Demetri D. Spyropoulos

Hemorrhage, impaired hematopoiesis, and lethality in mouse embryos carrying a targeted disruption of the Fli1 transcription 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.

slc26a3 (dra)-deficient Mice Display Chloride-losing Diarrhea, Enhanced Colonic Proliferation, and Distinct Up-regulation of Ion Transporters in the Colon

Mutations in the SLC26A3 (DRA (down-regulated in adenoma)) gene constitute the molecular etiology of congenital chloride-losing diarrhea in humans. To ascertain its role in intestinal physiology, gene targeting was used to prepare mice lacking slc26a3. slc26a3-deficient animals displayed postpartum lethality at low penetrance. Surviving dra-deficient mice exhibited high chloride content diarrhea, volume depletion, and growth retardation. In addition, the large intestinal loops were distended, with colonic mucosa exhibiting an aberrant growth pattern and the colonic crypt proliferative zone being greatly expanded in slc26a3-null mice. Apical membrane chloride/base exchange activity was sharply reduced, and luminal content was more acidic in slc26a3-null mouse colon. The epithelial cells in the colon displayed unique adaptive regulation of ion transporters; NHE3 expression was enhanced in the proximal and distal colon, whereas colonic H,K-ATPase and the epithelial sodium channel showed massive up-regulation in the distal colon. Plasma aldosterone was increased in slc26a3-null mice. We conclude that slc26a3 is the major apical chloride/base exchanger and is essential for the absorption of chloride in the colon. In addition, slc26a3 regulates colonic crypt proliferation. Deletion of slc26a3 results in chloride-rich diarrhea and is associated with compensatory adaptive up-regulation of ion-absorbing transporters.

Mouse models in the study of the Ets family of transcription factors.

The Ets family of transcription factors is one of a growing number of master regulators of development. This family was originally defined by the presence of a conserved DNA binding domain, the Ets domain. To date, nearly 30 members of this family have been identified and implicated in a wide range of physiological and pathological processes. Despite the likely importance of Ets-family members, each of their precise roles has not been delineated. Herein, we describe the elucidation of essential functions of a few of these family members in vivo using knockout mouse models. Of the knockouts generated to date, the majority shows important functions in hematopoiesis, ranging from PU.1, a principle regulator of myelo-lymphopoiesis, to Spi-B which regulates the proper function of terminally differentiated cells. Ets1 was shown to be of intermediate importance as a regulator of pan-lymphoid development. Other Ets family members such as Fli1 and TEL1 display distinct and/or overlapping functions in vasculo/angiogenesis, hemostasis and hematopoiesis. The remaining knockouts generated, Ets2 and Er81, show non-hematopoietic defects related to extraembryonic development and neurogenesis, respectively. The pioneering group of knockout models described reveals only the most distinct functions of each of these Ets family members. A better understanding of the roles and hierarchies of Ets family members in cellular differentiation will come with the generation of new null alleles in previously untargeted family members, more mutant alleles in members already disrupted, double knockouts, ES cell differentiation and chimera rescue experiments, and tissue-specific inducible knockouts.

Control of neurulation by the nucleosome assembly protein-1–like 2

Neurulation is a complex process of histogenesis involving the precise temporal and spatial organization of gene expression. Genes influencing neurulation include proneural genes determining primary cell fate, neurogenic genes involved in lateral inhibition pathways and genes controlling the frequency of mitotic events. This is reflected in the aetiology and genetics of human and mouse neural tube defects, which are of both multifactorial and multigenic origin. The X-linked gene Nap1l2, specifically expressed in neurons, encodes a protein that is highly similar to the nucleosome assembly (NAP) and SET proteins. We inactivated Nap1l2 in mice by gene targeting, leading to embryonic lethality from mid-gestation onwards. Surviving mutant chimaeric embryos showed extensive surface ectoderm defects as well as the presence of open neural tubes and exposed brains similar to those observed in human spina bifida and anencephaly. These defects correlated with an overproduction of neuronal precursor cells. Protein expression studies showed that the Nap1l2 protein binds to condensing chromatin during S phase and in apoptotic cells, but remained cytoplasmic during G1 phase. Nap1l2 therefore likely represents a class of tissue-specific factors interacting with chromatin to regulate neuronal cell proliferation.

