Evidence of linearly patterned cell apoptosis and embryo vasculogenic mimicry in mouse embryonic vasculogenesis. (A) Morphological observation of embryonic development by the naked eye (A1-A5) and under microscopy (A6-A10). The boundary between inner and outer zones is indicated by arrows. (B) Morphological observation of vessel pattern changed during E5.5-E9.5 in LPCA (H & E staining, ×200), embryo VM (CD31/PAS staining, ×400), and endothelium-dependent vessels (CD31 staining, ×400). Embryo cells (green arrow) displayed pyknosis, cytoplasm concentration, and chromatin condensation in LPCA areas. These darkly stained cells were distributed in lines and network patterns (B1-B3). The embryonic cells undergoing apoptosis displayed positive TUNEL staining (black arrows, ×400). They also had a distribution in lines and network patterns (B4-B6). The channels (yellow arrow) lined with embryo cells containing red blood cells was embryo VM. Embryo cells were negative for CD31 and positive for PAS staining (B7-B9). The endothelium-dependent vessels from E5.5 to E9.5 were shown by the red arrow (B10-B12). (C) The bar diagram represents the changed in LPCA, embryo VM, and endothelium-dependent vessels with time from E5.5 to E9.5 in the inner (C1) and outer zones (C2), respectively (p < 0.05).