Abstract 1058: Ets-2 Acts in a Common Pathway with Tbx5 to Regulate Coronary Blood Vessel Development
TBX5, a T-box transcription factor, plays a critical role in the development of the cardiovascular system. Mutations in the human TBX5 cause the familial disorder Holt-Oram syndrome, characterized by congenital heart malformations in the setting of upper limb deformity. Tbx5 is expressed not only in the myocardium, but also in the coronary vasculature and epicardium and the proepicardial organ. Coronary vascular endothelium and smooth muscle arise from cells that originate the proepicardial organ, migrate over the heart to form epicardium, and then migrate into the myocardium and undergo epithelial to mesenchymal transformation. Our studies show that Tbx5 modulates migration of proepicardial cells and coronary blood vessel development. We hypothesized that Ets2 might be a downstream mediator of Tbx5. Using qRT-PCR, we show proepicardial expression of Ets2 is Tbx5 dependent. Inhibition or overexpression of Tbx5 in proepicardial cells decreases or increases Ets2 expression respectively. By in situ hybridization, we demonstrate that Ets2 and Tbx5 are co-expressed in the proepicardium in stage 14–17 chick embryos and in the epicardium at stage 20 –24 chick embryos, a critical point in which their shared effects may mediate coronary vasculogenesis. Differential expression of Ets2 and Tbx5 is noted in non-proepicardially derived cardiac outflow tract myocardium, suggesting that, in addition to their linked activities in the proepicardial lineage, Tbx5 and Ets2 have independent activities in other lineages. To determine the functional contribution of these transcription factors to coronary vasculogenesis, we employ antisense technology to knockdown either Tbx5 or Ets2 expression. We previously reported that antisense knockdown of Tbx5 impairs proepicardial migration. We now report significant (p < 0.05) inhibition of cell migration by Ets2 knockdown in primary proepicardial explant cultures. These findings support the hypothesis that Ets2 acts in a common pathway with Tbx5 to regulate proepicardial cell migration and coronary vasculogenesis.