Scl^Δ/Δ MKs show ultrastructural defects.Cre;Scl^wt/wt (A-B) and Cre;Scl^fl/fl (C-D) bone marrow MKs were analyzed by electron microscopy. Note the absence of organized DMS in mutant MKs. Note the presence of 6 cells within the mutant MK (emperipolesis). N indicates polylobulated nucleus; and ER, endoplasmic reticulum. Arrowheads indicate α-granules; and arrows, crystalline structure. (A,C) Scale bars represent 500 nm. (B,D) Scale bars represent 2 μm.