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L I Zon

Publications and source records attributed to L I Zon.

At least 73 records · Page 4Linked to original sources
PubMed1998

SCL/Tal-1 transcription factor acts downstream of cloche to specify hematopoietic and vascular progenitors in zebrafish.

SCL/Tal-1 is a transcription factor necessary for hematopoietic stem cell differentiation. Although SCL is also expressed in endothelial and neural progenitors, SCL function in these cells remains unknown. In the zebrafish mutant cloche (clo), SCL expression is nearly abolished in hematopoietic and vascular tissues. Correspondingly, it was shown previously that clo fails to differentiate blood and angioblasts. Genetic analysis demonstrates that the clo mutation is not linked to the SCL locus. Forced expression of SCL in clo embryos rescues the blood and vascular defects, suggesting that SCL acts downstream of clo to specify hematopoietic and vascular differentiation.

Amino Acid Sequence↗
PubMed1998

Forced GATA-1 expression in the murine myeloid cell line M1: induction of c-Mpl expression and megakaryocytic/erythroid differentiation.

The "zinc-finger" transcription factor GATA-1 was first shown in cells of erythroid lineage. It is also expressed in cells of other hematopoietic lineages including megakaryocytes, mast cells, and eosinophils. GATA-1 is now considered to be one of the central regulators in hematopoietic cell differentiation. To further analyze the role of GATA-1 in controlling differentiation from hematopoietic stem cells, we investigated the phenotypic changes induced by the overexpression of murine GATA-1 in the murine myeloid leukemic cell line, M1. Forced expression of GATA-1 induced the appearance of erythroid cells and megakaryocytes as assessed by cellular morphology, acetylcholinesterase activity, and expression of platelet factor 4 and beta-globin mRNA synthesis. Because the c-mpl ligand, thrombopoietin, plays an important role in megakaryopoiesis, the expression of c-mpl and c-mpl ligand (thrombopoietin) mRNA was analyzed by Northern blot and reverse transcription-polymerase chain reaction (RT-PCR) in M1 cells overexpressing GATA-1. The c-mpl ligand mRNA was equally expressed both in parental M1 cells and in those transfected with the GATA-1 expression vector. In contrast, the mRNA expression of c-mpl was increased only in GATA-1 expressing M1 cells differentiated towards erythroid and megakaryocyte lineages. The increased expression of c-mpl mRNA induced by GATA-1 raised the question as to whether or not GATA-1 transactivated the c-mpl promoter. The activity of the c-mpl promoter in the presence of cotransfected GATA-1 was significantly increased compared with that of the control. A plasmid with the mutated GATA-binding site did not show transactivation ability in the cotransfection with a GATA expression vector. These findings suggest that the upregulation of c-mpl induced by GATA-1 expression in M1 cells is closely associated with erythroid and megakaryocytic differentiation.

Animals↗
PubMed1998

Cloning and genetic mapping of zebrafish BMP-2.

The BMP family of polypeptide growth factors has been shown to play diverse roles in establishing embryonic patterning and tissue fates. We report the cloning of the zebrafish homologue of BMP-2, examine its expression during embryogenesis, and find that it is localized to the distal end of the long arm of zebrafish chromosome 20. A missense mutation of the bmp2 gene has recently been shown to be responsible for the early dorsalized phenotype of the zebrafish swirl mutant [Kishimoto et al., 1997]. Given the dynamic expression of bmp2 in the developing embryo and the complex interactions of BMP signaling response in vertebrates, it is possible that other mutant phenotypes, due to altered bmp2 gene expression, will eventually map to or interact with this genetic locus.

Amino Acid Sequence↗
PubMed1998

Use of the zebrafish (Danio rerio) to define hematopoiesis.

Hematopoiesis in the vertebrate is characterized by the induction of ventral mesoderm to form hematopoietic stem cells and the eventual differentiation of these progenitors to form the peripheral blood lineages. Several genes have been implicated in the differentiation and development of hematopoietic and vascular progenitor cells, yet our understanding of the discrete steps involved in the induction of these cells from the ventral mesoderm is still incomplete. One method of delineating these processes is based on the use of lower vertebrates. The zebrafish (Danio rerio) is an especially robust vertebrate system for both isolating and characterizing genes involved in these processes. Hematopoietic mutants have been generated with defects in many of the steps of both the primitive and definitive hematopoietic programs. Cloning of the genes that underlie these mutations should yield valuable details of hematopoiesis and may have therapeutic implications for bone marrow transplantation and stem cell gene therapy.

Animals↗
PubMed1998

Use of the zebrafish (Danio rerio) to define hematopoiesis.

