Proliferative rate of EPCs in vitro. Accumulation of WT and SK-1-KO BM cells cultured for 5 days on fibronectin-coated plates in CS-FCS–containing media as assessed by the MTS assay. Results show the mean plus or minus SEM of a representative of 4 separate mice, where each group was performed in quadruplicate. *P < .05, compared with WT, 1-way analysis of variance.