Fig. 1.

YRS^ACT promotes platelet production in vivo. (A) Schematic representation of YRS domains. A Rossmann fold catalytic domain and anticodon-recognition domain, both essential for tRNA^Tyr aminoacylation, constitute YRS^Mini. YRS^ACT contains a gain-of-function mutation (Y341A) in the context of full-length YRS. (B) A single injection of YRS^ACT (30 mg/kg), compared with vehicle (PBS), increased the blood platelet count of WT mice (n =14 in each group). (C) WT mice received one i.v. injection of anti-GPIbα monoclonal antibody (5A7; day 0) to deplete platelets. YRS^ACT (30 mg/kg) or vehicle (PBS) was injected on days 2 and 5 (n = 4) and blood cell counts were monitored at the indicated times. (D) Plasma samples were collected before and after (day 2) 5A7 injection, and TPO levels were determined by ELISA (n = 12). (E) BM cells of WT mice (n = 4) injected with YRS^ACT or vehicle (PBS) were harvested on day 3 and analyzed for MK ploidy by flow cytometry. Data are shown as mean ± 95% confidence interval (CI) (B–D) or 25th to 75th percentile bars with median and min to max whiskers (E); in the latter panel, color-coded lines join the mean values (marked by a cross indicated inside each bar) of each ploidy distribution. ***P < 0.001 determined by one-way ANOVA with Dunn’s multiple comparison test (D) or two-way ANOVA with Sidak’s multiple comparison test (B, C, and E).