Expression analysis of T-ALL transcription factor oncogenes during T-cell development. Thymocyte subsets were purified by flow cytometry according to their surface markers, as indicated by the schematic diagram. The earliest T-cell precursors are characterized by the lack of expression of CD4 and CD8 surface markers (double-negative thymocytes) and can be subdivided into 4 different stages of development (DN1 to DN4). The rearrangement of the TCRβ chain at the end of the double-negative (DN) stage of development drives the production of intermediate-single-positive (ISP) cells that differentiate into CD4, CD8 double-positive (DP) cells. DP cells undergo a selection process that results in the production of functionally competent mature CD4 or CD8 single-positive (SP) cells.10 Semiquantitative RT-PCR was performed by using specific primers for Tal1, Tal2, Lyl1, Bhlhb1, Lmo2, Lmo1, Hox11, Hox11l2, and S16 as control for the amounts of cDNA. PCR products were transferred to membranes and hybridized with internal oligonucleotide probes. cDNA prepared from E11.5 or E13.5 embryonic heads or total bone marrow (Lmo2) were used as positive controls for PCR amplification (CTL).
