Retroviral Insertional Mutagenesis Screen in a C/EBPalpha Proliferative Genetic Background.

The CCAAT enhancer binding protein alpha (C/EBPalpha) transcription factor plays a key role in the regulation of growth and differentiation of the granulocytic lineage in the hematopoietic system. Consistently, mice lacking C/EBPalpha have no mature neutrophils and die within a few hours after birth. In contrast, homozygous knockin mice in which the wild type Cebpa allele has been replaced with a mutant allele (BRM2) deficient in repressing the activity of E2F family members, are viable. At 8 weeks of age these animals display myeloid dysplasia with absence of neutrophil granulocytes. Strikingly, in older BRM2/BRM2 knockin mice the myeloid dysplastic phenotype progress into other myeloid malignancies such as myeloid proliferative syndrome and acute myeloid leukemia. These findings strongly suggest that secondary mutations in other loci must occur during the phenotypic progression. In order to identify genes that cooperate with C/EBPalpha in the development of leukemia in BRM2/BRM2 mice a so-called retroviral insertion mutagenesis screen was performed. Inbred newborn BRM2/BRM2 and wildtype mice were injected with SRS19-6 retrovirus and when disease is evident the mice are euthanized and analyzed. As expected the BRM2/BRM2 mice have a shorter latency than wildtype mice (182 vs. 260 days). The mice have enlarged spleen, thymus, and lymph nodes and were further characterized by histology, flow cytometry and Southern blotting in order to determine the hematopoietic phenotypes. Most abundantly was the AML-like phenotype, but also T-cell lymphomas are developing. Finally, the loci carrying retroviral insertions loci are identified through a splinkerette-aided PCR strategy. This study provides a better understanding of the genes involved in the development of myeloid leukemia.