Tie2Cre-mediated Gene Ablation Defines the Stem-cell Leukemia Gene (SCL/tal1)-dependent Window During Hematopoietic Stem-cell Development

Blood. May, 2005  |  Pubmed ID: 15677556

The stem-cell leukemia gene (SCL/tal1) is essential for the formation of all blood lineages. SCL is first expressed in mesodermal cells that give rise to embryonic blood cells, and continues to be expressed in fetal and adult hematopoietic stem cells (HSCs). However, SCL is not required for the maintenance of established long-term repopulating (LTR) HSCs in the adult. The time point at which HSC development becomes SCL independent has not been defined. Tyrosine kinase with immunoglobulin and epidermal growth factor homology domains-2 (Tie2) expression appears in hemogenic and vasculogenic sites shortly after SCL. We therefore used the Tie2Cre mouse to inactivate SCL early during embryonic and fetal hematopoiesis. Tie2Cre completely inactivated SCL in yolk sac, the aortagonad-mesonephros (AGM) region, and fetal liver hematopoietic cells and circulating blood cells. However, the fetal liver was colonized by functional LTR-HSCs. Yet SCL remained crucial for proper differentiation of both primitive and definitive red cells and megakaryocytes. These results indicate that the SCL-dependent phase of HSC development ends before Tie2Cre-mediated gene ablation becomes effective.

The Placenta is a Niche for Hematopoietic Stem Cells

Developmental Cell. Mar, 2005  |  Pubmed ID: 15737932

The hematopoietic system develops during embryogenesis at temporally and anatomically restricted sites. The anatomical origin of definitive HSCs is not fully resolved, and little is known about how the different fetal hematopoietic microenvironments direct HSC development. Here, we show that the mouse placenta functions as a hematopoietic organ that harbors a large pool of pluripotent HSCs during midgestation. The onset of HSC activity in the placenta parallels that of the AGM (aorta-gonad-mesonephros) region starting at E10.5-E11.0. However, the placental HSC pool expands until E12.5-E13.5 and contains >15-fold more HSCs than the AGM. The expansion of the CD34(+)c-kit(+) HSC pool in the placenta occurs prior to and during the initial expansion of HSCs in the fetal liver. Importantly, the placental HSC pool is not explained by rare circulating HSCs, which appear later. These data support an important, but unappreciated, role for the placenta in establishing the mammalian definitive hematopoietic system.

DNA-binding Dependent and Independent Functions of WT1 Protein During Human Hematopoiesis

Experimental Cell Research. Aug, 2005  |  Pubmed ID: 15907324

The Wilms tumor gene 1 (WT1) encodes a zinc-finger-containing transcription factor highly expressed in immature hematopoietic progenitor cells. Overexpression and presence of somatic mutations in acute leukemia indicate a role for WT1 in the pathogenesis of leukemia. CD34+ progenitor cells were transduced with one splice variant of human WT1 without the KTS insert in the zinc-finger domain, WT1(+/-), and with a deleted mutant of WT1 lacking the entire zinc-finger region, WT1(delZ), thus incapable of binding DNA. We show that inhibition of erythroid colony formation and differentiation is absolutely dependent on the DNA-binding zinc-finger domain of WT1. Unexpectedly, however, WT1(delZ) was equally effective as wild type protein in the reduction of myeloid clonogenic growth as well as in stimulation of myeloid differentiation, as judged by the expression of cell surface CD11b. Expression of neither WT1(+/-) nor WT1(delZ) upregulated mRNA for the cdk inhibitor p21(Waf1/Cip1) or p27Kip1. Our results demonstrate that WT1 affects proliferation and differentiation in erythroid and myeloid cells by different molecular mechanisms, and suggest that mutations affecting the zinc-finger domain of WT1 could interfere with normal differentiation in the pathogenesis of leukemia.

Placenta As a Site for Hematopoietic Stem Cell Development

Experimental Hematology. Sep, 2005  |  Pubmed ID: 16140153

The discovery of a major hematopoietic stem cell (HSC) pool in mid-gestation mouse placenta has defined the placenta as yet another important anatomical site that participates in HSC development. Placental HSC activity starts in parallel with the AGM region, before HSCs are found in circulation or have colonized the fetal liver. Moreover, placental hematopoietic activity culminates in a rapid expansion of the definitive HSC pool, which occurs during the time when the fetal liver HSC reservoir begins to grow. Furthermore, hematopoietic cells in mid-gestation mouse placenta are not instructed for differentiation along the myeloerythroid lineage, as in the fetal liver. These findings suggest that the placenta provides a supportive niche where the definitive hematopoietic stem cell pool can be temporarily established during development. Future studies are needed to characterize the developmental events that lead to the establishment of placental HSC pool, and to define the microenvironmental signals that support this process. Furthermore, if the stem cell-promoting properties of the placental niche can be harnessed in vitro to support HSC formation, maturation, and/or expansion in culture, these assets may greatly improve hematopoietic stem cell-based therapies in the future.

