AP-1 and TEAD4 co-operatively promote the vascular program during hemangioblast specification [expression]

Embryonic blood cell development occurs via well-defined developmental stages which are recapitulated in vitro by differentiation of embryonic stem cells. This process is tightly regulated by the interaction of tissue- specific and ubiquitous transcription factors with the chromatin landscape in response to outside signals. We previously identified binding motifs for the commonly expressed AP-1 transcription factor family in open chromatin regions specific for early stages of blood specification and thus aimed to study the role of AP-1 for hemangioblast differentiation. Here we show that FOS and JUN together bind to and activate a core set of vascular genes in the hemogenic endothelium and that upon global inhibition of AP-1 by expression of a dominant negative FOS peptide the balance between endothelial and hematopoietic fate is shifted towards blood. Moreover, we demonstrate that in the hemogenic endothelium AP-1 is required for de novo binding of TEAD4, a transcription factor connected to Hippo signaling, to vascular genes. Notably, after the endothelial-to-hematopoietic transition TEAD4 binding is no longer persisting. These findings provide novel mechanistic insights into vascular and hematopoietic development. Gene expression patterns in developing hemogenic and hematopoietic cells with and without AP-1