p16 inhibits polyploidization. (A) qRT-PCR of mRNA isolated from wild-type and GATA-1 KD megakaryocytes for p16, p21, and p27. GATA-1 KD mRNA levels are shown relative to wild-type expression. P values determined using Student t test. Asterisk indicates P ≤ .01. One representative of 2 experiments, each in triplicate, is shown. For each study, the mean ± 1 SD is shown. (B) Purified, untreated wild-type megakaryocytes were differentiated for 3 days and stained with DAPI. (C,E) Wild-type megakaryocytes were treated with either wild-type TAT-p16 fusion peptide or a charge-matched mutant TAT-p16 peptide at a concentration of 1 μM. Peptide was added 3 times during the second day of differentiation due to instability of the TAT peptides. Cells were fixed and stained with DAPI on day 3 of differentiation. (D,F) Wild-type megakaryocytes were treated with the peptides used in panels C and E at a concentration of 10 μM. Cells were fixed and stained with DAPI on day 3 of differentiation. Gates indicate the percentage of cells at a ploidy class of 8N or greater. One representative of 2 experiments is shown.