Figure 2

Summary of cell transplantation experiments and results at 23 to 27 hours post fertilization. (A) A mesomere pair from a 16-cell embryo injected with actβ-cat mRNA (shaded embryo) was recombined with the eight mesomeres of an uninjected animal half (AH). (B-G) Bright field images of chimeras in which a labeled mesomere pair injected with 0.5 pg/pL actβ-cat mRNA was recombined with an uninjected AH. (B’-G’) Corresponding fluorescent images. Labeled/injected mesomeres formed mesenchyme-like cells and pigment cells. Absence of label in the gut (gut indicated with arrowheads in B’, C’, D’) suggests that this tissue is induced in mesomeres from the uninjected AH. Some embryos were similar to uninjected controls (B, B’, C, C’, F, F’, G, G’), forming a complete gut, mesenchyme-like cells (indicated with arrows in B’) that produced spicules, and pigment cells (development in the injected cells and transplants is delayed compared to that in uninjected embryos). Others (D, D’) only formed a partial gut or lacked a gut (E, E’). (F, F’-G, G’) In some, the labeled cells were observed at the tip of the archenteron (arrowheads in F’ and G’). In this Figure, labeled mesenchymal cells are also clearly evident in the blastocoel. These are likely skeletogenic mesoderm and/or non-skeletogenic mesoderm cells such as pigment cells, but it is interesting that, unlike other chimeras, many of the labeled cells in these individuals remain concentrated at the tip of the archenteron. Orientation: (B, B’) vegetal view, (C-E, C’-E’) lateral views. (F-G, F’-G’) Frontal views with the animal pole at the top of the photograph.