cells (MCCs) have core roles in organ formation and function, where they control fluid flow and particle displacement. MCCs direct fluid movement in the brain and spinal cord, clearance of respiratory mucus, and ovum transport from the ovary to the uterus. Deficiencies in MCC functionality lead to hydrocephalus, chronic respiratory infections, and infertility. Prostaglandins are lipids that are used to coordinate cellular functions. Here, we discovered that prostaglandin signaling is required for MCC development in the embryonic zebrafish kidney. Understanding renal MCC genesis can lend insights into the puzzling origins of MCCs in several chronic kidney diseases, where it is unclear whether MCCs are a cause or phenotypic outcome of the condition.

Multiciliated cells (MCCs) are specialized epithelia with apical bundles of motile cilia that direct fluid flow. MCC dysfunction is associated with human diseases of the respiratory, reproductive, and central nervous systems. Further, the appearance of renal MCCs has been cataloged in several kidney conditions, where their function is unknown. Despite their pivotal health importance, many aspects of MCC development remain poorly understood. Here, we utilized a chemical screen to identify molecules that affect MCC ontogeny in the zebrafish embryo kidney, and found prostaglandin signaling is essential both for renal MCC progenitor formation and terminal differentiation. Moreover, we show that prostaglandin activity is required downstream of the transcription factor ets variant 5a (etv5a) during MCC fate choice, where modulating prostaglandin E₂ (PGE₂) levels rescued MCC number. The discovery that prostaglandin signaling mediates renal MCC development has broad implications for other tissues, and could provide insight into a multitude of pathological states.

Developing zebrafish disease models for in vivo small molecule screens

The zebrafish is a model organism that allows in vivo studies to be performed at a scale usually restricted to in vitro studies. As such, the zebrafish is well suited to in vivo screens, in which thousands of small molecules are tested for their ability to modify disease phenotypes in zebrafish disease models. Numerous approaches have been developed for modeling human diseases in zebrafish, including mutagenesis, transgenesis, pharmacological approaches, wounding, and exposure to infectious or cancerous agents. We review the various strategies for modeling human diseases in zebrafish and discuss important considerations when developing zebrafish models for use in in vivo small molecule screens.

15-keto-prostaglandin E2 activates host peroxisome proliferator-activated receptor gamma (PPAR-γ) to promote Cryptococcus neoformans growth during infection

Cryptococcus neoformans is one of the leading causes of invasive fungal infection in humans worldwide. C. neoformans uses macrophages as a proliferative niche to increase infective burden and avoid immune surveillance. However, the specific mechanisms by which C. neoformans manipulates host immunity to promote its growth during infection remain ill-defined. Here we demonstrate that eicosanoid lipid mediators manipulated and/or produced by C. neoformans play a key role in regulating pathogenesis. C. neoformans is known to secrete several eicosanoids that are highly similar to those found in vertebrate hosts. Using eicosanoid deficient cryptococcal mutants Δplb1 and Δlac1, we demonstrate that prostaglandin E₂ is required by C. neoformans for proliferation within macrophages and in vivo during infection. Genetic and pharmacological disruption of host PGE₂ synthesis is not required for promotion of cryptococcal growth by eicosanoid production. We find that PGE₂ must be dehydrogenated into 15-keto-PGE₂ to promote fungal growth, a finding that implicated the host nuclear receptor PPAR-γ. C. neoformans infection of macrophages activates host PPAR-γ and its inhibition is sufficient to abrogate the effect of 15-keto-PGE₂ in promoting fungal growth during infection. Thus, we describe the first mechanism of reliance on pathogen-derived eicosanoids in fungal pathogenesis and the specific role of 15-keto-PGE₂ and host PPAR-γ in cryptococcosis.

Cryptococcus neoformans is an opportunistic fungal pathogen that is responsible for significant numbers of deaths in the immunocompromised population worldwide. Here we address whether eicosanoids produced by C. neoformans manipulate host innate immune cells during infection. Cryptococcus neoformans produces several eicosanoids that are notable for their similarity to vertebrate eicosanoids, it is therefore possible that fungal-derived eicosanoids may provoke physiological effects in the host. Using a combination of in vitro and in vivo infection models we identify a specific eicosanoid species—prostaglandin E2 –that is required by C. neoformans for growth during infection. We subsequently show that prostaglandin E₂ must be converted to 15-keto-prostaglandin E₂ within the host before it has these effects. Furthermore, we find that prostaglandin E₂/15-keto-prostaglandin E₂ mediated virulence is via activation of host PPAR-γ –an intracellular eicosanoid receptor known to interact with 15-keto-PGE₂.

Development of the hematopoietic system: Role of inflammatory factors

Hematopoietic stem cells (HSCs) have two defining features, multipotency and self-renewal, both of which are tightly controlled by cell autonomous programs and environmental factors throughout the lifetime of an organism. During development, HSCs are born in the aorta-gonad-mesonephros region, and migrate to distinct hematopoietic organs such as the placenta, fetal liver and spleen, continuously self-renewing and expanding to reach a homeostatic number. HSCs ultimately seed the bone marrow around the time of birth and become dormant to sustain lifelong hematopoiesis. In this review, we will summarize the recent findings on the role of inflammatory factors regulating HSC development, that is, emergence, trafficking and differentiation. An understanding of HSC kinetics during developmental processes will provide useful knowledge on HSC behavior under physiological and pathophysiological conditions. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Adult Stem Cells, Tissue Renewal, and Regeneration > Tissue Stem Cells and Niches Adult Stem Cells, Tissue Renewal, and Regeneration > Environmental Control of Stem Cells.

IFN Signaling in Inflammation and Viral Infections: New Insights from Fish Models

The overarching structure of the type I interferon (IFN) system is conserved across vertebrates. However, the variable numbers of whole genome duplication events during fish evolution offer opportunities for the expansion, diversification, and new functionalization of the genes that are involved in antiviral immunity. In this review, we examine how fish models provide new insights about the implication of virus-driven inflammation in immunity and hematopoiesis. Mechanisms that have been discovered in fish, such as the strong adjuvant effect of type I IFN that is used with DNA vaccination, constitute good models to understand how virus-induced inflammatory mechanisms can interfere with adaptive responses. We also comment on new discoveries regarding the role of pathogen-induced inflammation in the development and guidance of hematopoietic stem cells in zebrafish. These findings raise issues about the potential interferences of viral infections with the establishment of the immune system. Finally, the recent development of genome editing provides new opportunities to dissect the roles of the key players involved in the antiviral response in fish, hence enhancing the power of comparative approaches.

