RESUMO
The transcription factors Scl and Lmo2 are crucial for development of all blood. An important early requirement for Scl in endothelial development has also been revealed recently in zebrafish embryos, supporting previous findings in scl(-/-) embryoid bodies. Scl depletion culminates most notably in failure of dorsal aorta formation, potentially revealing a role in the formation of hemogenic endothelium. We now present evidence that the requirements for Lmo2 in zebrafish embryos are essentially the same as for Scl. The expression of important hematopoietic regulators is lost, reduced, or delayed, panendothelial gene expression is down-regulated, and aorta-specific marker expression is lost. The close similarity of the phenotypes for Scl and Lmo2 suggest that they perform these early functions in hemangioblast development within a multiprotein complex, as shown for erythropoiesis. Consistent with this, we find that scl morphants cannot be rescued by a non-Lmo2-binding form of Scl but can be rescued by non-DNA-binding forms, suggesting tethering to target genes through DNA-binding partners linked via Lmo2. Interestingly, unlike other hematopoietic regulators, the Scl/Lmo2 complex does not appear to autoregulate, as neither gene's expression is affected by depletion of the other. Thus, expression of these critical regulators is dependent on continued expression of upstream regulators, which may include cell-extrinsic signals.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Proteínas de Ligação a DNA/metabolismo , Hematopoese , Metaloproteínas/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Proteínas de Peixe-Zebra/metabolismo , Peixe-Zebra/sangue , Peixe-Zebra/metabolismo , Proteínas Adaptadoras de Transdução de Sinal , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Linhagem Celular , DNA/metabolismo , Proteínas de Ligação a DNA/deficiência , Proteínas de Ligação a DNA/genética , Embrião não Mamífero/citologia , Embrião não Mamífero/embriologia , Embrião não Mamífero/metabolismo , Células Endoteliais/citologia , Células Endoteliais/metabolismo , Células Eritroides/citologia , Células Eritroides/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Células-Tronco Hematopoéticas/citologia , Células-Tronco Hematopoéticas/metabolismo , Proteínas com Domínio LIM , Metaloproteínas/deficiência , Metaloproteínas/genética , Camundongos , Células Mieloides/citologia , Células Mieloides/metabolismo , Fenótipo , Ligação Proteica , Proteínas Proto-Oncogênicas/genética , Proteína 1 de Leucemia Linfocítica Aguda de Células T , Fatores de Transcrição , Peixe-Zebra/embriologia , Peixe-Zebra/genética , Proteínas de Peixe-Zebra/deficiência , Proteínas de Peixe-Zebra/genéticaRESUMO
Blood and endothelial cells arise in close association in developing embryos, possibly from a shared precursor, the hemangioblast, or as hemogenic endothelium. The transcription factor, Scl/Tal1 (stem cell leukemia protein), is essential for hematopoiesis but thought to be required only for remodeling of endothelium in mouse embryos. By contrast, it has been implicated in hemangioblast formation in embryoid bodies. To resolve the role of scl in endothelial development, we knocked down its synthesis in zebrafish embryos where early precursors and later phenotypes can be more easily monitored. With respect to blood, the zebrafish morphants phenocopied the mouse knockout and positioned scl in the genetic hierarchy. Importantly, endothelial development was also clearly disrupted. Dorsal aorta formation was substantially compromised and gene expression in the posterior cardinal vein was abnormal. We conclude that scl is especially critical for the development of arteries where adult hematopoietic stem cells emerge, implicating scl in the formation of hemogenic endothelium.