Critical Role of FLT3 Ligand in IL-7 Receptor Independent T Lymphopoiesis and Regulation of Lymphoid-primed Multipotent Progenitors

Blood. Oct, 2007  |  Pubmed ID: 17540845

The molecular pathways regulating lymphoid priming, fate, and development of multipotent bone marrow (BM) stem/progenitor cells that continuously replace thymic progenitors remain largely unknown. Herein, we show that fms-like tyrosine kinase 3 (Flt3) ligand (Fl)-deficient mice have distinct reductions in the earliest thymic progenitors in fetal, postnatal, and adult thymus. A critical role of FL in thymopoiesis was particularly evident in the absence of interleukin-7 receptor alpha (IL-7Ralpha) signaling. Fl-/-Il-7r-/- mice have extensive reductions in fetal and postnatal thymic progenitors that result in a loss of active thymopoiesis in adult mice, demonstrating an indispensable role of FL in IL-7Ralpha-independent fetal and adult T lymphopoiesis. Moreover, we establish a unique and critical role of FL, distinct from that of IL-7Ralpha, in regulation of the earliest lineage-negative (Lin(-)) Lin(-)SCA1+KIT+ (LSK) FLT3(hi) lymphoid-primed multipotent progenitors in BM, demonstrating a key role of FLT3 signaling in regulating the very earliest stages of lymphoid progenitors.

The Emergence of Hematopoietic Stem Cells is Initiated in the Placental Vasculature in the Absence of Circulation

Cell Stem Cell. Mar, 2008  |  Pubmed ID: 18371450

The mouse placenta was unveiled as an important reservoir for hematopoietic stem cells (HSCs), yet the origin of placental HSCs was unknown. By tracking developing HSCs by expression of Runx1-lacZ and CD41, we have found that HSCs emerge in large vessels in the placenta. Analysis of Ncx1(-/-) embryos, which lack a heartbeat, verified that HSC development is initiated in the placental vasculature independent of blood flow. However, fewer CD41+ hematopoietic cells were found in Ncx1(-/-) placentas than in controls, implying that some HSCs/progenitors colonize the placenta via circulation and/or HSC emergence is compromised without blood flow. Importantly, placentas from Ncx1(-/-) embryos possessed equal potential to generate myelo-erythroid and B and T lymphoid cells upon explant culture, verifying intact multilineage hematopoietic potential, characteristic of developing HSCs. These data suggest that, in addition to providing a niche for a large pool of HSCs prior to liver colonization, the placenta is a true site of HSC generation.

Reprogrammed Mouse Fibroblasts Differentiate into Cells of the Cardiovascular and Hematopoietic Lineages

Stem Cells (Dayton, Ohio). Jun, 2008  |  Pubmed ID: 18450826

Forced expression of the four transcription factors Oct4, Sox2, c-Myc, and Klf4 is sufficient to confer a pluripotent state upon the murine fibroblast genome, generating induced pluripotent stem (iPS) cells. Although the differentiation potential of these cells is thought to be equivalent to that of embryonic stem (ES) cells, it has not been rigorously determined. In this study, we sought to identify the capacity of iPS cells to differentiate into Flk1-positive progenitors and their mesodermal progeny, including cells of the cardiovascular and hematopoietic lineages. Immunostaining of tissues from iPS cell-derived chimeric mice demonstrated that iPS cells could contribute in vivo to cardiomyocytes, smooth muscle cells, endothelial cells, and hematopoietic cells. To compare the in vitro differentiation potential of murine ES and iPS cells, we either induced embryoid body (EB) formation of each cell type or cultured the cells on collagen type IV (ColIV), an extracellular matrix protein that had been reported to direct murine ES cell differentiation to mesodermal lineages. EB formation and exposure to ColIV both induced iPS cell differentiation into cells that expressed cardiovascular and hematopoietic markers. To determine whether ColIV-differentiated iPS cells contained a progenitor cell with cardiovascular and hematopoietic differentiation potential, Flk1-positive cells were isolated by magnetic cell sorting and exposed to specific differentiation conditions, which induced differentiation into functional cardiomyocytes, smooth muscle cells, endothelial cells, and hematopoietic cells. Our data demonstrate that murine iPS cells, like ES cells, can differentiate into cells of the cardiovascular and hematopoietic lineages and therefore may represent a valuable cell source for applications in regenerative medicine. Disclosure of potential conflicts of interest is found at the end of this article.

Do Different Vascular Risk Factors Affect All Arteries Equally?

Angiology. Aug-Sep, 2008  |  Pubmed ID: 18505745

Established vascular risk factors (ie, smoking, hypertension, diabetes mellitus, and dyslipidemia) play an important role in the development of vascular disease. Emerging evidence suggests that some of these risk factors may have a more intense effect on specific arterial beds, a finding that holds implications for a prognostic role for certain types of vascular disease.