How HSCs Colonize and Expand in the Fetal Niche of the Vertebrate Embryo: An Evolutionary Perspective

Rare hematopoietic stem cells (HSCs) can self-renew, establish the entire blood system and represent the basis of regenerative medicine applied to hematological disorders. Clinical use of HSCs is however limited by their inefficient expansion ex vivo, creating a need to further understand HSC expansion in vivo. After embryonic HSCs are born from the hemogenic endothelium, they migrate to the embryonic/fetal niche, where the future adult HSC pool is established by considerable expansion. This takes place at different anatomical sites and is controlled by numerous signals. HSCs then migrate to their adult niche, where they are maintained throughout adulthood. Exactly how HSC expansion is controlled during embryogenesis remains to be characterized and is an important step to improve the therapeutic use of HSCs. We will review the current knowledge of HSC expansion in the different fetal niches across several model organisms and highlight possible clinical applications.

Leukocyte Trafficking and Regulation of Murine Hematopoietic Stem Cells and Their Niches

Hematopoietic stem cells (HSC) are the most powerful type of adult stem cell found in the body. Hematopoietic stem cells are multipotent and capable of giving rise to all other types of hematopoietic cells found in the organism. A single HSC is capable of regenerating a functional hematopoietic system when transplanted into a recipient. Hematopoietic stem cells reside in the bone marrow in specific multicellular structures called niches. These niches are indispensable for maintaining and regulating HSC numbers and function. It has become increasingly clearer that HSC and their niches can also be regulated by migrating leukocytes. Here we will discuss the composition of murine bone marrow niches and how HSC and their niches are regulated by different types of leukocytes that traffic between the periphery and the niche. Unless otherwise indicated all the studies discussed below were performed in mouse models.

Impact of aging on bone, marrow and their interactions

Hematopoiesis in land dwelling vertebrates and marine mammals occurs within the bone marrow, continually providing mature progeny over the course of an organism's lifetime. This conserved dependency highlights the critical relationship between these two organs, yet the skeletal and hematopoietic systems are often thought of as separate. In fact, data are beginning to show that skeletal disease pathogenesis influences hematopoiesis and viceversa, offering novel opportunities to approach disease affecting bone and blood. With a growing global population of aged individuals, interest has focused on cell autonomous changes in hematopoietic and skeletal systems that result in dysfunction. The purpose of this review is to summarize the literature on aging effects in both fields, and provide critical examples of organ cross-talk in the aging process.

An FDA-Approved Drug Screen for Compounds Influencing Craniofacial Skeletal Development and Craniosynostosis

Neural crest stem/progenitor cells (NCSCs) populate a variety of tissues, and their dysregulation is implicated in several human diseases including craniosynostosis and neuroblastoma. We hypothesised that small molecules that inhibit NCSC induction or differentiation may represent potential therapeutically relevant drugs in these disorders. We screened 640 FDA-approved compounds currently in clinical use for other conditions to identify those which disrupt development of NCSC-derived skeletal elements that form the zebrafish jaw. In the primary screen, we used heterozygous transgenic sox10:gfp zebrafish to directly visualise NCSC-derived jaw cartilage. We noted partial toxicity of this transgene in relation to jaw patterning, suggesting that our primary screen was sensitised for NCSC defects, and we confirmed 10 novel, 4 previously reported, and 2 functional analogue drug hits in wild-type embryos. Of these drugs, 9/14 and 7/14, respectively, are known to target pathways implicated in osteoarthritis pathogenesis or to cause reduced bone mineral density/increased fracture risk as side effects in patients treated for other conditions, suggesting that our screen enriched for pathways targeting skeletal tissue homeostasis. We selected one drug that inhibited NCSC induction and one drug that inhibits bone mineralisation for further detailed analyses which reflect our initial hypotheses. These drugs were leflunomide and cyclosporin A, respectively, and their functional analogues, teriflunomide and FK506 (tacrolimus). We identified their critical developmental windows of activity, showing that the severity of defects observed related to the timing, duration, and dose of treatment. While leflunomide has previously been shown to inhibit NCSC induction, we demonstrate additional later roles in cartilage remodelling. Both drugs altered expression of extracellular matrix metalloproteinases. As proof-of-concept, we also tested drug treatment of disease-relevant mammalian cells. While leflunomide treatment inhibited the viability of several human NCSC-derived neuroblastoma cell lines coincident with altered expression of genes involved in ribosome biogenesis and transcription, FK506 enhanced murine calvarial osteoblast differentiation and prevented fusion of the coronal suture in calvarial explants taken from Crouzon syndrome mice.

Dissecting metabolism using zebrafish models of disease

Zebrafish (Danio rerio) are becoming an increasingly powerful model organism to study the role of metabolism in disease. Since its inception, the zebrafish model has relied on unique attributes such as the transparency of embryos, high fecundity and conservation with higher vertebrates, to perform phenotype-driven chemical and genetic screens. In this review, we describe how zebrafish have been used to reveal novel mechanisms by which metabolism regulates embryonic development, obesity, fatty liver disease and cancer. In addition, we will highlight how new approaches in advanced microscopy, transcriptomics and metabolomics using zebrafish as a model system have yielded fundamental insights into the mechanistic underpinnings of disease.

Platelet-Inspired Nanocells for Targeted Heart Repair After Ischemia/Reperfusion Injury

Cardiovascular disease is the leading cause of mortality worldwide. While reperfusion therapy is vital for patient survival post-heart attack, it also causes further tissue injury, known as myocardial ischemia/reperfusion (I/R) injury in clinical practice. Exploring ways to attenuate I/R injury is of clinical interest for improving post-ischemic recovery. A platelet-inspired nanocell (PINC) that incorporates both prostaglandin E2 (PGE2)-modified platelet membrane and cardiac stromal cell-secreted factors to target the heart after I/R injury is introduced. By taking advantage of the natural infarct-homing ability of platelet membrane and the overexpression of PGE2 receptors (EPs) in the pathological cardiac microenvironment after I/R injury, the PINCs can achieve targeted delivery of therapeutic payload to the injured heart. Furthermore, a synergistic treatment efficacy can be achieved by PINC, which combines the paracrine mechanism of cell therapy with the PGE2/EP receptor signaling that is involved in the repair and regeneration of multiple tissues. In a mouse model of myocardial I/R injury, intravenous injection of PINCs results in augmented cardiac function and mitigated heart remodeling, which is accompanied by the increase in cycling cardiomyocytes, activation of endogenous stem/progenitor cells, and promotion of angiogenesis. This approach represents a promising therapeutic delivery platform for treating I/R injury.

