Total RNA from sorted cells was isolated using an RNeasy minikit (Qiagen, Valencia, CA) by following the manufacturer's protocol. One microgram of RNA was reverse transcribed in a total volume of 20 ml using the QuantiTect RT kit (Qiagen). PCR was performed in triplicate in a MyiQ single color real time PCR detection system (Bio-Rad, Hercules, CA) using SYBR Green PCR kit (Qiagen) according to the manufacturer's protocol. Amplification was confirmed by ethidium bromide staining of the PCR products on an agarose gel. The expression of each target gene was normalized to the expression of 18 S RNA and presented as the ratio of the target gene to 18 S RNA, expressed as 2 2DCt , where Ct is the threshold cycle and DCt = Ct Target 