Expression of integrin 4 subunit mRNA in CMCs at 2, 4, 6, and 8 weeks after initiation of the culture. RNAs (5.0 μg) obtained from +/+ or mi/mi CMCs were reverse-transcribed and PCR-amplified with 4 or β-actin primer. PCR products were electrophoresed in 2.0% agarose gel containing ethidium bromide.