Transcriptional regulation of fibroblast generation in the embryonic mouse heart.

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During embryonic development, epithelial cells, such as those that cover the growing heart (epicardium), undergo a process termed Epithelial to Mesenchymal Transition (EMT) and convert into mesenchymal progenitors, which give rise to the fibroblast, endothelial and vascular smooth muscle cell populations of the developing heart. Cardiac fibroblasts can also be generated by a variation of the EMT program in endothelial cells termed Endothelial to Mesenchymal Transition (EndMT), which is important for cardiac valve morphogenesis. A key regulator of EMT and EndMT is the cytokine Transforming Growth Factor-ß (TGF-ß). The Mesenchyme Homeobox 2 (MEOX2) transcription factor blocks TGF-ß mediated EMT. Our previous work has demonstrated that MEOX2 inhibits endothelial cell proliferation and promotes endothelial senescence. In contrast to MEOX2, the Zinc Finger E Box-Binding Homeobox 2 protein (ZEB2) is activated by TGF-ß treatment and ZEB2 represses the expression of Meox2 and epithelial markers such as E-Cadherin. Whether the ZEB2/MEOX2 transcriptional switch is required for embryonic cardiac fibroblast development is not known. The overall goal of my research program is to identify the transcription factor networks that are required for cardiac fibroblast differentiation during embryonic development. My goals for the next 5 years are to: Goal 1. Examine the role of the ZEB2/MEOX2 pathway in the generation of embryonic cardiac fibroblasts both in vitro and in vivo. We will use both gain and loss of function approaches to test the roles of these transcriptional switches during mesenchymal transition of cardiac cells (epicardial and endothelial) into fibroblasts. To build on our in vitro studies of the ZEB2/MEOX2 switch, we will use transgenic mouse approaches to specifically delete these genes in cardiac endothelial cells and the cardiac epicardium. Goal 2. Identify enhancer elements that control cell type specific expression of Zeb2 and Meox2. The genomic regulatory elements that control expression of these two regulatory genes during embryonic development are not known. By identifying and validating the enhancer elements required to regulate the expression of Meox2 and Zeb2, we will be able to establish the transcription factor network that controls the development of cardiac fibroblasts. Together, these studies conducted by my HQP (2 PhD students and 1 MSc student) will delineate how ZEB2/MEOX2 control embryonic fibroblast generation. This research program will characterize a novel mechanism that controls an important pathway in embryonic development of the mammalian cardiovascular system. Through these studies, my HQP will acquire skills in laboratory research (experimental design, conducting experiments, analyzing results) as well as skills in disseminating their findings (manuscript writing and presenting talks) that will enable them to succeed in in a wide range of future careers.