Fig. 3.

LSK cells were cultured alone or were co-cultured with freshly prepared OBs or with OBs cultured for 1 week. After 7 days of co-culture, hematopoietic cells were removed by washing and cell cycle status was assessed by staining with propidium iodide. No differences in the percentage of hematopoietic cells in the S/G2 + M phases of cell cycle were observed. In parallel studies, fresh and 1-week OBs were cultured alone and OB cell cycle status determined as above. As would be expected, a higher percentage of fresh OBs were in the active phases of cell cycle than those cultured for 1 week. In data not shown, we also analyzed both hematopoietic and OB cells for the expression of annexin V. In all cases, less than 1% of the cells were annexin V positive, suggesting that apoptosis was not detected.