Proepicardium (PE) cells generate cardiac fibroblasts, smooth muscle cells (SMCs) and endothelial cells that form coronary arteries. T-box18 (Tbx18) is a well-known marker of PE cells and epicardium. We examined whether Tbx18-positive cells differentiated from murine embryonic stem (ES) cells serve as PE progenitors to give rise to vascular SMCs and fibroblasts. To collect Tbx18-positive cells, we established Tbx18-EGFP knock-in mouse ES cells using the CRISPR/Cas9 system. We harvested the Tbx18-EGFP-positive cells on day 8, 10 and 14 after the initiation of differentiation; Tbx18 mRNA was enriched on day 8 to 14 and Snai2 mRNA was enriched on day 8 and 10, indicating successful collection of Tbx18-positive cells. Tbx18-EGFP-positive cells expressed the PE marker WT1 on day 8 and 10. They also expressed the SMC marker Acta2 and fibroblast markers Thy1 and Fsp1 on day 8 to 14, but did not express the endothelial cell marker PECAM or the cardiac cell marker CD166 or Myh7. In conclusion, Tbx18-positive cells represent a part of PE cells in the initial phase of differentiation and subsequently include SMCs as well as fibroblasts. These results indicate that Tbx18-positive cells serve as a PE progenitor to supply a variety of cells that contribute to the formation of coronary arteries.Application of cell-based regenerative medicine to cardiovascular diseases is expected as an alternative medicine to reduce damage and remodeling of the heart after myocardial infarction (11). Several cell sources for cell-based regenerative medicine are being investigated. Epicardium is localized on the outer surface of the heart and composes the heart together with the inner endocardium and the central myocardium. Epicardium contributes not only to proper embryonic development of the heart but also to cardiac repair during a disease (23). This indicates that progenitor cells of epicardium could be one of the cell sources for cell-based regenerative medicine in patients with heart diseases. Progenitors for epicardium originate from proepicardium (PE). PE cells appear at proximal to the heart along the septum transversum in mouse development (20). Subsequently PE cells migrate from the surface of septum transversum mesenchyme onto the surface of the heart and give rise to an outer epithelial layer, epicardium (13,18). Epicardial cells undergo an epithelial to mesenchymal transition (EMT) followed by vasculogenesis, giving rise to a

We present a rare case of embryonal renal remnant found by chance as a mass in the gubernaculum testis during an operation on a right undescended testis. We discuss the relationship between this tissue and paradidymis or supernumerary kidney.

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