Phenotypes of CBP homozygous mutant embryos. (A) The E9.5 yolk sac from wild-type (left) and CBP (right) homozygous mutant embryos. (B) Section of the yolk sac from a wild-type (top) and a CBP homozygous mutant (bottom) at E9.5. Note the small number of erythrocytes in the yolk sac derived from CBP homozygous mutants. Scale bar indicates 100 μm. (C) Numbers of nucleated erythroid cells present in yolk sac cells from embryos at E9.5. (D) Staining of blood cells from a wild-type (left) and CBP homozygous mutant (right) yolk sac with antibodies to ɛ1-globin (top) and β-globin (bottom). Scale bar indicates 30 μm.