Unique Expression of Platelet Endothelial Cell Adhesion Molecule-1 (PECAM-1/CD31) on Embryonic Stem Cells.

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is widely used as endothelial marker during vasculogenesis and angiogenesis from embryonic stem (ES) cells. Here, we demonstrate that undifferentiated ES cells expressed high level PECAM-1, but low levels of other endothelium markers, including VE-cadherin, Flk-1 and CD34. Kinetic analysis revealed that the expression of PECAM-1 was sharply down-regulated during early ES cell differentiation. PECAM-1 was expressed in the vascular-like area along with other endothelium makers during differentiation of ES cells. In the absence of angiogenic growth factors, embryonic bodies (EBs) were lack of vascular-like structures, and PECAM-1 was detected in the cells without organized structure. Furthermore, undifferentiated ES cells were found to express all eight known alternatively spliced isoforms of PECAM-1, among them, the expression of PECAM-1 isoforms lacking exon 15, (D15), or 14&15 (D14&15) was predominant. Only the expression of PECAM-1 isoform lacking exon 12&14&15 (D12&14&15) was significantly increased as vascular development of ES cells. These results indicate that PECAM-1 is a constitutive marker of undifferentiated murine ES cells and suggest that the diversity in the expression of cytoplasmic PECAM-1 isoforms may affect its function during vasculogenesis and angiogenesis.