Syk and Zap-70 function redundantly to promote angioblast migration

Towards a new model of trained immunity: Exposure to bacteria and β-glucan protects larval zebrafish against subsequent infections

Once thought to be a feature exclusive to lymphocyte-driven adaptive immunity, immune memory has also been shown to operate as part of the innate immune system following infection to provide an elevated host response to subsequent pathogenic challenge. This evolutionarily conserved process, termed 'trained immunity', enables cells of the innate immune system to 'remember' previous pathogen encounters and mount stronger responses to the same, or different, pathogens after returning to a non-activated state. Here we show that challenging larval zebrafish, that exclusively rely on innate immunity, with live or heat-killed Salmonella typhimurium provides protection to subsequent infection with either Salmonella typhimurium or Streptococcus iniae, that lasts for at least 12 days. We also show that larvae injected with β-glucan, the well-known trigger of trained immunity, demonstrate enhanced survival to similar live bacterial infections, a phenotype supported by increased cxcl8 expression and neutrophil recruitment to the infection site. These results support the conservation of a trained immunity-like phenotype in larval zebrafish and provide a foundation to exploit the experimental attributes of larval zebrafish to further understand this form of immunological memory.

Isoflucypram cardiovascular toxicity in zebrafish (Danio rerio)

Isoflucypram belongs to the new generation of succinate dehydrogenase inhibitor (SDHI) fungicides that are commonly used in crop fungal disease control. Evidence indicates that isoflucypram poses a potential risk to aquatic organisms. However, the effects of isoflucypram during early embryogenesis are not fully understood. In the present study, zebrafish embryos were exposed to 0.025, 0.25, or 2.5 μM isoflucypram for three days. Isoflucypram caused severe developmental abnormalities (yolk sac edema, pericardial edema, and blood clotting clustering), hatching delay, and decreased heart rates in zebrafish. The expression levels of cardiac-specific genes (nkx2.5, myh7, myl7, and myh6) and erythropoiesis-related genes (gata1a, hbbe1, hbbe2, and alas2) were disrupted after isoflucypram exposure. Furthermore, enrichment analysis indicated that most of the differentially expressed genes (DEGs) were enriched in heart development or hemopoiesis processes. Overall, these findings suggest that exposure to isoflucypram is associated with developmental and cardiovascular toxicity in zebrafish.

Modeling hematopoietic disorders in zebrafish

Zebrafish offer a powerful vertebrate model for studies of development and disease. The major advantages of this model include the possibilities of conducting reverse and forward genetic screens and of observing cellular processes by in vivo imaging of single cells. Moreover, pathways regulating blood development are highly conserved between zebrafish and mammals, and several discoveries made in fish were later translated to murine and human models. This review and accompanying poster provide an overview of zebrafish hematopoiesis and discuss the existing zebrafish models of blood disorders, such as myeloid and lymphoid malignancies, bone marrow failure syndromes and immunodeficiencies, with a focus on how these models were generated and how they can be applied for translational research.

Summary: This At A Glance article and poster summarize the last 20 years of research in zebrafish models for hematopoietic disorders, highlighting how these models were created and are being applied for translational research.

β-glucan-dependent shuttling of conidia from neutrophils to macrophages occurs during fungal infection establishment

The initial host response to fungal pathogen invasion is critical to infection establishment and outcome. However, the diversity of leukocyte–pathogen interactions is only recently being appreciated. We describe a new form of interleukocyte conidial exchange called “shuttling.” In Talaromyces marneffei and Aspergillus fumigatus zebrafish in vivo infections, live imaging demonstrated conidia initially phagocytosed by neutrophils were transferred to macrophages. Shuttling is unidirectional, not a chance event, and involves alterations of phagocyte mobility, intercellular tethering, and phagosome transfer. Shuttling kinetics were fungal-species–specific, implicating a fungal determinant. β-glucan serves as a fungal-derived signal sufficient for shuttling. Murine phagocytes also shuttled in vitro. The impact of shuttling for microbiological outcomes of in vivo infections is difficult to specifically assess experimentally, but for these two pathogens, shuttling augments initial conidial redistribution away from fungicidal neutrophils into the favorable macrophage intracellular niche. Shuttling is a frequent host–pathogen interaction contributing to fungal infection establishment patterns.

