Transcription and chromatin determinants of the rate of de novo DNA methylation in oocytes

We generated genome-wide methylation and transcriptome maps of size-selected, growing oocytes to capture the onset and progression of methylation. We find that the major transitions in the oocyte transcriptome occur well before the de novo methylation phase; nevertheless, transcription level does correlate with rate of methylation. Conversely, timing of methylation of CpG islands (CGIs) correlates inversely with enrichment of histone modifications inhibitory to DNA methylation and dependence on histone 3 lysine-4 demethylases, implicating chromatin remodelling as a major determinant of methylation timing. RNA-Seq, PBAT and RRBS in mouse oocytes at different stages of folliculogenesis