Figure 4.
Reversal of v-Ski transformation by retinoids. (A) Ski BM cells were cultivated in medium containing thyroid/retinoid-free serum plus retinoid-free anemic serum, stem cell factor, insulin-like growth factor 1, estradiol, and the indicated amounts of an equimolar mixture of RARα- and RXR-specific agonists. Cells were maintained at densities between 3 and 6 × 106 cells/ml by daily dilution or by the addition of fresh medium plus all factors; they were counted daily. The cumulative cell numbers as calculated according to ref. 17 are shown. (B) At 3 days (filled bars) or 5 days (hatched bars) after retinoid addition, aliquots of the cultures were stained with acid benzidine, and the number of benzidine-positive cells was determined (17). The values shown are the mean of four independent determinations. (C) Five days after retinoid additions, aliquots from the culture containing 10−7 M RARα antagonist plus 10−7 M RXR agonist (Left) or 10−8 M RARα agonist plus 10−8 M RXR agonist (Right) were cytocentrifuged onto slides, stained with neutral benzidine plus histological dyes (17), and photographed under green light to reveal histological details. Arrow, mature macrophage; arrowhead, benzidine-positive, partially mature erythroid cell.