In vitro organogenesis of pancreas in Xenopus laevis dorsal lips treated with retinoic acid

Dorsal lips of Xenopus laevis may differentiate into pancreas after treatme nt with retinoic acid in vitro. The dorsal lip region is fated to be dorsal mesoderm and anterior endoderm. Dorsal lip cells isolated from stage 10 ea rly gastrula differentiate into tissues such as notochord, muscle and phary nx. However, in the present study, dorsal lips treated with 10(-4) M retino ic acid for 3 h differentiated into pancreas-like structures accompanied by notochord and thick endodermal epithelium. Sections of the explants showed that some cells gathered and formed an acinus-like structure as observed u nder microscopes. In addition to the morphological changes, expressions of the pancreas-specific molecular markers, XIHbox8 and insulin, were induced in retinoic acid-treated dorsal lip explants. Therefore, it is suggested th at retinoic acid may induce the dorsal lip cells to differentiate into a fu nctional pancreas. However, continuous treatment with retinoic acid did not induce pancreas differentiation at any concentration. Dorsal lips treated with retinoic acid within 5 h after isolation differentiated into pancreas- like cells, while those treated after 15 h or more did not. The present stu dy provided a suitable test system for analyzing pancreas differentiation i n early vertebrate development.