Cloning of the Zebrafish retsina Blood Mutation: A Genetic Model for Dyserythropoiesis and Erythroid Cytokinesis

Novel evolutionary-conserved role for the activity-dependent neuroprotective protein (ADNP) family that is important for erythropoiesis

BACKGROUND

ADNP is vital for embryonic development. Is this function conserved for the homologous protein ADNP2?

RESULTS

Down-regulation/silencing of ADNP or ADNP2 in zebrafish embryos or mouse erythroleukemia cells inhibited erythroid maturation, with ADNP directly associating with the β-globin locus control region.

CONCLUSION

ADNPs are novel molecular regulators of erythropoiesis.

SIGNIFICANCE

New regulators of globin synthesis are suggested. Activity-dependent neuroprotective protein (ADNP) and its homologue ADNP2 belong to a homeodomain, the zinc finger-containing protein family. ADNP is essential for mouse embryonic brain formation. ADNP2 is associated with cell survival, but its role in embryogenesis has not been evaluated. Here, we describe the use of the zebrafish model to elucidate the developmental roles of ADNP and ADNP2. Although we expected brain defects, we were astonished to discover that the knockdown zebrafish embryos were actually lacking blood and suffered from defective hemoglobin production. Evolutionary conservation was established using mouse erythroleukemia (MEL) cells, a well studied erythropoiesis model, in which silencing of ADNP or ADNP2 produced similar results as in zebrafish. Exogenous RNA encoding ADNP/ADNP2 rescued the MEL cell undifferentiated state, demonstrating phenotype specificity. Brg1, an ADNP-interacting chromatin-remodeling protein involved in erythropoiesis through regulation of the globin locus, was shown here to interact also with ADNP2. Furthermore, chromatin immunoprecipitation revealed recruitment of ADNP, similar to Brg1, to the mouse β-globin locus control region in MEL cells. This recruitment was apparently diminished upon dimethyl sulfoxide (DMSO)-induced erythrocyte differentiation compared with the nondifferentiated state. Importantly, exogenous RNA encoding ADNP/ADNP2 significantly increased β-globin expression in MEL cells in the absence of any other differentiation factors. Taken together, our results reveal an ancestral role for the ADNP protein family in maturation and differentiation of the erythroid lineage, associated with direct regulation of β-globin expression.

Ddx18 is essential for cell-cycle progression in zebrafish hematopoietic cells and is mutated in human AML

In a zebrafish mutagenesis screen to identify genes essential for myelopoiesis, we identified an insertional allele hi1727, which disrupts the gene encoding RNA helicase dead-box 18 (Ddx18). Homozygous Ddx18 mutant embryos exhibit a profound loss of myeloid and erythroid cells along with cardiovascular abnormalities and reduced size. These mutants also display prominent apoptosis and a G1 cell-cycle arrest. Loss of p53, but not Bcl-xl overexpression, rescues myeloid cells to normal levels, suggesting that the hematopoietic defect is because of p53-dependent G1 cell-cycle arrest. We then sequenced primary samples from 262 patients with myeloid malignancies because genes essential for myelopoiesis are often mutated in human leukemias. We identified 4 nonsynonymous sequence variants (NSVs) of DDX18 in acute myeloid leukemia (AML) patient samples. RNA encoding wild-type DDX18 and 3 NSVs rescued the hematopoietic defect, indicating normal DDX18 activity. RNA encoding one mutation, DDX18-E76del, was unable to rescue hematopoiesis, and resulted in reduced myeloid cell numbers in ddx18(hi1727/+) embryos, indicating this NSV likely functions as a dominant-negative allele. These studies demonstrate the use of the zebrafish as a robust in vivo system for assessing the function of genes mutated in AML, which will become increasingly important as more sequence variants are identified by next-generation resequencing technologies.

How to create the vascular tree? (Latest) help from the zebrafish

The cardiovascular system provides oxygen, nutrients and hormones to organs, it directs traffic of metabolites and it maintains tissue homeostasis. It is one of the first organs assembled during vertebrate development and it is essential to life from early stages to adult. For these reasons, the process of vessel formation has being studied for more than a century, but it is only in the late eighties that there has been an explosion of research in the field with the employment of various in vitro and in vivo model systems. The zebrafish (Danio rerio) offers several advantages for in vivo studies; it played a fundamental role in new discoveries and helped to refine our knowledge of the vascular system. This review recapitulates the zebrafish data on vasculogenesis and angiogenesis, including the specification of the haemangioblasts from the mesoderm, their migration to form the vascular cord followed by axial vessels specification, the primary and secondary sprouting of intersomitic vessels, the formation of the lumen, the arterial versus venous specification and patterning. To emphasize the strengths of the zebrafish system in the vascular field, we summarize main tools, such as gene expression and mutagenesis screens, knock down technologies, transgenic lines and imaging, which played a major role in the development of the field and allowed significant discoveries, for instance the recent visualization of the lymphatic system in zebrafish. This information contributes to the prospective of drug discovery to cure human diseases linked to angiogenesis, not last tumours.

