Figure 1

Summary of the controls used in experiments. (A-D) Controls, bright field images. (C’, D’) Controls, fluorescent images. (A) Uninjected embryo at 27 hours post fertilization (hpf). (B) The uninjected animal half (AH) forms a hollow ciliated ball of ectoderm lacking endomesoderm and patterning along the oral-aboral axis (dauerblastula), 24 hpf. (C, C’) A chimera was made at the 16-cell stage in which micromeres removed from an embryo injected with rhodamine-dextran (RDX) were recombined with the uninjected AH. This produces a nearly normal prism stage embryo, although few pigment cells were present in many individuals. The RDX-labeled micromeres contributed to mesenchyme-like cells and occasionally to pigment cells (not shown). (D, D’) When RDX-labeled mesomeres from a 16-cell embryo were recombined with an AH, the chimera formed a dauerblastula and most of the labeled cells remained in the ectoderm. Note the expanded apical plate at the animal pole (B and D, D’). This is a typical feature of the dauerblastula. Orientations of the embryos are as follows: (A) Lateral view, oral side up. (B, C, C’, D, D’) All other images are frontal views with the animal pole oriented towards the top. Scale bars = 100 μm.