Molecular cloning, genetic mapping, and expression analysis of four zebrafish c/ebp genes

Comparative transcriptomics coupled to developmental grading via transgenic zebrafish reporter strains identifies conserved features in neutrophil maturation

Neutrophils are evolutionarily conserved innate immune cells playing pivotal roles in host defense. Zebrafish models have contributed substantially to our understanding of neutrophil functions but similarities to human neutrophil maturation have not been systematically characterized, which limits their applicability to studying human disease. Here we show, by generating and analysing transgenic zebrafish strains representing distinct neutrophil differentiation stages, a high-resolution transcriptional profile of neutrophil maturation. We link gene expression at each stage to characteristic transcription factors, including C/ebp-β, which is important for late neutrophil maturation. Cross-species comparison of zebrafish, mouse, and human samples confirms high molecular similarity of immature stages and discriminates zebrafish-specific from pan-species gene signatures. Applying the pan-species neutrophil maturation signature to RNA-sequencing data from human neuroblastoma patients reveals association between metastatic tumor cell infiltration in the bone marrow and an overall increase in mature neutrophils. Our detailed neutrophil maturation atlas thus provides a valuable resource for studying neutrophil function at different stages across species in health and disease.

Differentiation and Maturation of Muscle and Fat Cells in Cultivated Seafood: Lessons from Developmental Biology

Cultivated meat, also known as cultured or cell-based meat, is meat produced directly from cultured animal cells rather than from a whole animal. Cultivated meat and seafood have been proposed as a means of mitigating the substantial harms associated with current production methods, including damage to the environment, antibiotic resistance, food security challenges, poor animal welfare, and-in the case of seafood-overfishing and ecological damage associated with fishing and aquaculture. Because biomedical tissue engineering research, from which cultivated meat draws a great deal of inspiration, has thus far been conducted almost exclusively in mammals, cultivated seafood suffers from a lack of established protocols for producing complex tissues in vitro. At the same time, fish such as the zebrafish Danio rerio have been widely used as model organisms in developmental biology. Therefore, many of the mechanisms and signaling pathways involved in the formation of muscle, fat, and other relevant tissue are relatively well understood for this species. The same processes are understood to a lesser degree in aquatic invertebrates. This review discusses the differentiation and maturation of meat-relevant cell types in aquatic species and makes recommendations for future research aimed at recapitulating these processes to produce cultivated fish and shellfish.

Single-cell analyses reveal early thymic progenitors and pre-B cells in zebrafish

The zebrafish has proven to be a valuable model organism for studying hematopoiesis, but relatively little is known about zebrafish immune cell development and functional diversity. Elucidating key aspects of zebrafish lymphocyte development and exploring the breadth of effector functions would provide valuable insight into the evolution of adaptive immunity. We performed single-cell RNA sequencing on ∼70,000 cells from the zebrafish marrow and thymus to establish a gene expression map of zebrafish immune cell development. We uncovered rich cellular diversity in the juvenile and adult zebrafish thymus, elucidated B- and T-cell developmental trajectories, and transcriptionally characterized subsets of hematopoietic stem and progenitor cells and early thymic progenitors. Our analysis permitted the identification of two dendritic-like cell populations and provided evidence in support of the existence of a pre-B cell state. Our results provide critical insights into the landscape of zebrafish immunology and offer a foundation for cellular and genetic studies.

A single-cell resolution developmental atlas of hematopoietic stem and progenitor cell expansion in zebrafish

The caudal hematopoietic tissue (CHT) is characterized as a hematopoietic organ for fetal hematopoietic stem and progenitor cell (HSPC) expansion in zebrafish. In this study, we used scRNA-seq combined with functional assays to decode the developing CHT. First, we resolved fetal HSPC heterogeneity, manifested as lineage priming and metabolic gene signatures. We further analyzed the cellular interactions among nonhematopoietic niche components and HSPCs and identified an endothelial cell-specific factor, Gpr182, followed by experimental validation of its role in promoting HSPC expansion. Finally, we uncovered the conservation and divergence of developmental hematopoiesis between human fetal liver and zebrafish CHT. Our study provides a valuable resource for fetal HSPC development and clues to establish a supportive niche for HSPC expansion in vitro.

During vertebrate embryogenesis, fetal hematopoietic stem and progenitor cells (HSPCs) exhibit expansion and differentiation properties in a supportive hematopoietic niche. To profile the developmental landscape of fetal HSPCs and their local niche, here, using single-cell RNA-sequencing, we deciphered a dynamic atlas covering 28,777 cells and 9 major cell types (23 clusters) of zebrafish caudal hematopoietic tissue (CHT). We characterized four heterogeneous HSPCs with distinct lineage priming and metabolic gene signatures. Furthermore, we investigated the regulatory mechanism of CHT niche components for HSPC development, with a focus on the transcription factors and ligand–receptor networks involved in HSPC expansion. Importantly, we identified an endothelial cell-specific G protein–coupled receptor 182, followed by in vivo and in vitro functional validation of its evolutionally conserved role in supporting HSPC expansion in zebrafish and mice. Finally, comparison between zebrafish CHT and human fetal liver highlighted the conservation and divergence across evolution. These findings enhance our understanding of the regulatory mechanism underlying hematopoietic niche for HSPC expansion in vivo and provide insights into improving protocols for HSPC expansion in vitro.

Cebpα is essential for the embryonic myeloid progenitor and neutrophil maintenance in zebrafish

In vertebrates, myeloid cells arise from multiple waves of development: the first or embryonic wave of myelopoiesis initiates early from non-hematopoietic stem cell (HSC) precursors and gives rise to myeloid cells transiently during early development; whereas the second or adult wave of myelopoiesis emerges later from HSCs and produces myeloid cells continually during fetal and adult life. In the past decades, a great deal has been learnt about the development of myeloid cells from adult myelopoiesis, yet the genetic network governing embryonic myelopoiesis remains poorly defined. In this report, we present an in vivo study to delineate the role of Cebpα during zebrafish embryonic myelopoiesis. We show that embryonic myelopoiesis in cebpα-deficient zebrafish mutants initiates properly but fails to produce macrophages and neutrophils. The lack of macrophages and neutrophils in the mutants is largely attributed to the cell cycle arrest of embryonic myeloid progenitors, resulting in the impairment of their maintenance and subsequent differentiation. We further show that Cebpα, perhaps acting cooperatively with Runx1, plays a critical role in embryonic neutrophil maintenance. Our findings reveal a new role of Cebpα in embryonic myelopoiesis.

c-myb hyperactivity leads to myeloid and lymphoid malignancies in zebrafish

The c-MYB transcription factor is a key regulator of hematopoietic cell proliferation and differentiation, and dysregulation of c-MYB activity often associates with various hematological disorders. Yet, its pathogenic role remains largely unknown due to lack of suitable animal models. Here, we report a detail characterization of a c-myb-gfp transgenic zebrafish harboring c-Myb hyperactivity (named c-myb^hyper). This line exhibits abnormal granulocyte expansion that resembles human myelodysplastic syndrome (MDS) from embryonic stage to adulthood. Strikingly, a small portion of c-myb^hyper adult fish develops acute myeloid leukemia-like or acute lymphoid leukemia-like disorders with age. The myeloid and lymphoid malignancies in c-myb^hyper adult fish are likely caused by the hyperactivity of c-myb, resulting in the dysregulation of a number of cell-cycle-related genes and hyperproliferation of hematopoietic precursor cells. Finally, treatment with c-myb target drug flavopiridol can relieve the MDS-like symptoms in both c-myb^hyper embryos and adult fish. Our study establishes a zebrafish model for studying the cellular and molecular mechanisms underlying c-Myb-associated leukemogenesis as well as for anti-leukemic drug screening.