Hematopoiesis in the vertebrate is characterized by the induction of ventral mesoderm to form hematopoietic stem cells and the eventual differentiation of these progenitors to form the peripheral blood lineages. Several genes have been implicated in the differentiation and development of hematopoietic and vascular progenitor cells, yet our understanding of the discrete steps involved in the induction of these cells from the ventral mesoderm is still incomplete. One method of delineating these processes is based on the use of lower vertebrates. The zebrafish (Danio rerio) is an especially robust vertebrate system for both isolating and characterizing genes involved in these processes. Hematopoietic mutants have been generated with defects in many of the steps of both the primitive and definitive hematopoietic programs. Cloning of the genes that underlie these mutations should yield valuable details of hematopoiesis and may have therapeutic implications for bone marrow transplantation and stem cell gene therapy.

Animals↗
PubMed1998

Transcriptional regulation of blood formation during Xenopus development.

Hematopoiesis is the generation, proliferation and differentiation of hematopoietic stem cells (HSCs) into the erythroid, myeloid and lymphoid lineages. The HSC is a ventral mesodermal derivative that arises due to inductive and patterning processes triggered by bone morphogenetic protein 4 (BMP-4). Recent studies in Xenopus laevis have identified families of transcription factors that participate in hematopoietic development. Transcription factor families, such as the SMADs, Mixs and Vents pattern mesoderm to a ventral fate which ultimately results in the expression of hematopoietic-specific transcription factors such as GATA-1 and SCL. This transcriptional regulatory network enforces the correct temporal and spatial expression of the blood program.

Animals↗
PubMed1998

SEK1/MKK4 is required for maintenance of a normal peripheral lymphoid compartment but not for lymphocyte development.

SAPK is a member of the group of evolutionary conserved stress-activated kinases that mediate control of cellular death and proliferation. In lymphocytes, the SAPK pathway has been implicated in signaling from antigen, costimulatory, and death receptors; SEK1, which directly activates SAPK, is required for early embryonic development and has also been reported to be essential for normal lymphocyte development. In contrast to the latter findings, we have used RAG-2-deficient blastocyst complementation to show that SEK1-deficient embryonic stem cells support unimpaired T and B lymphocyte development. Moreover, mature SEK1-deficient lymphocytes are capable of SAPK activation. Surprisingly, however, aging SEK1-deficient chimeric mice frequently develop lymphadenopathy and polyclonal B and T cell expansions. Thus, SEK1 is not required for lymphocyte development, but is required for maintaining peripheral lymphoid homeostasis.

Animals↗
PubMed1998

Positional cloning of the zebrafish sauternes gene: a model for congenital sideroblastic anaemia.

Many human anaemias are caused by defects in haemoglobin synthesis. The zebrafish mutant sauternes (sau) has a microcytic, hypochromic anaemia, suggesting that haemoglobin production is perturbed. During embryogenesis, sau mutants have delayed erythroid maturation and abnormal globin gene expression. Using positional cloning techniques, we show that sau encodes the erythroid-specific isoform of delta-aminolevulinate synthase (ALAS2; also known as ALAS-E), the enzyme required for the first step in haem biosynthesis. As mutations in ALAS2 cause congenital sideroblastic anaemia (CSA) in humans, sau represents the first animal model of this disease.

5-Aminolevulinate Synthetase↗
PubMed1998

Vertebrate genome evolution and the zebrafish gene map.

In chordate phylogeny, changes in the nervous system, jaws, and appendages transformed meek filter feeders into fearsome predators. Gene duplication is thought to promote such innovation. Vertebrate ancestors probably had single copies of genes now found in multiple copies in vertebrates and gene maps suggest that this occurred by polyploidization. It has been suggested that one genome duplication event occurred before, and one after the divergence of ray-finned and lobe-finned fishes. Holland et al., however, have argued that because various vertebrates have several HOX clusters, two rounds of duplication occurred before the origin of jawed fishes. Such gene-number data, however, do not distinguish between tandem duplications and polyploidization events, nor whether independent duplications occurred in different lineages. To investigate these matters, we mapped 144 zebrafish genes and compared the resulting map with mammalian maps. Comparison revealed large conserved chromosome segments. Because duplicated chromosome segments in zebrafish often correspond with specific chromosome segments in mammals, it is likely that two polyploidization events occurred prior to the divergence of fish and mammal lineages. This zebrafish gene map will facilitate molecular identification of mutated zebrafish genes, which can suggest functions for human genes known only by sequence.

Animals↗
PubMed1998

Analysis of the role of MKK-4/Sek-1 in T cell development and apoptosis.

