Induction of DNA synthesis in amphibian erythroid nuclei in Rana eggs following conditioning in meiotic oocytes

Erythrocyte nuclei from adult Rana pipiens were injected into the cytoplasm of diplotene oocytes, which were then stimulated to mature in vitro with progesterone. Thirty percent of the nuclei transformed into condensed chromosomes aligned on metaphase spindles. After the matured oocytes were activated parthenogenetically, 56% of the nuclei enlarged and transformed into pronuclei and over 75% synthesized DNA. A larger percentage of adult erythroblast nuclei responded in a similar fashion. These induced chromosomal and nuclear changes of injected nuclei simulated the events occurring in the oocyte's own nucleus. Since only 0.1% of erythrocyte nuclei synthesized DNA in vitro and only 24% did so in a limited way after injection into eggs, we suggest that the cytoplasm of meiotic oocytes contains molecular factors which act on the chromatin of noncycling and terminally differentiated erythrocyte nuclei and prepare them to respond to activated egg cytoplasm where they are induced to synthesize DNA. These results indicate that conditioning in meiotic oocyte cytoplasm may enhance the genetic and developmental potential of nuclei from specialized cells.