Defective Megakaryopoiesis and Abnormal Erythroid Development in Fli-1 Gene-Targeted Mice

Mouse embryos homozygous for a targeted disruption in theFli-1 gene show hemorrhage into the neural tube and brain on embryonic day (E)11.0 and die shortly thereafter. Livers from the mutant embryos contain drastically reduced numbers of pronormoblasts, basophilic normoblasts, and colony-forming cells.To determine the nature of impaired hematopoiesis, we carried out cell culture studies of mutant embryonic stem (ES) cells and cells from the aorta-gonad-mesonephros (AGM) region of E10.0 mutant embryos. There was a striking reduction in the number of megakaryocytes in cultures of mutant AGM cells compared with cultures of AGM cells from wild-type or heterozygous embryos. Furthermore,Fli-1 mutant ES cells failed to produce megakaryocyte colonies and multilineage colonies containing megakaryocytes. Consistent with the observed defect in megakaryopoiesis, we also demonstrated the down-regulation of c-mpl in the AGM of mutant embryos. The percentages of pronormoblasts and basophilic normoblasts were significantly reduced in cultures of mutant AGM embryos, which contained primarily polychromatophilic and orthochromatic normoblasts. These results provide further evidence for the role ofFli-1 in the regulation of hematopoiesis and for c-mpl as aFli-1 target gene.

Differential mammary morphogenesis along the anteroposterior axis in Hoxc6 gene targeted mice

Mammary epithelial cell proliferation, branching, and differentiation span from the appearance of the mammary bud in midgestation through to the cycling mammary gland in adulthood. Here, we show that females homozygous for a targeted disruption of the Hoxc6 homeobox gene produce thoracic mammary glands that are slightly under‐developed at birth and completely cleared of epithelium by adulthood, and inguinal mammary ducts that are dilated and fail to regress in response to ovariectomy. Mammary buds are detected in E12.5 Hoxc6 homozygous embryos. However, in newborn Hoxc6 homozygous females, branching ductal structures and fat pad development are reduced. Whole‐mount and histologic analyses of mammary glands from adult Hoxc6 homozygous females show the absence of mammary epithelium in thoracic glands and dilated ducts in inguinal glands at 100% penetrance. Histologic analysis of inguinal mammary glands from ovariectomized Hoxc6 homozygous females demonstrates no signs of the expected regression of epithelium, suggesting that these glands are not responsive to the loss of ovarian hormone signals. We further observe repression of Hoxc6 expression specifically within mammary stroma by estrogen and progesterone. Hoxc6 homozygous mice also exhibit a homeotic transformation of the second thoracic vertebra into the first (T2 to T1 conversion with 60% penetrance), corresponding to both the genes anterior boundary of expression and the most extreme appearance of mammary defects. The position‐specific phenotypes observed and the potential role for Hoxc6 in mediating hormone‐regulated ductal expansion and regression in the adult female are discussed.

Targeted disruption of cubilin reveals essential developmental roles in the structure and function of endoderm and in somite formation

BackgroundCubilin is a peripheral membrane protein that interacts with the integral membrane proteins megalin and amnionless to mediate ligand endocytosis by absorptive epithelia such as the extraembryonic visceral endoderm (VE).ResultsHere we report the effects of the genetic deletion of cubilin on mouse embryonic development. Cubilin gene deletion is homozygous embryonic lethal with death occurring between 7.5–13.5 days post coitum (dpc). Cubilin-deficient embryos display developmental retardation and do not advance morphologically beyond the gross appearance of wild-type 8–8.5 dpc embryos. While mesodermal structures such as the allantois and the heart are formed in cubilin mutants, other mesoderm-derived tissues are anomalous or absent. Yolk sac blood islands are formed in cubilin mutants but are unusually large, and the yolk sac blood vessels fail to undergo remodeling. Furthermore, somite formation does not occur in cubilin mutants. Morphological abnormalities of endoderm occur in cubilin mutants and include a stratified epithelium in place of the normally simple columnar VE epithelium and a stratified cuboidal epithelium in place of the normally simple squamous epithelium of the definitive endoderm. Cubilin-deficient VE is also functionally defective, unable to mediate uptake of maternally derived high-density lipoprotein (HDL).ConclusionIn summary, cubilin is required for embryonic development and is essential for the formation of somites, definitive endoderm and VE and for the absorptive function of VE including the process of maternal-embryo transport of HDL.

