ZNF574 is a quality control factor for defective ribosome biogenesis intermediates

Eukaryotic ribosome assembly is an intricate process that involves four ribosomal RNAs, 80 ribosomal proteins, and over 200 biogenesis factors that participate in numerous interdependent steps. The complexity and essentiality of this process create opportunities for deleterious mutations to occur, accumulate, and impact downstream cellular processes. "Dead-end" ribosome intermediates that result from biogenesis errors are rapidly degraded, affirming the existence of quality control (QC) pathway(s) that monitor ribosome assembly. However, the factors that differentiate between on-path and dead-end intermediates are unknown. We engineered a system to perturb ribosome assembly in human cells and discovered that faulty ribosomes are degraded via the ubiquitin-proteasome system. We identified ZNF574 as a key component of a QC pathway, which we term the ribosome assembly surveillance pathway (RASP). In an animal model, loss of ZNF574 leads to developmental defects, emphasizing the importance of RASP in organismal health.

Cebpa is required for haematopoietic stem and progenitor cell generation and maintenance in zebrafish

The CCAAT enhancer binding protein alpha (CEBPA) is crucial for myeloid differentiation and the balance of haematopoietic stem and progenitor cell (HSPC) quiescence and self-renewal, and its dysfunction can drive leukemogenesis. However, its role in HSPC generation has not been fully elucidated. Here, we utilized various zebrafish cebpa mutants to investigate the function of Cebpa in the HSPC compartment. Co-localization analysis showed that cebpa expression is enriched in nascent HSPCs. Complete loss of Cebpa function resulted in a significant reduction in early HSPC generation and the overall HSPC pool during embryonic haematopoiesis. Interestingly, while myeloid differentiation was impaired in cebpa N-terminal mutants expressing the truncated zP30 protein, the number of HSPCs was not affected, indicating a redundant role of Cebpa P42 and P30 isoforms in HSPC development. Additionally, epistasis experiments confirmed that Cebpa functions downstream of Runx1 to regulate HSPC emergence. Our findings uncover a novel role of Cebpa isoforms in HSPC generation and maintenance, and provide new insights into HSPC development.

Disruption of the ZFP574-THAP12 complex suppresses B cell malignancies in mice

Despite the availability of life-extending treatments for B cell leukemias and lymphomas, many of these cancers remain incurable. Thus, the development of new molecular targets and therapeutics is needed to expand treatment options. To identify new molecular targets, we used a forward genetic screen in mice to identify genes required for development or survival of lymphocytes. Here, we describe Zfp574, an essential gene encoding a zinc finger protein necessary for normal and malignant lymphocyte survival. We show that ZFP574 interacts with zinc finger protein THAP12 and promotes the G1-to-S-phase transition during cell cycle progression. Mutation of ZFP574 impairs nuclear localization of the ZFP574-THAP12 complex. ZFP574 or THAP12 deficiency results in cell cycle arrest and impaired lymphoproliferation. Germline mutation, acute gene deletion, or targeted degradation of ZFP574 suppressed Myc-driven B cell leukemia in mice, but normal B cells were largely spared, permitting long-term survival, whereas complete lethality was observed in control animals. Our findings support the identification of drugs targeting ZFP574-THAP12 as a unique strategy to treat B cell malignancies.

Temporal and cellular analysis of granuloma development in mycobacterial infected adult zebrafish

Because granulomas are a hallmark of tuberculosis pathogenesis, the study of the dynamic changes in their cellular composition and morphological character can facilitate our understanding of tuberculosis pathogenicity. Adult zebrafish infected with Mycobacterium marinum form granulomas that are similar to the granulomas in human patients with tuberculosis and therefore have been used to study host-mycobacterium interactions. Most studies of zebrafish granulomas, however, have focused on necrotic granulomas, while a systematic description of the different stages of granuloma formation in the zebrafish model is lacking. Here, we characterized the stages of granulomas in M. marinum-infected zebrafish, including early immune cell infiltration, nonnecrotizing granulomas, and necrotizing granulomas, using corresponding samples from patients with pulmonary tuberculosis as references. We combined hematoxylin and eosin staining and in situ hybridization to identify the different immune cell types and follow their spatial distribution in the different stages of granuloma development. The macrophages in zebrafish granulomas were shown to belong to distinct subtypes: epithelioid macrophages, foamy macrophages, and multinucleated giant cells. By defining the developmental stages of zebrafish granulomas and the spatial distribution of the different immune cells they contain, this work provides a reference for future studies of mycobacterial granulomas and their immune microenvironments.