Goldfish (Carassius auratus L.) as a model system to study the growth factors, receptors and transcription factors that govern myelopoiesis in fish

The process of myeloid cell development (myelopoiesis) in fish has mainly been studied in three cyprinid species: zebrafish (Danio rerio), ginbuna carp (Carassius auratus langsdorfii) and goldfish (C. auratus, L.). Our studies on goldfish myelopoiesis have utilized in vitro generated primary kidney macrophage (PKM) cultures and isolated primary kidney neutrophils (PKNs) cultured overnight to study the process of macrophage (monopoiesis) and neutrophil (granulopoiesis) development and the key growth factors, receptors, and transcription factors that govern this process in vitro. The PKM culture system is unique in that all three subpopulations of macrophage development, namely progenitor cells, monocytes, and mature macrophages, are simultaneously present in culture unlike mammalian systems, allowing for the elucidation of the complex mixture of cytokines that regulate progressive and selective macrophage development from progenitor cells to fully functional mature macrophages in vitro. Furthermore, we have been able to extend our investigations to include the development of erythrocytes (erythropoiesis) and thrombocytes (thrombopoiesis) through studies focusing on the progenitor cell population isolated from the goldfish kidney. Herein, we review the in vitro goldfish model systems focusing on the characteristics of cell sub-populations, growth factors and their receptors, and transcription factors that regulate goldfish myelopoiesis.

CCAAT/enhancer-binding protein α is required for hepatic outgrowth via the p53 pathway in zebrafish

CCAAT/enhancer-binding protein α (C/ebpα) is a transcription factor that plays important roles in the regulation of hepatogenesis, adipogenesis and hematopoiesis. Disruption of the C/EBPα gene in mice leads to disturbed liver architecture and neonatal death due to hypoglycemia. However, the precise stages of liver development affected by C/ebpα loss are poorly studied. Using the zebrafish embryo as a model organism, we show that inactivation of the cebpa gene by TALENs results in a small liver phenotype. Further studies reveal that C/ebpα is distinctively required for hepatic outgrowth but not for hepatoblast specification. Lack of C/ebpα leads to enhanced hepatic cell proliferation and subsequent increased cell apoptosis. Additional loss of p53 can largely rescue the hepatic defect in cebpa mutants, suggesting that C/ebpα plays a role in liver growth regulation via the p53 pathway. Thus, our findings for the first time demonstrate a stage-specific role for C/ebpα during liver organogenesis.

Lipid Abundance in Zebrafish Embryos Is Regulated by Complementary Actions of the Endocannabinoid System and Retinoic Acid Pathway

The endocannabinoid system (ECS) and retinoic acid (RA) signaling have been associated with influencing lipid metabolism. We hypothesized that modulation of these pathways could modify lipid abundance in developing vertebrates and that these pathways could have a combinatorial effect on lipid levels. Zebrafish embryos were exposed to chemical treatments altering the activity of the ECS and RA pathway. Embryos were stained with the neutral lipid dye Oil-Red-O (ORO) and underwent whole-mount in situ hybridization (WISH). Mouse 3T3-L1 fibroblasts were differentiated under exposure to RA-modulating chemicals and subsequently stained with ORO and analyzed for gene expression by qRT-PCR. ECS activation and RA exposure increased lipid abundance and the expression of lipoprotein lipase. In addition, RA treatment increased expression of CCAAT/enhancer-binding protein alpha. Both ECS receptors and RA receptor subtypes were separately involved in modulating lipid abundance. Finally, increased ECS or RA activity ameliorated the reduced lipid abundance caused by peroxisome proliferator-activated receptor gamma (PPARγ) inhibition. Therefore, the ECS and RA pathway influence lipid abundance in zebrafish embryos and have an additive effect when treated simultaneously. Furthermore, we demonstrated that these pathways act downstream or independently of PPARγ to influence lipid levels. Our study shows for the first time that the RA and ECS pathways have additive function in lipid abundance during vertebrate development.

Zebrafish as a model for leukemia and other hematopoietic disorders

Zebrafish is an established model for the study of vertebrate development, and is especially amenable for investigating hematopoiesis, where there is strong conservation of key lineages, genes, and developmental processes with humans. Over recent years, zebrafish has been increasingly utilized as a model for a range of human hematopoietic diseases, including malignancies. This review provides an overview of zebrafish hematopoiesis and describes its application as a model of leukemia and other hematopoietic disorders.

Oceans of opportunity: exploring vertebrate hematopoiesis in zebrafish

Exploitation of the zebrafish model in hematology research has surged in recent years, becoming one of the most useful and tractable systems for understanding regulation of hematopoietic development, homeostasis, and malignancy. Despite the evolutionary distance between zebrafish and humans, remarkable genetic and phenotypic conservation in the hematopoietic system has enabled significant advancements in our understanding of blood stem and progenitor cell biology. The strengths of zebrafish in hematology research lie in the ability to perform real-time in vivo observations of hematopoietic stem, progenitor, and effector cell emergence, expansion, and function, as well as the ease with which novel genetic and chemical modifiers of specific hematopoietic processes or cell types can be identified and characterized. Further, myriad transgenic lines have been developed including fluorescent reporter systems to aid in the visualization and quantification of specified cell types of interest and cell-lineage relationships, as well as effector lines that can be used to implement a wide range of experimental manipulations. As our understanding of the complex nature of blood stem and progenitor cell biology during development, in response to infection or injury, or in the setting of hematologic malignancy continues to deepen, zebrafish will remain essential for exploring the spatiotemporal organization and integration of these fundamental processes, as well as the identification of efficacious small molecule modifiers of hematopoietic activity. In this review, we discuss the biology of the zebrafish hematopoietic system, including similarities and differences from mammals, and highlight important tools currently utilized in zebrafish embryos and adults to enhance our understanding of vertebrate hematology, with emphasis on findings that have impacted our understanding of the onset or treatment of human hematologic disorders and disease.

