Loss of cyclin D1 alone does not significantly inhibit polyploidization. (A) Megakaryocytes were derived from wild-type and cyclin D1^−/− bone marrow (BM) and fetal liver (FL). After enrichment on a BSA gradient, cells were stained with DAPI for DNA content and analyzed by flow cytometry. The percentages of cells with DNA content of 8N or more are shown. A reproducible reduction in polyploid cells was observed in the cyclin D1–deficient megakaryocytes. One representative of 2 experiments is shown. (B) Real-time quantitative PCR for cyclins D1, D2, and D3. mRNA was isolated from BSA gradient–purified megakaryocytes generated from wild-type and cyclin D1^−/− bone marrow–derived megakaryocytes. Expression of cyclins D1, D2, and D3 were determined using primer sets specific for each transcript. Expression levels are shown relative to wild-type mRNA levels. For each study, the mean ± 1 SD is shown. Asterisks indicate P values determined by Student t test to be of .05 or less. One representative of 2 experiments, each in triplicate, is shown.