[Autoradiographic Studies on RNA and Protein Synthesis in the Early Embryogenesis ofMusca domestica]

1) ³H-Uridine incorporation into the RNA of eggs ofMusca domestica was measured by means of autoradiography. In addition, protein synthesis was studied by measuring incorporation of³H-amino acids. 2) The onset of embryonic RNA synthesis was found to occur after the 10. division of the cleavage nuclei. 3) Protein synthesis occurs in mature oocytes as well as in freshly laid eggs. The rate of synthesis in fertilized eggs begins to increase when the cleavage nuclei penetrate the periplasma. At the end of blastodermal development, the rate of protein synthesis reaches a value which remains constant until differentiation of the germ layers. Immediately after deposition of the eggs, the rate of incorporation of³H-amino acids is higher in unfertilized eggs than in fertilized ones. 4) At oviposition the radioactivity is uniformly distributed over the whole egg. During further development more radioactivity is accumulated in the periplasm than in the inner part of the egg. Already before penetration of the cleavage nuclei, a higher rate of protein synthesis is observed in the posterior pole-plasm than in any other part of the periplasm. 5) Immediately before the beginning of organogenesis, a region specific incorporation of³H-amino acids into nuclei can be observed. 6) The rÔle of the maternal RNA in protein synthesis in the developing egg as well as its rÔle in the determination of certain egg regions (especially of the posterior pole-plasm) is discussed. The beginning of RNA synthesis and the simultaneous increase in the rate of protein synthesis are interpreted as processes of embryonic differentiation. It is assumed that the maternal RNA stored in the pole-plasm has a determinative function.