RNA amplification: a single round of amplification was performed with 3 mg of total RNA using the MessageAmp RNA Amplification Kit (Ambion, Austin, USA) and following the protocol provided with the kit. Next, 5 mg of amplified RNA was mixed with 9 mg random primers (Cat. No. 4819001; Invitrogen, Carlsbad, USA) in 19 ml of water, heated for 5 minutes at 70uC and then immediately transferred to ice.