Estradiol induces cell proliferation in MCF‑7 mammospheres through HER2/COX‑2

Cluster of differentiation (CD)44+/CD24- breast cancer cells have stem cell‑like characteristics and are potent initiators of tumorigenesis. Mammosphere cells can partially initiate breast tumorigenesis by inducing estradiol (E2)‑dependent breast cancer cells. However, the mechanisms by which E2 mediates cancer formation in MCF‑7 mammosphere (MS) cells have remained elusive. In the present study, MS cells were isolated by sphere culture. It was possible to maintain these MS cells in culture for long periods of time, while retaining the CD44+/CD24- stem cell marker status. The CD44+/CD24- status was confirmed by flow cytometry. Furthermore, the stem‑cell markers Musashi‑1, cytokeratin (CK)7 and CK19 were identified by immunofluorescence microscopy. It was revealed that treatment of MS cells with E2 increased the expression of CD44, whereas decreased the expression of CD24 on MS cells. In addition, treatment with E2 increased colony formation by MS cells. E2 also induced cyclooxygenase‑2 (COX‑2) expression in MS cells, which promoted their proliferation through the estrogen receptor/human epidermal growth factor receptor 2 (HER2)/mitogen‑activated protein kinase/phosphoinositide‑3 kinase signaling pathway. The results suggested a tumorigenic mechanism by which E2 promotes tumor cell proliferation via HER2/COX‑2 signaling. The present study provided evidence for the molecular impact of E2 on breast tumorigenesis, and suggested possible strategies for preventing and treating human breast cancer.

Zebrafish disease models in hematology: Highlights on biological and translational impact

Zebrafish (Danio rerio) has proven to be a versatile and reliable in vivo experimental model to study human hematopoiesis and hematological malignancies. As vertebrates, zebrafish has significant anatomical and biological similarities to humans, including the hematopoietic system. The powerful genome editing and genome-wide forward genetic screening tools have generated models that recapitulate human malignant hematopoietic pathologies in zebrafish and unravel cellular mechanisms involved in these diseases. Moreover, the use of zebrafish models in large-scale chemical screens has allowed the identification of new molecular targets and the design of alternative therapies. In this review we summarize the recent achievements in hematological research that highlight the power of the zebrafish model for discovery of new therapeutic molecules. We believe that the model is ready to give an immediate translational impact into the clinic.

Peripheral blood stem cell mobilization; a look ahead

THE PURPOSE OF REVIEW

Mobilized peripheral blood is the predominant source of stem and progenitor cells for hematologic transplantation. Successful transplant requires sufficient stem cells of high enough quality to recapitulate lifelong hematopoiesis, but in some patients and normal donors, reaching critical threshold stem cell numbers are difficult to achieve. Novel strategies, particularly those offering rapid mobilization and reduced costs, remains an area of interest.This review summarizes critical scientific underpinnings in understanding the process of stem cell mobilization, with a focus on new or improved strategies for their efficient collection and engraftment.

RECENT FINDINGS

Studies are described that provide new insights into the complexity of stem cell mobilization. Agents that target new pathways such HSC egress, identify strategies to collect more potent competing HSC and new methods to optimize stem cell collection and engraftment are being evaluated.

SUMMARY

Agents and more effective strategies that directly address the current shortcomings of hematopoietic stem cell mobilization and transplantation and offer the potential to facilitate collection and expand use of mobilized stem cells have been identified.

ppargc1a controls nephron segmentation during zebrafish embryonic kidney ontogeny

Nephron segmentation involves a concert of genetic and molecular signals that are not fully understood. Through a chemical screen, we discovered that alteration of peroxisome proliferator-activated receptor (PPAR) signaling disrupts nephron segmentation in the zebrafish embryonic kidney (Poureetezadi et al., 2016). Here, we show that the PPAR co-activator ppargc1a directs renal progenitor fate. ppargc1a mutants form a small distal late (DL) segment and an expanded proximal straight tubule (PST) segment. ppargc1a promotes DL fate by regulating the transcription factor tbx2b, and restricts expression of the transcription factor sim1a to inhibit PST fate. Interestingly, sim1a restricts ppargc1a expression to promote the PST, and PST development is fully restored in ppargc1a/sim1a-deficient embryos, suggesting Ppargc1a and Sim1a counterbalance each other in an antagonistic fashion to delineate the PST segment boundary during nephrogenesis. Taken together, our data reveal new roles for Ppargc1a during development, which have implications for understanding renal birth defects.

In vitro and in vivo evaluation of possible pro-survival activities of PGE2, EGF, TPO and FLT3L on human hematopoiesis

Myelosuppression is a major and frequently dose-limiting side effect of anticancer therapy and is responsible for most treatment-related morbidity and mortality. In addition, repeated cycles of DNA damage and cell death of hematopoietic stem and progenitor cells, followed by compensatory proliferation and selection pressure, lead to genomic instability and pave the way for therapy-related myelodysplastic syndromes and secondary acute myeloid leukemia. Protection of hematopoietic stem and progenitor cells from chemo- and radiotherapy in patients with solid tumors would reduce both immediate complications and long-term sequelae. Epidermal growth factor (EGF) and prostaglandin E2 (PGE2) were reported to prevent chemo- or radiotherapy-induced myelosuppression in mice. We tested both molecules for potentially protective effects on human CD34⁺ cells in vitro and established a xenograft mouse model to analyze stress resistance and regeneration of human hematopoiesis in vivo. EGF was neither able to protect human stem and progenitor cells in vitro nor to promote hematopoietic regeneration following sublethal irradiation in vivo. PGE2 significantly reduced in vitro apoptotic susceptibility of human CD34⁺ cells to taxol and etoposide. This could, however, be ascribed to reduced proliferation rather than to a change in apoptosis signaling and BCL-2 protein regulation. Accordingly, 16,16-dimethyl-PGE2 (dmPGE2) did not accelerate regeneration of the human hematopoietic system in vivo. Repeated treatment of sublethally irradiated xenograft mice with known antiapoptotic substances, such as human FLT3L and thrombopoietin (TPO), which suppress transcription of the proapoptotic BCL-2 proteins BIM and BMF, also only marginally promoted human hematopoietic regeneration in vivo.

Maintenance of human haematopoietic stem and progenitor cells in vitro using a chemical cocktail

Identification of effective culture conditions to maintain and possibly expand human HSPCs in vitro is an important goal. Recent advances highlight the efficacy of chemicals in maintaining and converting cell fates. We screened 186 chemicals and found that a combination of CHIR-99021, Forskolin and OAC1 (CFO) maintained human CD34-positive cells in vitro. Efficiency of the culture system was characterized using flow cytometry for CD34-positive cells, a colony-forming assay and xeno-transplants. We found that human CD34-positive cells treated with this combination had enhanced expression of human HSPC markers and increased haematopoietic re-populating ability in immune-deficient mice. Single-cell RNA-seq analyses showed that the in vitro cultured human CD34-positive cells were heterogeneous. We found that CFO supports maintenance of human CD34-positive cells by activating HOXA9, GATA2 and AKT-cAMP signaling pathway. These data have implications in therapies requiring maintenance and/or expansion of human HSPCs.

