Expression of HOXA9 in normal marrow cells and lymphocytes. (A) Southern blot analysis of total amplified cDNA derived from various fractions of normal human bone marrow. Lane 1, CD34⁺Lin⁻ cells enriched for LTC-IC; lane 2, CD34⁺CD45RA⁺ cells enriched for myeloid progenitors; lane 3, CD34⁺CD71⁺ cells enriched for erythroid progenitors; lanes 4 and 7, total marrow cells; lanes 5 and 8, CD34⁺ marrow cells; lanes 6 and 9, CD34⁻ marrow cells. HOXA9 message is clearly detectable in CD34⁺ cell fractions, particularly those enriched for LTC-IC and myeloid progenitors, and not in CD34⁻ cells. (B) Southern blot analysis of total amplified cDNA from fractionated murine bone marrow, T cells, and B cells. HOXA9 is clearly detectable in primitive Sca1⁺/lin⁻ marrow cells (lanes 2 and 4), but not in total marrow (lanes 1, 3, and 10). Within the T-cell fractions, there is detectable HOXA9 message in CD4⁺/CD8⁺ (lane 7) and in CD4⁺/CD8⁻ (lane 8) cells. In B220⁺ B-cell populations, HOXA9 is expressed weakly in CD43⁺ cells (lane 11) and more strongly in IgM⁺ (lane 12) and IgM⁺/IgD⁺ (lane 13) cells.