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N Benvenisty

Publications and source records attributed to N Benvenisty.

At least 19 recordsLinked to original sources
PubMed2006

Factors involved in self-renewal and pluripotency of embryonic stem cells.

Embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass of blastocyst stage embryos. These cells possess two unique characteristics: an indefinite self-renewal capacity and pluripotency, the ability to differentiate to cells from the three germ layers. Both human and mouse ES cells are currently at the center of intensive research. One of the burning issues in this research is the way in which these cells remain undifferentiated and maintain their pluripotency. In the past years, data has accumulated concerning the pathways responsible for the unique phenotype of these cells, in both human and mouse. This paper will review the main extrinsic factors and intrinsic transcriptional pathways currently implicated in the self-renewal and pluripotency of ES cells.

Animals↗
PubMed2001

Induced neuronal differentiation of human embryonic stem cells.

Human embryonic stem (ES) cells are pluripotent cells capable of forming differentiated embryoid bodies (EBs) in culture. We examined the ability of growth factors under controlled conditions to increase the number of human ES cell-derived neurons. Retinoic acid (RA) and nerve growth factor (betaNGF) were found to be potent enhancers of neuronal differentiation, eliciting extensive outgrowth of processes and the expression of neuron-specific molecules. Our findings show that human ES cells have great potential to become an unlimited cell source for neurons in culture. These cells may then be used in transplantation therapies for neural pathologies.

Antineoplastic Agents↗
PubMed2001

A DNA microarray screen for genes involved in c-MYC and N-MYC oncogenesis in human tumors.

MYC proto-oncogenes play a major role in various types of human tumors. The products of these genes are transcription factors that bind to specific sequences and activate the expression of target genes. Identifying these target genes and their downstream effectors is a crucial step in understanding and preventing MYC induced oncogenesis. Until now, most of the efforts to identify such genes were performed by analysing in vitro systems whose relevance to the malignant process in vivo remains unclear. We aimed at identifying genes that play a major role in the malignant process of MYC induced carcinogenesis. Thus, we analysed the expression profiles of human MYC induced tumors and compared them to similar, non-MYC tumors. Moreover, we looked for the common characteristics of different types of MYC induced tumors. We identified several genes, most of them involved in cell cycle regulation, that are over expressed in MYC induced lymphomas as well as MYC induced neuronal-like tumors. In order to determine whether MYC induced oncogenesis is similar in human and in the mouse model system, we analysed the expression of the identified genes in cells derived from transgenic mice tumors. We also present the distribution of MYC putative binding sites in the regulatory sequences of the genes identified in our analysis. This analysis pointed to two genes (E2F1 and TSC2) as candidates to be targets of Myc activity. We thus further analysed the expression of these genes in the tumor cell lines, and examined the plausibility that elements in their promoter bind the Myc protein. Our data points to several genes that may be involved in c-MYC and N-MYC induced tumors and to two genes that may be targets for MYC activity.

Animals↗
PubMed2001

Establishment of human embryonic stem cell-transfected clones carrying a marker for undifferentiated cells.

Human embryonic stem (ES) cells are pluripotent cell lines that have been derived from the inner cell mass (ICM) of blastocyst stage embryos [1--3]. They are characterized by their ability to be propagated indefinitely in culture as undifferentiated cells with a normal karyotype and can be induced to differentiate in vitro into various cell types [1, 2, 4-- 6]. Thus, human ES cells promise to serve as an unlimited cell source for transplantation. However, these unique cell lines tend to spontaneously differentiate in culture and therefore are difficult to maintain. Furthermore, colonies may contain several cell types and may be composed of cells other than pluripotent cells [1, 2, 6]. In order to overcome these difficulties and establish lines of cells with an undifferentiated phenotype, we have introduced a reporter gene that is regulated by a promoter of an ES cell-enriched gene into the cells. For the introduction of DNA into human ES cells, we have established a specific transfection protocol that is different from the one used for murine ES cells. Human ES cells were transfected with enhanced green fluorescence protein (EGFP), under the control of murine Rex1 promoter. The transfected cells show high levels of GFP expression when in an undifferentiated state. As the cells differentiate, this expression is dramatically reduced in monolayer cultures as well as in the primitive endoderm of early stage (simple) embryoid bodies (EBs) and in mature EBs. The undifferentiated cells expressing GFP can be analyzed and sorted by using a Fluorescence Activated Cell Sorter (FACS). Thus, we have established lines of human ES cells in which only undifferentiated cells are fluorescent, and these cells can be followed and selected for in culture. We also propose that the pluripotent nature of the culture is made evident by the ability of the homogeneous cell population to form EBs. The ability to efficiently transfect human ES cells will provide the means to study and manipulate these cells for the purpose of basic and applied research.