Zebrafish: Speeding Up the Cancer Drug Discovery Process

Zebrafish (Danio rerio) is an ideal in vivo model to study a wide variety of human cancer types. In this review, we provide a comprehensive overview of zebrafish in the cancer drug discovery process, from (i) approaches to induce malignant tumors, (ii) techniques to monitor cancer progression, and (iii) strategies for compound administration to (iv) a compilation of the 355 existing case studies showing the impact of zebrafish models on cancer drug discovery, which cover a broad scope of scenarios. Finally, based on the current state-of-the-art analysis, this review presents some highlights about future directions using zebrafish in cancer drug discovery and the potential of this model as a prognostic tool in prospective clinical studies. Cancer Res; 78(21); 6048-58. ©2018 AACR.

Bloody Zebrafish: Novel Methods in Normal and Malignant Hematopoiesis

Hematopoiesis is an optimal system for studying stem cell maintenance and lineage differentiation under physiological and pathological conditions. In vertebrate organisms, billions of differentiated hematopoietic cells need to be continuously produced to replenish the blood cell pool. Disruptions in this process have immediate consequences for oxygen transport, responses against pathogens, maintenance of hemostasis and vascular integrity. Zebrafish is a widely used and well-established model for studying the hematopoietic system. Several new hematopoietic regulators were identified in genetic and chemical screens using the zebrafish model. Moreover, zebrafish enables in vivo imaging of hematopoietic stem cell generation and differentiation during embryogenesis, and adulthood. Finally, zebrafish has been used to model hematopoietic diseases. Recent technological advances in single-cell transcriptome analysis, epigenetic regulation, proteomics, metabolomics, and processing of large data sets promise to transform the current understanding of normal, abnormal, and malignant hematopoiesis. In this perspective, we discuss how the zebrafish model has proven beneficial for studying physiological and pathological hematopoiesis and how these novel technologies are transforming the field.

Zebrafish: an emerging real-time model system to study Alzheimer's disease and neurospecific drug discovery

Zebrafish (Danio rerio) is emerging as an increasingly successful model for translational research on human neurological disorders. In this review, we appraise the high degree of neurological and behavioural resemblance of zebrafish with humans. It is highly validated as a powerful vertebrate model for investigating human neurodegenerative diseases. The neuroanatomic and neurochemical pathways of zebrafish brain exhibit a profound resemblance with the human brain. Physiological, emotional and social behavioural pattern similarities between them have also been well established. Interestingly, zebrafish models have been used successfully to simulate the pathology of Alzheimer’s disease (AD) as well as Tauopathy. Their relatively simple nervous system and the optical transparency of the embryos permit real-time neurological imaging. Here, we further elaborate on the use of recent real-time imaging techniques to obtain vital insights into the neurodegeneration that occurs in AD. Zebrafish is adeptly suitable for Ca²⁺ imaging, which provides a better understanding of neuronal activity and axonal dystrophy in a non-invasive manner. Three-dimensional imaging in zebrafish is a rapidly evolving technique, which allows the visualisation of the whole organism for an elaborate in vivo functional and neurophysiological analysis in disease condition. Suitability to high-throughput screening and similarity with humans makes zebrafish an excellent model for screening neurospecific compounds. Thus, the zebrafish model can be pivotal in bridging the gap from the bench to the bedside. This fish is becoming an increasingly successful model to understand AD with further scope for investigation in neurodevelopment and neurodegeneration, which promises exciting research opportunities in the future.

How Surrogate and Chemical Genetics in Model Organisms Can Suggest Therapies for Human Genetic Diseases

Genetic diseases are both inherited and acquired. Many genetic diseases fall under the paradigm of orphan diseases, a disease found in < 1 in 2000 persons. With rapid and cost-effective genome sequencing becoming the norm, many causal mutations for genetic diseases are being rapidly determined. In this regard, model organisms are playing an important role in validating if specific mutations identified in patients drive the observed phenotype. An emerging challenge for model organism researchers is the application of genetic and chemical genetic platforms to discover drug targets and drugs/drug-like molecules for potential treatment options for patients with genetic disease. This review provides an overview of how model organisms have contributed to our understanding of genetic disease, with a focus on the roles of yeast and zebrafish in gene discovery and the identification of compounds that could potentially treat human genetic diseases.

Zebrafish (Danio rerio): A valuable tool for predicting the metabolism of xenobiotics in humans?

Zebrafish has become a popular model organism in several lines of biological research sharing physiological, morphological and histological similarities with mammals. In fact, many human cytochrome P450 (CYP) enzymes have direct orthologs in zebrafish, suggesting that zebrafish xenobiotic metabolic profiles may be similar to those in mammals. The focus of the review is to analyse the studies that have evaluated the metabolite production in zebrafish over the years, either of the drugs themselves or xenobiotics in general (environmental pollutants, natural products, etc.), bringing a vision of how these works were performed and comparing, where possible, with human metabolism. Early studies that observed metabolic production by zebrafish focused on environmental toxicology, and in recent years the main focus has been on toxicity screening of pharmaceuticals and drug candidates. Nevertheless, there is still a lack of standardization of the model and the knowledge of the extent of similarity with human metabolism. Zebrafish screenings are performed at different life stages, typically being carried out in adult fish through in vivo assays, followed by early larval stages and embryos. Studies comparing metabolism at the different zebrafish life stages are also common. As with any non-human model, the zebrafish presents similarities and differences in relation to the profile of generated metabolites compared to that observed in humans. Although more studies are still needed to assess the degree to which zebrafish metabolism can be compared to human metabolism, the facts presented indicate that the zebrafish is an excellent potential model for assessing xenobiotic metabolism.

Identification and expression of prostaglandin E synthase (PGES) gene in the central nervous system and ovary during ovarian maturation of the female mud crab, Scylla olivacea

Prostaglandins have important physiological roles in marine invertebrates, including larval development and reproduction. The prostaglandin E concentration fluctuates during the ovarian development of crustaceans. The biosynthetic pathway of prostaglandin, however, has not been well studied in portunid crabs, including in the mud crab, Scylla olivacea. In this study, the aim was to investigate the presence of prostaglandin E synthase (PGES), enzyme that catalyzes the terminal conversion in the prostaglandin E2 (PGE₂) biosynthesis, and its gene expression in the central nervous system (CNS) and ovary during ovarian maturation of S. olivacea. cDNA sequence encoding PGES was cloned from the S. olivacea ovary. The PGES transcript of S. olivacea (Scyol-PGES) consists of 1258 nucleotides, which encodes for 420 amino acid PGES protein precursor. Investigation of gene expression by RT-PCR indicated that Scyol-PGES was detected in all organs studied. Based on in situ hybridization, Scyol-PGES was detected in the I to III stages for oocyte development of Stage 3 of ovarian development, and in the CNS, including the various neuronal clusters of the brain. In the ventral nerve cord, the Scyol-PGES gene was expressed in the neurons within the subesophageal, thoracic and abdominal ganglia. The Scyol-PGES gene expression as indicated by relative abundance of mRNA in the Stage 4 of ovarian development was greater than that at Stages 1 to 3 of ovarian development. This is the first report on PGES in the mud crab, S. olivacea, and its gene expression suggested the involvement of PGES in the ovarian development of this species.