Exploring hematopoiesis in zebrafish using forward genetic screening

Zebrafish have emerged as a powerful animal model for investigating the genetic basis of hematopoiesis. Owing to its close genetic and developmental similarities to humans, combined with its rapid reproduction and extensive genomic resources, zebrafish have become a versatile and efficient platform for genetic studies. In particular, the forward genetic screening approach has enabled the unbiased identification of novel genes and pathways related to blood development, from hematopoietic stem cell formation to terminal differentiation. Recent advances in mutant gene mapping have further expanded the scope of forward genetic screening, facilitating the identification of previously unknown genes and pathways relevant to hematopoiesis. In this review, we provide an overview of the zebrafish forward screening approach for hematopoietic gene discovery and highlight the key genes and pathways identified using this method. This review emphasizes the importance of zebrafish as a model system for understanding the genetic basis of hematopoiesis and its associated disorders.

Learning from Zebrafish Hematopoiesis

Hematopoiesis is a complex process that tightly regulates the generation, proliferation, differentiation, and maintenance of hematopoietic cells. Disruptions in hematopoiesis can lead to various diseases affecting both hematopoietic and non-hematopoietic systems, such as leukemia, anemia, thrombocytopenia, rheumatoid arthritis, and chronic granuloma. The zebrafish serves as a powerful vertebrate model for studying hematopoiesis, offering valuable insights into both hematopoietic regulation and hematopoietic diseases. In this chapter, we present a comprehensive overview of zebrafish hematopoiesis, highlighting its distinctive characteristics in hematopoietic processes. We discuss the ontogeny and modulation of both primitive and definitive hematopoiesis, as well as the microenvironment that supports hematopoietic stem/progenitor cells. Additionally, we explore the utility of zebrafish as a disease model and its potential in drug discovery, which not only advances our understanding of the regulatory mechanisms underlying hematopoiesis but also facilitates the exploration of novel therapeutic strategies for hematopoietic diseases.

Csf1rb regulates definitive hematopoiesis in zebrafish

In vertebrates, hematopoietic stem and progenitor cells (HSPCs) are capable of self-renewal and continuously replenishing all mature blood lineages throughout life. However, the molecular signaling regulating the maintenance and expansion of HSPCs remains incompletely understood. Colony-stimulating factor 1 receptor (CSF1R) is believed to be the primary regulator for the myeloid lineage but not HSPC development. Here, we show a surprising role of Csf1rb, a zebrafish homolog of mammalian CSF1R, in preserving the HSPC pool by maintaining the proliferation of HSPCs. Deficiency of csf1rb leads to a reduction in both HSPCs and their differentiated progenies, including myeloid, lymphoid and erythroid cells at early developmental stages. Likewise, the absence of csf1rb conferred similar defects upon HSPCs and leukocytes in adulthood. Furthermore, adult hematopoietic cells from csf1rb mutants failed to repopulate immunodeficient zebrafish. Interestingly, loss-of-function and gain-of-function assays suggested that the canonical ligands for Csf1r in zebrafish, including Csf1a, Csf1b and Il34, were unlikely to be ligands of Csf1rb. Thus, our data indicate a previously unappreciated role of Csf1r in maintaining HSPCs, independently of known ligands.

Down-Regulating HAUS6 Suppresses Cell Proliferation by Activating the p53/p21 Pathway in Colorectal Cancer

Background: HAUS6 participates in microtubule-dependent microtubule amplification, but its role in malignancies including colorectal cancer (CRC) has not been explored. We therefore assessed the potential oncogenic activities of HAUS6 in CRC. Results: HAUS6 mRNA and protein expression is higher in CRC tissues, and high HAUS6 expression is correlated with shorter overall survival in CRC patients. HAUS6 knockdown in CRC cell lines suppressed cell growth in vitro and in vivo by inhibiting cell viability, survival and arresting cell cycle progression at G0/G1, while HAUS6 over-expression increased cell viability. We showed that these effects are dependent on activation of the p53/p21 signalling pathway by reducing p53 and p21 degradation. Moreover, combination of HAUS6 knockdown and 5-FU treatment further enhanced the suppression of cell proliferation of CRC cells by increasing activation of the p53/p21 pathway. Conclusion: Our study highlights a potential oncogenic role for HAUS6 in CRC. Targeting HAUS6 may be a promising novel prognostic marker and chemotherapeutic target for treating CRC patients.

