Effect of actinomycin D on the quail oocyte nucleolus during meiotic prophase I.

Actinomycine D alters profoundly the distribution of the nucleolar constituents in the quail oocyte at prophase I of meiosis. As a consequence of nucleolar segregation, the normally existing relations between the nucleolus fibrillar centers and the microchromosomes are ruptured. The relations between the fibrillar center and the dense fibrills which surround it remain intact, suggesting that they constitute together a functional unit.