Genetic Models of Leukemia in Zebrafish

The zebrafish animal model is gaining increasing popularity as a tool for studying human disease. Over the past 15 years, many models of leukemia and other hematological malignancies have been developed in the zebrafish. These confer some significant advantages over similar models in other animals and systems, representing a powerful resource for investigation of the molecular basis of human leukemia. This review discusses the various zebrafish models of lymphoid and myeloid leukemia available, the major discoveries that have been made possible by them, and opportunities for future exploration.

Endometrial Stem Cells in Farm Animals: Potential Role in Uterine Physiology and Pathology

The endometrium is an accessible source of mesenchymal stem cells. Most investigations of endometrial mesenchymal stem cells (eMSCs) have been conducted in humans. In animals, particularly in livestock, eMSC research is scarce. Such cells have been described in the bovine, ovine, caprine, porcine, and equine endometrium. Here we provide the state of the art of eMSCs in farm animals with a focus on the bovine species. In bovines, eMSCs have been identified during the phases of the estrous cycle, during which their functionality and the presence of eMSC-specific markers has been shown to change. Moreover, postpartum inflammation related to endometritis affects the presence and functionality of eMSCs, and prostaglandin E₂ (PGE₂) may be the mediator of such changes. We demonstrated that exposure to PGE₂ in vitro modifies the transcriptomic profile of eMSCs, showing its potential role in the fate of stem cell activation, migration, and homing during pathological uterine inflammation in endometritis and in healthy puerperal endometrium. Farm animal research on eMSCs can be of great value in translational research for certain uterine pathologies and for immunomodulation of local responses to pathogens, hormones, and other substances. Further research is necessary in areas such as in vivo location of the niches and their immunomodulatory and anti-infective properties.

Zebrafish blastomere screen identifies retinoic acid suppression of MYB in adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is a salivary gland malignancy that has no effective therapy and is caused by translocations involving MYB. A zebrafish chemical genetic screen identifies the retinoic acid class of compounds as potential MYB-inhibitory agents. Preclinical ACC mouse xenotransplantation models confirm the in vivo efficacy of retinoic acid, which represents a potential therapy for ACC.

Pluripotent cells have been used to probe developmental pathways that are involved in genetic diseases and oncogenic events. To find new therapies that would target MYB-driven tumors, we developed a pluripotent zebrafish blastomere culture system. We performed a chemical genetic screen and identified retinoic acid agonists as suppressors of c-myb expression. Retinoic acid treatment also decreased c-myb gene expression in human leukemia cells. Translocations that drive overexpression of the oncogenic transcription factor MYB are molecular hallmarks of adenoid cystic carcinoma (ACC), a malignant salivary gland tumor with no effective therapy. Retinoic acid agonists inhibited tumor growth in vivo in ACC patient–derived xenograft models and decreased MYB binding at translocated enhancers, thereby potentially diminishing the MYB positive feedback loop driving ACC. Our findings establish the zebrafish pluripotent cell culture system as a method to identify modulators of tumor formation, particularly establishing retinoic acid as a potential new effective therapy for ACC.

Genetic Renal Diseases: The Emerging Role of Zebrafish Models

The structural and functional similarity of the larval zebrafish pronephros to the human nephron, together with the recent development of easier and more precise techniques to manipulate the zebrafish genome have motivated many researchers to model human renal diseases in the zebrafish. Over the last few years, great advances have been made, not only in the modeling techniques of genetic diseases in the zebrafish, but also in how to validate and exploit these models, crossing the bridge towards more informative explanations of disease pathophysiology and better designed therapeutic interventions in a cost-effective in vivo system. Here, we review the significant progress in these areas giving special attention to the renal phenotype evaluation techniques. We further discuss the future applications of such models, particularly their role in revealing new genetic diseases of the kidney and their potential use in personalized medicine.

PGE2 production at sites of tissue injury promotes an anti-inflammatory neutrophil phenotype and determines the outcome of inflammation resolution in vivo

Neutrophils are the first immune cells recruited to a site of injury or infection, where they perform many functions. Having completed their role, neutrophils must be removed from the inflammatory site-either by apoptosis and efferocytosis or by reverse migration away from the wound-for restoration of normal tissue homeostasis. Disruption of these tightly controlled physiological processes of neutrophil removal can lead to a range of inflammatory diseases. We used an in vivo zebrafish model to understand the role of lipid mediator production in neutrophil removal. Following tailfin amputation in the absence of macrophages, neutrophillic inflammation does not resolve, due to loss of macrophage-dependent handling of eicosanoid prostaglandin E2 (PGE2) that drives neutrophil removal via promotion of reverse migration. Knockdown of endogenous PGE synthase gene reveals PGE2 as essential for neutrophil inflammation resolution. Furthermore, PGE2 is able to signal through EP4 receptors during injury, causing an increase in Alox12 production and switching toward anti-inflammatory eicosanoid signaling. Our data confirm regulation of neutrophil migration by PGE2 and LXA4 (lipoxin A4) in an in vivo model of inflammation resolution. This pathway may contain therapeutic targets for driving inflammation resolution in chronic inflammatory disease.

Specific oxylipins enhance vertebrate hematopoiesis via the receptor GPR132

Epoxyeicosatrienoic acids (EETs) are lipid-derived signaling molecules with cardioprotective and vasodilatory actions. We recently showed that 11,12-EET enhances hematopoietic induction and engraftment in mice and zebrafish. EETs are known to signal via G protein-coupled receptors, with evidence supporting the existence of a specific high-affinity receptor. Identification of a hematopoietic-specific EET receptor would enable genetic interrogation of EET signaling pathways, and perhaps clinical use of this molecule. We developed a bioinformatic approach to identify an EET receptor based on the expression of G protein-coupled receptors in cell lines with differential responses to EETs. We found 10 candidate EET receptors that are expressed in three EET-responsive cell lines, but not expressed in an EET-unresponsive line. Of these, only recombinant GPR132 showed EET-responsiveness in vitro, using a luminescence-based β-arrestin recruitment assay. Knockdown of zebrafish gpr132b prevented EET-induced hematopoiesis, and marrow from GPR132 knockout mice showed decreased long-term engraftment capability. In contrast to high-affinity EET receptors, GPR132 is reported to respond to additional hydroxy-fatty acids in vitro, and we found that these same hydroxy-fatty acids enhance hematopoiesis in the zebrafish. We conducted structure-activity relationship analyses using both cell culture and zebrafish assays on diverse medium-chain fatty acids. Certain oxygenated, unsaturated free fatty acids showed high activation of GPR132, whereas unoxygenated or saturated fatty acids had lower activity. Absence of the carbon-1 position carboxylic acid prevented activity, suggesting that this moiety is required for receptor activation. GPR132 responds to a select panel of oxygenated polyunsaturated fatty acids to enhance both embryonic and adult hematopoiesis.