Slc20a1b is essential for hematopoietic stem/progenitor cell expansion in zebrafish

Hematopoietic stem and progenitor cells (HSPCs) are able to self-renew and can give rise to all blood lineages throughout their lifetime, yet the mechanisms regulating HSPC development have yet to be discovered. In this study, we characterized a hematopoiesis defective zebrafish mutant line named smu07, which was obtained from our previous forward genetic screening, and found the HSPC expansion deficiency in the mutant. Positional cloning identified that slc20a1b, which encodes a sodium phosphate cotransporter, contributed to the smu07 blood phenotype. Further analysis demonstrated that mutation of slc20a1b affects HSPC expansion through cell cycle arrest at G2/M phases in a cell-autonomous manner. Our study shows that slc20a1b is a vital regulator for HSPC proliferation in zebrafish early hematopoiesis and provides valuable insights into HSPC development.

Sub-centrosomal mapping identifies augmin-γTuRC as part of a centriole-stabilizing scaffold

Centriole biogenesis and maintenance are crucial for cells to generate cilia and assemble centrosomes that function as microtubule organizing centers (MTOCs). Centriole biogenesis and MTOC function both require the microtubule nucleator γ-tubulin ring complex (γTuRC). It is widely accepted that γTuRC nucleates microtubules from the pericentriolar material that is associated with the proximal part of centrioles. However, γTuRC also localizes more distally and in the centriole lumen, but the significance of these findings is unclear. Here we identify spatially and functionally distinct subpopulations of centrosomal γTuRC. Luminal localization is mediated by augmin, which is linked to the centriole inner scaffold through POC5. Disruption of luminal localization impairs centriole integrity and interferes with cilium assembly. Defective ciliogenesis is also observed in γTuRC mutant fibroblasts from a patient suffering from microcephaly with chorioretinopathy. These results identify a non-canonical role of augmin-γTuRC in the centriole lumen that is linked to human disease.

The spliceosome factor sart3 regulates hematopoietic stem/progenitor cell development in zebrafish through the p53 pathway

Hematopoietic stem cells (HSCs) possess the potential for self-renew and the capacity, throughout life, to differentiate into all blood cell lineages. Yet, the mechanistic basis for HSC development remains largely unknown. In this study, we characterized a zebrafish smu471 mutant with hematopoietic stem/progenitor cell (HSPC) defects and found that sart3 was the causative gene. RNA expression profiling of the sart3^smu471 mutant revealed spliceosome and p53 signaling pathway to be the most significantly enriched pathways in the sart3^smu471 mutant. Knock down of p53 rescued HSPC development in the sart3^smu471 mutant. Interestingly, the p53 inhibitor, mdm4, had undergone an alternative splicing event in the mutant. Restoration of mdm4 partially rescued HSPC deficiency. Thus, our data suggest that HSPC proliferation and maintenance require sart3 to ensure the correct splicing and expression of mdm4, so that the p53 pathway is properly inhibited to prevent definitive hematopoiesis failure. This study expands our knowledge of the regulatory mechanisms that impact HSPC development and sheds light on the mechanistic basis and potential therapeutic use of sart3 in spliceosome-mdm4-p53 related disorders.

Augmin deficiency in neural stem cells causes p53-dependent apoptosis and aborts brain development

Microtubules that assemble the mitotic spindle are generated by centrosomal nucleation, chromatin-mediated nucleation, and nucleation from the surface of other microtubules mediated by the augmin complex. Impairment of centrosomal nucleation in apical progenitors of the developing mouse brain induces p53-dependent apoptosis and causes non-lethal microcephaly. Whether disruption of non-centrosomal nucleation has similar effects is unclear. Here, we show, using mouse embryos, that conditional knockout of the augmin subunit Haus6 in apical progenitors led to spindle defects and mitotic delay. This triggered massive apoptosis and abortion of brain development. Co-deletion of Trp53 rescued cell death, but surviving progenitors failed to organize a pseudostratified epithelium, and brain development still failed. This could be explained by exacerbated mitotic errors and resulting chromosomal defects including increased DNA damage. Thus, in contrast to centrosomes, augmin is crucial for apical progenitor mitosis, and, even in the absence of p53, for progression of brain development.

