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Biomedical subjects

U Lendahl

Publications and source records attributed to U Lendahl.

At least 91 records · Page 5Linked to original sources
PubMed1994

Thyroid abnormalities and hepatocellular carcinoma in mice transgenic for v-erbA.

The v-erbA oncogene consists of an avian retroviral gag gene fused to a mutated thyroid hormone receptor. To define better its role as an oncogene in mammals and its ability to function as a dominant negative transcription factor, transgenic mice expressing v-erbA ubiquitously were generated. The effects of v-erbA are pleiotropic, tissue-specific and dose dependent. Mice have breeding disorders, abnormal behavior, reduced adipose tissue, hypothyroidism with inappropriate TSH response, and enlarged seminal vesicles. This provides an animal model consistent with the proposal that v-ErbA functions as a dominant negative receptor by transcriptional interference or squelching of normal receptors or associated proteins. Finally, male animals develop hepatocellular carcinoma, demonstrating that v-erbA can promote neoplasia in mammals.

Adipose Tissue↗
PubMed1994

Expression of the neuroectodermal intermediate filament nestin in human melanomas.

Nestin is a newly identified intermediate filament expressed in proliferating neuronal progenitor cells, but not in the adult brain. Nestin expression reappears in many tumors of the central nervous system and has in human glioblastomas been associated with a high degree of malignancy. Because melanocytes are of neuroectodermal origin, we studied nestin expression in benign and malignant cells of the melanocytic lineage using Northern blot and immunohistochemical analyses. Nestin mRNA was detected in 24 of 34 metastatic melanomas and in 1 of 4 benign nevi, whereas the protein was expressed in 10 of 15 primary melanomas, in 29 of 34 metastatic tumors, and in 3 of 4 nevi. Neither normal melanocytes nor any of 4 basal cell carcinomas showed detectable levels of the protein. The high fraction of melanocytic tumors which express nestin, particularly the metastatic melanomas, suggests that nestin may be a useful marker for such malignancies. Furthermore, although no significant correlation between nestin expression and tumor malignancy was observed, the protein was most abundantly expressed in the infiltrating part of the tumors, indicating a possible involvement of nestin in tumor invasion.

Biomarkers, Tumor↗
PubMed1994

Lipopolysaccharide-dependent transactivation of the temporally regulated immunoglobulin heavy chain 3' enhancer.

To execute different biological functions, the expression pattern of immunoglobulin heavy chain genes (IgH) is altered during B lymphocyte differentiation. Early in B cell differentiation, it is assumed that the heavy chain promoter and the intragenic enhancer (E mu) ensure VDJ recombination. This leads to the expression of the immunoglobulin receptor on the cell surface. An additional strong enhancer in the far 3' end of the IgH locus has, however, prompted a re-evaluation of the regulation of immunoglobulin gene expression. To define the temporal and spatial regulation of the IgH 3' enhancer, transgenic mice harboring an enhancer-dependent reporter gene construct were generated. Here we demonstrate that IgH 3' enhancer activity is largely restricted to activated immunocompetent B cells. Furthermore, the enhancer can be transactivated following mitogen stimulation with lipopolysaccharide and 12-O-tetradecanoylphorbol 13-acetate. We propose a model whereby 3' enhancer activation is linked to the activation of resting immunocompetent B cells. The implications of the enhancer being active in late B lymphocyte differentiation, when heavy chain class switching occurs, are discussed.

Animals↗
PubMed1994

Colocalization of nestin and vimentin/desmin in skeletal muscle cells demonstrated by three-dimensional fluorescence digital imaging microscopy.

