Rescue of primitive erythropoiesis in VAD explants by exogenous BMP4.

Posterior nodal piece explants were taken at stage 4 from normal (A) or VAD (B, C) embryos and were cultured either alone (A, B) or in the presence of 2.5 μg/mL recombinant purified BMP4 (C). Shown are representative photographs of explants that were stained in whole-mount preparations using benzidine (top panels, dark stain indicates erythroid cells; original magnification × 32.) or in cytospin preparations from explants that were first dissociated and then stained with benzidine (lower panels, original magnification × 200.). With whole-mount staining, large benzidine-positive regions were identified in 93% of the normal explants (n = 15), 22% of the VAD explants (n = 9), or 76% of the VAD explants cultured with BMP4 (n = 21). The recovery of erythroid cell number is similarly reflected quantitatively by the cytospin preparations.