Blastocyst↗
PubMed2001

Involvement of branched-chain amino acid aminotransferases in the production of fusel alcohols during fermentation in yeast.

Organoleptic compounds produced by yeast during the fermentation of wort have a great impact on beer smell and taste. Among them, fusel alcohols are the major abundant volatile compounds. The availability of Saccharomyces cerevisiae mutants in which the genes coding for the two branched-chain amino acid aminotransferases have been deleted offers the possibility of further defining the role of these enzymes in the formation of higher alcohols. Comparing the production profiles of different strains, it is clear that they are not all influenced in the same way by branched-chain amino acid aminotransferase mutations. First of all, as propanol is synthesised from alpha-ketobutyrate, the first metabolic intermediate in the anabolic pathway of isoleucine, neither the eca39 nor eca40 mutations have any effect on the production of this higher alcohol. On the other hand, it can be concluded that the eca40 mutation has a drastic effect on the production of isobutanol. To a certain extent, the same conclusion can be made for the production of active amyl alcohol and isoamyl alcohol, although the results suggest that another route could lead to the formation of these two higher alcohols.

1-Propanol↗
PubMed2000

Effects of eight growth factors on the differentiation of cells derived from human embryonic stem cells.

Human embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass of in vitro fertilized human blastocysts. We examined the potential of eight growth factors [basic fibroblast growth factor (bFGF), transforming growth factor beta1 (TGF-beta1), activin-A, bone morphogenic protein 4 (BMP-4), hepatocyte growth factor (HGF), epidermal growth factor (EGF), beta nerve growth factor (betaNGF), and retinoic acid] to direct the differentiation of human ES-derived cells in vitro. We show that human ES cells that have initiated development as aggregates (embryoid bodies) express a receptor for each of these factors, and that their effects are evident by differentiation into cells with different epithelial or mesenchymal morphologies. Differentiation of the cells was assayed by expression of 24 cell-specific molecular markers that cover all embryonic germ layers and 11 different tissues. Each growth factor has a unique effect that may result from directed differentiation and/or cell selection, and we can divide the overall effects of the factors into three categories: growth factors (Activin-A and TGFbeta1) that mainly induce mesodermal cells; factors (retinoic acid, EGF, BMP-4, and bFGF) that activate ectodermal and mesodermal markers; and factors (NGF and HGF) that allow differentiation into the three embryonic germ layers, including endoderm. None of the growth factors directs differentiation exclusively to one cell type. This analysis sets the stage for directing differentiation of human ES cells in culture and indicates that multiple human cell types may be enriched in vitro by specific factors.

Cell Differentiation↗
PubMed2000

Hereditary cancer and developmental abnormalities.

About 1% of all cancers are hereditary, caused by germ-line mutations in specific cancer-related genes. More than 25 different hereditary cancer syndromes are known, most of them involving mutations in tumor suppressor genes. These genes, which are related to cellular proliferation, might also be involved in differentiation. Hence, the phenotype of hereditary cancer syndromes might include developmental abnormalities, in addition to cancer predisposition. The information summarized here indicates that developmental phenotypes appear in both human patients and mouse models of the various hereditary cancer syndromes. These developmental abnormalities, which involve a variety of tissues and organs, usually lead to embryonic malformation that prevents the birth of viable homozygous offspring, but can also be detected in heterozygotes. In some of the syndromes a correlation exists between tumor types and developmentally affected tissues. Comparison of mice and human phenotypes from both the cancer and the developmental aspects indicates that many of the mouse models mimic the human syndromes. Our analysis indicates that most tumor suppressor genes participate not only in the regulation of cell proliferation, but also in differentiation and embryogenesis.

Animals↗
PubMed2000

Differentiation of human embryonic stem cells into embryoid bodies compromising the three embryonic germ layers.

