Abstract 785: MesP1 Induces Vertebrate Cardiovascular Differentiationby Dkk-1 Mediated Blockage Of Wnt-signalling
Cardiovascular diseases are the most frequent cause of death in the western world. Stem cell based cardiovascular repair will require in-depth understanding of molecular mechanisms underlying cardiovascular ES cell differentiation in vitro. A candidate cardiovascular fate inducer is the bHLH transcription factor Mesp1. As one of the earliest cardiovascular markers it is specifically expressed in almost all precursors of the cardiovascular system and required for cardiac morphogenesis. However, the mode of action of MesP1 in the underlying processes is unknown. Here we show in overexpression experiments using Xenopus embryos that MesP1 is the first known single transcription factor sufficient to induce ectopic beating heart tissue in vertebrates. Furthermore, MesP1 overexpression in ES cells results in significantly increased cardiovasculogenesis. Electrophysiological analysis of isolated beating cardiomyocytes showed all subtypes described for cardiac ES cell differentiation. Our results from RT-PCRs reveal a prominent function of MesP1 within a gene regulatory cascade causing Dkk-1 mediated blockage of canonical wnt signaling non cell autonomously leading to upregulation of the endodermal transcription factor Hex. In ChiP and bandshift assays we confirmed the Dkk-1 promoter as a direct target for MesP1. We consider our studies as a starting point to further decipher the detailed molecular position of MesP1 within the complex networks involved in cardiovasculogenesis. This knowledge will be a prerequisite to program ES cells towards a cardiovascular fate for cell therapy and cardiovascular tissue engineering. Likewise, it will be of great interest to transfer this approach to various subpopulations of human adult stem cells which still have not definitively been shown to bear cardiac transdifferentiation potential in their native state.