During skeletal muscle development three intermediate filament proteins are expressed: nestin, vimentin, and desmin. Vimentin and desmin belong to the class III intermediate filaments and are closely related to each other, whereas nestin is a more distantly related, class VI, intermediate filament. It was previously observed by conventional immunocytochemistry that the intracellular patterns of nestin, desmin, and vimentin appeared indistinguishable, despite nestin's more distant evolutionary relationship. We here extend this analysis by applying three-dimensional fluorescence digital imaging microscopy to compare the intracellular distribution of nestin with that of desmin, vimentin, actin, and tubulin in G6 human fetal skeletal muscle cells. We show that in vitro differentiation of G6 cells can produce an intermediate filament expression pattern similar to that observed during myogenesis in vivo, i.e., downregulation of vimentin but not of nestin and desmin during myotube maturation. The image analysis demonstrated that the degree of overlap between nestin and desmin/vimentin was very extensive in myoblasts and in multinucleate myotubes in all regions of the cells. In contrast, nestin did not colocalize with tubulin or actin in G6 myoblasts. In particular, nestin immunoreactivity was not detected at the microtubule-organizing center, and it was only sparsely observed at the cell periphery where actin stress fibers were seen. Our data lend further support to the notion that nestin interacts very closely with the two more distantly related class III intermediate filament proteins desmin and vimentin in the entire muscle cell, before and after myotube formation. A comparison of conserved amino acid residues in the different IFs suggest that charged amino acid residues in the alpha-helical rod domain may play a role in the interaction.

Amino Acid Sequence↗
PubMed1994

Independent regulatory elements in the nestin gene direct transgene expression to neural stem cells or muscle precursors.

Changes in intermediate filament gene expression occur at key steps in the differentiation of cell types in the mammalian CNS. Neuroepithelial stem cells express the intermediate filament protein nestin and down-regulate it sharply at the transition from proliferating stem cell to postmitotic neuron. Nestin is also expressed in muscle precursors but not in mature muscle cells. We show here that in transgenic mice, independent cell type-specific elements in the first and second introns of the nestin gene consistently direct reporter gene expression to developing muscle and neural precursors, respectively. The second intron contains an enhancer that functions in CNS stem cells, suggesting that there may be a single transcriptional mechanism regulating the CNS stem cell state. This enhancer is much less active in the PNS. The identification of these elements facilitates analysis of mechanisms controlling the switch in gene expression that occurs when muscle and brain precursors terminally differentiate.

Animals↗
PubMed1994

The novel Notch homologue mouse Notch 3 lacks specific epidermal growth factor-repeats and is expressed in proliferating neuroepithelium.

In Drosophila, the Notch gene is pivotal for cell fate decisions at many stages of development and, in particular, during the formation of the nervous system. Absence of Notch results in the generation of excessive numbers of neural cells at the expense of epidermal cells. Two previously identified mammalian Notch homologous encode all the principal features of the Drosophila gene, e.g. 36 EGF-repeats and 3 Notch/lin-12 repeats extracellularly and 6 intracellular cdc10/SWI6 repeats. We report here the characterisation of a third mammalian homologue, mouse Notch 3, which shares the same remarkable conservation relative to the Drosophila gene as the two previously identified homologues, but with three important distinctions. First, Notch 3 specifically lacks the equivalent of EGF-repeat 21; second, it lacks an EGF-repeat-sized region comprising parts of EGF-repeats 2 and 3; and third, it encodes a considerably shorter intracellular domain. The Notch 3 gene is expressed at high levels in proliferating neuroepithelium and expression is downregulated at later stages. The expression patterns of the Notch 1, 2 and 3 genes are quite distinct during central nervous system (CNS) development, and all possible combinations of expression, i.e. none, one, two, or all three genes, are seen, suggesting a combinatorial code of Notch function in mammals. Considering the predominantly early expression in CNS and its distinct structural features, the Notch 3 gene is likely to contribute significantly to vertebrate Notch function during CNS development.

Amino Acid Sequence↗
PubMed1994

Myofibers from Duchenne/Becker muscular dystrophy and myositis express the intermediate filament nestin.

The intermediate filament nestin is transiently expressed in developing skeletal muscle. In the present investigation, we analyzed by immunohistochemistry the presence of nestin, as well as vimentin and desmin, in skeletal muscle affected by two diseases characterized by various degrees of necrosis and muscle regeneration: Duchenne/Becker muscular dystrophy and myositis. Nestin-positive areas were found in all analyzed muscle biopsies of both diseases. The same areas were, in most cases, also positive for vimentin and stained more intensely for desmin than surrounding myofibers. Only nestin was found specifically in myopathic muscle fibers; vimentin was in addition present in muscle fibroblasts and desmin in all myofibers. The areas staining positive for nestin were typically basophilic, small-diameter myofibers, often with centrally located nuclei. With the interesting exception of a 73-year-old healthy control with abundant ring fibers, nestin was not detected in the muscle of healthy controls. The intracellular distribution of nestin in the myopathic muscle fibers, as well as in the ring fibers, was confined to the vicinity of Z-bands. The presence of nestin protein in myopathic regenerating areas and in ring fibers correlated more closely to the presence of desmin than to vimentin immunoreactivity. Our results suggest that nestin is specifically expressed in newly formed muscle fibers also during regeneration, and that nestin may serve as a useful marker of regenerating muscle fibers in pathological conditions.

