A Gene Dosage Requirement for Transcription Factor Gfi1 in the Regulation of Myelopoiesis and Myeloproliferative Disorders.

The generation of mature myeloid lineage cells from hematopoietic stem cells (HSCs) requires a precise synergy between cytokine signaling and lineage-specific transcription factors. Gfi1 (Growth Factor Independence 1) is a zinc finger transcription factor that is necessary for normal myelopoiesis. Gfi1 knockout mice display an abnormal ratio of phenotypic common myeloid progenitors (CMP) and granulocyte/monocyte progenitors (GMP), and such mice completely lack mature neutrophils. In contrast, the Gfi1 heterozygote mouse presents no obvious phenotype. Here we show a gene dosage requirement for Gfi1 in the differentiation of mature myeloid cells. While bone marrow from wild type littermates generates granulocytic, monocytic and mixed methylcellulose colonies, Gfi1 knockout bone marrow cells yield mainly monocytic colonies. In comparison to wild type littermates, Gfi1+/− bone marrow cells generate lower numbers of granulocytic colonies and higher numbers of monocytic colonies. Interestingly, methylcellulose colonies from both Gfi1 knockout mice and heterozygotes display increased serial replating capacity in comparison to wild type littermates. These data suggest that Gfi1 gene dosage may control self renewal and may relate to oncogenic transformation. Activating mutations in K-Ras are common genetic abnormalities in human acute myeloid leukemia and myeloproliferative disease (MPD). However, expression of activated Ras from endogenous regulatory sequences (knock-in) results in an MPD of varying lethality. The severity of the K-Ras-induced MPD depends on unknown genetic modifiers, as lethality is increased in a Balb/c genetic background. Given the effect of Gfi1 gene dosage on serial replating, we have analyzed the effect of Gfi1 gene dosage on the activated Ras knock-in mouse model of MPD. Preliminary data indicate that lowering Gfi1 gene dosage modifies the phenotype of activated Ras MPD by dramatically increasing the number of immature circulating myeloid progenitors. These results reveal that Gfi1 is a modifier of Ras induced disease pathogenesis.