title: GSM5944394: Control_rep1; Bos taurus; ChIP-Seq
library_construction_protocol: Morula-stage embryos at 144 h post IVF were collected as approximately 50 embryos per biological replicate for ChIP. ChIP for small cell numbers was performed with a Low Cell ChIP-Seq Kit (Active Motif) according to the manufacturer's manual (version A3) with some modifications. The morulae were freed from the zona pellucida by using pronase before crosslinking with formaldehyde. After crosslink-quenching, the sample was sonicated to shear chromatin using a Bioruptor UCD-250 (Cosmo Bio) for 30 x 30 s with 30-s pauses in ice-water. The sample was centrifuged for 2 min at 18,000 x g and the supernatant (200 μL) was transferred to a new tube. The 200-µL sample of sheared chromatin was processed for ChIP using 3.2 µg anti-H3K27me3 antibody (C15410069, Diagenode). For the normalization of sequencing read count, Drosophila-derived chromatin (0.17 ng, Active Motif) and corresponding antibody (1 µg, Active Motif) were added as spike-in. The ChIPed DNA was decrosslinked, purified, and resuspended in 40 µL low-EDTA TE buffer. Sequencing libraries of the ChIPed DNA were constructed by using Next Gen DNA Library Kit and Next Gen Indexing Kit (Active Motif) following the manufacturer's instruction.