Methylated promoters in early Xenopus embryos are able to initiate transcription. (A) Unlike Xenopus oocytes, gastrula embryos fail to repress transcription from the injected hsp70 methylated (SssI) promoter. Levels of injected plasmid DNA recovered from embryos were similar for all samples. (B) Effects of DNA methylation on stably integrated transgenes. A fully methylated CMV-luciferase transgene is robustly expressed compared to its unmethylated counterpart during blastula and gastrula stages. Strong DNA methylation-dependent repression observed in the oocyte is restored gradually at neurula and tailbud stages. The results represent three independent experiments and were normalized for the number of transgene insertions. (C) When targeted to the injected hsp70 promoter by the heterologous Gal4 DNA-binding domain in oocytes, the transcription repression domain of MECP2 shuts down reporter construct transcription. Such an effect is not observed in gastrula embryos where the Gal4-TRD fusion is expressed at equivalent levels (see Supplemental Fig. S15). Error bars represent the SEM of three experiments.
