The Zebrafish Homologue of the Murine Ecotropic Viral Integration Site-1 (. Evi-1) gene Regulates Zebrafish Embryonic Blood Development.

Abstract 1461

Poster Board I-484

The ecotropic viral integration site-1 (Evi-1) locus was originally identified as a common site of retroviral integration in murine myeloid tumors and was later shown to be one of the most potent oncogenenes associated with murine and human myeloid leukemia. More recent data suggest involvement of Evi-1 in embryonic hematopoiesis (Goyama et al, Cell Stem Cell 2008; Yuasa et al, EMBO J, 2005), yet the precise role and molecular regulation of Evi-1 during blood development remains poorly understood. The zebrafish model offers powerful tools for genetic and embryonic studies. Here, we study zebrafish embryonic development and human pluripotent stem cells to understand how evi-1 modulates early hematopoietic development.

Loss-of-function studies were performed in vivo by injecting Morpholino oligonucleotides in zebrafish zygotes to inhibit evi-1 pre-mRNA splicing. To control for off-target effects, two separate morpholinos were designed and injected. N=100 zebrafish were analysed pro experiment in each group. Inhibition of evi-1 was confirmed by quantitative PCR comparison in morpholino-injected and control embryos. Hematopoietic development was followed in both morphants and wild-type embryos by simple microscopy and in situ hybridizations using known hematopoeitic markers in order to investigate the developmental time-point in which evi-1 regulates blood development. evi-1 morpholino injected zebrafisch embryo showed severely reduced numbers of circulating blood cells, consistent with the phenotype observed in Evi-1^−/− mice. Additionally, hemorrhages were observed, suggesting concomittant defects of the endothelial lineage in evi-1 deficient fish. In situ hybridization analysis on 11-12 somite stage embryos revealed strong reduction of myeloid embryonic hematopoiesis (measured by pu.1 expression in the anterior lateral plate mesoderm), while no change was observed in primitive erythroid progenitor cells (monitored by gata1 expression) or overall in blood and endothelial precursors in the posterior lateral plate mesoderm (as monitored by scl expression). Taken together, our studies demonstrate a strong impact of evi-1 on zebrafish blood development, confirming the results from Evi-1^−/− mice. As gata1 expression and therefore erythroid precursor cells in the posterior blood islands are unaffected in evi-1 morphants, our results support the hypothesis that the reduction of primitive yolk-sac erythrocytes in mutant mice was caused from hemorrhages from pericardial effusions. Since erythroid and myeloid cells derive from a common precursor, but gata1 expression was unaffected in knock-down embryos, we anticipate that evi-1 plays a specific role in the myeloid lineage, as shown by abolished pu.1 expression in the anterior LPM. evi-1 therefore probably affects differentiation, survival or proliferation of myeloid cells.

Previous reports in adult hematopoietic cells show that evi-1 can interact with both gata1 and pu.1. However, our data suggest that this is not the case during embryonic development, since gata1 expression remained unaltered in morpholino-injected embryos. Furthermore, data in mice suggest that Evi-1 may modulate embryonic hematopoiesis by affecting hematopoietic stem cell proliferation through regulation of Gata2. Currently ongoing experiments in our laboratories focus on characterization of genetic interactions between evi-1, gata2 and pu.1 during zebrafish blood development. Amongst other, gata2 and respectively pu.1 mRNA are co-injected in evi-1 morphants to analyse whether they can rescue the blood phenotype. Moreover, selected findings in zebrafish embryonic development will be verified in the human using using in vitro differentiating human induced pluripotent stem (iPS) cells. First expression data generated by real-time PCR analysis showed differential expression of EVI-1 in embryoid bodies generated from human iPS cells, confirming our hypothesis that EVI-1 has specific effects during human blood development.