Plasticity of cell internalization. (A) Ectopic internalization of cells in pop-1 RNAi embryos. (Left) Three-dimensional (3D) projection still images: endoderm is outlined with a dashed line, ectopic endodermal cells are labeled 'MSa' and 'MSp'. (Right) Schematic representation of cells involved in covering in wild-type and pop-1 RNA interference (RNAi) and timeline of AB extension formation in wild-type and pop-1 RNAi embryos (n = 4). (B) Lack of contractile flow, extensions and/internalization in lit-1 RNAi embryos (representation as in (A)). MS and transformed E cells are outlined with a dashed line. The transformed endoderm did not gastrulate but rather divided on the surface (white lines in panel at 40 minutes). (C) Internalization of a fused MS-E hybrid blastomere in a rho-1 RNAi embryo (representations as in (A)).