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.

Distinct Roles for SCL in Erythroid Specification and Maturation in Zebrafish

The stem cell leukemia (SCL) transcription factor is essential for vertebrate hematopoiesis. Using the powerful zebrafish model for embryonic analysis, we compared the effects of either reducing or ablating Scl using morpholino-modified antisense RNAs. Ablation of Scl resulted in the loss of primitive and definitive hematopoiesis, consistent with its essential role in these processes. Interestingly, in embryos with severely reduced Scl levels, erythroid progenitors expressing gata1 and embryonic globin developed. Erythroid maturation was deficient in these Scl hypomorphs, supporting that Scl was required both for the erythroid specification and for the maturation steps, with maturation requiring higher Scl levels than specification. Although all hematopoietic functions were rescued by wild-type Scl mRNA, an Scl DNA binding mutant rescued primitive and definitive hematopoiesis but did not rescue primitive erythroid maturation. Together, we showed that there is a distinct Scl hypomorphic phenotype and demonstrated that distinct functions are required for the roles of Scl in the specification and differentiation of primitive and definitive hematopoietic lineages. Our results revealed that Scl participates in multiple processes requiring different levels and functions. Further, we identified an Scl hypomorphic phenotype distinct from the null state.

Modeling human hematopoietic and cardiovascular diseases in zebrafish

Zebrafish have emerged as a useful vertebrate model system in which unbiased large-scale screens have revealed hundreds of mutations affecting vertebrate development. Many zebrafish mutants closely resemble known human disorders, thus providing intriguing prospects for uncovering the genetic basis of human diseases and for the development of pharmacologic agents that inhibit or correct the progression of developmental disorders. The rapid pace of advances in genomic sequencing and map construction, in addition to morpholino targeting and transgenic techniques, have facilitated the identification and analysis of genes associated with zebrafish mutants, thus promoting the development of zebrafish as a model for human disorders. This review aims to illustrate how the zebrafish has been used to identify unknown genes, to assign function to known genes, and to delineate genetic pathways, all contributing valuable leads toward understanding human pathophysiology.

The state of the art of the zebrafish model for toxicology and toxicologic pathology research--advantages and current limitations

The zebrafish (Danio rerio) is now the pre-eminent vertebrate model system for clarification of the roles of specific genes and signaling pathways in development. The zebrafish genome will be completely sequenced within the next 1-2 years. Together with the substantial historical database regarding basic developmental biology, toxicology, and gene transfer, the rich foundation of molecular genetic and genomic data makes zebrafish a powerful model system for clarifying mechanisms in toxicity. In contrast to the highly advanced knowledge base on molecular developmental genetics in zebrafish, our database regarding infectious and noninfectious diseases and pathologic lesions in zebrafish lags far behind the information available on most other domestic mammalian and avian species, particularly rodents. Currently, minimal data are available regarding spontaneous neoplasm rates or spontaneous aging lesions in any of the commonly used wild-type or mutant lines of zebrafish. Therefore, to fully utilize the potential of zebrafish as an animal model for understanding human development, disease, and toxicology we must greatly advance our knowledge on zebrafish diseases and pathology.

A nonsense mutation in zebrafish gata1 causes the bloodless phenotype in vlad tepes

Vlad tepes (vlt(m651)) is one of only five "bloodless" zebrafish mutants isolated through large-scale chemical mutagenesis screening. It is characterized by a severe reduction in blood cell progenitors and few or no blood cells at the onset of circulation. We now report characterization of the mutant phenotype and the identification of the gene mutated in vlt(m651). Embryos homozygous for the vlt(m651) mutation had normal expression of hematopoietic stem cell markers through 24 h postfertilization, as well as normal expression of myeloid and lymphoid markers. Analysis of erythroid development revealed variable expression of erythroid markers. Through positional and candidate gene cloning approaches we identified a nonsense mutation in the gata1 gene, 1015C --> T (Arg-339 --> Stop), in vlt(m651). The nonsense mutation was located C-terminal to the two zinc fingers and resulted in a truncated protein that was unable to bind DNA or mediate GATA-specific transactivation. A BAC clone containing the zebrafish gata1 gene was able to rescue the bloodless phenotype in vlt(m651). These results show that the vlt(m651) mutation is a previously uncharacterized gata1 allele in the zebrafish. The vlt(m651) mutation sheds new light on Gata1 structure and function in vivo, demonstrates that Gata1 plays an essential role in zebrafish hematopoiesis with significant conservation of function between mammals and zebrafish, and offers a powerful tool for future studies of the hematopoietic pathway.