INDUCTION OF DNA-REPLICATION IN GERMINAL VESICLES AND IN NUCLEI FORMED IN MATURING MOUSE OOCYTES BY 6-DMAP TREATMENT

Immature mouse oocytes (germinal vesicle stage, GV), oocytes at differ ent stages during maturation (prometaphase to anaphase I) and matured oocytes (metaphase II arrested) were cultured in 6-dimethylaminopurine (6-DMAP)-supplemented medium also containing bromodeoxyuridine for th e assessment of DNA replication in these cells. Immature oocytes remai ned arrested at the GV stage and DNA replication was never detected in them. On the other hand, oocytes at the prometaphase to anaphase-telo phase I stages responded to 6-DMAP treatment by forming nuclei which s ynthesised DNA. Mature (metaphase II) oocytes did not respond to 6-DMA P and their chromatin remained condensed. DNA synthesis could even be induced in GV-staged oocytes, but only when they were fused to freshly activated oocytes and incubated in 6-DMAP-supplemented medium.