Abstract 5273: Nkx2–5 Transactivates The Ets-related Protein 71 Gene And Specify An Endothelial/endocardial Fate Of The Developing Heart
Recent studies support the existence of a common progenitor for the cardiac and endothelial cell lineages, but the underlying transcriptional networks responsible for specification of these cell fates remain unclear. The overall goal of our study was to decipher transcriptional networks that regulate the fate of the multipotential cardiac progenitor during cardiac morphogenesis. We generated an Nkx2–5 enhancer-EYFP transgenic mouse and utilized FACS analysis to isolate wildtype and Nkx2–5 null cardiac progenitors from single, age-matched embryos at distinct developmental stages (E7.75, E8.25 and E9.5). Transcriptome and QRT-PCR analyses were used to identify Ets-related protein71 (Etsrp71), a transcript that was significantly downregulated in the Nkx2–5 null cardiac progenitors. Here we demonstrated that Ets-related protein 71 (Etsrp71), a newly discovered ETS family transcription factor, was a novel downstream target of Nkx2–5. Using genetic mouse models and molecular biological techniques, we demonstrated that Nkx2–5 binds to an evolutionarily conserved Nkx2–5 response element in the Etsrp71 promoter and induces the Etsrp71 gene expression in vitro and in vivo. Etsrp71 was transiently expressed in the endocardium/endothelium of the developing embryo (E7.75–E9.5) and was extinguished during the latter stages of development. We have further demonstrated that overexpression of Etsrp71, in an Etsrp71-inducible ES/EB system, promoted an endothelial/endocardial fate. Moreover, using a gene disruption strategy, Etsrp71 mutant embryos lacked endocardial/endothelial lineages and were nonviable. Tie2 expression is severely decreased in the absence of Etsrp71 and initial studies support the conclusion that Etsrp71 is a direct upstream transactivator of Tie2 gene expression. Our results uncover a novel functional role for Nkx2–5 and define a transcriptional network that specifies an endocardial/endothelial fate in the developing heart and embryo.