BACKGROUND: Embryonic stem (ES) cells are lines of cells that are isolated from blastocysts. The murine ES cells were demonstrated to be true pluripotent cells as they differentiate into all embryonic lineages. Yet, in vitro differentiation of rhesus ES cells was somewhat inconsistent and disorganized. The recent isolation of human ES cells calls for exploring their pluripotential nature. MATERIALS AND METHODS: Human ES cells were grown in suspension to induce their differentiation into embryoid bodies (EBs). The differentiation status of the human ES cells and EBs was analyzed by following the expression pattern of several lineage-specific molecular markers using reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization. RESULTS: Here we report the induction in vitro of cystic embryoid bodies from human ES cells. Our findings demonstrate induction of expression of cell-specific genes during differentiation of the human ES cells into EBs. In the human EBs, we could show a characteristic regional expression of embryonic markers specific to different cellular lineages, namely, zeta-globin (mesoderm), neurofilament 68Kd (ectoderm), and alpha-fetoprotein (endoderm). Moreover, we present a synchronously pulsing embryoid body that expresses the myocardium marker alpha-cardiac actin. In addition, dissociating the embryoid bodies and plating the cells as monolayers results in multiple morphologies, among them cells with neuronal appearance that express neurofilament 68Kd chain. CONCLUSION: Human ES cells can reproducibly differentiate in vitro into EBs comprising the three embryonic germ layers. The ability to induce formation of human embryoid bodies that contain cells of neuronal, hematopoietic and cardiac origins will be useful in studying early human embryonic development as well as in transplantation medicine.

Animals↗
PubMed1999

Involvement of branched-chain amino acid aminotransferase (Bcat1/Eca39) in apoptosis.

The branched-chain amino acid aminotransferase, Bcat1/Eca39, catalyzes the first step of branched-chain amino acid catabolism. Bcat1/Eca39 was originally isolated from a c-myc-induced tumor and was proven to be a direct target for c-Myc regulation. The gene is highly conserved in evolution and disruption of its yeast homolog affects cell growth. To assess the role of Bcat1/Eca39 in mammalian cells, we overexpressed Bcat1/Eca39 in murine cells and studied effects on cell growth. Overexpression of Bcat1/Eca39 had no apparent effect on the proliferation of cells grown with high serum concentrations, but under serum deprivation conditions, led to a decrease in cell viability. Cell death under these conditions displayed apoptotic features. The branched-chain keto acid, alpha-ketoisocaproate, a metabolite of leucine catabolism produced by BCAT1/ECA39, was previously found to inhibit cell growth. We show that alpha-ketoisocaproate can induce rapid apoptotic cell death. This observation suggests that the growth inhibitory effect of BCAT1/ECA39 and its apoptosis promoting effect may be mediated by the levels of the products of BCAT1/ECA39 activity, namely, branched-chain keto acids.

3T3 Cells↗
PubMed1999

The tmp gene, encoding a membrane protein, is a c-Myc target with a tumorigenic activity.

The c-Myc oncoprotein induces cell proliferation and transformation through its activity as a transcription factor. Uncovering the genes regulated by c-Myc is an essential step for understanding these processes. We recently isolated the tumor-associated membrane protein gene, Tmp, from a c-myc-induced mouse brain tumor. Here we show that Tmp is specifically highly expressed in mammary tumors and T-cell lymphomas which develop in c-myc transgenic mice, suggesting that Tmp expression is a general characteristic of c-Myc-induced tumors. In addition, Tmp expression is induced upon serum stimulation of fibroblasts as shown in a time course closely correlated with c-myc expression. We have isolated the Tmp promoter region and identified a putative c-Myc binding element, CACGTG, located in the first intron of the gene. We show here that constructs containing the Tmp regulatory region fused to a reporter gene are activated by c-Myc through this CACGTG element and that the c-Myc-Max protein complex can bind to this element. Moreover, an inducible form of c-Myc, the MycER fusion protein, can activate the endogenous Tmp gene. We also show that Tmp-overexpressing fibroblasts induce rapidly growing tumors when injected into nude mice, suggesting that Tmp may possess a tumorigenic activity. Thus, TMP, a member of a novel family of membrane glycoproteins with a suggested role in cellular contact, is a c-Myc target and is possibly involved in c-Myc-induced transformation.

Animals↗
PubMed1998

Involvement of Myc targets in c-myc and N-myc induced human tumors.