Generation and Application of the Zebrafish heg1 Mutant as a Cardiovascular Disease Model

Cardiovascular disease (CVD) is the leading cause of global mortality, which has caused a huge burden on the quality of human life. Therefore, experimental animal models of CVD have become essential tools for analyzing the pathogenesis, developing drug screening, and testing potential therapeutic strategies. In recent decades, zebrafish has entered the field of CVD as an important model organism. HEG1, a heart development protein with EGF like domains 1, plays important roles in the development of vertebrate cardiovascular system. Loss of HEG1 will affect the stabilization of vascular endothelial cell connection and eventually lead to dilated cardiomyopathy (DCM). Here, we generated a heg1-specific knockout zebrafish line using CRISPR/Cas9 technology. Zebrafish heg1 mutant demonstrated severe cardiovascular malformations, including atrial ventricular enlargement, heart rate slowing, venous thrombosis and slow blood flow, which were similar to human heart failure and thrombosis phenotype. In addition, the expression of zebrafish cardiac and vascular markers was abnormal in heg1 mutants. In order to apply zebrafish heg1 mutant in cardiovascular drug screening, four Traditional Chinese Medicine (TCM) herbs and three Chinese herbal monomers were used to treat heg1 mutant. The pericardial area, the distance between sinus venosus and bulbus arteriosus (SV-BA), heart rate, red blood cells (RBCs) accumulation in posterior cardinal vein (PCV), and blood circulation in the tail vein were measured to evaluate the therapeutic effects of those drugs on DCM and thrombosis. Here, a new zebrafish model of DCM and thrombosis was established, which was verified to be suitable for drug screening of cardiovascular diseases. It provided an alternative method for traditional in vitro screening, and produced potential clinical related drugs in a rapid and cost-effective way.

Loss of runx1 function results in B cell immunodeficiency but not T cell in adult zebrafish

Transcription factor RUNX1 holds an integral role in multiple-lineage haematopoiesis and is implicated as a cofactor in V(D)J rearrangements during lymphocyte development. Runx1 deficiencies resulted in immaturity and reduction of lymphocytes in mice. In this study, we found that runx1^W84X/W84X mutation led to the reduction and disordering of B cells, as well as the failure of V(D)J rearrangements in B cells but not T cells, resulting in antibody-inadequate-mediated immunodeficiency in adult zebrafish. By contrast, T cell development was not affected. The decreased number of B cells mainly results from excessive apoptosis in immature B cells. Disrupted B cell development results in runx1^W84X/W84X mutants displaying a similar phenotype to common variable immunodeficiency—a primary immunodeficiency disease primarily characterized by frequent susceptibility to infection and deficient immune response, with marked reduction of antibody production of IgG, IgA and/or IgM. Our studies demonstrated an evolutionarily conserved function of runx1 in maturation and differentiation of B cells in adult zebrafish, which will serve as a valuable model for the study of immune deficiency diseases and their treatments.

Comparison of village dog and wolf genomes highlights the role of the neural crest in dog domestication

BACKGROUND

Domesticated from gray wolves between 10 and 40 kya in Eurasia, dogs display a vast array of phenotypes that differ from their ancestors, yet mirror other domesticated animal species, a phenomenon known as the domestication syndrome. Here, we use signatures persisting in dog genomes to identify genes and pathways possibly altered by the selective pressures of domestication.

RESULTS

Whole-genome SNP analyses of 43 globally distributed village dogs and 10 wolves differentiated signatures resulting from domestication rather than breed formation. We identified 246 candidate domestication regions containing 10.8 Mb of genome sequence and 429 genes. The regions share haplotypes with ancient dogs, suggesting that the detected signals are not the result of recent selection. Gene enrichments highlight numerous genes linked to neural crest and central nervous system development as well as neurological function. Read depth analysis suggests that copy number variation played a minor role in dog domestication.

CONCLUSIONS

Our results identify genes that act early in embryogenesis and can confer phenotypes distinguishing domesticated dogs from wolves, such as tameness, smaller jaws, floppy ears, and diminished craniofacial development as the targets of selection during domestication. These differences reflect the phenotypes of the domestication syndrome, which can be explained by alterations in the migration or activity of neural crest cells during development. We propose that initial selection during early dog domestication was for behavior, a trait influenced by genes which act in the neural crest, which secondarily gave rise to the phenotypes of modern dogs.

