Hemorrhage, Impaired Hematopoiesis, and Lethality in Mouse Embryos Carrying a Targeted Disruption of the Fli1Transcription Factor

Abstract

The Ets family of transcription factors have been suggested to function as key regulators of hematopoeisis. Here we describe aberrant hematopoeisis and hemorrhaging in mouse embryos homozygous for a targeted disruption in the Ets family member, Fli1. Mutant embryos are found to hemorrhage from the dorsal aorta to the lumen of the neural tube and ventricles of the brain (hematorrhachis) on embryonic day 11.0 (E11.0) and are dead by E12.5. Histological examinations and in situ hybridization reveal disorganization of columnar epithelium and the presence of hematomas within the neuroepithelium and disruption of the basement membrane lying between this and mesenchymal tissues, both of which express Fli1 at the time of hemorrhaging. Livers from mutant embryos contain few pronormoblasts and basophilic normoblasts and have drastically reduced numbers of colony forming cells. These defects occur with complete penetrance of phenotype regardless of the genetic background (inbred B6, hybrid 129/B6, or outbred CD1) or the targeted embryonic stem cell line used for the generation of knockout lines. Taken together, these results provide in vivo evidence for the role of Fli1 in the regulation of hematopoiesis and hemostasis.The human FLI1 gene, which we originally cloned from the leukemia T-cell line, CEM, is a member of the Ets gene family of transcription factors (38). As observed with all other members of the Ets gene family, FLI1 encodes a protein that retains a region of conserved sequence, the Ets domain (37, 38). This minimal 85-amino-acid region has been shown to be the DNAbinding domain. Ets proteins bind to DNA sequences that contain a consensus GGA(A/T) core motif (Ets-binding site) and, in the majority of cases, function as transcriptional activators. Ets proteins control the expression of genes that are critical for the control of cellular proliferation, differentiation, and programmed cell death. The presence of multiple Ets family proteins in a variety of cell types and the overlapping DNA-binding specificity of the Ets proteins have made it difficult to identify target genes that are specific for individual Ets factors. The generation and analysis of targeted disruptions in individual family members, coupled with the identification of such target genes, however, is one approach to understanding the role of Ets transcription factors in normal and dysregulated development. A variety of studies including the analysis of expression of members of the Ets transcription factor family in hematopoietic tissues and cell lines and the generation and analysis of targeted mutations in Ets gene family members in mouse suggest that they play important roles in the regulation of normal hematopoietic development (13,14,29).FLI1 was found to be highly related to the human ERG gene, and we originally named it ERGB to reflect this homology (38). Sequence alignments of the predicted 452-amino-acid protein product of human FLI1 with those of the ERG and mouse Fli1 products (5) demonstrated 80 and 96% similarity, respectively. FLI1 ha...

Continuous Fli-1 expression plays an essential role in the proliferation and survival of F-MuLV-induced erythroleukemia and human erythroleukemia

“…26 Mice carrying a targeted deletion in the Ets domain at the fli-1 locus display abnormal hematopoiesis and vasculogenesis, and die between embryonic day 11.5 and 12.5. 27,28 The first targeted disruption at the fli-1 locus, deleting the first ATG start site, resulted in the expression of a truncated protein and generated a non-lethal minor phenotype, including a reduction in thymus size and in the number of total thymocytes. 29 Interestingly, these mice remain susceptible to the development of erythroleukemia following infection with F-MuLV, however, the latency period is significantly increased.…”

Persistent Down-Regulation of Fli1, a Suppressor of Collagen Transcription, in Fibrotic Scleroderma Skin

“…1,44 Fli1 is known to play an essential, although not fully defined, role in endothelial cell function. 22,23 Mice with a targeted mutation in Fli1 locus, die of hemorrhage at day 11.5 of embryogenesis because of , at least in part, the loss of vascular integrity. Interestingly, Fli1 Ϫ/Ϫ embryos are able to form a functional network of blood vessels, but appear to fail to recruit pericytes or smooth muscle cells during late embryonic angiogenesis and vascular remodeling.…”

“…22 Collagen type I mRNA and protein levels versus Fli1 levels were examined in Fli1 Ϫ/Ϫ , Fli1 ϩ/Ϫ , and Fli1 ϩ/ϩ MEFs. As shown in Figure 3, A and B, COL1A1 mRNA and collagen type I protein levels are inversely proportional to Fli1 expression levels.…”

“…20 Fli1, a member of the Ets family of transcription factors, has been shown to play roles in hematopoiesis, embryonic development, and vasculogenesis. [21][22][23][24] Collective evidence indicates that Ets transcription factors are the important mediators of cellular programs involved in extracellular matrix degradation, 25 and are frequently dysregulated in diseases characterized by abnormal matrix turnover, including invasive tumors and arthritis. 26 In contrast, the specific role(s) of the Ets factors in the maintenance of collagen level homeostasis in healthy skin and their possible role in fibroproliferative disorders, including SSc, has not yet been adequately assessed.…”

Ets factors and a newly identified polymorphism regulate Fli1 promoter activity in lymphocytes

“…Murine Fli1 was first identified as a proto-oncogene as a site for retroviral integration of Friend virus-induced erythroleukemias (Ben-David et al, 1990). It is expressed in hematopoietic tissues in both embryos and adults, as well as in other tissues (Ben-David et al, 1991;Melet et al, 1996;Watson et al, 1992) and is essential for embryogenesis (Hart et al, 2000;Masuya et al, 2005;Spyropoulos et al, 2000). During lymphocyte development, Fli1 is first detected in the developing spleen and thymus of the embryo and later in mature B cells and throughout T cell development (Anderson et al, 1999;Melet et al, 1996), but is down-regulated in activated T cells (Mao et al, 1994;Zhang and Watson, 2005).…”