Distinct regulation of the anterior and posterior myeloperoxidase expression by Etv2 and Gata1 during primitive Granulopoiesis in zebrafish

Neutrophilic granulocytes are the most abundant type of myeloid cells and form an essential part of the innate immune system. In vertebrates the first neutrophils are thought to originate during primitive hematopoiesis, which precedes hematopoietic stem cell formation. In zebrafish embryos, it has been suggested that primitive neutrophils may originate in two distinct sites, the anterior (ALPM) and posterior lateral plate mesoderm (PLPM). An ETS-family transcription factor Etsrp/Etv2/ER71 has been implicated in vasculogenesis and hematopoiesis in multiple vertebrates. However, its role during neutrophil development is not well understood. Here we demonstrate using zebrafish embryos that Etv2 has a specific cell-autonomous function during primitive neutropoiesis in the anterior lateral plate mesoderm (ALPM) but has little effect on erythropoiesis or the posterior lateral plate mesoderm (PLPM) expression of neutrophil marker myeloperoxidase mpo/mpx. Our results argue that ALPM-derived neutrophils originate from etv2-expressing cells which downregulate etv2 during neutropoiesis. We further show that Scl functions downstream of Etv2 in anterior neutropoiesis. Additionally, we demonstrate that mpx expression within the PLPM overlaps with gata1 expression, potentially marking the cells with a dual myelo-erythroid potential. Intriguingly, initiation of mpx expression in the PLPM is dependent on gata1 but not etv2 function. Our results demonstrate that mpx expression is controlled differently in the ALPM and PLPM regions and describe novel roles for etv2 and gata1 during primitive neutropoiesis.

Molecular cloning and characterization of the promoter region of the porcine apolipoprotein E gene

Apolipoprotein E (APOE), a component of lipoproteins plays an important role in the transport and metabolism of cholesterol, and is associated with hyperlipoproteinemia and Alzheimer's disease. In order to further understand the characterization of APOE gene, the promoter of APOE gene of Landrace pigs was analyzed in the present study. The genomic structure and amino acid sequence in pigs were analyzed and found to share high similarity in those of human but low similarity in promoter region. Real-time PCR revealed the APOE gene expression pattern of pigs in diverse tissues. The highest expression level was observed in liver, relatively low expression in other tissues, especially in stomach and muscle. Furthermore, the promoter expressing in Hepa 1-6 was significantly better at driving luciferase expression compared with C2C12 cell. After analysis of porcine APOE gene promoter regions, potential transcription factor binding sites were predicted and two GC signals, a TATA box were indicated. Results of promoter activity analysis indicated that one of potential regulatory elements was located in the region -669 to -259, which was essential for a high expression of the APOE gene. Promoter mutation and deletion analysis further suggested that the C/EBPA binding site within the APOE promoter was responsible for the regulation of APOE transcription. Electrophoretic mobility shift assays also showed the binding site of the transcription factor C/EBPA. This study advances our knowledge of the promoter of the porcine APOE gene.

Molecular and functional analyses of the fast skeletal myosin light chain2 gene of the Korean oily bitterling, Acheilognathus koreensis

We identified and characterized the primary structure of the Korean oily bitterling Acheilognathus koreensis fast skeletal myosin light chain 2 (Akmlc2f), gene. Encoded by seven exons spanning 3955 bp, the deduced 168-amino acid AkMLC2f polypeptide contained an EF-hand calcium-binding motif and showed strong homology (80%-98%) with the MLC2 proteins of Ictalurus punctatus and other species, including mammals. Akmlc2f mRNA was highly enriched in skeletal muscles, and was detectable in other tissues. The upstream regions of Akmlc2f included a TATA box, one copy of a putative MEF-2 binding site and several putative C/EBPβ binding sites. The functional activity of the promoter region of Akmlc2f was examined using luciferase and red fluorescent protein reporters. The Akmlc2f promoter-driven reporter expressions were detected and increased by the C/EBPβ transcription factor in HEK293T cells. The activity of the promoter of Akmlc2f was also confirmed in the developing zebrafish embryo. Although the detailed mechanism underlying the expression of Akmlc2f remains unknown, these results suggest the muscle-specific expression of Akmlc2f transcript and the functional activation of Akmlc2f promoter by C/EBPβ.

Wdr68 requires nuclear access for craniofacial development

Wdr68 is a highly conserved scaffolding protein required for craniofacial development and left-right asymmetry. A Ras-Map3k-Wdr68-Dyrk1 signaling relay may mediate these and other diverse signaling events important in development and disease. While the sub-cellular localization of Wdr68 has been shown to be dependent on that of its interaction partners, it is not clear where Wdr68 activity is required during development. Here we show that while a GFP-Wdr68 fusion functionally substituted for craniofacial development in the zebrafish, that a Nuclear Export Signal (NES) fusion protein (GFPNESWdr68) failed to support craniofacial development. As control for NES activity, we show that while GFP-Wdr68 exhibited a pan-cellular distribution in C2C12 cells, the GFPNESWdr68 fusion predominantly localized to the cell cytoplasm, as expected. Interestingly, while GFP-Wdr68 and RFP-Dyrk1a co-localized to the cell nucleus as expected based on the known sub-cellular localization for Dyrk1a, we found that the GFPNESWdr68 fusion redistributed RFP-Dyrk1a to the cell cytoplasm potentially disconnecting the Ras/Dyrk1 signal relay from further downstream targets. Consistent with a nuclear role in gene regulation, we also found that while a transcriptional activation domain fusion, CebpFlagWdr68, functionally substituted for endogenous Wdr68 for craniofacial development, that a transcriptional repression domain fusion, MadFlagWdr68, failed to support craniofacial development. Dyrk1b is required for myogenin (myog) expression in differentiating mouse C2C12 cells and here we report that wdr68 is also important for myog expression in differentiating C2C12 cells. Using a C2C12 cell myog promoter-reporter system, we found that Wdr68 overexpression increased reporter activity while moderate expression levels of MadFlagWdr68 interfered with reporter activity. Taken together, these findings support a nuclear role for Wdr68-containing complexes.

White adipose tissue development in zebrafish is regulated by both developmental time and fish size

Adipocytes are heterogeneous. Whether their differences are attributed to anatomical location or to different developmental origins is unknown. We investigated whether development of different white adipose tissue (WAT) depots in zebrafish occurs simultaneously or whether adipogenesis is influenced by the metabolic demands of growing fish. Like mammals, zebrafish adipocyte morphology is distinctive and adipocytes express cell-specific markers. All adults contain WAT in pancreatic, subcutaneous, visceral, esophageal, mandibular, cranial, and tail-fin depots. Unlike most zebrafish organs that form during embryogenesis, WAT was not found in embryos or young larvae. Instead, WAT was first identified in the pancreas on 12 days postfertilization (dpf), and then in visceral, subcutaneous, and cranial stores in older fish. All 30 dpf fish exceeding 10.6 mm standard length contained the adult repertoire of WAT depots. Pancreatic, esophageal, and subcutaneous WAT appearance correlated with size, not age, as found for other features appearing during postembryonic zebrafish development.

Pre-gastrula expression of zebrafish extraembryonic genes

Background

Many species form extraembryonic tissues during embryogenesis, such as the placenta of humans and other viviparous mammals. Extraembryonic tissues have various roles in protecting, nourishing and patterning embryos. Prior to gastrulation in zebrafish, the yolk syncytial layer - an extraembryonic nuclear syncytium - produces signals that induce mesoderm and endoderm formation. Mesoderm and endoderm precursor cells are situated in the embryonic margin, an external ring of cells along the embryo-yolk interface. The yolk syncytial layer initially forms below the margin, in a domain called the external yolk syncytial layer (E-YSL).

