crosslinking was performed for 15 min in the presence of 1.8% formaldehyde during tissue homogenization. Chromatin extracts of embryos were sonicated using a Bioruptor (Diagenode) for 15 min (settings 30 sec on, 30 sec off, high power). To obtain the recommended quantity of DNA several Ips were prepared, pooled and resuspended in a volume of 20ml (12 to 14 Ips for Pc or Ph, 3 to 4 Ips for H3K27me3 and 3 Ips for H3K27ac). Sample preparation was done with Illumina kit (ref. IP-102-1001) following manufacturer’s instructions.