Polysome profiling and western blot show that MARCKS is enriched in proplatelet-producing MKs. (A) Lysates from either round, mature murine MKs preceding proplatelet formation (day 4) or proplatelet-producing MKs (day 5) were subject to sucrose gradient, fractionation, and RNA-seq, as described in Methods. A representative ribosomal profile used in polysome profiling is shown. (B) Murine fetal liver MKs were cultured as described in Methods and lysed at indicated times. Western blots were quantified relative to the loading control, and then normalized to amount of protein on day 3 (n = 3; **P < .005, compared with day 3).