Total RNA was extracted from intestine using TRIzol (Invitrogen) as described (Hong et al., 2006; Park et al., 2008). Five micrograms of total RNA were treated with 1.0 U of DNase I and 1.0 L of 10 reaction buffer (Sigma), incubated for 15 min at room temperature, 1.0 L of stop solution was added, and the mixture was heated at 70C for 10 min. RNA was reverse transcribed using the StrataScript first-strand synthesis system (Stratagene, La Jolla, CA) according to the manufacturer’s recommendations.