Abstract 16786: Er71 Transcriptionally Activates Lmo2 and Regulates Endothelial Development

During early embryonic development, mesodermal progenitor cells give rise to multiple lineages including the cardiovascular, endothelial and hematopoietic lineages. Studies suggest that the extraembryonic yolk sac is a progenitor source for endothelial and hematopoietic lineages during embryogenesis. We have previously shown that Ets related protein 71(ER71) regulates the development of endothelial and hematopoietic lineages in the early yolk sac and embryo proper utilizing an ER71 gene knock out mouse model, an ER71 promoter driven EYFP-expressing transgenic mouse model and an doxycycline-inducible ER71-overexpressing ES/EB model. To decipher the ER71 mediated mechanism for lineage specification, we evaluated candidate downstream targets of ER71 using qPCR, transcriptome analysis, ChIP and transcriptional assays in the ER71 global gene knockout mouse and doxycycline inducible ER71 overexpressing ES/EB models. Using qPCR, we observed an absence of hematopoietic and endothelial restricted genes in the ER71 mutant yolk sacs and embryo proper compared to their wildtype littermates. We further observed a significant downregulation of Lmo2 in the mutant embryo compared to the wildtype control. Moreover, forced overexpression of ER71 using an inducible ES/EB system revealed that Lmo2 was significantly upregulated within 12 hours following ER71 induction. Analysis of approximately 100kb of the Lmo2 gene revealed multiple potential Ets binding motifs and evaluation of each of these sites using ChIP assays focused our efforts on the 1 kb region in the first intron of the Lmo2 gene. Using an array of biochemical techniques including EMSA, transcriptional assays and mutagenesis our data collectively support the hypothesis that Lmo2 is a direct downstream target of ER71. In summary, the present studies define an ER71-Lmo2 transcriptional network that governs endothelial specification and differentiation during cardiovascular development.