Results

We hypothesize that key components of the yolk syncytial layer's mesoderm and endoderm inducing activity are expressed as mRNAs in the E-YSL. To identify genes expressed in the E-YSL, we used microarrays to compare the transcription profiles of intact pre-gastrula embryos with pre-gastrula embryonic cells that we had separated from the yolk and yolk syncytial layer. This identified a cohort of genes with enriched expression in intact embryos. Here we describe our whole mount in situ hybridization analysis of sixty-eight of them. This includes ten genes with E-YSL expression (camsap1l1, gata3, znf503, hnf1ba, slc26a1, slc40a1, gata6, gpr137bb, otop1 and cebpa), four genes with expression in the enveloping layer (EVL), a superficial epithelium that protects the embryo (zgc:136817, zgc:152778, slc14a2 and elovl6l), three EVL genes whose expression is transiently confined to the animal pole (elovl6l, zgc:136359 and clica), and six genes with transient maternal expression (mtf1, wu:fj59f04, mospd2, rftn2, arrdc1a and pho). We also assessed the requirement of Nodal signaling for the expression of selected genes in the E-YSL, EVL and margin. Margin expression was Nodal dependent for all genes we tested, including the concentrated margin expression of an EVL gene: zgc:110712. All other instances of EVL and E-YSL expression that we tested were Nodal independent.

Conclusion

We have devised an effective strategy for enriching and identifying genes expressed in the E-YSL of pre-gastrula embryos. To our surprise, maternal genes and genes expressed in the EVL were also enriched by this strategy. A number of these genes are promising candidates for future functional studies on early embryonic patterning.

Crucial role of phosphatidylinositol 4-kinase IIIalpha in development of zebrafish pectoral fin is linked to phosphoinositide 3-kinase and FGF signaling

Phosphatidylinositol 4-kinases (PI4Ks) catalyze the first committed step in the synthesis of phosphoinositides, important lipid regulators of signaling and trafficking pathways. Here we cloned Pik4a, one of the zebrafish PI4K enzymes, and studied its role(s) in vertebrate development using morpholino oligonucleotide-based gene silencing in zebrafish. Downregulation of Pik4a led to multiple developmental abnormalities, affecting the brain, heart, trunk and most prominently causing loss of pectoral fins. Strikingly similar defects were caused by treatment of the developing embryos with the phosphoinositide 3-kinase (PI3K) inhibitor, LY294002. To investigate the cause of the pectoral fin developmental defect, we focused on fibroblast growth factor (FGF) signaling pathways because vertebrate limb development requires the concerted action of a series of FGF ligands. Using in situ hybridization, the pectoral fin defect was traced to disruption of the early FGF signaling loops that are crucial for the establishment of the sharp signaling center formed by the apical ectodermal ridge and the underlying mesenchyme. This, in turn caused a prominent loss of the induction of one of the mitogen-activated protein kinase (MAPK) phosphatases, Mkp3, an essential intermediate in vertebrate limb development. These changes were associated with impaired proliferation in the developing fin bud due to a loss of balance between the MAPK and PI3K branch of FGF-initiated signals. Our results identify Pik4a as an upstream partner of PI3Ks in the signaling cascade orchestrated by FGF receptors with a prominent role in forelimb development.

Cyp26 enzymes function in endoderm to regulate pancreatic field size

The control of organ size and position relies, at least in part, upon appropriate regulation of the signals that specify organ progenitor fields. Pancreatic cell fates are specified by retinoic acid (RA), and proper size and localization of the pancreatic field are dependent on tight control of RA signaling. Here we show that the RA-degrading Cyp26 enzymes play a critical role in defining the normal anterior limit of the pancreatic field. Disruption of Cyp26 function causes a dramatic expansion of pancreatic cell types toward the anterior of the embryo. The cyp26a1 gene is expressed in the anterior trunk endoderm at developmental stages when RA is signaling to specify pancreas, and analysis of cyp26a1/giraffe (gir) mutant zebrafish embryos confirms that cyp26a1 plays the primary role in setting the anterior limit of the pancreas. Analysis of the gir mutants further reveals that cyp26b1 and cyp26c1 function redundantly to partially compensate for loss of Cyp26a1 function. We used cell transplantation to determine that Cyp26a1 functions directly in endoderm to modulate RA signaling and limit the pancreatic field. Taken together with our finding that endodermal expression of cyp26 genes is subject to positive regulation by RA, our data reveal a feedback loop within the endoderm. Such feedback can maintain consistent levels of RA signaling, despite environmental fluctuations in RA concentration, thus ensuring a consistent size and location of the pancreatic field.

Transcriptional regulation of a myeloid-lineage specific gene lysozyme C during zebrafish myelopoiesis

lysozyme C (lyz), a glycoside hydrolase expressed exclusively in myeloid cells, is involved in the host defense against bacterial infection. We isolated a 2.4kb zebrafish lyz promoter region and established transgenic lines that drive enhanced green fluorescent protein (EGFP) to examine how lyz expression is regulated during myelopoiesis. We found that the 2.4kb lyz promoter is sufficient to drive myeloid-specific expression of EGFP in zebrafish. We identified potential transcriptional regulatory elements including a Runx element (TGTGGT at -1.70kb) and a C/ebp element (TTTGGCAAT at -1.46kb) in the lyz promoter, and showed that they are required for myeloid-specific expression of EGFP. We found that the myeloid-lineage transcription factors C/ebp1, Runx1 and Pu.1 can bind to the 2.4kb lyz promoter. Forced expression of runx1, c/ebp1 and pu.1 together induced ectopic lyz expression in the intermediated cell mass (ICM). Thus, we propose that c/ebp1 and runx1 presumably cooperated with pu.1 in the transcriptional regulation of lyz during zebrafish myelopoiesis.

Maternal Interferon Regulatory Factor 6 is required for the differentiation of primary superficial epithelia in Danio and Xenopus embryos

Early in the development of animal embryos, superficial cells of the blastula form a distinct lineage and adopt an epithelial morphology. In different animals, the fate of these primary superficial epithelial (PSE) cells varies, and it is unclear whether pathways governing segregation of blastomeres into the PSE lineage are conserved. Mutations in the gene encoding Interferon Regulatory Factor 6 (IRF6) are associated with syndromic and non-syndromic forms of cleft lip and palate, consistent with a role for Irf6 in development of oral epithelia, and mouse Irf6 targeted null mutant embryos display abnormal differentiation of oral epithelia and skin. In Danio rerio (zebrafish) and Xenopus laevis (African clawed frog) embryos, zygotic irf6 transcripts are present in many epithelial tissues including the presumptive PSE cells and maternal irf6 transcripts are present throughout all cells at the blastula stage. Injection of antisense oligonucleotides with ability to disrupt translation of irf6 transcripts caused little or no effect on development. By contrast, injection of RNA encoding a putative dominant negative Irf6 caused epiboly arrest, loss of gene expression characteristic of the EVL, and rupture of the embryo at late gastrula stage. The dominant negative Irf6 disrupted EVL gene expression in a cell autonomous fashion. These results suggest that Irf6 translated in the oocyte or unfertilized egg suffices for early development. Supporting the importance of maternal Irf6, we show that depletion of maternal irf6 transcripts in X. laevis embryos leads to gastrulation defects and rupture of the superficial epithelium. These experiments reveal a conserved role for maternally-encoded Irf6 in differentiation of a simple epithelium in X. laevis and D. rerio. This epithelium constitutes a novel model tissue in which to explore the Irf6 regulatory pathway.

