MBECs express endothelial-specific genes and display endothelial functional characteristics. (A) Primarily passaged MBECs were collected, and total RNA was isolated and prepared for reverse-transcriptase PCR analysis for expression of multiple endothelial cell genes. VE-cadherin, VWF, VEGFR-2, and PECAM (CD31) were all expressed by MBECs, confirming their endothelial cell lineage. (B) Primary MBECs (5 × 104) were plated in 24-well tissue culture plates precoated with Matrigel to analyze for evidence of capillary tube forming capability. As shown, MBECs readily formed tubelike structures, consistent with an endothelial cell lineage.