Cardiovascular Risk Factor Modification: a Sine Qua Non in the Management of Vascular Surgery Patients

Current Vascular Pharmacology. Jul, 2008  |  Pubmed ID: 18673155

Erectile Dysfunction in Stroke Patients: a Multifactorial Problem with Important Psychosocial Consequences

International Urology and Nephrology. 2008  |  Pubmed ID: 18683073

Isolation and Visualization of Mouse Placental Hematopoietic Stem Cells

Current Protocols in Stem Cell Biology. Aug, 2008  |  Pubmed ID: 18729047

This unit describes the isolation of hematopoietic stem cells (HSCs) from the mouse placenta. The placenta was recently identified as an important hematopoietic site that generates HSCs de novo and provides a transitory niche for a large pool of HSCs during midgestation. This protocol includes a dissection technique for murine placenta, the mechanical and enzymatic steps of placental tissue dissociation, and phenotypical identification and isolation of HSCs. It also contains a method for immunohistochemical analysis of placenta tissue sections to visualize developing HSCs in the placenta.

Anatomical Variation of Co-existence of 4th and 5th Short Metacarpal Bones, Sesamoid Ossicles and Exostoses of Ulna and Radius in the Same Hand: a Case Report

Cases Journal. 2008  |  Pubmed ID: 18959780

ABSTRACT:

Mef2C is a Lineage-restricted Target of Scl/Tal1 and Regulates Megakaryopoiesis and B-cell Homeostasis

Blood. Apr, 2009  |  Pubmed ID: 19211936

The basic helix-loop-helix transcription factor stem cell leukemia gene (Scl) is a master regulator for hematopoiesis essential for hematopoietic specification and proper differentiation of the erythroid and megakaryocyte lineages. However, the critical downstream targets of Scl remain undefined. Here, we identified a novel Scl target gene, transcription factor myocyte enhancer factor 2 C (Mef2C) from Scl(fl/fl) fetal liver progenitor cell lines. Analysis of Mef2C(-/-) embryos showed that Mef2C, in contrast to Scl, is not essential for specification into primitive or definitive hematopoietic lineages. However, adult VavCre(+)Mef2C(fl/fl) mice exhibited platelet defects similar to those observed in Scl-deficient mice. The platelet counts were reduced, whereas platelet size was increased and the platelet shape and granularity were altered. Furthermore, megakaryopoiesis was severely impaired in vitro. Chromatin immunoprecipitation microarray hybridization analysis revealed that Mef2C is directly regulated by Scl in megakaryocytic cells, but not in erythroid cells. In addition, an Scl-independent requirement for Mef2C in B-lymphoid homeostasis was observed in Mef2C-deficient mice, characterized as severe age-dependent reduction of specific B-cell progenitor populations reminiscent of premature aging. In summary, this work identifies Mef2C as an integral member of hematopoietic transcription factors with distinct upstream regulatory mechanisms and functional requirements in megakaryocyte and B-lymphoid lineages.

Combined Endovascular/surgical Management of a Ruptured Para-anastomotic Aneurysm of the Left Common Iliac Artery

The Open Cardiovascular Medicine Journal. 2009  |  Pubmed ID: 19834625

A 75-year old man presented with signs and symptoms of acute abdomen and a clinical picture of hypovolemic shock. An emergency CT scan revealed a ruptured para-anastomotic left common iliac artery aneurysm. The patient had undergone an elective abdominal aortic aneurysm repair operation and placement of an aortoiliac bifurcated graft 10 years before. Para-anastomotic aneurysms had developed in all 3 (aortic and the 2 iliac) anastomosis. As the patient was highrisk, a combined endovascular/surgical approach was undertaken. The patient was discharged 4 days later.This article discusses the applicability of endovascular procedures in emergency settings to high-risk patients.

Hematopoietic Stem Cell Development in the Placenta

The International Journal of Developmental Biology. 2010  |  Pubmed ID: 20711986

The placenta is a highly vascularized organ that mediates fetal-maternal exchange during pregnancy and is thereby vital for the survival and growth of the developing embryo. In addition to having this well-established role in supporting pregnancy, the placenta was recently shown to function as a hematopoietic organ. The placenta is unique among other fetal hematopoietic organs, as it is capable of both generating multipotential hematopoietic cells de novo and establishing a major hematopoietic stem cell (HSC) pool in the conceptus, while protecting HSCs from premature differentiation. The mouse placenta contains two distinct vascular regions that support hematopoiesis: the large vessels in the chorionic plate where HSCs/progenitors are thought to emerge and the labyrinth vasculature where nascent HSCs/progenitors may colonize for expansion and possible functional maturation. Defining how this cytokine- and growth factor rich organ supports HSC generation, maturation and expansion may ultimately help to establish culture protocols for HSC expansion or de novo generation from pluripotent cells.

Induced Pluripotent Stem Cell-derived Human Platelets: One Step Closer to the Clinic

The Journal of Experimental Medicine. Dec, 2010  |  Pubmed ID: 21173109

The era of induced pluripotent stem (iPS) cells carries with it the promise of virtually unlimited sources of autologous cells for regenerative medicine. However, efficiently differentiating iPS cells into fully functional mature cell types remains challenging. A new study reporting the formation of fully functional platelets from human iPS (hiPS) cells improves upon recent efforts to generate this enucleated cell type, which remains in high demand for therapeutic transfusions. Notably, their lack of nucleus renders platelets unable to retain the pluripotent or tumorigenic properties of iPS cells.