[Oogenesis of Mozambique tilapia. II. Synthesis of RNA and development of the nucleoli]

Using methods of light and electron microscopy and authoradiography, morphology and biosynthetic activity of nucleoli and RNA synthesis in developing oocytes of Tilapia mossambique were studied. In previtellogenic oocytes nucleoli are mostly composed of fibrils, while the granular component is poorly developed. 3H-uridine is poorly incorporated in their peripheral parts. With the start of vitellogenesis, fibrils and granules are seen randomly located throughout the whole volume of the nucleoli, with primary granule concentrations in their peripheral region. 3H-uridine is intensely incorporated in the whole volume of nucleoli, and the labeled RNA migrates to the cytoplasm. In early previtellogenic oocytes chromosomes are strongly labeled with 3H-uridine, and RNA quickly migrates to the cytoplasm.