St3gal1-deficient MKs differentiate and mature normally. (A) Percentage of hematopoietic progenitors, defined as lineage negative, cKit⁺, and Sca-1^– cells (LSK) in the BM (n = 5-6). (B) Percentage of MK progenitors MkP (Lineage^–, cKit⁺, Sca-1^–, CD150⁺, and CD41⁺ cells) and bipotent precursors, PreMegE (Lineage^–, cKit⁺, Sca-1^–, CD16/32⁺, CD105⁺, CD150^– cells) in the BM (n = 5-6). (C) Plasma TPO levels determined by enzyme-linked immunosorbent assay. (D) Flow cytometric quantification of BM MK ploidy in control (blue) and ST3Gal1^MK−/− (red) mice (n = 4-6). (E) Transmission electron microscopy images of MKs flushed from control and St3gal1^MK−/− BMs. Scale bars, 1 μm. **P < .01.