The myc proto-oncogenes are transcription factors that directly regulate the expression of other genes, by binding to the specific DNA sequence, CACGTG. Among the target genes for c-Myc regulation are ECA39, p53, ornithine decarboxylase (ODC), alpha-prothymosin and Cdc25A. In this study we examined the involvement of c-Myc target genes in human oncogenesis induced by c-myc or N-myc. In MCF-7 breast cancer cells, the induction of c-myc expression by estrogen was followed by the induction of all the Myc targets that we examined, indicating that those genes can serve as c-Myc targets in human oncogenesis. Moreover, in breast tumors exhibiting c-myc overexpression, several Myc targets were also overexpressed. A clear correlation between the expression of c-myc and its targets was also detected in Burkitt's lymphomas, which involve a specific translocation of c-myc gene, but not in other lymphoma cells. Yet, in cells derived from a neuronal origin the pattern of expression of Myc targets was more complex. In a neuroepithelioma cell line that overexpresses c-myc, only some targets were expressed. In addition in neuroblastomas, in which N-myc is amplified and overexpressed, only ODC was overexpressed in all cell lines, while all other target genes were expressed in only some of the cell lines. The more complex expression pattern found for the Myc targets in neuroblastomas suggests that genes that were identified originally as targets for c-Myc regulation may be regulated by N-Myc, but other cell specific factors are also needed for transcription of the target genes.

Breast Neoplasms↗
PubMed1998

Chromosomal mapping of Tmp (Emp1), Xmp (Emp2), and Ymp (Emp3), genes encoding membrane proteins related to Pmp22.

We have recently characterized a novel mammalian gene family, encoding membrane glycoproteins with four trans-membrane domains. This gene family includes the previously studied PMP22, which is involved in the Charcot-Marie-Tooth neuropathy, and three novel genes: TMP, XMP, and YMP (HGMW-approved symbols EMP1, EMP2 and EMP3, respectively). The Tmp (tumor-associated membrane protein) gene was isolated from a c-myc induced mouse brain tumor and is expressed in several highly proliferative cell types. We have now isolated cDNAs of the mouse Xmp and Ymp genes and determined the chromosomal localization of mouse Tmp, Xmp, and Ymp. Tmp was mapped to mouse chromosome 6, Xmp was mapped to chromosome 16, and Ymp was mapped to chromosome 7. Tmp and Ymp map to paralogous chromosomal regions, whereas Xmp maps to a chromosomal region that is putatively paralogous to a region on chromosome 11, to which Pmp22 was previously mapped. These data suggest that this family of membrane glycoproteins evolved as a result of chromosomal duplications.

Amino Acid Sequence↗
PubMed1998

Characterization of a branched-chain amino-acid aminotransferase from Schizosaccharomyces pombe.

The Saccharomyces cerevisiae genes for the cytosolic and mitochondrial branched-chain amino-acid aminotransferases (BCAT) were isolated recently. These genes show significant homology to mammalian ECA39, originally isolated as a gene regulated by the c-myc oncogene. We now report the isolation of the Schizosaccharomyces pombe eca39/BCAT gene. The S. pombe protein shows 47-52% identity to other eukaryotic BCAT proteins isolated from S. cerevisiae, nematode, mouse and man. A genetic growth assay for BCAT activity was established using an S. cerevisiae strain disrupted in both BCAT isoenzymes. Consequently, the activity of the S. pombe BCAT was demonstrated by genetic and biochemical means. Possible applications of BCAT-encoding genes as selection markers in yeast transformation are proposed.

Amino Acid Sequence↗
PubMed1998

Computer analysis of the entire budding yeast genome for putative targets of the GCN4 transcription factor.

The completion of the yeast genome project enables an analysis of various phenomena for a whole eukaryotic genome. We aimed at characterizing a full spectrum of target genes for a transcription activator, and specifically characterized putative targets for GCN4 in the budding yeast. The results suggest that about 1% of the genes are regulated by GCN4 and that these genes code for proteins involved in amino-acid and nucleotide metabolism. Our analysis proposes that, when enough data about the binding nature of a transcription factor exists, it is possible to identify its putative targets and also to try and assign a physiological role for this transcription factor.

Binding Sites↗
PubMed1997

Involvement of hepatocyte nuclear factor 3 in endoderm differentiation of embryonic stem cells.

