WASP gene expression in hematopoietic precursors. (A) The enriched CD34⁺ population isolated from cord blood was further purified by the cell sorting procedure as shown. In addition, CD34⁺ cells were stained with the CD45RA MoAb and the two subsets, CD34⁺CD45RA⁺ and CD34⁺CD45RA⁻, were selected, as represented. (B) RNA from CD34⁺, CD34⁺CD45RA⁺, and CD34⁺CD45RA⁻ sorted cells; from the T-cell line MOLT-4 (used as a positive control for WASP amplification); and from the carcinoma cell line A431 (negative control for WASP expression) was reverse transcribed and subsequently amplified (25 cycles) either with primers specific for WASP cDNA that determine a PCR product of 900 bp or with primers specific for the G3PDH sequence (300 bp). The PCR products were shown by hybridization with the specific cDNA ³²P-labeled probe. A WASP signal in A431 cell line was not detected even after extended autoradiographic exposure. The lane with H₂O represents the PCR-negative control.