The stress-activated protein kinases (SAPK) are a group of dual-specificity kinases with potential roles in the control of apoptosis and proliferation. In most cells they are regulated through phosphorylation by MKK-4. We have investigated the role of MKK-4 in T cell development and function by generating transgenic animals expressing catalytically inactive MKK-4 (dMKK-4) in the thymus. Our results show that overexpression of dMKK-4 does not interfere with normal T cell development. Furthermore, expression of dMKK-4 inhibits Fas- but not phorbol ester plus ionomycin-induced activation of SAPK, suggesting that a SAPK kinase different from MKK-4 is responsible for the regulation of SAPK activation after stimulation of T cells with phorbol ester plus ionomycin. We then analyzed the effect of dMKK-4 on Fas-induced apoptosis of thymocytes. Our results show that activation of SAPK is not a necessary event in Fas-induced apoptosis of thymocytes.

Animals↗
PubMed1998

Molecular insights into early hematopoiesis.

During embryogenesis, a pool of pluripotential, self-renewing hematopoietic stem cells is specified from undifferentiated ventral mesoderm. These cells proliferate and differentiate to yield all the peripheral blood lineages. Although the mechanisms involved in the commitment and differentiation of multipotential progenitors have been well documented, little focus has been directed to the molecular events underlying the formation of hematopoietic stem cells. In this review we discuss the recent advances made in defining a bone morphogenetic protein-responsive signal cascade that regulates the earliest phase of blood formation during embryogenesis.

Animals↗
PubMed1998

SCL specifies hematopoietic mesoderm in Xenopus embryos.

Targeted gene disruption experiments in the mouse have demonstrated an absolute requirement for several transcription factors for the development of hematopoietic progenitors during embryogenesis. Disruption of the basic helix-loop-helix gene SCL (stem cell leukemia) causes a block early in the hematopoietic program with defects in all hematopoietic lineages. To understand how SCL participates in the organogenesis of blood, we have isolated cDNAs encoding Xenopus SCL and characterized the function of SCL during embryogenesis. We demonstrate that SCL is expressed in ventral mesoderm early in embryogenesis. SCL expression is induced by BMP-4, and a dominant negative BMP-4 receptor inhibits SCL expression in the ventral region of the embryo. Expression of SCL in either bFGF-treated animal pole explants or dorsal marginal zone explants leads to the expression of globin protein. Furthermore, over-expression of SCL does not alter normal dorsal-ventral patterning in the embryo, indicating that SCL acts to specify mesoderm to a hematopoietic fate after inductive and patterning events have occurred. We propose that SCL is both necessary and sufficient to specify hematopoietic mesoderm, and that it has a similar role in specifying hematopoietic cell fate as MyoD has in specifying muscle cell fate.

Amino Acid Sequence↗
PubMed1997

MST/MLK2, a member of the mixed lineage kinase family, directly phosphorylates and activates SEK1, an activator of c-Jun N-terminal kinase/stress-activated protein kinase.

c-Jun N-terminal kinases/stress-activated protein kinases (JNKs/SAPKs) are mitogen-activated protein kinase (MAPK)-related protein kinases that are involved in several cellular events, including growth, differentiation, and apoptosis. Mixed lineage kinases (MLKs) form a family of protein kinases sharing two leucine zipper-like motifs and a kinase domain whose primary structure is similar to both the tyrosine-specific and the serine/threonine-specific kinase classes. We have reported that a member of the MLK family, MUK/DLK/ZPK, can activate JNK/SAPK in vivo, and here we show that another member of the MLK family, MST/MLK2, activates JNK/SAPK. Both MUK/DLK/ZPK and MST/MLK2 cause a slight activation of p38/Mpk2 when overexpressed in COS-1 cells, whereas MST/MLK2, but not MUK/DLK/ZPK, activates extracellular response kinase (ERK) to a certain degree. The activity of SEK1/MKK4/JNKK, a MAPK kinase class protein kinase designated as a direct activator of JNK/SAPK, is also induced by MUK/DLK/ZPK or MST/MLK2 overexpression. Furthermore, recombinant MST/MLK2 produced in bacteria directly phosphorylates and activates SEK1/MKK4/JNKK in vitro, showing that MST/MLK2 acts like a MAPK kinase kinase. Taken together, these results suggest that MLK family members are MAPK kinase kinases preferentially acting on the JNK/SAPK pathway.

Animals↗
PubMed1997

Cdc42Hs, but not Rac1, inhibits serum-stimulated cell cycle progression at G1/S through a mechanism requiring p38/RK.