Imaging of the behaviour of white blood cells in living zebrafish embryos infected with fungi reveals “shuttling,” a specific and previously undescribed form of microorganism exchange between neutrophils and macrophages.

Rare Genetic Blood Disease Modeling in Zebrafish

Hematopoiesis results in the correct formation of all the different blood cell types. In mammals, it starts from specific hematopoietic stem and precursor cells residing in the bone marrow. Mature blood cells are responsible for supplying oxygen to every cell of the organism and for the protection against pathogens. Therefore, inherited or de novo genetic mutations affecting blood cell formation or the regulation of their activity are responsible for numerous diseases including anemia, immunodeficiency, autoimmunity, hyper- or hypo-inflammation, and cancer. By definition, an animal disease model is an analogous version of a specific clinical condition developed by researchers to gain information about its pathophysiology. Among all the model species used in comparative medicine, mice continue to be the most common and accepted model for biomedical research. However, because of the complexity of human diseases and the intrinsic differences between humans and other species, the use of several models (possibly in distinct species) can often be more helpful and informative than the use of a single model. In recent decades, the zebrafish (Danio rerio) has become increasingly popular among researchers, because it represents an inexpensive alternative compared to mammalian models, such as mice. Numerous advantages make it an excellent animal model to be used in genetic studies and in particular in modeling human blood diseases. Comparing zebrafish hematopoiesis to mammals, it is highly conserved with few, significant differences. In addition, the zebrafish model has a high-quality, complete genomic sequence available that shows a high level of evolutionary conservation with the human genome, empowering genetic and genomic approaches. Moreover, the external fertilization, the high fecundity and the transparency of their embryos facilitate rapid, in vivo analysis of phenotypes. In addition, the ability to manipulate its genome using the last genome editing technologies, provides powerful tools for developing new disease models and understanding the pathophysiology of human disorders. This review provides an overview of the different approaches and techniques that can be used to model genetic diseases in zebrafish, discussing how this animal model has contributed to the understanding of genetic diseases, with a specific focus on the blood disorders.

The Immune Signaling Adaptor LAT Contributes to the Neuroanatomical Phenotype of 16p11.2 BP2-BP3 CNVs

Copy-number changes in 16p11.2 contribute significantly to neuropsychiatric traits. Besides the 600 kb BP4-BP5 CNV found in 0.5%-1% of individuals with autism spectrum disorders and schizophrenia and whose rearrangement causes reciprocal defects in head size and body weight, a second distal 220 kb BP2-BP3 CNV is likewise a potent driver of neuropsychiatric, anatomical, and metabolic pathologies. These two CNVs are engaged in complex reciprocal chromatin looping, intimating a functional relationship between genes in these regions that might be relevant to pathomechanism. We assessed the drivers of the distal 16p11.2 duplication by overexpressing each of the nine encompassed genes in zebrafish. Only overexpression of LAT induced a reduction of brain proliferating cells and concomitant microcephaly. Consistently, suppression of the zebrafish ortholog induced an increase of proliferation and macrocephaly. These phenotypes were not unique to zebrafish; Lat knockout mice show brain volumetric changes. Consistent with the hypothesis that LAT dosage is relevant to the CNV pathology, we observed similar effects upon overexpression of CD247 and ZAP70, encoding members of the LAT signalosome. We also evaluated whether LAT was interacting with KCTD13, MVP, and MAPK3, major driver and modifiers of the proximal 16p11.2 600 kb BP4-BP5 syndromes, respectively. Co-injected embryos exhibited an increased microcephaly, suggesting the presence of genetic interaction. Correspondingly, carriers of 1.7 Mb BP1-BP5 rearrangements that encompass both the BP2-BP3 and BP4-BP5 loci showed more severe phenotypes. Taken together, our results suggest that LAT, besides its well-recognized function in T cell development, is a major contributor of the 16p11.2 220 kb BP2-BP3 CNV-associated neurodevelopmental phenotypes.