Making HSCs in vitro: don't forget the hemogenic endothelium

Generating a hematopoietic stem cell (HSC) in vitro from nonhematopoietic tissue has been a goal of experimental hematologists for decades. Until recently, no in vitro-derived cell has closely demonstrated the full lineage potential and self-renewal capacity of a true HSC. Studies revealing stem cell ontogeny from embryonic mesoderm to hemogenic endothelium to HSC provided the key to inducing HSC-like cells in vitro from a variety of cell types. Here we review the path to this discovery and discuss the future of autologous transplantation with in vitro-derived HSCs as a therapeutic modality.

Suppression of m6A reader Ythdf2 promotes hematopoietic stem cell expansion

Transplantation of hematopoietic stem cells (HSCs) from human umbilical cord blood (hUCB) holds great promise for treating a broad spectrum of hematological disorders including cancer. However, the limited number of HSCs in a single hUCB unit restricts its widespread use. Although extensive efforts have led to multiple methods for ex vivo expansion of human HSCs by targeting single molecules or pathways, it remains unknown whether it is possible to simultaneously manipulate the large number of targets essential for stem cell self-renewal. Recent studies indicate that N⁶-methyladenosine (m⁶A) modulates the expression of a group of mRNAs critical for stem cell-fate determination by influencing their stability. Among several m⁶A readers, YTHDF2 is recognized as promoting targeted mRNA decay. However, the physiological functions of YTHDF2 in adult stem cells are unknown. Here we show that following the conditional knockout (KO) of mouse Ythdf2 the numbers of functional HSC were increased without skewing lineage differentiation or leading to hematopoietic malignancies. Furthermore, knockdown (KD) of human YTHDF2 led to more than a 10-fold increase in the ex vivo expansion of hUCB HSCs, a fivefold increase in colony-forming units (CFUs), and more than an eightfold increase in functional hUCB HSCs in the secondary serial of a limiting dilution transplantation assay. Mapping of m⁶A in RNAs from mouse hematopoietic stem and progenitor cells (HSPCs) as well as from hUCB HSCs revealed its enrichment in mRNAs encoding transcription factors critical for stem cell self-renewal. These m⁶A-marked mRNAs were recognized by Ythdf2 and underwent decay. In Ythdf2 KO HSPCs and YTHDF2 KD hUCB HSCs, these mRNAs were stabilized, facilitating HSC expansion. Knocking down one of YTHDF2's key targets, Tal1 mRNA, partially rescued the phenotype. Our study provides the first demonstration of the function of YTHDF2 in adult stem cell maintenance and identifies its important role in regulating HSC ex vivo expansion by regulating the stability of multiple mRNAs critical for HSC self-renewal, thus identifying potential for future clinical applications.

TGF-β receptor 1 regulates progenitors that promote browning of white fat

Objective

Beige/brite adipose tissue displays morphological characteristics and beneficial metabolic traits of brown adipose tissue. Previously, we showed that TGF-β signaling regulates the browning of white adipose tissue. Here, we inquired whether TGF-β signals regulated presumptive beige progenitors in white fat and investigated the TGF-β regulated mechanisms involved in beige adipogenesis.

Methods

We deleted TGF-β receptor 1 (TβRI) in adipose tissue (TβRI^AdKO mice) and, using flow-cytometry based assays, identified and isolated presumptive beige progenitors located in the stromal vascular cells of white fat. These cells were molecularly characterized to examine beige/brown marker expression and to investigate TGF-β dependent mechanisms. Further, the cells were transplanted into athymic nude mice to examine their adipogenesis potential.

Results

Deletion of TβRI promotes beige adipogenesis while reducing the detrimental effects of high fat diet feeding. Interaction of TGF-β signaling with the prostaglandin pathway regulated the appearance of beige adipocytes in white fat. Using flow cytometry techniques and stromal vascular fraction from white fat, we isolated presumptive beige stem/progenitor cells (iBSCs). Upon genetic or pharmacologic inhibition of TGF-β signaling, these cells express high levels of predominantly beige markers. Transplantation of TβRI-deficient stromal vascular cells or iBSCs into athymic nude mice followed by high fat diet feeding and stimulation of β-adrenergic signaling via CL316,243 injection or cold exposure promoted robust beige adipogenesis in vivo.

Conclusions

TβRI signals target the prostaglandin network to regulate presumptive beige progenitors in white fat capable of developing into beige adipocytes with functional attributes. Controlled inhibition of TβRI signaling and concomitant PGE2 stimulation has the potential to promote beige adipogenesis and improve metabolism.

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Loss of TβRI in adipose tissue promotes beige adipogenesis.

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TβRI regulates presumptive beige adipocyte progenitors in white fat.

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TβRI signals interact with the PGE2/Cox2 pathway during beige adipogenesis.

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TβRI regulates thermogenesis, mitochondrial bioenergetics and beige adipogenesis.

Interference Potential of Tannins and Chlorophylls in Zebrafish Phenotypic-Based Assays

Natural products are prolific producers of diverse chemical scaffolds, which have yielded several clinically useful drugs. However, the complex features of natural products present challenges for identifying bioactive molecules using high-throughput screens. For most assays, measured endpoints are either colorimetric or luminescence based. Thus, the presence of the major metabolites, tannins, and chlorophylls, in natural products could potentially interfere with these measurements to give either false-positive or false-negative hits. In this context, zebrafish phenotypic assays provide an alternative approach to bioprospect naturally occurring bioactive compounds. Whether tannins and/or chlorophylls interfere in zebrafish phenotypic assays, is unclear. In this study, we evaluated the interference potential of tannins and chlorophylls against efficacy of known small-molecule inhibitors that are known to cause phenotypic abnormalities in developing zebrafish embryos. First, we fractionated tannin-enriched fraction (TEF) and chlorophyll-enriched fraction (CEF) from Camellia sinensis and cotreated them with PD0325901 [mitogen-activated protein kinase-kinase (MEK) inhibitor] and sunitinib malate (SM; anti-[lymph]angiogenic drug). While TEF and CEF did not interfere with phenotypic or molecular endpoints of PD0325901, TEF at 100 μg/mL partially masked the antiangiogenic effect of SM. On the other hand, CEF (100 μg/mL) was toxic when treated up to 6 dpf. Furthermore, CEF at 100 μg/mL potentially enhanced the activity of γ-secretase inhibitors, resulting in toxicity of treated embryos. Our study provides evidence that the presence of tannin and/or chlorophyll in natural products do interfere with zebrafish phenotype assays used for identifying potential hits. However, this may be target/assay dependent and thus requiring additional optimization steps to assess interference potential of tannins and chlorophylls before performing any screening assay.