Decreased expression of the Ets family transcription factor Fli-1 markedly prolongs survival and significantly reduces renal disease in MRL/lpr mice

Increased Fli-1 mRNA is present in PBLs from systemic lupus erythematosus patients, and transgenic overexpression of Fli-1 in normal mice leads to a lupus-like disease. We report in this study that MRL/lpr mice, an animal model of systemic lupus erythematosus, have increased splenic expression of Fli-1 protein compared with BALB/c mice. Using mice with targeted gene disruption, we examined the effect of reduced Fli-1 expression on disease development in MRL/lpr mice. Complete knockout of Fli-1 is lethal in utero. Fli-1 protein expression in heterozygous MRL/lpr (Fli-1+/−) mice was reduced by 50% compared with wild-type MRL/lpr (Fli-1+/+) mice. Fli-1+/− MRL/lpr mice had significantly decreased serum levels of total IgG and anti-dsDNA Abs as disease progressed. Fli-1+/− MRL/lpr mice had significantly increased splenic CD8+ and naive T cells compared with Fli-1+/+ MRL/lpr mice. Both in vivo and in vitro production of MCP-1 were significantly decreased in Fli-1+/− MRL/lpr mice. The Fli-1+/− mice had markedly decreased proteinuria and significantly lower pathologic renal scores. At 48 wk of age, survival was significantly increased in the Fli-1+/− MRL/lpr mice, as 100% of Fli-1+/− MRL/lpr mice were alive, in contrast to only 27% of Fli-1+/+ mice. These findings indicate that Fli-1 expression is important in lupus-like disease development, and that modulation of Fli-1 expression profoundly decreases renal disease and improves survival in MRL/lpr mice.

The Transcription Factor Fli-1 Modulates Marginal Zone and Follicular B Cell Development in Mice

Fli-1 belongs to the Ets transcription factor family and is expressed primarily in hematopoietic cells, including most cells active in immunity. To assess the role of Fli-1 in lymphocyte development in vivo, we generated mice that express a truncated Fli-1 protein, lacking the C-terminal transcriptional activation domain (Fli-1ΔCTA). Fli-1ΔCTA/Fli-1ΔCTA mice had significantly fewer splenic follicular B cells, and an increased number of transitional and marginal zone B cells, compared with wild-type controls. Bone marrow reconstitution studies demonstrated that this phenotype is the result of lymphocyte intrinsic effects. Expression of Igα and other genes implicated in B cell development, including Pax-5, E2A, and Egr-1, are reduced, while Id1 and Id2 are increased in Fli-1ΔCTA/Fli-1ΔCTA mice. Proliferation of B cells from Fli-1ΔCTA/Fli-1ΔCTA mice was diminished, although intracellular Ca2+ flux in B cells from Fli-1ΔCTA/Fli-1ΔCTA mice was similar to that of wild-type controls after anti-IgM stimulation. Immune responses and in vitro class switch recombination were also altered in Fli-1ΔCTA/Fli-1ΔCTA mice. Thus, Fli-1 modulates B cell development both centrally and peripherally, resulting in a significant impact on the in vivo immune response.

Genome-Wide Analysis of the Homeobox C6 Transcriptional Network in Prostate Cancer

Homeobox transcription factors are developmentally regulated genes that play crucial roles in tissue patterning. Homeobox C6 (HOXC6) is overexpressed in prostate cancers and correlated with cancer progression, but the downstream targets of HOXC6 are largely unknown. We have performed genome-wide localization analysis to identify promoters bound by HOXC6 in prostate cancer cells. This analysis identified 468 reproducibly bound promoters whose associated genes are involved in functions such as cell proliferation and apoptosis. We have complemented these data with expression profiling of prostates from mice with homozygous disruption of the Hoxc6 gene to identify 31 direct regulatory target genes of HOXC6. We show that HOXC6 directly regulates expression of bone morphogenic protein 7, fibroblast growth factor receptor 2, insulin-like growth factor binding protein 3, and platelet-derived growth factor receptor alpha (PDGFRA) in prostate cells and indirectly influences the Notch and Wnt signaling pathways in vivo. We further show that inhibition of PDGFRA reduces proliferation of prostate cancer cells, and that overexpression of HOXC6 can overcome the effects of PDGFRA inhibition. HOXC6 regulates genes with both oncogenic and tumor suppressor activities as well as several genes such as CD44 that are important for prostate branching morphogenesis and metastasis to the bone microenvironment.