Generation of a novel Fli-1 protein by gene targeting leads to a defect in thymus development and a delay in Friend virus-induced erythroleukemia.
The proto-oncogene Fli-1 is a member of the ets family of transcription factor genes. Its activation by either chromosomal translocation or proviral insertion leads to Ewing's sarcoma in humans or erythroleukemia in mice, respectively, Fli-1 is preferentially expressed in hematopoietic and endothelial cells. This expression pattern resembled that of c-ets-1, another ets gene closely related and physically linked to Fli-1. We also generated a germ line mutation in Fli-1 by homologous recombination in embryonic stem cells. Homozygous mutant mice exhibit thymic hypocellularity which is not related to a defect in a specific subpopulation of thymocytes or to increased apoptosis, suggesting that Fli-1 is an important regulator of a prethymic T-cell progenitor. This phenotype was corrected by crossing the Fli-1 deficient mice expressing Fli-1 cDNA. Homozygous mutant mice remained susceptible to erythroleukemia induction by Friend murine leukemia virus, although the latency period was significantly increased. Surprisingly, the mutant Fli-1 allele was still a target for Friend murine leukemia virus integration, and leukemic spleens with a rearranged Fli-1 gene expressed a truncated Fli-1 protein that appears to arise from an internal translation initiation site and alternative splicing around the neo cassette used in the gene targeting. The fortuitous discovery of the mutant Fli-1 protein, revealed only as the result of the clonal expansion of leukemic cells harboring a rearranged Fli-1 gene, suggests caution in the interpretation of gene-targeting experiments that result in either no or only a subtle phenotypic alteration.
Mélet
F
F
Program in Molecular Biology and Cancer, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
Motro
B
B
Rossi
D J
DJ
Zhang
L
L
Bernstein
A
A
D000818:Animals; D001483:Base Sequence; D003433:Crosses, Genetic; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000502:physiology*; D005260:Female; D005622:Friend murine leukemia virus; D018507:Gene Expression Regulation, Developmental; D015321:Gene Rearrangement; D018390:Gene Targeting; D006410:Hematopoiesis / Q000235:genetics / Q000502:physiology; D006720:Homozygote; D004915:Leukemia, Erythroblastic, Acute / Q000209:etiology* / Q000517:prevention & control; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D011247:Pregnancy; D000090063:Proto-Oncogene Mas; D051789:Proto-Oncogene Protein c-fli-1; D011518:Proto-Oncogene Proteins; D013950:Thymus Gland / Q000254:growth & development*; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics* / Q000502:physiology*
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C497426:Fli1 protein, mouse; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D051789:Proto-Oncogene Protein c-fli-1; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators