Abnormal hemorrhage within the developing central nervous system of Clec1b^−/− and Syk^−/− mice from E12.5. (A) Both constitutive (Clec1b^−/−; middle; n = 18 of 19) and platelet/megakaryocyte-specific (Clec1b^fl/flPF4-Cre; right; n = 3 of 5) ablation of Clec1b results in hemorrhaging within the brain and developing spinal column (blue arrows). (B) Constitutive (Syk^−/−; middle; n = 13 of 14) and platelet/megakaryocyte-specific (Syk^fl/flPF4-Cre; n = 10 of 13) ablation of Syk presented with a similar hemorrhaging phenotype in similar regions as the Clec1b^−/− embryos (blue arrows). None of the littermate wild-type controls (+/+; left; n ≥ 5) showed this phenotype. Scale bars = 1 mm. (C) H&E-stained sections from E12.5 brains show that hemorrhages in Clec1b^−/− embryos were localized to at least 1 ventricle (middle; red arrowhead) and within the parenchyma (right; yellow arrowhead). (D) Sections from E12.5 Syk^−/− embryos showed no hemorrhaging in the ventricles, but consistent hemorrhaging in the parenchyma (middle; yellow arrowhead). None of the wild-type controls showed hemorrhaging in any section (left). Scale Bars = 100 μm.