Endoderm differentiation and inductive effect of activin‐treated ectoderm in Xenopus

Abstract

When presumptive ectoderm is treated with high concentrations of activin A, it mainly differentiates into axial mesoderm (notochord, muscle) in Xenopus and into yolk‐rich endodermal cells in newt (Cynops pyrrhogaster). Xenopus ectoderm consists of multiple layers, different from the single layer of Cynops ectoderm. This multilayer structure of Xenopus ectoderm may prevent complete treatment of activin A and subsequent whole differentiation into endoderm. In the present study, therefore, Xenopus ectoderm was separated into an outer layer and an inner layer, which were individually treated with a high concentration of activin A (100 ng/mL). Then the differentiation and inductive activity of these ectodermal cells were examined in explantation and transplantation experiments. In isolation culture, ectoderm treated with activin A formed endoderm. Ectodermal and mesodermal tissues were seldom found in these explants. The activin‐treated ectoderm induced axial mesoderm and neural tissues, and differentiated into endoderm when it was sandwiched between two sheets of ectoderm or was transplanted into the ventral marginal zone of other blastulae. These findings suggest that Xenopus ectoderm treated with a high concentration of activin A forms endoderm and mimics the properties of the organizer as in Cynops.

In vitro organogenesis from undifferentiated cells in Xenopus

“…For example, lower concentrations of activin A (0.5-1.0 ng/ml) act on animal caps to induce ventral mesodermal cells, including blood cells, medium concentrations of activin A (5-10 ng/ml) induce the more dorsal mesodermal cells, includ-ing muscle cells, and higher concentrations of activin A (50 -100 ng/ml) induce the most dorsal mesodermal structures, such as the notochord (Okabayashi and Asashima, 2003). We have also found that Xenopus animal cap cells treated with high concentrations of activin differentiate into anterior endodermal tissue, and can function as the cells of the organizer region when the activin-treated animal cap is transplanted into early gastrula (Ninomiya et al, 1999). Using activin as a key factor, we investigated the establishment of an experimental system that would allow the induction of various mesodermal and endodermal cells and tissues of the heart, kidney, pancreas, and so on.…”

Induction of tooth and eye by transplantation of activin A-treated, undifferentiated presumptive ectodermal Xenopus cells into the abdomen

“…As previously described (Ninomiya et al, 1999) tissues with endoderm gene expression were induced in the AAaggregates composing of all of the cells treated with high concentration of activin A (25 ng/ml). In the 1:1 aggregate of mixture of activin-treated and untreated animal cap cells at the ratio of 1:1, the trunk-tail region consisting of mesodermal tissues, such as notochord and muscle were induced with gene expression of maxillofacial structure consisting of muscle, cartilage, neural and eye tissues was developed in the 1:5 aggregates transplanted into the abdominal region.…”

Comparison of induction during development between Xenopus tropicalis and Xenopus laevis

“…At high doses of activin, axial mesoderm tissues, such as notochord and endodermal cells were induced in the animal cap explants (Ariizumi et al, 1991). In addition, the animal cap cells treated with a high dose of activin could be induced to form head structures in conjugation and transplantation experiments, indicating that the animal cap cells treated with high doses of activin act as the head organizer (Ariizumi and Asashima, 1995, Ninomiya et al, 1999, Sedohara et al, 2002.…”