TRANSDIFFERENTIATION IN MEDUSAE

This chapter discusses the in vitro transdifferentiation system that is established using isolated medusa tissues of differentiated cells. Transdifferentiation can be defined as a switch (or reprogramming or rechanneling) of cells that have already expressed specific differentiated traits into another cell type distinguished from the original cells by a set of phenotypic characters. In all known cases of true transdifferentiation the newly acquired state is stable and a switch to the original cell type has never been reported. Medusae (jellyfish) belong to Cnidaria, a group of animals that lack a true mesoderm and are essentially classified as bilayered animals. They have two properties that have been of crucial importance for the establishment of an experimental transdifferentiation system: (1) many species are able to regenerate most of their body parts, and (2) the swimming organ (the umbrella or bell) is composed of three tissue layers, of which two consist of only one well-differentiated cell type. The transdifferentiation processes observed in medusa demonstrate that well-differentiated animal cells can retain the ability to change cellular commitment and to form various new cell types that can be organized into a functional regenerate. © 1992, Academic Press Inc.