RNA was isolated following cell lysis (lysis buffer: 0.1 M LiCl; 0.01M Na2EDTA; 0.01M Tris-HCl pH 7.4; 0.2% SDS, dissolved in bi-distillated sterile water) using the glass bead method and phenol:chloroform extraction. Samples were then vortexed 10 minutes at 4ºC and centrifugation at 14000 rpm to separate the organic from the aqueous fraction. The aqueous fraction was transferred to a microcentrifuge tube, ethanol 100% was added and RNA was precipitated overnight at -20ºC. RNA was collected by centrifugation at 14000 rpm for 15 minutes and the pellet was resuspended in RNAse free water and incubated 15 minutes at 65ºC to help the solubilisation of the pellet. RNA samples were treated with DNAse (TURBO DNAse Ambion) according to manufacturer's instructions, at 37ºC for 40 minutes. RNA samples were then purified using RNeasy Mini Kit (QIAGEN).The integrity of RNA samples was evaluated by agarose gel electrophoresis. RNA libraries were prepared for sequencing by the Genomics Facility of the Gulbenkian Institute of Science, Oeiras, Portugal, using the SMART-SEQ2 protocol.