Inappropriate apoptosis is present in blood island regions of VAD embryos.

Sections derived from normal (A, C) or VAD (B, D) embryos isolated at stage 8 (A, B) or stage 11 (C, D) were analyzed by TUNEL staining to identify cells undergoing apoptosis. Large clusters of dying cells are evident in the VAD blood islands, indicated by bright yellow. A few positive cells are found in the yolky endoderm (YE) of normal and VAD embryos, but only VAD embryos show extensive apoptosis in the primitive erythroid (PE) clusters and in at least some of the surrounding endothelial (EN) cells. Original magnification × 100.