Sex- and tissue-specific, but hormonally independent, demethylation at the 3'-end of Xenopus vitellogenin gene B1

We describe three HpaII-specifying sequences in 6 kbp of DNA at the 3'-end of Xenopus vitellogenin gene B1 (two within the coding sequence and one downstream) which remain methylated in all tissues of adult male Xenopus. These sites are however fully demethylated exclusively in adult female Xenopus liver parenchymal cells but not in oviduct, kidney or erythrocytes. Developmental studies suggest that this tissue- and sex-specific demethylation may occur gradually after metamorphosis. The methylation of these 3'-sites is independent of transcriptional activation by oestrogen of vitellogenin genes in male or female Xenopus.