[The role of inducing factors in early embryonic development].

In the field of early embryonic induction and differentiation we can observe an exponential increase of research activities over the last three years. The reasons for this rapid exploration are the application of powerful techniques of molecular biology and molecular genetics and the recent accumulation of knowledge about the close functional correlation between growth factors, embryonic induction factors, the products of oncogenes (or proto-oncogenes), and transcription factors. The highly probable role of the cellular and viral oncogenes in regulation of the differentiation and function of normal and malignant cells has stimulated the interest of scientists working on the molecular basis of malignant cell transformation. An excellent model to study mesoderm and neural induction and differentiation on the cellular and molecular level is the embryo of the south African clawed frog (Xenopus laevis), which is now a favored vertebrate system in many laboratories.