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...

Human nm23 has been implicated in suppression of metastasis in various cancers, but the underlying mechanism of such activity has not been fully understood. Using Drosophila tracheal system as a genetic model, we examined the function of the Drosophila homolog of nm23, the awd gene, in cell migration. We show that loss of Drosophila awd results in dysregulated tracheal cell motility. This phenotype can be suppressed by reducing the dosage of the chemotactic FGF receptor (FGFR) homolog, breathless (btl), indicating that btl and awd are functionally antagonists. In addition, mutants of shi/dynamin show similar tracheal phenotypes as in awd and exacerbate those in awd mutant, suggesting defects in vesicle-mediated turnover of FGFR in the awd mutant. Consistent with this, Btl-GFP chimera expressed from a cognate btl promoter-driven system accumulate at high levels on tracheal cell membrane of awd mutants as well as in awd RNA duplex-treated cultured cells. Thus, we propose that awd regulates tracheal cell motility by modulating the FGFR levels, through a dynamin-mediated pathway.[Keywords: awd/nm23; btl/FGFR; shi/dynamin; tracheal development; Drosophila; cell migration] Supplemental material is available at http://www.genesdev.org.

We investigated the inter-relationship between two downstream effectors of vascular endothelial growth factor (VEGF), the serine-threonine kinase Akt (or protein kinase B) and the transcription factor ETS1, in tubulogenesis. We show that VEGF upregulates ETS1 transcription through an Aktdependent pathway in primary endothelial cells. Activation of Akt also results in tubule formation in vitro, a process requiring ETS1 activity. In vivo, the Drosophila ETS1 is required for cell motility per se while Akt is responsible for organized cell movement. Thus, ETS1 and Akt control different aspects of cell migration that are integrated in the regulation of vascular tubule formation. KeywordsAkt; ETS1; angiogenesis; Drosophila; tubulogenesis; tracheal development Angiogenesis is the mechanism by which new blood vessels are formed from the pre-existing vascular network (Shiojima and Walsh 2002). It is widely accepted that vascular endothelial growth factor (VEGF) is the main activator of angiogenesis, inducing basement membrane degradation, endothelial cell proliferation and cell motility (Merenmies et al. 1997). Among the cellular mechanisms that underlie angiogenesis, cell motility is the least understood. Angiogenic tubulogenesis requires, a priori, migratory potential of the vascular cells. However, the cell migration events that lead to blood vessel formation needs to be both organized and directional. In other words, simple mobilization of vascular cells does not necessarily lead to tubule formation. How organized cell movement is regulated remains unresolved. Since VEGF is sufficient for inducing tube-like structures in three dimensional cell culture systems (Nehls and Drenckhahn 1995;Papapetropoulos et al. 1997), this model provides a good approximation for dissecting the complex mechanisms involved in organized cell migration. VEGF can activate many different signaling pathways, depending on cellular context and environmental cues (Veikkola et al. 2000). Among the various responses VEGF can elicit, Akt and ETS1 have emerged as two important down-stream regulators of angiogenic cell movement.Upon growth factor stimulation, phosphatidylinositol-3-kinase (PI3K) is activated which leads to recruitment of Akt to the plasma membrane where it binds phosphoinositol lipids via its pleckstrin homology domain (Chan et al. 1999). PI3K-Akt-mediated signaling has been implicated in many aspects of cellular functions, including cell survival and cell size control, which are regulated by other growth factors such as EGF and the insulin family of proteins (Brazil et al. 2002). These Akt functions are evolutionarily conserved at least in Drosophila (Scanga et al. 2000;Potter et al. 2002;Radimerski et al. 2002). Recently PI3K and by extension, Akt, have been implicated in upregulation of angiogenesis in vivo and tubule formation in vitro (Jiang et al. 2000;Morales-Ruiz et al. 2000). Although the inductive effect of PI3K on angiogenesis has been ascribed to promoting cell migration, no studies have clearly On the other hand, ...

We investigated pineal function as well as reproductive and energetic characteristics in male deer mice (Peromyscus maniculatus) that differentially respond to short photoperiod with full, partial or no gonadal regression. In mice at both high (23 degrees C) and low temperature (1 degree C), these phenotypic differences in reproductive responses to short days were not reflected by differences in urinary excretion of 6-sulphatoxy-melatonin, the main metabolite of pineal melatonin. Neither duration nor amplitude or phase-angle of nocturnal peaks in 6-sulphatoxymelatonin significantly differed between reproductive phenotypes at either temperature. Differences in testis size were, however, associated with different energy requirements. In gonadally regressed males only, food intake and body weight were significantly (P < 0.01) reduced by up to 29% and 13% respectively. Chronic cold exposure (5 degrees C) had no effect on the proportion of males undergoing testicular regression under short days, but caused a general elevation in body weights among all mice (P < 0.05). Phenotypic differences in body weight and food intake were maintained in the cold. Together, these results suggest that within-population variation of reproductive responses in male deer mice is based on post-pineal differences in the regulation of gonadal function, and that phenotypic characteristics in reproductive and energetic responses to short days are largely unaffected by ambient temperature.

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