Gene expression profiles in zebrafish brain after acute exposure to domoic acid at symptomatic and asymptomatic doses

Domoic acid (DA) is a neuroexcitatory amino acid that is naturally produced by some marine diatom species of the genus Pseudo-nitzschia. Ingestion of DA-contaminated seafood by humans results in a severe neurotoxic disease known as amnesic shellfish poisoning (ASP). Clinical signs of ASP include seizures and neuronal damage from activation of ionotropic glutamate receptors. However, the impacts of DA exposure at levels below those known to induce outward signs of neurobehavioral exicitotoxicity have not been well characterized. To further understand the mechanisms of neurotoxic injury associated with DA exposure, we examined the transcriptome of whole brains from zebrafish (Danio rerio) receiving intracoelomic (IC) injection of DA at both symptomatic and asymptomatic doses. A majority of zebrafish exposed to high-dose DA (1.2 microg DA/g) exhibited clinical signs of neuroexcitotoxicity (EC(50) of 0.86 microg DA/g) within 5-20 min of IC injection. All zebrafish receiving low-dose DA (0.47 microg DA/g) or vehicle only maintained normal behavior. Microarray analysis of symptomatic and asymptomatic exposures collectively yielded 306 differentially expressed genes (1.5-fold, p </= 0.05) predominately represented by signal transduction, ion transport, and transcription factor functional categories. Transcriptional profiles were suggestive of neuronal apoptosis following an overwhelming of protective adaptive pathways. Further, potential molecular biomarkers of neuropathic injury, including the zebrafish homolog of human NDRG4, were identified and may be relevant to DA exposure levels below that causing neurobehavioral injury. In general, DA-modulated gene expression was consistent with other model species thereby validating zebrafish as an appropriate vertebrate model to study mechanisms of DA neurotoxicity. These data provide a basis for identifying pathways of DA-induced injury as well as biomarkers of asymptomatic and symptomatic DA exposure levels.

Carboxypeptidase A5 identifies a novel mast cell lineage in the zebrafish providing new insight into mast cell fate determination

Mast cells (MCs) play critical roles in allergy and inflammation, yet their development remains controversial due to limitations posed by traditional animal models. The zebrafish provides a highly efficient system for studying vertebrate hematopoiesis. We have identified zebrafish MCs in the gill and intestine, which resemble their mammalian counterparts both structurally and functionally. Carboxypeptidase A5 (cpa5), a MC-specific enzyme, is expressed in zebrafish blood cells beginning at 24 hours post fertilization (hpf). At 28 hpf, colocalization is observed with pu.1, mpo, l-plastin, and lysozyme C, but not fms or cepbα, identifying these early MCs as a distinct myeloid population arising from a common granulocyte/monocyte progenitor. Morpholino “knock-down” studies demonstrate that transcription factors gata-2 and pu.1, but not gata-1 or fog-1, are necessary for early MC development. These studies validate the zebrafish as an in vivo tool for studying MC ontogeny and function with future capacity for modeling human MC diseases.

PIASy represses CCAAT/enhancer-binding protein delta (C/EBPdelta) transcriptional activity by sequestering C/EBPdelta to the nuclear periphery

CCAAT/enhancer binding proteindelta (C/EBPdelta) plays a key role in mammary epithelial cell G(0) growth arrest, and "loss of function" alterations in C/EBPdelta have been reported in breast cancer and acute myeloid leukemia. C/EBPdelta is regulated at the transcriptional, post-transcriptional, and post-translational levels, suggesting tight control of C/EBPdelta content and function. Protein inhibitors of activated STATs (PIASs) regulate a growing number of transcription factors, including C/EBPs. HC11 nontransformed mammary epithelial cells express PIAS3, PIASxbeta, and PIASy, and all three PIAS family members repress C/EBPdelta transcriptional activity. PIASy is the most potent, however, repressing C/EBPdelta transcriptional activity by >80%. PIASy repression of C/EBPdelta transcriptional activity is dependent upon interaction between the highly conserved PIASy N-terminal nuclear matrix binding domain (SAPD) and the C/EBPdelta transactivation domain (TAD). PIASy repression of C/EBPdelta transcriptional activity is independent of histone deacetylase activity, PIASy E3 SUMO ligase activity, and C/EBPdelta sumoylation status. PIASy expression is associated with C/EBPdelta translocation from nuclear foci, where C/EBPdelta co-localizes with p300, to the nuclear periphery. PIASy-mediated translocation of C/EBPdelta is dependent upon the PIASy SAPD and C/EBPdelta TAD. PIASy reduces the expression of C/EBPdelta adhesion-related target genes and enhances repopulation of open areas within a cell monolayer in the in vitro "scratch" assay. These results demonstrate that PIASy represses C/EBPdelta by a mechanism that requires interaction between the PIASy SAPD and C/EBPdelta TAD and does not require PIASy SUMO ligase activity or C/EBPdelta sumoylation. PIASy alters C/EBPdelta nuclear localization, reduces C/EBPdelta transcriptional activity, and enhances cell proliferation/migration.

Zebrafish in hematology: sushi or science?

After a decade of the "modern era" of zebrafish hematology research, what have been their major contributions to hematology and what challenges does the model face? This review argues that, in hematology, zebrafish have demonstrated their suitability, are proving their utility, have supplied timely and novel discoveries, and are poised for further significant contributions. It presents an overview of the anatomy, physiology, and genetics of zebrafish hematopoiesis underpinning their use in hematology research. Whereas reverse genetic techniques enable functional studies of particular genes of interest, forward genetics remains zebrafish's particular strength. Mutants with diverse and interesting hematopoietic defects are emerging from multiple genetic screens. Some mutants model hereditary blood diseases, occasionally leading to disease genes first; others provide insights into developmental hematology. Models of malignant hematologic disorders provide tools for drug-target and pharmaceutics discovery. Numerous transgenic zebrafish with fluorescently marked blood cells enable live-cell imaging of inflammatory responses and host-pathogen interactions previously inaccessible to direct observation in vivo, revealing unexpected aspects of leukocyte behavior. Zebrafish disease models almost uniquely provide a basis for efficient whole animal chemical library screens for new therapeutics. Despite some limitations and challenges, their successes and discovery potential mean that zebrafish are here to stay in hematology research.

