Gastrulation in Xenopus:

Keller Sandwich

The surface location of a sandwich

Look at the cross-sectional location of a
Look at the sandwich though its thickness

Because amphibian embryos are opaque and because the movements of gastrulation are inherently complicated, it would be desirable to take out those regions that perform convergence and extension to study them in more detail. Detailed study of the marginal zone of the amphibian gastrula can be performed in this way using Keller sandwiches, named in honor of Ray Keller, who first worked out the procedures for their microsurgical isolation, and in collaboration with his colleagues, worked out the culture conditions for their subsequent development.

Keller sandwiches make it possible to do several things that were previously impossible, or could only be inferred:

  1. The permit the analysis of region-specific behavior in the marginal zone, i.e., they allow us to see whether or not different region sof the marginal zone behave differently (they do!).
  2. They also permit the analysis of converging and extending cells at the single-cell level, i.e., the motility displayed by individual cells engaged in rearrangement can be analyzed in certain types of Keller explants.
  3. They also allow us to study planar signals that may be sent by the dorsal lip of the blastopore to nearby ectoderm as part of neural induction.