Antimitogenic stimuli such as environmental or genotoxic stress, transforming growth factor-beta, and the inflammatory cytokines tumor necrosis factor and interleukin-1 activate two extracellular signal-regulated kinase (ERK)-based signaling pathways: the stress-activated protein kinase (SAPK/JNK) pathway and the p38 pathway. Activated p38 phosphorylates transcription factors important in the regulation of cell growth and apoptosis, including activating transcription factor 2 (ATF2), Max, cAMP response element-binding protein-homologous protein/growth arrest DNA damage 153 (CHDP/GADD153). In turn, p38 lies downstream of the Rho family GTPases Cdc42Hs and Rac1, as well as at least three mitogen-activated protein kinase (MAPK)/ERK-kinases (MEKs): MAPK kinases-3, -6, and SAPK/ERK-kinase-1. Although many of the stimuli that activate p38 can also inhibit cell cycle progression, a clear-cut role for the p38 pathway in cell cycle regulation has not been established. Using a quantitative microinjection approach, we show here that Cdc42Hs, but not Rac1 or RhoA, can inhibit cell cycle progression at G1/S through a mechanism requiring activation of p38. These results suggest a novel role for Cdc42Hs in cell cycle inhibition. Furthermore, these results suggest that although both Cdc42Hs and Rac1 can activate p38 in situ, the effects of Cdc42Hs and Rac1 on cell cycle progression are, in fact, quite distinct.

3T3 Cells↗
PubMed1997

Characterization of adult alpha- and beta-globin genes in the zebrafish.

Developmental switching of hemoglobins (Hbs) occurs in most vertebrates, yet the cellular and molecular basis for this process remains elusive. The zebrafish is a new genetic and developmental system that can be used to study embryogenesis, and mutants with a variety of defects in hematopoiesis have recently been derived. To initiate our studies on Hb switching in this organism, we have characterized the globins expressed in the adult. Reversed-phase high performance liquid chromatography and mass spectrometric analyses of adult peripheral blood hemolysates showed that there are three major alpha globins and two beta globins in circulating erythroid cells. In addition, we have isolated and characterized zebrafish adult alpha- and beta-globin cDNA clones that encode some of these globins. High levels of alpha- and beta-globin gene expression were detected in adult erythroid cells, whereas embryonic erythroid cells expressed little, if any, of these RNAs. We have also shown that the alpha- and beta-globin genes are tightly linked on the same chromosome and are arrayed in a 3'-5' to 5'-3' configuration, respectively. The characterization of these genes and regulatory elements in this globin locus will provide insight into the process of globin gene transcription. With these reagents, future studies of Hb switching in zebrafish mutants with defective hematopoiesis will be possible.

Amino Acid Sequence↗
PubMed1997

Bipotential primitive-definitive hematopoietic progenitors in the vertebrate embryo.

Two regions of the vertebrate embryo, the blood islands and the dorsal lateral plate (DLP), participate in early hematopoietic development. In Xenopus, primitive erythrocytes are derived solely from the ventral blood islands (VBI), while definitive hematopoietic cells such as lymphocytes are derived from both VBI and DLP. We have utilized a transplantation technique to demonstrate in vivo that all hematopoietic cells (embryonic, fetal, or adult) originate from ventral mesoderm. Reciprocal grafts between VBI and DLP demonstrated that both regions are bipotential with respect to primitive and definitive hematopoiesis. Commitment of the VBI to primitive erythropoiesis and restriction of the DLP to definitive hematopoiesis occurs during neurula stages. Thus, hematopoietic development involves the induction of the blood program on the ventral axis of the embryo followed by environmentally regulated specification to the primitive or definitive lineages.

Animals↗
PubMed1997

Genetics of erythropoiesis: induced mutations in mice and zebrafish.

Production of red blood cells (erythropoiesis) in the vertebrate embryo is critical to its survival and subsequent development. As red cells are the first blood cells to appear in embryogenesis, their origin reflects commitment of mesoderm to an hematopoietic fate and provides an avenue by which to examine the development of the hematopoietic system, including the hematopoietic stem cell (HSC). We discuss the genetics of erythropoiesis as studied in two systems: the mouse and zebrafish (Danio rerio). In the mouse, targeted disruption has established several genes as essential at different stages of hematopoiesis or erythroid precursor cell maturation. In the zebrafish, numerous mutants displaying a wide range of phenotypes have been isolated, although the affected genes are unknown. In comparing mouse knockout and zebrafish mutant phenotypes, we propose a pathway for erythropoiesis that emphasizes the apparent similarity of the mutants and the complementary nature of investigation in the two species. We speculate that further genetic studies in mouse and zebrafish will identify the majority of essential genes and define a regulatory network for hematopoiesis in vertebrates.

Animals↗