A zebrafish and mouse model for selective pruritus via direct activation of TRPA1

Little is known about the capacity of lower vertebrates to experience itch. A screen of itch-inducing compounds (pruritogens) in zebrafish larvae yielded a single pruritogen, the TLR7 agonist imiquimod, that elicited a somatosensory neuron response. Imiquimod induced itch-like behaviors in zebrafish distinct from those induced by the noxious TRPA1 agonist, allyl isothiocyanate. In the zebrafish, imiquimod-evoked somatosensory neuronal responses and behaviors were entirely dependent upon TRPA1, while in the mouse TRPA1 was required for the direct activation of somatosensory neurons and partially responsible for behaviors elicited by this pruritogen. Imiquimod was found to be a direct but weak TRPA1 agonist that activated a subset of TRPA1 expressing neurons. Imiquimod-responsive TRPA1 expressing neurons were significantly more sensitive to noxious stimuli than other TRPA1 expressing neurons. Together, these results suggest a model for selective itch via activation of a specialized subpopulation of somatosensory neurons with a heightened sensitivity to noxious stimuli.

Itch is a common and uncomfortable sensation that creates a strong desire to scratch. This mechanism may have evolved so animals can remove harmful parasites or substances from themselves. Feelings like touch, pain, and itch arise when stimuli such as mechanical pressure, temperature, or chemicals activate groups of specialized neurons in the skin. This response takes place when certain proteins – or receptors – at the surface of the neurons are stimulated. For instance, TRP ion channels such as TRPA1 play an important role in both the itch and pain responses. In mammals, directly activating these channels elicits pain. Itch is felt when itch responsive receptors are activated on a distinct set of neurons, which in turn activate TRP receptors. Although these processes have been well-studied in mammals, little is known about the existence of itch sensation in other animals.

To explore this, Esancy, Condon, Feng et al. exposed zebrafish to chemicals that induce itch in mammals, and found that imiquimod, a medicine used to treat certain skin conditions, can elicit itch in fish. When this chemical was injected into the lips of a fish, the animal rubbed them against the walls of its tank, akin to scratching an itch. Further experiments showed that imiquimod directly activated the pain-sensing ion channel TRPA1. In fact, this receptor was essential to the ‘scratching’ behavior: fish genetically engineered to lack TRPA1 did not react to the drug.

Fluorescent proteins were then used to track when the neurons that carry TRPA1 were activated.This revealed that, in the skin of zebrafish, there are at least two functionally distinct populations neurons that express TRPA1. One population, whose activation is associated with the animal ‘scratching’, responds even when TRPA1 receives a low level of stimulation. The other population is less sensitive: it responds only to high-intensity stimuli and is associated with a pain response such as freezing and slower movements. Further experiments in the mouse suggest that this mechanism is present in mammals as well. This coding strategy explains how pain and itch can be experienced when the same receptors are being activated.

Studying how animals like fish experience itch gives an insight into how detecting these sensations could have evolved. In turn, understanding this mechanism at the molecular and cellular levels may help find new ways to design better treatments for itch and pain disorders.

Engineering Hematopoietic Stem Cells: Lessons from Development

Cell engineering has brought us tantalizingly close to the goal of deriving patient-specific hematopoietic stem cells (HSCs). While directed differentiation and transcription factor-mediated conversion strategies have generated progenitor cells with multilineage potential, to date, therapy-grade engineered HSCs remain elusive due to insufficient long-term self-renewal and inadequate differentiated progeny functionality. A cross-species approach involving zebrafish and mammalian systems offers complementary methodologies to improve understanding of native HSCs. Here, we discuss the role of conserved developmental timing processes in vertebrate hematopoiesis, highlighting how identification and manipulation of stage-specific factors that specify HSC developmental state must be harnessed to engineer HSCs for therapy.

Metaphase Spindle Assembly

A microtubule-based bipolar spindle is required for error-free chromosome segregation during cell division. In this review I discuss the molecular mechanisms required for the assembly of this dynamic micrometer-scale structure in animal cells.

Understanding the regulation of vertebrate hematopoiesis and blood disorders - big lessons from a small fish

Hematopoietic stem cells (HSCs) give rise to all differentiated blood cells. Understanding the mechanisms that regulate self-renewal and lineage specification of HSCs is key for developing treatments for many human diseases. Zebrafish have emerged as an excellent model for studying vertebrate hematopoiesis. This review will highlight the unique strengths of zebrafish and important findings that have emerged from studies of blood development and disorders using this system. We discuss recent advances in our understanding of hematopoiesis, including the origin of HSCs, molecular control of their development, and key signaling pathways involved in their regulation. We highlight significant findings from zebrafish models of blood disorders and discuss their application for investigating stem cell dysfunction in disease and for the development of new therapeutics.

