Reconfiguration of mouse embryos.

Early stage mouse embryos can be reconfigured into a planar format by removing the ectoplacental cone (not shown), then cutting/tearing the extraembryonic tissue along a line perpendicular to the embryonic axis (A, dashed lines) and finally opening the amniotic sac (B, dashed crescent). These procedures allow the embryo to assume a planar orientation. Prominent features of the early embryo provided as points of reference for this protocol include the blood islands (BI), the somites (S), and the allantois (AL).