AML1-ETO reprograms hematopoietic cell fate by downregulating scl expression

AML1-ETO is one of the most common chromosomal translocation products associated with acute myelogenous leukemia (AML). Patients carrying the AML1-ETO fusion gene exhibit an accumulation of granulocyte precursors in the bone marrow and the blood. Here, we describe a transgenic zebrafish line that enables inducible expression of the human AML1-ETO oncogene. Induced AML1-ETO expression in embryonic zebrafish causes a phenotype that recapitulates some aspects of human AML. Using this highly tractable model, we show that AML1-ETO redirects myeloerythroid progenitor cells that are developmentally programmed to adopt the erythroid cell fate into the granulocytic cell fate. This fate change is characterized by a loss of gata1 expression and an increase in pu.1 expression in myeloerythroid progenitor cells. Moreover, we identify scl as an early and essential mediator of the effect of AML1-ETO on hematopoietic cell fate. AML1-ETO quickly shuts off scl expression, and restoration of scl expression rescues the effects of AML1-ETO on myeloerythroid progenitor cell fate. These results demonstrate that scl is an important mediator of the ability of AML1-ETO to reprogram hematopoietic cell fate decisions, suggesting that scl may be an important contributor to AML1-ETO-associated leukemia. In addition, treatment of AML1-ETO transgenic zebrafish embryos with a histone deacetylase inhibitor, Trichostatin A, restores scl and gata1 expression, and ameliorates the accumulation of granulocytic cells caused by AML1-ETO. Thus, this zebrafish model facilitates in vivo dissection of AML1-ETO-mediated signaling, and will enable large-scale chemical screens to identify suppressors of the in vivo effects of AML1-ETO.

Combinatorial regulation of novel erythroid gene expression in zebrafish

OBJECTIVE

The specification and differentiation of hematopoietic stem cells into red blood cells requires precise coordination by multiple transcription factors. Most genes important for erythroid maturation are regulated by the Gata family of DNA-binding proteins. Previously, we identified three novel genes kelch-repeat containing protein (krcp), kiaa0650, and testhymin/glucocorticoid inducible transcript 1 (glcci1) to be expressed in erythroid cells in a Gata-independent manner, and we sought to further understand how these transcripts are regulated during zebrafish hematopoiesis.

MATERIALS AND METHODS

We employed a loss-of-function approach, using combinations of antisense morpholinos to hematopoietic transcription factors and assayed for changes in gene expression in zebrafish embryos.

RESULTS

Upon examination of embryos deficient for Gata1, Gata2, Biklf, and/or Scl, we found distinct gene combinations were required for expression of the novel genes. While krcp expression was dependent upon Gata1 and Biklf, kiaa0650 expression was greatly reduced and glcci1 was maintained in Gata1/Gata2/Biklf-deficient embryos. As with the gata1 gene, kiaa0650 and krcp required Scl for blood expression. Although reduced, glcci1 was expressed in posterior blood precursors in the absence of Scl and Gata2.

CONCLUSIONS

This work identifies glcci1 as having Scl-independent expression in the posterior hematopoietic mesoderm, suggesting that its posterior expression is activated by factors upstream or parallel to Scl and Gata2. Additionally, these studies establish that blood gene expression programs are regulated by transcription factors acting in combination during erythroid maturation.

Cdx4 is required in the endoderm to localize the pancreas and limit beta-cell number

Cdx transcription factors have crucial roles in anteroposterior patterning of the nervous system and mesoderm. Here we focus on the role of cdx4 in patterning the endoderm in zebrafish. We show that cdx4 has roles in determining pancreatic beta-cell number, directing midline convergence of beta-cells during early pancreatic islet formation, and specifying the anteroposterior location of foregut organs. Embryos deficient in cdx4 have a posteriorly shifted pancreas, liver and small intestine. The phenotype is more severe with knockdown of an additional Cdx factor, cdx1a. We show that cdx4 functions within the endoderm to localize the pancreas. Morpholino knockdown of cdx4 specifically in the endoderm recapitulates the posteriorly shifted pancreas observed in cdx4 mutants. Conversely, overexpression of cdx4 specifically in the endoderm is sufficient to shift the pancreas anteriorly. Together, these results suggest a model in which cdx4 confers posterior identity to the endoderm. Cdx4 might function to block pancreatic identity by preventing retinoic acid (RA) signal transduction in posterior endoderm. In support of this, we demonstrate that in cdx4-deficient embryos treated with RA, ectopic beta-cells are located well posterior to the normal pancreatic domain.

Identification and real-time imaging of a myc-expressing neutrophil population involved in inflammation and mycobacterial granuloma formation in zebrafish

By enhancer trap screening we identified a transgenic zebrafish line showing leukocyte-specific YFP expression during late embryo and early larval development. Its enhancer detection insertion was mapped near a novel member of the myc proto-oncogene family, encoding transcription factors known to be important for regulating human myelopoiesis. Characterization of the zebrafish myc family showed that only this particular myc gene is strongly expressed in leukocytes. To identify the myc/YFP-expressing cell type, we re-examined specificity of described myeloid markers by multiplex fluorescent in situ hybridization, showing that lcp1 can be considered as a general leukocyte marker, csf1r as a macrophage-specific marker, and mpx and lyz as neutrophil-specific markers. Subsequent colocalization analysis defined the YFP-positive cells as a subset of the neutrophil population. Using real-time confocal imaging we demonstrate that these cells migrate to sites of inflammation and are involved in innate immune responses towards infections, including Mycobacterium marinum-induced granuloma formation.

Dominant-interfering C/EBPalpha stimulates primitive erythropoiesis in zebrafish

OBJECTIVE

We investigated the role of CCAAT enhancer-binding protein-alpha (C/EBPalpha) during zebrafish embryonic blood development.

METHODS

Whole-mount mRNA in situ hybridization was performed to determine the spatio-temporal expression pattern of zebrafish cebpa in developing hematopoietic progenitors. A deletion mutation of cebpa (zD420), which mimics the human dominant-negative mutations of C/EBPalpha, was transfected into CV1 cell line to evaluate its transcriptional activity in vitro and injected into zebrafish embryos at the one- to two-cell stage to examine its effects on primitive hematopoiesis during early zebrafish development.

RESULTS

Zebrafish cebpa is expressed in the anterior and posterior lateral plate mesoderm at 12 hours postfertilization, along with scl, pu.1, and gata1 in developing hematopoietic progenitors. In vitro, the deletion mutation of cebpa (zD420) prevents expression of the full-length protein, allowing the expression of truncated isoforms from internal translational initiation sites. As in the human, the truncated zebrafish C/EBPalpha proteins did not activate the expression of known target granulocytic genes, and in fact suppressed transactivation that was induced in vitro by the full-length protein. Forced expression of the zD420 mRNA in zebrafish embryos led to an expansion of primitive erythropoiesis, without a discernible effect on granulopoiesis.

CONCLUSION

Expression of the truncated isoforms of cebpa alters the developmental pattern of hematopoietic progenitor cells during embryogenesis.

Acute phase response in zebrafish upon Aeromonas salmonicida and Staphylococcus aureus infection: Striking similarities and obvious differences with mammals

Zebrafish has emerged as a valuable model for immunological studies. However, little is known about the overall picture of its immune response to infectious pathogens. Here we present the first systematic study of its immune response to Aeromonas salmonicida and Staphylococcus aureus, a Gram-negative and a Gram-positive bacteria, respectively. Genes induced upon infection were identified with suppression subtractive hybridization, with many of them encoding acute phase proteins (APPs). When compared with mammals, striking similarities and obvious differences have been observed. Both similar APPs (SAA, hepcidin and haptoglobin, etc.) and a similar system for the induction of APPs (which involves the TLRs, pro-inflammatory cytokines and C/EBPs) were identified, implying evolutionary conserved mechanisms among fish and mammals. Some novel APPs were also discovered, suggesting different immune strategies adopted by fish species. Among which, LECT2 was induced by up to 1000-fold upon infection, shedding new lights on the function of this gene. Our results constitute the first demonstration of a similar while different immune response in zebrafish and open new avenues for the investigation of evolutionary conserved and fish specific mechanisms of innate immunity.