Intra-spindle Microtubule Assembly Regulates Clustering of Microtubule-Organizing Centers during Early Mouse Development

Errors during cell division in oocytes and early embryos are linked to birth defects in mammals. Bipolar spindle assembly in early mouse embryos is unique in that three or more acentriolar microtubule-organizing centers (MTOCs) are initially formed and are then clustered into two spindle poles. Using a knockout mouse and live imaging of spindles in embryos, we demonstrate that MTOC clustering during the blastocyst stage requires augmin, a critical complex for MT-dependent MT nucleation within the spindle. Functional analyses in cultured cells with artificially increased numbers of centrosomes indicate that the lack of intra-spindle MT nucleation, but not loss of augmin per se or overall reduction of spindle MTs, is the cause of clustering failure. These data suggest that onset of mitosis with three or more MTOCs is turned into a typical bipolar division through augmin-dependent intra-spindle MT assembly.

RNA polymerase III component Rpc9 regulates hematopoietic stem and progenitor cell maintenance in zebrafish

Hematopoietic stem and progenitor cells (HSPCs) are capable of self-renewal and replenishing all lineages of blood cells throughout the lifetime and thus critical for tissue homeostasis. However, the mechanism regulating HSPC development is still incompletely understood. Here, we isolate a zebrafish mutant with defective T lymphopoiesis and positional cloning identifies that Rpc9, a component of DNA-directed RNA polymerase III (Pol III) complex, is responsible for the mutant phenotype. Further analysis shows that rpc9-deficiency leads to the impairment of HSPCs and their derivatives in zebrafish embryos. Excessive apoptosis is observed in the caudal hematopoietic tissue (CHT, the equivalent of fetal liver in mammals) of rpc9−/− embryos and the hematopoietic defects in rpc9−/− embryos can be fully rescued by suppression of p53. Thus, our work illustrate that Rpc9, a component of Pol III, plays an important tissue-specific role in HSPC maintenance during zebrafish embryogenesis and that it might be conserved across vertebrates including mammals.

Fishing the targets of myeloid malignancies in the era of next generation sequencing

Recent advent in next generation sequencing (NGS) and bioinformatics has generated an unprecedented amount of genetic information in myeloidmalignancies. This information may shed lights to the pathogenesis, diagnosis and prognostication of these diseases and provide potential targets for therapeutic intervention. However, the rapid emergence of genetic information will quickly outpace their functional validation by conventional laboratory platforms. Foundational knowledge about zebrafish hematopoiesis accumulated over the past two decades and novel genomeediting technologies and research strategies in thismodel organismhavemade it a unique and timely research tool for the study of human blood diseases. Recent studies modeling human myeloid malignancies in zebrafish have also highlighted the technical feasibility and clinical relevance of thesemodels. Careful validation of experimental protocols and standardization among laboratorieswill further enhance the application of zebrafish in the scientific communities and provide important insights to the personalized treatment ofmyeloid malignancies.

TopBP1 Governs Hematopoietic Stem/Progenitor Cells Survival in Zebrafish Definitive Hematopoiesis

In vertebrate definitive hematopoiesis, nascent hematopoietic stem/progenitor cells (HSPCs) migrate to and reside in proliferative hematopoietic microenvironment for transitory expansion. In this process, well-established DNA damage response pathways are vital to resolve the replication stress, which is deleterious for genome stability and cell survival. However, the detailed mechanism on the response and repair of the replication stress-induced DNA damage during hematopoietic progenitor expansion remains elusive. Here we report that a novel zebrafish mutantcas003 with nonsense mutation in topbp1 gene encoding topoisomerase II β binding protein 1 (TopBP1) exhibits severe definitive hematopoiesis failure. Homozygous topbp1cas003 mutants manifest reduced number of HSPCs during definitive hematopoietic cell expansion, without affecting the formation and migration of HSPCs. Moreover, HSPCs in the caudal hematopoietic tissue (an equivalent of the fetal liver in mammals) in topbp1cas003 mutant embryos are more sensitive to hydroxyurea (HU) treatment. Mechanistically, subcellular mislocalization of TopBP1cas003 protein results in ATR/Chk1 activation failure and DNA damage accumulation in HSPCs, and eventually induces the p53-dependent apoptosis of HSPCs. Collectively, this study demonstrates a novel and vital role of TopBP1 in the maintenance of HSPCs genome integrity and survival during hematopoietic progenitor expansion.

