Cytochemical and Biochemical Analysis of Development of Urechis Oocytes

The echiuroid marine worm Urechis caupo is uniquely suited forthe study of oogenesis. A relatively large quantity of oocytesat various developmental stages can be obtained and subjectedto coordinated cytochemical and biochemical analysis Oocytesat the cluster, early diplotene, mid-diplotene, and diffusediplotene or lampbrush stages are active in the synthesis andaccumulation of ribosomal RNA, several proteins, carbohydrates,lipids, and also, perhaps, yolk constituents. Only corticalgranule formation, which occurs during later stages of oogenesis,appears to be stage specific. Ribosomal RNA genes are also transcribedin the nucleolus of the mature oocytes or unfertilized eggs.However, the rate of production in these eggs appears to beregulated at the level of maturation of rRNA precursor molecules.