ABSTRACT
Many laboratories are studying the molecular basis of neural induction in Xenopus. It has become clear that similarities throughout the animal kingdom are greater than was once believed regarding the molecular interactions that cause development. Increasing numbers of scientists have turned to the study of molecular embryology because it contains the major unsolved problems of molecular biology. The eye imaginal disc arises by division of six epithelial cells of the early Drosophila embryo to form a sheet, which is one cell thick. Also, messenger RNAs that will direct the formation of certain growth factors have been injected into early embryos in which mesoderm formation has been inhibited by ultraviolet radiation, and these RNAs restore the formation of mesoderm cells. One way of testing the importance to the embryo of a growth factor is to inject the messenger RNA for a dominant negative receptor. The effects were remarkably specific: the embryos were unable to complete the cell movements of gastrulation.