Functional and molecular features of the calmodulin-interacting protein IQCG required for haematopoiesis in zebrafish

We previously reported a fusion protein NUP98-IQCG in an acute leukaemia, which functions as an aberrant regulator of transcriptional expression, yet the structure and function of IQCG have not been characterized. Here we use zebrafish to investigate the role of iqcg in haematopoietic development, and find that the numbers of haematopoietic stem cells and multilineage-differentiated cells are reduced in iqcg-deficient embryos. Mechanistically, IQCG binds to calmodulin (CaM) and acts as a molecule upstream of CaM-dependent kinase IV (CaMKIV). Crystal structures of complexes between CaM and IQ domain of IQCG reveal dual CaM-binding footprints in this motif, and provide a structural basis for a higher CaM-IQCG affinity when deprived of calcium. The results collectively allow us to understand IQCG-mediated calcium signalling in haematopoiesis, and propose a model in which IQCG stores CaM at low cytoplasmic calcium concentrations, and releases CaM to activate CaMKIV when calcium level rises.

MiR-144 regulates hematopoiesis and vascular development by targeting meis1 during zebrafish development

Hematopoiesis is a dynamic process by which peripheral blood lineages are developed. It is a process tightly regulated by many intrinsic and extrinsic factors, including transcriptional factors and signaling molecules. However, the epigenetic regulation of hematopoiesis, for example, regulation via microRNAs (miRNAs), remains incompletely understood. Here we show that miR-144 regulates hematopoiesis and vascular development in zebrafish. Overexpression of miR-144 inhibited primitive hematopoiesis as demonstrated by a reduced number of circulating blood cells, reduced o-dianisidine staining of hemoglobin, and reduced expression of hbαe1, hbβe1, gata1 and pu.1. Overexpression of miR-144 also inhibited definitive hematopoiesis as shown by reduced expression of runx1 and c-myb. Mechanistically, miR-144 regulates hematopoiesis by repressing expression of meis1 involved in hematopoiesis. Both real-time RT-PCR and Western blot analyses showed that overexpression of miR-144 repressed expression of meis1. Bioinformatic analysis predicts a target binding sequence for miR-144 at the 3'-UTR of meis1. Deletion of the miR-144 target sequence eliminated the repression of meis1 expression mediated by miR-144. The miR-144-mediated abnormal phenotypes were partially rescued by co-injection of meis1 mRNA and could be almost completely rescued by injection of both meis1 and gata1 mRNA. Finally, because meis1 is involved in vascular development, we tested the effect of miR-144 on vascular development. Overexpression of miR-144 resulted in abnormal vascular development of intersegmental vessels in transgenic zebrafish with Flk1p-EGFP, and the defect was rescued by co-injection of meis1 mRNA. These findings establish miR-144 as a novel miRNA that regulates hematopoiesis and vascular development by repressing expression of meis1.

Molecular mechanisms of angiogenesis effect of active sub-fraction from root of Rehmannia glutinosa by zebrafish sprout angiogenesis-guided fractionation

ETHNOPHARMACOLOGICAL IMPORTANCE

The root of Rehmannia glutinosa (Rehmanniae Radix (RR)) is clinically used as a wound-healing agent in traditional Chinese medicine. Angiogenesis acts crucially in the pathogenesis of chronic wound healing. The present study investigated the angiogenesis effect and its underlying mechanism of RR through zebrafish sprout angiogenesis guided-fractionation.

MATERIALS AND METHODS

The in vivo angiogenesis effect was studied by analyzing the number of ectopic sprouts formed upon sub-intestinal vessel of transgenic TG(fli1:EGFP)(y1)/+(AB) zebrafish embryos by fluorescence microscopy. Quantitative real-time PCR gene expression of the zebrafish embryos was further performed using a panel of 30 angiogenesis-associated genes designed for zebrafish sprout angiogenesis. Classical in vitro angiogenesis assays using human microvascular endothelial cells (HMEC-1) was accompanied.

RESULTS

We demonstrated that among all RR sub-fractions tested, C1-1 treated-zebrafish embryos possessed the most potent angiogenesis activities (from 190 to 780 ng/ml, p<0.001) in sprout formation in the zebrafish model. Quantitative gene expression of the treated embryos demonstrated significant up-regulation in MMP-9 (p<0.05), ANGPT1 (p<0.05), EGFR (p<0.05), EPHB4 (p<0.01), and significant down-regulation in Ephrin B2 (p<0.05), Flt-1 (p<0.05) and Ets-1 (p<0.05). C1-1 treatment could also significantly (p<0.001-0.05) stimulate HMEC-1 cell migration in scratch assay. Significant increase (p<0.05) in mean tubule length was observed in the C1-1-treated HMEC-1 cells in the tubule formation assay.

