In vitro pancreas formation from Xenopus ectoderm treated with activin and retinoic acid

In the present study, isolated presumptive ectoderm from Xenopus blastula was treated with activin and retinoic acid to induce differentiation into pancreas. The presumptive ectoderm region of the blastula consists of undifferentiated cells and is fated to become epidermis and neural tissue in normal development. When the region is isolated and cultured in vitro, it develops into atypical epidermis. Isolated presumptive ectoderm was treated with activin and retinoic acid. The ectoderm frequently differentiated into pancreas-like structures accompanied by an intestinal epithelium-like structure. Sections of the explants viewed using light and electron microscopy showed some cells clustered and forming an acinus-like structure, including secretory granules. The pancreas-specific molecular markers insulin and XIHbox8 were also expressed in the treated explants. The pancreatic hormones, insulin and glucagon, were detected in the explants using immunohistochemistry. Therefore, sequential treatment with activin and retinoic acid can induce presumptive ectoderm to differentiate into a morphological and functional pancreas in vitro. When ectoderm was immediately treated with retinoic acid after treatment with activin, well-differentiated pronephric tubules were seen in a few of the differentiated pancreases. Treatment with retinoic acid 3-5 h after activin treatment induced frequent pancreatic differentiation. When the time lag was longer than 15h, the explants developed into axial mesoderm and pharynx. The present study provides an effective system for analyzing pancreas differentiation in vertebrate development.