C/EBPalpha and C/EBPbeta are markers of early liver development

Pancreatic cells can be converted to hepatocytes by overexpression of C/EBPbeta (Shen, C-N, Slack, J.M.W. and Tosh, D., 2000. Molecular basis of transdifferentiation of pancreas to liver. Nature Cell Biology 2: 879-887). This suggested that expression of one or more C/EBP factors may distinguish liver and pancreas in early development. We have now studied the early expression of C/EBPalpha and C/EBPbeta in the mouse embryo and show that both are expressed exclusively in the early liver bud and not in the pancreatic buds. Their expression is identical to that of hepatocyte nuclear factor 4 (HNF4), another key hepatic transcription factor and alpha-fetoprotein (AFP), a differentiation product characteristic of immature hepatocytes. Both are complementary to the early expression of Pdx1, a key pancreatic transcription factor. These results are consistent with the idea that C/EBP factors are master regulators for liver development.

Characterization of the zebrafish matrix metalloproteinase 9 gene and its developmental expression pattern

Members of the matrix metalloproteinase (MMP) family are important for the remodeling of the extracellular matrix in a number of biological processes including a variety of immune responses. Two members of the family, MMP2 and MMP9, are highly expressed in specific myeloid cell populations in which they play a role in the innate immune response. To further expand the repertoire of molecular reagents available to study zebrafish myeloid cell development, the matrix metalloproteinase 9 (mmp9) gene from this organism has been identified and characterized. The encoded protein is 680 amino acids with high homology to known MMP9 proteins, particularly those of other teleost fish. Maternal transcripts of mmp9 are deposited in the oocyte and dispersed throughout the early embryo. These are replaced by specific zygotic transcripts in the notochord from 12h post fertilization (hpf) and also transiently in the anterior mesoderm from 14 to 16h post fertilization. From 24h post fertilization, mmp9 expression was detected in a population of circulating white blood cells that are distinct from macrophages, and which migrate to the site of trauma, and so likely represent zebrafish heterophils. In the adult, mmp9 expression was most prominent in the splenic cords, a site occupied by mature myeloid cells in other species. These results suggest that mmp9 will serve as a useful marker of mature myeloid cells in the zebrafish.

Use of the zebrafish system to study primitive and definitive hematopoiesis

The zebrafish (Danio rerio) has emerged as an ideal organism for the study of hematopoiesis, the process by which all the cellular elements of the blood are formed. These elements, including erythrocytes, granulocytes, monocytes, lymphocytes, and thrombocytes, are formed through complex genetic signaling pathways that are highly conserved throughout phylogeny. Large-scale forward genetic screens have identified numerous blood mutants in zebrafish, helping to elucidate specific signaling pathways important for hematopoietic stem cells (HSCs) and the various committed blood cell lineages. Here we review both primitive and definitive hematopoiesis in zebrafish, discuss various genetic methods available in the zebrafish model for studying hematopoiesis, and describe some of the zebrafish blood mutants identified to date, many of which have known human disease counterparts.

Zebrafish as a model for myelopoiesis during embryogenesis

Zebrafish produce nearly identical hematopoeitic cell lineages to those found in mammals and other higher vertebrates. As in mammals, blood cell development proceeds in distinct waves, constituting embryonic (primitive) and adult (definitive) hematopoiesis. The conservation of genes such as scl, pu.1, c/ebpalpha, mpo, l-plastin, and lysozyme C in myelopoiesis and the corresponding expression patterns in zebrafish suggests that shared genetic pathways regulate this complex developmental process. In the zebrafish model system, experimental approaches have been applied, including RNA in situ hybridization, morpholino injections, and the analysis of mutant and transgenic fish lines, leading to improved understanding of the regulation in vivo of key molecular pathways with conserved roles in vertebrate myelopoiesis.

Transcriptome profiling of adult zebrafish at the late stage of chronic tuberculosis due to Mycobacterium marinum infection

The Mycobacterium marinum-zebrafish infection model was used in this study for analysis of a host transcriptome response to mycobacterium infection at the organismal level. RNA isolated from adult zebrafish that showed typical signs of fish tuberculosis due to a chronic progressive infection with M. marinum was compared with RNA from healthy fish in microarray analyses. Spotted oligonucleotide sets (designed by Sigma-Compugen and MWG) and Affymetrix GeneChips were used, in total comprising 45,465 zebrafish transcript annotations. Based on a detailed comparative analysis and quantitative reverse transcriptase-PCR analysis, we present a validated reference set of 159 genes whose regulation is strongly affected by mycobacterial infection in the three types of microarrays analyzed. Furthermore, we analyzed the separate datasets of the microarrays with special emphasis on the expression profiles of immune-related genes. Upregulated genes include many known components of the inflammatory response and several genes that have previously been implicated in the response to mycobacterial infections in cell cultures of other organisms. Different marker genes of the myeloid lineage that have been characterized in zebrafish also showed increased expression. Furthermore, the zebrafish homologs of many signal transduction genes with relationship to the immune response were induced by M. marinum infection. Future functional analysis of these genes may contribute to understanding the mechanisms of mycobacterial pathogenesis. Since a large group of genes linked to immune responses did not show altered expression in the infected animals, these results suggest specific responses in mycobacterium-induced disease.

Interplay of pu.1 and gata1 determines myelo-erythroid progenitor cell fate in zebrafish

The zebrafish is a powerful model system for investigating embryonic vertebrate hematopoiesis, allowing for the critical in vivo analysis of cell lineage determination. In this study, we identify zebrafish myeloerythroid progenitor cells (MPCs) that are likely to represent the functional equivalent of mammalian common myeloid progenitors. Utilizing transgenic pu.1-GFP fish, real-time MPC differentiation was correlated with dynamic changes in cell motility, morphology, and gene expression. Unlike mammalian hematopoiesis, embryonic zebrafish myelopoiesis and erythropoiesis occur in anatomically separate locations. Gene knockdown experiments and transplantation assays demonstrated the reciprocal negative regulation of pu.1 and gata1 and their non-cell-autonomous regulation that determines myeloid versus erythroid MPC fate in the distinct blood-forming regions. Furthermore, forced expression of pu.1 in the bloodless mutant cloche resulted in myelopoietic rescue, providing intriguing evidence that this gene can function in the absence of some stem cell genes, such as scl, in governing myelopoiesis.

