In the polychaete Ophryotrocha labronica each oocyte is during its growth period associated with a single nurse cell. The fact that the oocyte-nurse cell pairs occur isolated in the female coelom makes them easily removable for analysis of their developmental ability in vitro. Using Dulbecco's modified Eagle medium supplemented with amino acids, nucleosides, foetal calf serum and sea water, we have managed to support development in vitro of germ cell pairs from early and mid-oogenesis until maturation of the oocyte, when the nurse cell degenerates and the oocyte enters meiotic metaphase. Radiolabelling of germ cells in mid-oogenesis with tritiated amino acids and uridine during the first day of incubation indicates normal development with synthesis of RNA and protein, and pulses two days later verify a continued normal protein synthesis and yolk formation. The investigation confirms autosynthesis of yolk proteins in the germ cells of this species and indicates a leading role of the nurse cell in the process.

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