TRIzol reagent (Invitrogen) was used for total RNA extraction, and cDNA was synthesized from 0.5 mg total RNA by Superscript III reverse transcriptase (Invitrogen). qPCR amplification was done with 4 ng cDNA in 10 ml SYBR Green PCR master mix (Applied Biosystems) with 3 mM of primers in the ABI Prism 7000 Sequence Detection System (Applied Biosystems). Transcript levels were normalized to that of hypoxanthine phosphoribosyltransferase ( Table S1 .