RNA isolation and quantitative RT-PCR (RT-qPCR) were essentially performed as recently described (22 (link),44 (link)). In brief, total RNA extracted using Trizol served as template for cDNA synthesis by random priming. RT-qPCR was performed based on SYBRgreen I technology using SYBR Select Master Mix (Life Technologies) in a 7900HT-cycler (Applied Biosystems). Whenever possible, primer pairs spanning an exon/exon border were selected using the Primer Blast database (http://www.ncbi.nlm.nih.gov/tools/primer-blast/). For non-exon-border spanning primer pair, no-RT controls were performed. For all primer pairs an annealing temperature of 58°C in a three step protocol was used. Relative changes of RNA abundance were determined by the ΔΔCt method using ACTB and GAPDH for normalization, as previously described (44 (link)). For primers used see Supplementary Table S5.