Nonquantitative single-cell RT-PCR of mRNA derived from individual cells. Data from representative experiments are shown. Single CD34⁺Lin⁻ cells were induced to unilineage erythroid differentiation as described in Materials and Methods. When the 4-cell stage was reached (at round I, II, III, and IV), 2 individual daughter cells were removed from culture and processed separately for RT-PCR. mRNA was isolated from each cell and reverse transcribed into cDNA as described in Materials and Methods. The cDNA was divided into 3 aliquots that were processed in separate PCR reactions. Lane 0: Gene expression pattern of freshly isolated single CD34⁺Lin⁻ cells. Lane I: single daughter cell (first round). Lane II: single daughter cell (second round). Lane III: single daughter cell (third round). Lane IV: single daughter cell (fourth round). Note that only GATA-2, PU.1, and c-kit are expressed in freshly isolated highly purified CD34⁺Lin⁻ cells. Copurification of genomic DNA with mRNA from single cells was not detected by RT-PCR using intron-spanning primers for β-2 microglobulin (not shown).