An automated high-resolution in vivo screen in zebrafish to identify chemical regulators of myelination

Myelinating oligodendrocytes are essential for central nervous system (CNS) formation and function. Their disruption is implicated in numerous neurodevelopmental, neuropsychiatric and neurodegenerative disorders. However, recent studies have indicated that oligodendrocytes may be tractable for treatment of disease. In recent years, zebrafish have become well established for the study of myelinating oligodendrocyte biology and drug discovery in vivo. Here, by automating the delivery of zebrafish larvae to a spinning disk confocal microscope, we were able to automate high-resolution imaging of myelinating oligodendrocytes in vivo. From there, we developed an image analysis pipeline that facilitated a screen of compounds with epigenetic and post-translational targets for their effects on regulating myelinating oligodendrocyte number. This screen identified novel compounds that strongly promote myelinating oligodendrocyte formation in vivo. Our imaging platform and analysis pipeline is flexible and can be employed for high-resolution imaging-based screens of broad interest using zebrafish.

Caspase-independent cell death does not elicit a proliferative response in melanoma cancer cells

Background

Apoptosis, the most well-known type of programmed cell death, can induce in a paracrine manner a proliferative response in neighboring surviving cells called apoptosis-induced proliferation (AiP). While having obvious benefits when triggered in developmental processes, AiP is a serious obstacle in cancer therapy, where apoptosis is frequently induced by chemotherapy. Therefore, in this study, we evaluated the capacity of an alternative type of cell death, called caspase-independent cell death, to promote proliferation.

Results

Using a novel in vitro isogenic cellular model to trigger either apoptosis or caspase-independent cell death, we found that the later has no obvious compensatory proliferation effects on neighboring cells.

Conclusions

This study enforces the idea that alternative types of cell death such as caspase-independent cell death could be considered to replace apoptosis in the context of cancer treatment.

Electronic supplementary material

The online version of this article (10.1186/s12860-018-0164-1) contains supplementary material, which is available to authorized users.

Prostaglandin E2 Stimulates the Expansion of Regulatory Hematopoietic Stem and Progenitor Cells in Type 1 Diabetes

Hematopoietic stem and progenitor cells (HSPCs) are multipotent stem cells that have been harnessed as a curative therapy for patients with hematological malignancies. Notably, the discovery that HSPCs are endowed with immunoregulatory properties suggests that HSPC-based therapeutic approaches may be used to treat autoimmune diseases. Indeed, infusion with HSPCs has shown promising results in the treatment of type 1 diabetes (T1D) and remains the only “experimental therapy” that has achieved a satisfactory rate of remission (nearly 60%) in T1D. Patients with newly diagnosed T1D have been successfully reverted to normoglycemia by administration of autologous HSPCs in association with a non-myeloablative immunosuppressive regimen. However, this approach is hampered by a high incidence of adverse effects linked to immunosuppression. Herein, we report that while the use of autologous HSPCs is capable of improving C-peptide production in patients with T1D, ex vivo modulation of HSPCs with prostaglandins (PGs) increases their immunoregulatory properties by upregulating expression of the immune checkpoint-signaling molecule PD-L1. Surprisingly, CXCR4 was upregulated as well, which could enhance HSPC trafficking toward the inflamed pancreatic zone. When tested in murine and human in vitro autoimmune assays, PG-modulated HSPCs were shown to abrogate the autoreactive T cell response. The use of PG-modulated HSPCs may thus provide an attractive and novel treatment of autoimmune diabetes.

The caudal dorsal artery generates hematopoietic stem and progenitor cells via the endothelial-to-hematopoietic transition in zebrafish

Zebrafish hematopoietic stem and progenitor cells (HSPCs) originate from the hemogenic endothelium of the ventral wall of the dorsal aorta (DA) through the endothelial-to-hematopoietic transition (EHT) from approximately 30 to 60 hours post fertilization (hpf). However, whether other artery sites can generate HSPCs de novo remains unclear. In this study, using live imaging and lineage tracing, we found that the caudal dorsal artery (CDA) in the caudal hematopoietic tissue directly gave rise to HSPCs through EHT. This process initiated from approximately 60 hpf and terminated at approximately 156 hpf. Compared with that in the DA, fewer EHT events were observed in the CDA. The EHT events in the DA and CDA were similarly regulated by Runx1 but differentially influenced by blood flow (i.e., the EHT frequency in CDA was affected to a lesser extent when circulation was compromised in the tnnt2a-/- mutant). Therefore, the whole artery, including both DA and CDA, was endowed with the ability to produce HSPCs during a much longer time period. Coincidently, the lineage tracing results indicated that adult hematopoietic cells originated from the embryonic endothelium, and those produced later preferentially colonized the adult thymus. Collectively, our study revealed that the CDA serves as an additional source of hematopoiesis, and it shows similar but not identical properties with the DA.

A second-generation 15-PGDH inhibitor promotes bone marrow transplant recovery independently of age, transplant dose and granulocyte colony-stimulating factor support

Hematopoietic stem cell transplantation following myeloablative chemotherapy is a curative treatment for many hematopoietic malignancies. However, profound granulocytopenia during the interval between transplantation and marrow recovery exposes recipients to risks of fatal infection, a significant source of transplant-associated morbidity and mortality. We have previously described the discovery of a small molecule, SW033291, that potently inhibits the prostaglandin degrading enzyme 15-PGDH, increases bone marrow prostaglandin E2, and accelerates hematopoietic recovery following murine transplant. Here we describe the efficacy of (+)-SW209415, a second-generation 15-PGDH inhibitor, in an expanded range of models relevant to human transplantation. (+)-SW209415 is 10,000-fold more soluble, providing the potential for intravenous delivery, while maintaining potency in inhibiting 15-PGDH, increasing in vivo prostaglandin E2, and accelerating hematopoietic regeneration following transplantation. In additional models, (+)-SW209415: (i) demonstrated synergy with granulocyte colony-stimulating factor, the current standard of care; (ii) maintained efficacy as transplant cell dose was escalated; (iii) maintained efficacy when transplant donors and recipients were aged; and (iv) potentiated homing in xenotransplants using human hematopoietic stem cells. (+)-SW209415 showed no adverse effects, no potentiation of in vivo growth of human myeloma and leukemia xenografts, and, on chronic high-dose administration, no toxicity as assessed by weight, blood counts and serum chemistry. These studies provide independent chemical confirmation of the activity of 15-PGDH inhibitors in potentiating hematopoietic recovery, extend the range of models in which inhibiting 15-PGDH demonstrates activity, allay concerns regarding potential for adverse effects from increasing prostaglandin E2, and thereby, advance 15-PGDH as a therapeutic target for potentiating hematopoietic stem cell transplantation.

