One of June’s featured freely available protocols on CSH Protocols details the use of Keller explants and sandwiches, a tremendously useful Xenopus method originally developed to allow observation of gastrulation movements, particularly convergent extension. The key is that these explants remain flat instead of curling up, and the mesoderm elongates in a plane with the adjacent ectoderm, rather than involuting. This allows you to see what would normally be happening beneath the surface in an opaque embryo.

Keller explants have subsequently been used to investigate the roles and behaviors of different regions and tissue layers in gastrulation, and to answer questions about planar signaling and neural induction. Ray Keller was the first to work out the conditions for these explant cultures, hence the name, and his lab has employed them in a wide variety of studies, with a particular interest in patterning and biomechanics. A nice explanation and some animations explaining Keller explants can be found here. For those of you teaching Developmental Biology, Ray’s lab has supplied some superb illustrations and movies of amphibian gastrulation and the cellular movements involved.