NUCLEIC ACID AND PROTEIN SYNTHESIS IN THE DEVELOPING OOCYTES OF THE BUDDING FORM OF THE SYLLID, AUTOLYTUS EDWARSI (CLASS POLYCHAETA)

¹ Department of Biology, Wilson College, Chambersburg, Pennsylvania 17201 and the Kristineberg Zoological Station. Sweden

1. The incorporation of tritiated uridine, thymidine, and phenylalanine into nucleic acids and proteins was studied in the developing oocytes of stolons produced by asexual budding in Autolytus edwarsi.

2. Extremely rapid incorporation of uridine-H³ into the nucleolus of developing oocytes suggests the importance of the nucleolus in the synthesis of RNA. Oocytes exposed to uridine for successively longer periods than two to fifteen minutes show silver grains over the non-nucleolar regions of the nucleus as well as the nucleolus, and finally a number of grains appear over the cytoplasm (the relative number of cytoplasmic grains is greater in younger oocytes). Results indicate that RNA is synthesized mainly in the nucleolus of developing oocytes from which it migrates to non-nucleolar regions of the nucleus and then to the cytoplasm. Transfer of RNA to the cytoplasm is a relatively slow process in these eggs.

3. Fully grown oocytes at metaphase I (the stage at which Autolytus eggs are fertilizable) do not incorporate uridine-H³, indicating that no significant synthesis of RNA is occurring at the close of the growth period of oogenesis.

4. Phenylalanine-H³ was incorporated into all parts of the developing oocytes, and was not incorporated more rapidly into the nucleolus. Thus it seems apparent that all parts of developing eggs (nucleoli, non-nucleolar regions of the nucleus, and cytoplasm) are synthesizing protein. Fully grown oocytes in metaphase I, however, are synthesizing little, if any, protein. In contrast to ripe eggs, cleavage stages are synthesizing proteins, particularly in nuclear and spindle regions. The results for cleavage stages are similar to those of the sea urchin. The results for Autolytus suggest that in these eggs the proteins for the mitotic spindles are being synthesized during cleavage whereas the proteins for the meiotic spindles are synthesized prior to the maturation divisions.

5. Thymidine-H³ was not incorporated into developing oocytes, indicating that no significant DNA synthesis was occurring. Radioautographs and cytochemical tests indicate that DNA is diffusely distributed in the germinal vesicle of Autolytus edwarsi. Presumably in this species, DNA is synthesized very early in oogenesis.