library_construction_protocol: Cells were collected in TRIzol (Ambion, Life Technologies, UK), and total RNA was purified using membrane columns (RNAeasy minikit, Qiagen, UK). An on-column DNase step (Qiagen, UK) was used to ensure the removal of genomic DNA. RNA was eluted in nuclease free water, and stored at -80oC. Approx 500 ng of total RNA (16 samples) were prepared for sequencing using the Illumina Truseq Stranded Total RNA Kit (Manual part RS-122-9007DOC, part 15031048 Rev E, Oct 2013). Final average library size distribution (including adapters) was 335 bp.