Adolescent↗
PubMed1993

Transient expression of a human beta-actin promoter/lacZ gene introduced into mouse embryos correlates with a low degree of methylation.

We have analysed the correlation between expression and methylation for the human beta-actin promoter introduced into mouse embryos. The beta-actin promoter was fused to the reporter gene lacZ, and expression was analysed after pronuclear injection into fertilized mouse eggs. We analysed transient expression in in vitro cultured preimplantation embryos and expression after chromosomal integration in 5 independent lines of transgenic mice. The in vitro cultured preimplantation embryos expressed lacZ from the 2-cell to the blastocyst stages, and most abundantly at the morula stage. By increasing the amount of injected DNA, a larger proportion of embryos expressed lacZ. Embryos expressing lacZ in only a subset of the blastomeres were detected at all preimplantation stages. In contrast to the transient expression after injection, we have not detected lacZ expression in any of the 5 analysed lines of transgenic mice carrying the same construct. The lack of expression in transgenic mice correlates with hypermethylation of C residues in the vast majority of CG sequences in the integrated beta-actin/lacZ construct, whereas the injected construct was completely nonmethylated. We discuss methylation and other possible reasons for the observed differences in expression between injected and integrated copies of the beta-actin/lacZ construct and for lacZ expression in only a subset of blastomeres in preimplantation embryos.

Actins↗
PubMed1993

Motch A and motch B--two mouse Notch homologues coexpressed in a wide variety of tissues.

Notch is one of the neurogenic genes of Drosophila controlling the decision between ectodermal and neural fate for cells in the early embryo. We have used a polymerase chain reaction (PCR)-based strategy to identify cDNA clones representing two mouse homologues to the Drosophila Notch gene. One of the genes, Motch A, is the mouse orthologue to the previously cloned Notch genes in Xenopus, rat, and man. The other gene, Motch B, is more distantly related to the characterized vertebrate Notch genes, but of equal homology to the Drosophila Notch as is Motch A, and therefore represents a distinct branch of a vertebrate Notch gene family. The Motch A and Motch B branches probably arose by gene duplication early in vertebrate evolution. Both Motch A and Motch B retain the same principal structure, encode mRNAs of approximately 10 kilobases, are expressed during mouse embryogenesis, and have largely overlapping expression patterns in adult tissues. We discuss possible consequences of expressing two closely related Notch homologues in the same set of tissues in terms of cell-cell signaling and differentiation control.

Amino Acid Sequence↗
PubMed1993

Transient expression of the intermediate filament nestin during skeletal muscle development.

It has previously been established that skeletal muscle development is accompanied by changes in the composition of intermediate filaments: vimentin is expressed predominantly in myoblasts and desmin in adult myotubes. We show that the intermediate filament transitions during muscle development are more complex, and involve a transient expression of the recently discovered intermediate filament nestin. Nestin RNA is expressed predominantly early, in a biphasic pattern, and is markedly downregulated in adult rat muscle, whereas desmin RNA becomes more abundant throughout development. Nestin protein was found up to the postnatal myotube stage, where it colocalized with desmin in Z bands. The intracellular distribution of nestin, vimentin and desmin was analysed in the human myogenic cell line G6 before and after in vitro differentiation. Despite its more distant evolutionary and structural relationship to the other two intermediate filaments, nestin formed a cytoplasmic filamentous network indistinguishable from that of desmin and vimentin, both in undifferentiated myoblasts and after differentiation to multinuclear myotubes. In conclusion, our data suggest that nestin is an integrated component of the dynamic intermediate filament network during muscle development and that nestin copolymerizes with desmin and vimentin at stages of coexpression.

Animals↗
PubMed1992

Expression of the class VI intermediate filament nestin in human central nervous system tumors.

