Differential sensitization to deoxyribonuclease I of Xenopus vitellogenin and albumin genes during primary and secondary induction of vitellogenesis by oestradiol.

The sensitivity to DNAase (deoxyribonuclease) I (which preferentially digests transcribed sequences) of vitellogenin and albumin genes in liver and erythrocytes of male Xenopus after primary and secondary induction of vitellogenesis by oestrogen was measured by hybridization to cDNA (complementary DNA) of the residual DNA after enzymic digestion of isolated nuclei. Vitellogenin sequences were rendered selectively more sensitive to limited DNAase-I digestion (15-20% of DNA rendered acid-soluble) during primary hormonal activation (5 days) of vitellogenin genes in liver, but not erythrocyte, nuclei. Hormone withdrawal (25 days after first injection) did not result in reversion to a pre-activation gene configuration, nor did secondary hormonal stimulation (5 days after second and 25 days after first injection) augment the sensitivity of the genes to digestion by the nuclease. Similar hormone treatment did not affect the sensitivity of the constitutively expressed albumin genes in liver nuclei, nor their insensitivity in erythrocyte nuclei. Under the same conditions, globin genes remained indigestible in liver nuclei. It is concluded that primary induction of vitellogenesis in male Xenopus liver is accompanied by relatively long-lasting (3-4 weeks) change in the configuration of vitellogenin genes in hepatic nuclei which is not reversed or further modified during short-term oestrogen withdrawal or upon secondary stimulation.