Neural Crossroads in the Hematopoietic Stem Cell Niche

The hematopoietic stem cell (HSC) niche supports steady-state hematopoiesis and responds to changing needs during stress and disease. The nervous system is an important regulator of the niche, and its influence is established early in development when stem cells are specified. Most research has focused on direct innervation of the niche, however recent findings show there are different modes of neural control, including globally by the central nervous system (CNS) and hormone release, locally by neural crest-derived mesenchymal stem cells, and intrinsically by hematopoietic cells that express neural receptors and neurotransmitters. Dysregulation between neural and hematopoietic systems can contribute to disease, however new therapeutic opportunities may be found among neuroregulator drugs repurposed to support hematopoiesis.

Oncostatin M and Kit-Ligand Control Hematopoietic Stem Cell Fate during Zebrafish Embryogenesis

Understanding the molecular pathways controlling hematopoietic stem cell specification and expansion is a necessary milestone to perform regenerative medicine. Here, we used the zebrafish model to study the role of the ckit signaling pathway in this process. We show the importance of kitb/kitlgb signaling in the specification and expansion of hematopoietic stem cells (HSCs), in the hemogenic endothelium and caudal hematopoietic tissue (CHT), respectively. Moreover, we identified the zebrafish ortholog of Oncostatin M (osm) in the zebrafish genome. We show that the osm/osmr pathway acts upstream of kitb during specification of the hemogenic endothelium, while both pathways act synergistically to expand HSCs in the CHT. Moreover, we found that osm, in addition to its role in promoting HSC proliferation, inhibits HSC commitment to the lymphoid fate. Altogether, our data identified two cytokines, kitlgb and osm, secreted by the vascular niche, that control HSCs during early embryonic development.

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kitb/kitlgb signaling is necessary for HSCs in the zebrafish model

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osm is a new cytokine important for HSCs in the zebrafish model

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osmr and kitb signaling are required sequentially for HSC specification

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osmr and kitb synergize to expand HSCs in the caudal hematopoietic tissue

Isthmin 1 (ism1) is required for normal hematopoiesis in developing zebrafish

Hematopoiesis is an essential and highly regulated biological process that begins with hematopoietic stem cells (HSCs). In healthy organisms, HSCs are responsible for generating a multitude of mature blood cells every day, yet the molecular pathways that instruct HSCs to self-renew and differentiate into post-mitotic blood cells are not fully known. To understand these molecular pathways, we investigated novel genes expressed in hematopoietic-supportive cell lines from the zebrafish (Danio rerio), a model system increasingly utilized to uncover molecular pathways important in the development of other vertebrate species. We performed RNA sequencing of the transcriptome of three stromal cell lines derived from different stages of embryonic and adult zebrafish and identified hundreds of highly expressed transcripts. For our studies, we focused on isthmin 1 (ism1) due to its shared synteny with its human gene ortholog and because it is a secreted protein. To characterize ism1, we performed loss-of-function experiments to identify if mature blood cell production was disrupted. Myeloid and erythroid lineages were visualized and scored with transgenic zebrafish expressing lineage-specific markers. ism1 knockdown led to reduced numbers of neutrophils, macrophages, and erythrocytes. Analysis of clonal methylcellulose assays from ism1 morphants also showed a reduction in total hematopoietic stem and progenitor cells (HSPCs). Overall, we demonstrate that ism1 is required for normal generation of HSPCs and their downstream progeny during zebrafish hematopoiesis. Further investigation into ism1 and its importance in hematopoiesis may elucidate evolutionarily conserved processes in blood formation that can be further investigated for potential clinical utility.

Lipoprotein lipase regulates hematopoietic stem progenitor cell maintenance through DHA supply

Lipoprotein lipase (LPL) mediates hydrolysis of triglycerides (TGs) to supply free fatty acids (FFAs) to tissues. Here, we show that LPL activity is also required for hematopoietic stem progenitor cell (HSPC) maintenance. Knockout of Lpl or its obligatory cofactor Apoc2 results in significantly reduced HSPC expansion during definitive hematopoiesis in zebrafish. A human APOC2 mimetic peptide or the human very low-density lipoprotein, which carries APOC2, rescues the phenotype in apoc2 but not in lpl mutant zebrafish. Creating parabiotic apoc2 and lpl mutant zebrafish rescues the hematopoietic defect in both. Docosahexaenoic acid (DHA) is identified as an important factor in HSPC expansion. FFA-DHA, but not TG-DHA, rescues the HSPC defects in apoc2 and lpl mutant zebrafish. Reduced blood cell counts are also observed in Apoc2 mutant mice at the time of weaning. These results indicate that LPL-mediated release of the essential fatty acid DHA regulates HSPC expansion and definitive hematopoiesis.

Whole-organism phenotypic screening for anti-infectives promoting host health

To date, antibiotics have been identified on the basis of their ability to kill bacteria or inhibit their growth rather than directly for their capacity to improve clinical outcomes of infected patients. Although historically successful, this approach has led to the development of an antibiotic armamentarium that suffers from a number of shortcomings, including the inevitable emergence of resistance and, in certain infections, suboptimal efficacy leading to long treatment durations, infection recurrence, or high mortality and morbidity rates despite apparent bacterial sterilization. Conventional antibiotics fail to address the complexities of in vivo bacterial physiology and virulence, as well as the role of the host underlying the complex, dynamic interactions that cause disease. New interventions are needed, aimed at host outcome rather than microbiological cure. Here we review the role of screening models for cellular and whole-organism infection, including worms, flies, zebrafish, and mice, to identify novel therapeutic strategies and discuss their future implications.

Prostaglandin E2 Is Required for BMP4-Induced Mesoderm Differentiation of Human Embryonic Stem Cells

The accurate control of early cell fate specification during differentiation of human embryonic stem cells (hESCs) is critical for acquiring pure therapeutic cell populations of interest. Bone morphogenetic protein 4 (BMP4) is a key mesoderm inducer from ESCs. However, the molecular mechanism of the mesodermal cell fate decision induced by BMP4 remains unclear. Here, we demonstrate the requirement of a bioactive lipid, prostaglandin E₂ (PGE₂), for the mesoderm specification from hESCs by BMP4 induction. We show that BMP4 directly regulates the expression of the key enzyme for PGE₂ synthesis, COX-1, and promotes PGE₂ production. More importantly, in the absence of BMP4, forced COX-1 expression or PGE₂ treatment is sufficient to initiate mesoderm specification of hESCs by activation of EP2-PKA signaling and modulation of nuclear translocation of β-catenin. Together, our findings provide insights into the critical role of BMP regulation of PGE₂ synthesis and its downstream signaling in initiating mesoderm commitment of hESCs.

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COX-1 and PGE₂ played pivotal roles in the mesoderm specification of hESCs

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Specific inhibition of COX-1 suppressed mesoderm differentiation of hESCs

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BMP4 directly upregulated the transcription of the COX-1

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PGE₂ stimulated differentiation mainly via the EP2-PKA-GSK3β/β-catenin signaling pathway