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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Loss of expression of the Hoxa-9 homeobox gene impairs the proliferation and repopulating ability of hematopoietic stem cells.

The homeobox gene Hoxa-9 is normally expressed in primitive bone marrow cells, and overexpression of Hoxa-9 markedly expands hematopoietic stem cells, suggesting a function in early hematopoiesis. We present evidence for major functional defects in Hoxa-9-/- hematopoietic stem cells. Hoxa-9-/- marrow cells have normal numbers of immunophenotypic stem cells (Lin(-)c-kit(+)flk-2(-)Sca-1+ [KLFS] cells). However, sublethally irradiated Hoxa-9-/- mice develop persistent pancytopenia, indicating unusual sensitivity to ionizing irradiation. In competitive transplantation assays, Hoxa-9-/- cells showed an 8-fold reduction in multilineage long-term repopulating ability, a defect not seen in marrow cells deficient for the adjacent Hoxa-10 gene. Single-cell cultures of KLFS cells showed a 4-fold reduction in large high-proliferation potential colonies. In liquid cultures, Hoxa-9-deficient Lin(-)Sca-1(+) cells showed slowed proliferation (a 5-fold reduction in cell numbers at day 8) and delayed emergence of committed progenitors (a 5-fold decrease in colony-forming cells). Slowing of proliferation was accompanied by a delay in myeloid maturation, with a decrease in Gr-1hiMac-1hi cells at the end of the culture. Retroviral transduction with a Hoxa-9 expression vector dramatically enhanced the cytokine-driven proliferation and in vivo engraftment of Hoxa-9-/- marrow cells. Hoxa-9 appears to be specifically required for normal hematopoietic stem cell function both in vitro and in vivo.[1]


  1. Loss of expression of the Hoxa-9 homeobox gene impairs the proliferation and repopulating ability of hematopoietic stem cells. Lawrence, H.J., Christensen, J., Fong, S., Hu, Y.L., Weissman, I., Sauvageau, G., Humphries, R.K., Largman, C. Blood (2005) [Pubmed]
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