ARP₂₆ promotes proplatelet formation and nuclear polyploidization in human MEG01 promegakaryocytic cells. (A) ARP₂₆ dose-response and proplatelet formation. (i) Shown are the effects of the noted ARP₂₆ doses following 24 hours' incubation with MEG01 cells. Note increase in the splice factor SC35 and corresponding substitution of AChE-S mRNA with AChE-R mRNA, which appears to plateau under 2 nM ARP₂₆. (ii, iii) Scanning electron microscopy demonstration of proplatelet-like demarcations in ARP₂₆-treated cells. Shown are representative untreated (ii) and an ARP₂₆-treated cells (iii) for 24 hours after treatment. (B) Transmission electron microscopy. (i) Control cell. Inset: TUNEL analysis of control and treated cells, excluding the possibility of ARP₂₆-induced apoptosis. (ii) ARP₂₆-treated cell. Note intact nuclear membrane, numerous mitochondria, and peripheral membrane demarcations. (iii) Enlarged section, highlighting the numerous demarcations. (C) Enhanced nuclear polyploidization and caspase 3 activation under ARP₂₆ treatment of MEG01 cells. (i) Flow cytometric analysis. Note increase in both side and forward scatter of ARP₂₆-treated as compared to control (CTR) cells. (ii) Nuclear polyploidization. Note that within 24 hours, ARP₂₆ treatment increases the fractions of cells with 16 n and 32 n nuclei by approximately 2-fold while decreasing the fractions of cells with 2 n and 4 n nuclei. (iii) Caspase 3 activation. Throughout the 4 days after treatment, ARP₂₆ consistently enhances the levels of activated caspase-3. Error bars indicate standard evaluation of the mean (SEM).