Cultured mBM cells exhibit EC-like morphology and function. Cultured BM cells were seeded onto fibronectin-coated plated plates in CS-FCS–containing media. (A) The ECU formed from WT and SK-1-KO cells within 24 hours of plating. (B) Cells harvested at day 7 after seeding were replated and within 24 hours formed compact EC-like monolayers. (C) Cells were harvested after 10 days and stained for expression of the endothelial-specific marker, VE-cadherin. Ctl indicates an isotype-matched control. Expression was analyzed by flow cytometry. (D) Ten-day cultured BM cells were seeded onto Matrigel at 4 × 10⁴ cells/well. Tube formation was monitored periodically with images depicting tube formation 30 hours after seeding. Classic branching patterns protruding from large tube-like structures (arrows) can be seen. Results are representatives of at least 3 separate experiments. (E) ECU generated by WT and SK-1-KO BM cells on fibronectin were counted at times specified as “days in culture.” Results show the mean plus or minus SEM of 5 separate mice. *P < .05 compared with WT, 1-way analysis of variance.