Characterization of expanded intermediate cell mass in zebrafish chordin morphant embryos

We investigated the mechanisms of intermediate cell mass (ICM) expansion in zebrafish chordin (Chd) morphant embryos and examined the role of BMPs in relation to this phenotype. At 24 h post-fertilization (hpf), the expanded ICM of embryos injected with chd morpholino (MO) (ChdMO embryos) contained a monotonous population of hematopoietic progenitors. In situ hybridization showed that hematopoietic transcription factors were ubiquitously expressed in the ICM whereas vascular gene expression was confined to the periphery. BMP4 (but not BMP2b or 7) and smad5 mRNA were ectopically expressed in the ChdMO ICM. At 48 hpf, monocytic cells were evident in both the ICM and circulation of ChdMO but not WT embryos. While injection of BMP4 MO had no effect on WT hematopoiesis, co-injecting BMP4 with chd MOs significantly reduced ICM expansion. Microarray studies revealed a number of genes that were differentially expressed in ChdMO and WT embryos and their roles in hematopoiesis has yet to be determined. In conclusion, the expanded ICM in ChdMO embryos represented an expansion of embryonic hematopoiesis that was skewed towards a monocytic lineage. BMP4, but not BMP2b or 7, was involved in this process. The results provide ground for further research into the mechanisms of embryonic hematopoietic cell expansion.

Liver-enriched transcription factors in liver function and development. Part II: the C/EBPs and D site-binding protein in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation

In the first part of our review (see Pharmacol Rev 2002;54:129-158), we discussed the basic principles of gene transcription and the complex interactions within the network of hepatocyte nuclear factors, coactivators, ligands, and corepressors in targeted liver-specific gene expression. Now we summarize the role of basic region/leucine zipper protein family members and particularly the albumin D site-binding protein (DBP) and the CAAT/enhancer-binding proteins (C/EBPs) for their importance in liver-specific gene expression and their role in liver function and development. Specifically, regulatory networks and molecular interactions were examined in detail, and the experimental findings summarized in this review point to pivotal roles of DBP and C/EBPs in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation. These regulatory proteins are therefore of great importance in liver physiology, liver disease, and liver development. Furthermore, interpretation of the vast data generated by novel genomic platform technologies requires a thorough understanding of regulatory networks and particularly the hierarchies that govern transcription and translation of proteins as well as intracellular protein modifications. Thus, this review aims to stimulate discussions on directions of future research and particularly the identification of molecular targets for pharmacological intervention of liver disease.

Expression and distribution of transcription factor CCAAT/enhancer-binding protein in the central nervous system of Lymnaea stagnalis

The transcription factor, CCAAT/enhancer-binding protein (C/EBP), is involved in important physiological processes, such as cellular proliferation and differentiation, homeostasis, and higher-order functions of the brain. In the present study, we investigated the distribution of mRNA and protein of C/EBP in the central nervous system of the pond snail, Lymnaea stagnalis, by in situ hybridization and immunohistochemistry. Specificity of the anti-mammalian C/EBP antibody against Lymnaea C/EBP (LymC/EBP) was confirmed by combination of sodium dodecyl sulfate polyacrylamide gel electrophoresis or isoelectric focusing and immunoblotting. Cells positive for in situ hybridization were immunoreactive for LymC/EBP in all 11 ganglia. The motoneurons (B1, B2, B4, and B4 clusters) in the buccal ganglia and interneurons (cerebral giant cell, CGC) in the cerebral ganglia were positive for in situ hybridization and were immunopositive. In the pedal ganglion, the right pedal dorsal 1 (RPeD1), pedal A, and pedal C clusters exhibited positive signals of in situ hybridization and immunohistochemistry for LymC/EBP. CGC and RPeD1 are key neurons for associative learning. In addition, the neuropeptidergic cells in the cerebral, pleural, parietal, and visceral ganglia were positive for in situ hybridization and immunoreactive. Interestingly, although the cytoplasm of almost all immunopositive cells was stained, some neuropeptidergic cells located in the light parietal and visceral ganglia exhibited immunoreactivity in nuclei. Our results suggest that LymC/EBP is involved in learning and memory and in the expression and/or secretion of neuropeptides in Lymnaea.

Characterization of a CCAAT-enhancer element of trefoil factor family 2 (TFF2) promoter in MCF-7 cells

Trefoil factors family 2 (TFF2), also known as spasmolytic polypeptide, is primarily expressed in the mucus neck cells of gastrointestinal tracts. It has been proposed that TFF2 plays an important physiological role in protection, repair, and healing of gastrointestinal mucosa. To investigate the cis-acting regulatory element that control TFF2 tissue-specific expression, we studied the basal TFF2 promoter activity through transient transfection in several human cancer cell lines. Expression of TFF2 was found to be significantly greater in human breast cancer MCF-7 cells compared to other cancer cells. Results from TFF2 promoter luciferase reporter constructs revealed that the basal level of TFF2 promoter activity was overall more than two-fold higher in MCF-7 cells compared to that of other cell lines examined. Using EMSA assays and site-directed mutagenesis, we identified a cell line-specific transcriptional regulation element located in the TFF2 promoter 5'-flank sequence at -32/-27, and which contains a CCAAT/enhance binding proteins (C/EBPs) consensus-binding site. Mutation of this consensus site reduced the basal promoter activity by more than 50% in MCF-7 cells but had no effect in human gastric cancer cells. In conclusion, we have identified a CCAAT sequence as a cell line-specific cis-acting regulatory element that may contribute to the high level expression of TFF2 in MCF-7 cells. These results also suggest the possibility that TFF2 could play a role in mammary gland tumorigenesis.

CCAAT/enhancer-binding proteins: structure, function and regulation

CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that all contain a highly conserved, basic-leucine zipper domain at the C-terminus that is involved in dimerization and DNA binding. At least six members of the family have been isolated and characterized to date (C/EBP alpha[bond]C/EBP zeta), with further diversity produced by the generation of different sized polypeptides, predominantly by differential use of translation initiation sites, and extensive protein-protein interactions both within the family and with other transcription factors. The function of the C/EBPs has recently been investigated by a number of approaches, including studies on mice that lack specific members, and has identified pivotal roles of the family in the control of cellular proliferation and differentiation, metabolism, inflammation and numerous other responses, particularly in hepatocytes, adipocytes and haematopoietic cells. The expression of the C/EBPs is regulated at multiple levels during several physiological and pathophysiological conditions through the action of a range of factors, including hormones, mitogens, cytokines, nutrients and certain toxins. The mechanisms through which the C/EBP members are regulated during such conditions have also been the focus of several recent studies and have revealed an immense complexity with the potential existence of cell/tissue- and species-specific differences. This review deals with the structure, biological function and the regulation of the C/EBP family.

Retinoic acid signaling is required for a critical early step in zebrafish pancreatic development

The mechanisms that subdivide the endoderm into the discrete primordia that give rise to organs such as the pancreas and liver are not well understood. However, it is known that retinoic acid (RA) signaling is critical for regionalization of the vertebrate embryo: when RA signaling is either prevented or augmented, anteroposterior (AP) patterning of the CNS and mesoderm is altered and major developmental defects occur. We have investigated the role of RA signaling in regionalization of the zebrafish endoderm. Using a mutant that prevents RA synthesis and an antagonist of the RA receptors, we show that specification of both the pancreas and liver requires RA signaling. By contrast, RA signaling is not required for the formation of the endodermal germ layer or for differentiation of other endodermal organs. Timed antagonist and RA treatments show that the RA-dependent step in pancreatic specification occurs at the end of gastrulation, significantly earlier than the expression of known markers of pancreatic progenitors. In addition to being required for pancreatic specification, RA has the capacity to transfate anterior endoderm to a pancreatic fate.