Etv2 Is Expressed in the Yolk Sac Hematopoietic and Endothelial Progenitors and Regulates Lmo2 Gene Expression

Abstract

During embryogenesis, the endothelial and the hematopoietic lineages first appear during gastrulation in the blood island of the yolk sac. We have previously reported that an Ets variant gene 2 (Etv2/ER71) mutant embryo lacks hematopoietic and endothelial lineages, however, the precise roles of Etv2 in yolk sac development remains unclear. In the present study, we define the role of Etv2 in yolk sac blood island development using the Etv2 mutant and a novel Etv2-EYFP reporter transgenic line. Both the hematopoietic and the endothelial lineages are absent in the Etv2 mutant yolk sac. In the Etv2-EYFP transgenic mouse, the EYFP reporter is activated in the nascent mesoderm, expressed in the endothelial and blood progenitors, and in the Tie2+, c-kit+, CD41+ hematopoietic population. The hematopoietic activity in the E7.75 yolk sac was exclusively localized to the Etv2-EYFP+ population. In the Etv2 mutant yolk sac, Tie2+ cells are present but do not express hematopoietic or endothelial markers. In addition, these cells do not form hematopoietic colonies, indicating an essential role of Etv2 in the specification of the hematopoietic lineage. Forced overexpression of Etv2 during EB differentiation induces the hematopoietic and the endothelial lineages, and transcriptional profiling in this context identifies Lmo2 as a downstream target. Using EMSA, ChIP, transcriptional assays and mutagenesis, we demonstrate that Etv2 binds to the Lmo2 enhancer and transactivates its expression. Collectively, our studies demonstrate that Etv2 is expressed during and required for yolk sac hemato-endothelial development, and that Lmo2 is one of the downstream targets of Etv2.

Sox7Is Regulated by ETV2 During Cardiovascular Development

“…The Etv2 homozygous mutant embryos were lethal by E9.5, and lacked the endocardial/endothelial lineage [14]. Recent in vivo and in vitro results further support the hypothesis that ETV2 is a critical factor for the specification of the endocardial/endothelial and hematopoietic lineages [15,[20][21][22][23].…”

“…Recently, it was shown that continued enforced expression of SOX7 in hemangioblast-derived blast colonies resulted in sustained expression of endothelial markers while impairing hematopoietic differentiation [37]. This same study implicated Cdh5, a gene known to be downstream of ETV2, as a direct downstream target of SOX7 [21,55]. Although there is significant overlap of Etv2 and Sox7 function in early endothelial and hematopoietic development, as well as apparent overlap of transcriptional pathways, a direct linkage between Etv2 and Sox7 has not previously been described.…”

“…It was previously demonstrated that Etv2 is expressed early during embryogenesis in the endocardial/endothelial lineage and that Etv2-deficient embryos are lethal, lacking endocardial/endothelial and hematopoietic lineages [14,21,23,45]. In the zebrafish model system, Etv2 has also been shown to be important for vascular development, initially for EPC specification, and later in hemogenic endothelial cells [49,50].…”

VEGFA-dependent and -independent pathways synergise to drive Scl expression and initiate programming of the blood stem cell lineage in Xenopus

“…In support of this, Gata-and ETS-binding sites are required for Etv2 expression in endothelial cells (Veldman and Lin, 2012;De Val et al, 2008); and Gata2 is the only Gata factor available for Etv2 activation and Fli1 the only ETS TF available. Finally, as Scl and Lmo2 require Etv2, which is required for contemporaneous Gata2 expression, the inputs of both into these genes are also likely to be direct, a conclusion supported in the case of Etv2 on Lmo2 by recent binding assays, albeit in the primitive haemangioblast (Koyano-Nakagawa et al, 2012).…”

OVOL2 is a critical regulator of ER71/ETV2 in generating FLK1+, hematopoietic, and endothelial cells from embryonic stem cells

“…[5][6][7][8] ER71 activates genes critical for both hematopoiesis and vessel development including Flk1, VECadherin (VE-Cad), Scl, and Lmo2 through direct binding to gene-associated promoters/enhancers. 5,[8][9][10] Studies in zebrafish and Xenopus also reported er71's potent function, 11,12 indicating an evolutionally conserved and essential role for ER71 in the establishment of the cardiovascular system.…”