Abstract
Genes that are unexpressed in somatic cells have been activated by injecting cultured cell nuclei of the frog Xenopus laevis into oocytes of the newt Pleurodeles waltlii. The genes that were activated are normally expressed in oocytes but not in cultured cells. Conversely, genes that are normally expressed in cultured cells but not in oocytes became inactive when cultured cell nuclei were injected into oocytes. These changes in gene activity were detected by two-dimensional gel electrophoresis of proteins synthesized by oocytes injected with nuclei. Controls, which included the use of alpha-amanitin, showed that these changes in protein synthesis are dependent on gene transcription. We conclude that genes that become inactive during cell differentiation can be reactivated, in the absence of cell division, by normal components of oocyte cytoplasm.