T Cell Immune Deficiency in zap70 Mutant Zebrafish

ZAP70 [zeta-chain (TCR)-associated protein kinase, 70-kDa], is required for T cell activation. ZAP70 deficiencies in humans and null mutations in mice lead to severe combined immune deficiency. Here, we describe a zap70 loss-of-function mutation in zebrafish (zap70 ^y442 ) that was created using transcription activator-like effector nucleases (TALENs). In contrast to what has been reported for morphant zebrafish, zap70 ^y442 homozygous mutant zebrafish displayed normal development of blood and lymphatic vasculature. Hematopoietic cell development was also largely unaffected in mutant larvae. However, mutant fish had reduced lck:GFP ⁺ thymic T cells by 5 days postfertilization that persisted into adult stages. Morphological analysis, RNA sequencing, and single-cell gene expression profiling of whole kidney marrow cells of adult fish revealed complete loss of mature T cells in zap70 ^y442 mutant animals. T cell immune deficiency was confirmed through transplantation of unmatched normal and malignant donor cells into zap70 ^y442 mutant zebrafish, with T cell loss being sufficient for robust allogeneic cell engraftment. zap70 mutant zebrafish show remarkable conservation of immune cell dysfunction as found in mice and humans and will serve as a valuable model to study zap70 immune deficiency.

The LIM-homeodomain transcription factor Islet2a promotes angioblast migration

Angioblasts of the developing vascular system require many signaling inputs to initiate their migration, proliferation and differentiation into endothelial cells. What is less studied is which intrinsic cell factors interpret these extrinsic signals. Here, we show the Lim homeodomain transcription factor islet2a (isl2a) is expressed in the lateral posterior mesoderm prior to angioblast migration. isl2a deficient angioblasts show disorganized migration to the midline to form axial vessels and fail to spread around the tailbud of the embryo. Isl2a morphants have fewer vein cells and decreased vein marker expression. We demonstrate that isl2a is required cell autonomously in angioblasts to promote their incorporation into the vein, and is permissive for vein identity. Knockout of isl2a results in decreased migration and proliferation of angioblasts during intersegmental artery growth. Since Notch signaling controls both artery-vein identity and tip-stalk cell formation, we explored the interaction of isl2a and Notch. We find that isl2a expression is negatively regulated by Notch activity, and that isl2a positively regulates flt4, a VEGF-C receptor repressed by Notch during angiogenesis. Thus Isl2a may act as an intermediate between Notch signaling and genetic programs controlling angioblast number and migration, placing it as a novel transcriptional regulator of early angiogenesis.

Carp Il10 Has Anti-Inflammatory Activities on Phagocytes, Promotes Proliferation of Memory T Cells, and Regulates B Cell Differentiation and Antibody Secretion

In the current study, we investigated the effects of carp Il10 on phagocytes and lymphocytes. Carp Il10 shares several prototypical inhibitory activities on phagocytes with mammalian IL-10, including deactivation of neutrophils and macrophages, as shown by inhibition of oxygen and nitrogen radical production, as well as reduced expression of proinflammatory genes and mhc genes involved in Ag presentation. Similar to mammalian IL-10, carp Il10 acts through a signaling pathway involving phosphorylation of Stat3, ultimately leading to the early upregulation of socs3 expression. To our knowledge, this is the first study of the effects of Il10 on lymphocytes in fish. Although Il10 did not affect survival and proliferation of T cells from naive animals, it greatly promoted survival and proliferation of T cells in cultures from immunized animals, but only when used in combination with the immunizing Ag. Preliminary gene expression analysis suggests that, under these circumstances, carp Il10 stimulates a subset of CD8+ memory T cells while downregulating CD4+ memory Th1 and Th2 responses. In addition to the regulatory effect on T cells, carp Il10 stimulates proliferation, differentiation, and Ab secretion by IgM+ B cells. Overall, carp Il10 shares several prototypical activities with mammalian IL-10, including downregulation of the inflammatory response of phagocytes, stimulation of proliferation of subsets of memory T lymphocytes, and proliferation, differentiation, and Ab secretion by IgM+ B lymphocytes. To our knowledge, this is the first comprehensive analysis of biological activities of fish Il10 on both phagocytes and lymphocytes showing functional conservation of several properties of Il10.

