RNA and RT-PCR. (A) Schemes for the preparation of cells for microarray and RT-PCR analyses. Day 0 indicates initial samples of passage 2 hMSCs; 3wkSD and 3wkS, cells incubated without or with serum for 3 weeks; and +5dSDSS and +5dS, 3wkSD and 3wkS samples incubated for 5 days in medium containing 17% FCS. (B) RT-PCR analyses of RNA obtained from the samples described in panel A showing enhanced expression of genes that are expressed in very early progenitor cells.