CONCLUSIONS

Our zebrafish sprout angiogenesis model-guided fractionation revealed that C1-1 possessed the most potent angiogenesis effect in RR. The design of the panel with 30 tailor-made angiogenesis-associated genes exhibited in zebrafish gene expression analysis showed that C1-1 could trigger differential expression of various angiogenesis-associated genes, such as VEGFR3 and MMP9, which played key role in angiogenesis. The pro-angiogenic activity of C1-1 was further confirmed in the translated study in motogenic and tubule-inducing effect using HMEC-1.

SUMO1-activating enzyme subunit 1 is essential for the survival of hematopoietic stem/progenitor cells in zebrafish

In vertebrates, establishment of the hematopoietic stem/progenitor cell (HSPC) pool involves mobilization of these cells in successive developmental hematopoietic niches. In zebrafish, HSPCs originate from the ventral wall of the dorsal aorta (VDA), the equivalent of the mammalian aorta-gonad-mesonephros (AGM). The HSPCs subsequently migrate to the caudal hematopoietic tissue (CHT) for transitory expansion and differentiation during the larval stage, and they finally colonize the kidney, where hematopoiesis takes place in adult fish. Here, we report the isolation and characterization of a zebrafish mutant, tango(hkz5), which shows defects of definitive hematopoiesis. In tango(hkz5) mutants, HSPCs initiate normally in the AGM and subsequently colonize the CHT. However, definitive hematopoiesis is not sustained in the CHT owing to accelerated apoptosis and diminished proliferation of HSPCs. Positional cloning reveals that tango(hkz5) encodes SUMO1-activating enzyme subunit 1 (Sae1). A chimera generation experiment and biochemistry analysis reveal that sae1 is cell-autonomously required for definitive hematopoiesis and that the tango(hkz5) mutation produces a truncated Sae1 protein (ΔSae1), resulting in systemic reduction of sumoylation. Our findings demonstrate that sae1 is essential for the maintenance of HSPCs during fetal hematopoiesis in zebrafish.

Myelopoiesis and myeloid leukaemogenesis in the zebrafish

Over the past ten years, studies using the zebrafish model have contributed to our understanding of vertebrate haematopoiesis, myelopoiesis, and myeloid leukaemogenesis. Novel insights into the conservation of haematopoietic lineages and improvements in our capacity to identify, isolate, and culture such haematopoietic cells continue to enhance our ability to use this simple organism to address disease biology. Coupled with the strengths of the zebrafish embryo to dissect developmental myelopoiesis and the continually expanding repertoire of models of myeloid malignancies, this versatile organism has established its niche as a valuable tool to address key questions in the field of myelopoiesis and myeloid leukaemogenesis. In this paper, we address the recent advances and future directions in the field of myelopoiesis and leukaemogenesis using the zebrafish system.

cMyb regulates hematopoietic stem/progenitor cell mobilization during zebrafish hematopoiesis

The establishment of the HSC pool in vertebrates depends not only on the formation and the propagation of these stem cells but also on their proper trafficking among the defined hematopoietic organs. However, the physiologic mechanisms that regulate HSC mobilization remain elusive. Through analysis of the zebrafish cmyb mutant cmyb(hkz3), we show that the suppression of cMyb function abrogates larval and adult hematopoiesis, with concomitant accumulation of hematopoietic stem/progenitor cells (HSPCs) in their birthplace, the ventral wall of the dorsal aorta (VDA). Cell tracking and time-lapse recording reveal that the accumulation of HSPCs in cmyb(hkz3) mutants is caused by the impairment of HSPC egression from the VDA. Further analysis demonstrates that the HSPC migratory defects in cmyb(hkz3) mutants are at least partly because of adversely elevated levels of chemokine stromal cell-derived factor 1a (Sdf1a). Our study reveals that cMyb plays a hitherto unidentified role in dictating physiologic HSPC migration by modulating Sdf1a signaling.

Hematopoietic stem cell development: using the zebrafish to identify the signaling networks and physical forces regulating hematopoiesis

Hematopoietic stem cells (HSC) form the basis of the hematopoietic hierarchy, giving rise to each of the blood lineages found throughout the lifetime of the organism. The genetic programs regulating HSC development are highly conserved between vertebrate species. The zebrafish has proven to be an excellent model for discovering and characterizing the signaling networks and physical forces regulating vertebrate hematopoietic development.