Protein kinases and associated pathways in pluripotent state and lineage differentiation

Protein kinases (PKs) mediate the reversible conversion of substrate proteins to phosphorylated forms, a key process in controlling intracellular signaling transduction cascades. Pluripotency is, among others, characterized by specifically expressed PKs forming a highly interconnected regulatory network that culminates in a finely-balanced molecular switch. Current high-throughput phosphoproteomic approaches have shed light on the specific regulatory PKs and their function in controlling pluripotent states. Pluripotent cell-derived endothelial and hematopoietic developments represent an example of the importance of pluripotency in cancer therapeutics and organ regeneration. This review attempts to provide the hitherto known kinome profile and the individual characterization of PK-related pathways that regulate pluripotency. Elucidating the underlying intrinsic and extrinsic signals may improve our understanding of the different pluripotent states, the maintenance or induction of pluripotency, and the ability to tailor lineage differentiation, with a particular focus on endothelial cell differentiation for anti-cancer treatment, cell-based tissue engineering, and regenerative medicine strategies.

Nuclear receptor subfamily 2 group F member 1a (nr2f1a) is required for vascular development in zebrafish

Genetic regulators and signaling pathways are important for the formation of blood vessels. Transcription factors controlling vein identity, intersegmental vessels (ISV) growth and caudal vein plexus (CVP) formation in zebrafish are little understood as yet. Here, we show the importance of the nuclear receptor subfamily member 1A (nr2f1a) in zebrafish vascular development. Amino acid sequence alignment and phylogenetic analysis of nr2f1a is highly conserved among the vertebrates. Our in situ hybridization results showed nr2f1a mRNA is expressed in the lateral plate mesoderm at 18 somite stage and in vessels at 24-30 hpf, suggesting its roles in vasculization. Consistent with this morpholino-based knockdown of nr2fla impaired ISV growth and failed to develop fenestrated vascular structure in CVP, suggesting that nr2f1a has important roles in controlling ISV and CVP growth. Consequently, nr2f1a morphants showed pericardial edema and circulation defects. We further demonstrated reduced ISV cells and decreased CVP endothelial cells sprouting in nr2f1a morphants, indicating the growth impairment of ISV and CVP is due to a decrease of cell proliferation and migration, but not results from cell death in endothelial cells after morpholino knockdown. To test molecular mechanisms and signals that are associated with nr2f1a, we examined the expression of vascular markers. We found that a loss of nr2f1a results in a decreased expression of vein/ISV specific markers, flt4, mrc1, vascular markers stabilin and ephrinb2. This indicates the regulatory role of nr2f1a in controlling vascular development. We further showed that nr2f1a likely interact with Notch signaling by examining nr2f1a expression in rbpsuh morphants and DAPT-treatment embryos. Together, we show nr2f1a plays a critical role for vascular development in zebrafish.

Emerging from the PAC: studying zebrafish lymphatic development

Recently the zebrafish has emerged as a promising vertebrate model of lymphatic vasculature development. The establishment of numerous transgenic lines that label the lymphatic endothelium in the zebrafish has allowed the fine examination of the developmental timing and the anatomy of their lymphatic vasculature. Although many questions remain, studying lymphatic development in the zebrafish has resulted in the identification and characterization of novel and established mediators of lymphatic development and lymphangiogenesis. Here, we review the main stages involved in the development of the lymphatic vasculature in the zebrafish from its origins in the embryonic veins to the formation of the primary lymphatic vessels and highlight some of the key molecules necessary for these stages.

