SLIC-CAGE (Super-Low Input Carrier-CAGE) transcription start site mapping of mouse migratory and gonadal primordial germ cells, postnatal oocytes and early embryo

We used SLIC-CAGE to map transcription start sites (TSSs) of mouse primordial germ cells from embryonic days 9.5-16.5, postnatal oocytes (P6, P14 and MII), and early 2-cell and 4-cell mouse embryos. We use this TSS data to show that the mouse germline development starts with the somatic promoter code with a prominent switch to the maternal code (W-box dependent) occurring during the follicular oogenesis. We also find that the promoters of gonadal germ cells are characterised by a previously unknown divergence from the somatic transcription initiation. This divergence is distinct from the promoter code used later by the developing oocytes and reveals genome-wide promoter remodelling during early female and male germline development.