The transcription factors of the hepatocyte nuclear factor 3 (HNF3) family, which are active in the liver, are expressed early during endoderm differentiation. To study their involvement in early murine development, we examined their role in embryonic stem (ES) cells. HNF3alpha or HNF3beta mRNA transcripts were not detected in ES cells before differentiation, and only low levels of HNF3beta mRNA were detected at a late stage of differentiation of ES cells to embryoid bodies (EB) (20 days after induction of differentiation). To examine the consequences of overexpressing HNF3alpha or -beta in ES cells, we transfected the two genes into these cells and determined the levels of expression of tissue-specific genes during EB differentiation. Specifically, we examined expression of albumin, cystic fibrosis transmembrane conductance regulator (CFTR), phosphoenolpyruvate carboxykinase (PEPCK), alpha1-antitrypsin, transthyretin, zeta-globin, and neurofilament 68kd as markers for different cell lineages. Overexpression of HNF3beta (and to a lesser extent of HNF3alpha) induced the expression of genes associated with endodermal lineage, namely, the genes for CFTR and albumin, but did not induce the expression of genes involved in late endoderm differentiation, such as the genes for PEPCK and alpha1-antitrypsin. Moreover, expression of HNF1beta was highly induced in HNF3-overexpressing cells, while expression of HNF1alpha and HNF4 was only mildly induced in these cells. Therefore, HNF3alpha and -beta seem to be involved in early endoderm differentiation of ES cells and together with other developmental factors are apparently needed for the induction of the endodermal lineage in vivo.

Animals↗
PubMed1996

Identification of differentially expressed genes during hepatocytes development and characterization of their prenatal hormonal induction.

Upon birth, the liver acquires new functions as a result of the initiation of expression of key enzymes. One example is the initiation of gluconeogenesis which depends on the induced appearance of phosphoenolpyruvate carboxykinase (P-pyruvate-CK) at birth. To characterize other genes that undergo such regulation, a differential screening was performed on a cDNA library from well-differentiated hepatoma cells. The pattern of tissue-specific and developmental-specific expression was determined for seven genes. Three clones, out of which two encode for the known genes alcohol dehydrogenase class I (ADH) and phenylalanine 4-monooxygenase (PAH) and a new gene (clone 116-3), exhibited a pattern of expression similar to that of the P-pyruvate-CK gene, i.e. their expression was liver and kidney specific and induced in the liver upon birth. Determination of the sequence of clone 116-3 revealed that it belonged to the UDP-glucuronosyltransferases type 2 (UGT2) family and thus was named UGT2B-rH4. To examine whether expression of the various genes could be prematurely induced by hormones in the fetal liver, either high levels of cAMP or low levels of insulin were induced in utero. The results demonstrated that cAMP induced a marked expression only of the genes for P-pyruvate-CK and ADH but not of those for PAH or UGT2B-rH4, while insulin deficiency induced premature expression of all four genes. We suggest that a set of genes whose expression is specifically induced in the liver upon birth can be prematurely induced by the hormones in utero.

Alcohol Dehydrogenase↗
PubMed1996

Characterization of a tumor-associated gene, a member of a novel family of genes encoding membrane glycoproteins.

To isolate genes involved in tumor formation and in embryogenesis, a subtracted cDNA library was constructed from a c-myc-induced mouse brain tumor. A gene isolated in this screen, named TMP (tumor-associated membrane protein), codes for a putative glycoprotein with four transmembrane domains. The TMP gene was found to be highly expressed in brain tumor cells but not in normal brain. It is also expressed at high levels in undifferentiated embryonic stem cells, but markedly down-regulated in these cells after their differentiation into embryoid bodies. The TMP amino acid sequence bears high homology to the growth arrest specific protein PMP22/GAS-3, which is involved in several human peripheral neuropathies. The expression patterns of the TMP and PMP22 genes in NIH-3T3 fibroblasts were compared at different proliferation states. The results suggest an inverse pattern of expression for the two homologs, TMP expression being high during cell proliferation and PMP22 expression being high during growth arrest. To further characterize the TMP gene we have isolated its human homolog and examined its expression in embryonic and adult tissues. In our search for human sequences homologous to TMP and PMP22, we identified two new genes which we have named XMP and YMP. Thus, we present a novel family of membrane glycoproteins, one member of which is closely associated with proliferation and another with growth arrest.

3T3 Cells↗