Conservation and early expression of zebrafish tyrosine kinases support the utility of zebrafish as a model for tyrosine kinase biology

Tyrosine kinases have significant roles in cell growth, apoptosis, development, and disease. To explore the use of zebrafish as a vertebrate model for tyrosine kinase signaling and to better understand their roles, we have identified all of the tyrosine kinases encoded in the zebrafish genome and quantified RNA expression of selected tyrosine kinases during early development. Using profile hidden Markov model analysis, we identified 122 zebrafish tyrosine kinase genes and proposed unambiguous gene names where needed. We found them to be organized into 39 nonreceptor and 83 receptor type, and 30 families consistent with human tyrosine kinase family assignments. We found five human tyrosine kinase genes (epha1, bmx, fgr, srm, and insrr) with no identifiable zebrafish ortholog, and one zebrafish gene (yrk) with no identifiable human ortholog. We also found that receptor tyrosine kinase genes were duplicated more often than nonreceptor tyrosine kinase genes in zebrafish. We profiled expression levels of 30 tyrosine kinases representing all families using direct digital detection at different stages during the first 24 hours of development. The profiling experiments clearly indicate regulated expression of tyrosine kinases in the zebrafish, suggesting their role during early embryonic development. In summary, our study has resulted in the first comprehensive description of the zebrafish tyrosine kinome.

Chemokine signaling directs trunk lymphatic network formation along the preexisting blood vasculature

The lymphatic system is crucial for fluid homeostasis, immune responses, and numerous pathological processes. However, the molecular mechanisms responsible for establishing the anatomical form of the lymphatic vascular network remain largely unknown. Here, we show that chemokine signaling provides critical guidance cues directing early trunk lymphatic network assembly and patterning. The chemokine receptors Cxcr4a and Cxcr4b are expressed in lymphatic endothelium, whereas chemokine ligands Cxcl12a and Cxcl12b are expressed in adjacent tissues along which the developing lymphatics align. Loss- and gain-of-function studies in zebrafish demonstrate that chemokine signaling orchestrates the stepwise assembly of the trunk lymphatic network. In addition to providing evidence for a lymphatic vascular guidance mechanism, these results also suggest a molecular basis for the anatomical coalignment of lymphatic and blood vessels.

Fish T cells: recent advances through genomics

This brief review is intended to provide a concise overview of the current literature concerning T cells, advances in identifying distinct T cell functional subsets, and in distinguishing effector cells from memory cells. We compare and contrast a wealth of recent progress made in T cell immunology of teleost, elasmobranch, and agnathan fish, to knowledge derived from mammalian T cell studies. From genome studies, fish clearly have most components associated with T cell function and we can speculate on the presence of putative T cell subsets, and the ability to detect their differentiation to form memory cells. Some recombinant proteins for T cell associated cytokines and antibodies for T cell surface receptors have been generated that will facilitate studying the functional roles of teleost T cells during immune responses. Although there is still a long way to go, major advances have occurred in recent years for investigating T cell responses, thus phenotypic and functional characterization is on the near horizon.

Expression of T-cell markers during Atlantic halibut (Hippoglossus hippoglossus L.) ontogenesis

The immune system of Atlantic halibut is relatively undeveloped at the time of hatching, and thus larvae are vulnerable to bacterial and viral diseases that can result in high mortalities. To enable establishment of effective prophylactic measures, it is important to know when the adaptive immune system is developed. This depends on both B- and T-cell functions. In the present study the expression of RAG1, TCRα, TCRβ, CD3γδ, CD3ɛ, CD3ζ, CD4, CD4-2, CD8α, CD8β, Lck, and ZAP-70 was analyzed in larval and juvenile stages during halibut development. Using real time RT-PCR, low basal mRNA levels of all 12 genes could be detected at early stages. An increase in mRNA transcripts for the genes was seen at different time points, from 38 days post hatching (dph) about the time when the first anlage of thymus is found, and onwards. The transcription patterns of the 12 mRNAs were found to be similar throughout the developmental stages tested. In situ hybridization on larval cross-sections showed that RAG1 and Lck could be detected in lymphocyte like cells within the thymus at 42 dph. CD4 expression could not be detected within the thymus before 66 dph, however, positive cells were restricted to the cortical region. At 87 dph, the zonation of the thymus in a cortical, cortico-medullary, and a medullary region seemed to be more evident with CD8α expressing cells found in all regions, indicating the presence of mature T-cells. This correlates with previous results describing thymus development and the appearance of IgM(+) cells during halibut ontogenesis.