Tumor cells of a particular tissue may show a pattern of gene expression characteristic of the precursor cells of this tissue. To test this proposition for tumors of the central nervous system (CNS) we have used immunohistochemistry to analyze the expression of nestin in primary human CNS tumors and corresponding nonneoplastic brain tissue. Nestin defines a recently discovered sixth class of intermediate filament proteins and in the rat is expressed predominantly in CNS stem cells. In the adult nonneoplastic human brain we have detected only nestin expression in occasional endothelial cells. In contrast, a variety of primary CNS tumors contained substantially elevated nestin levels. The nestin-positive cells in the tumor tissue were tumor cells and/or endothelial cells. Glioblastomas expressed higher nestin levels than less malignant gliomas. This may indicate a correlation between nestin expression and malignancy within the glioma tumor group. In the primitive neuroectodermal class of tumors we observed both nestin-expressing and nonexpressing tumors, suggesting that nestin expression could be used to further characterize this complex and heterogeneous tumor group. Nine metastatic carcinomas were studied, and none showed nestin immunoreactivity in tumor cells. In conclusion, our data support the notion that primary CNS tumors share gene expression patterns with primitive, undifferentiated CNS cells and that nestin, like other intermediate filaments, may be useful in tumor diagnosis.

Adult↗
PubMed1992

Characterization of the human nestin gene reveals a close evolutionary relationship to neurofilaments.

Multipotential stem cells in the neural tube give rise to the different neuronal cell types found in the brain. Abrupt changes in intermediate filament gene expression accompany this transition out of the precursor state: transcription of the intermediate filament nestin is replaced by that of the neurofilaments. In order to identify human neural precursor cells, and to learn more about the evolution of the intermediate filaments expressed in the central nervous system, we have isolated the human nestin gene. Despite considerable divergence between the human and rat nestin genes, in particular in the repetitive parts of the carboxy-terminal region, the positions of the introns are perfectly conserved. Two of the three intron positions are also shared by the neurofilaments, but not by other classes of intermediate filaments. This implies that nestin and the neurofilaments had a common ancestor after branching off from the other classes of intermediate filaments, and that nestin separated from the neurofilament branch before the different neurofilament genes diverged. The characterization of human nestin also facilitates the identification of human multipotential neural precursor cells. This will be of importance for central nervous system (CNS) tumor diagnosis and transplant-based clinical approaches to human neurodegenerative diseases.

Amino Acid Sequence↗
PubMed1991

Differentiation and heterogeneity in T-antigen immortalized precursor cell lines from mouse cerebellum.

Recently, various techniques have been developed to transfer oncogenes into brain cells in order to generate immortalized neural cell lines. It is of interest to establish how well such cell lines reflect their cellular origin. Here we report the characterization of sixteen cell lines from mouse cerebellum and, as a control, six cell lines from skin. Lines were established by immortalizing postnatal primary cell cultures with a retrovirus carrying a modified temperature-sensitive variant of SV40 large T antigen. The cell lines reflect many properties of the cell type from which they were derived. All of the sixteen cerebellar lines expressed one or more markers of the neural precursor cells, namely, nestin and epitopes for NG2 and A2B5. In contrast, none of the six skin lines expressed neural precursor markers. Both types of cell lines expressed vimentin and fibronectin. Differentiation occurred in some of the cerebellar lines and was enhanced in defined medium. A small percentage of cerebellar cells, usually less than 5%, was positive for a marker of differentiation, e.g., glial fibrillary acidic protein (GFAP), galactocerebroside (GalC), or L1. Expression of GFAP colocalized with that of nestin at varying levels of intensity, indicating a gradual replacement of nestin by GFAP in the cytoskeleton. Both the cells positive for precursor markers and those positive for differentiation markers tended to be located in clusters, suggesting that stochastic processes or cell-cell interactions are important for the determination of the fate of cells within a clonal cell line in vitro. The degree of differentiation seemed to correlate with a shift from serum-containing to defined medium, but not with a shift from the permissive to the nonpermissive temperature for T antigen expression. The immortalization approach described here thus allows the establishment of cell lines which are "captured" in the precursor state of the developing mouse neuroepithelium.

Animals↗
PubMed1990

CNS stem cells express a new class of intermediate filament protein.

Multipotential CNS stem cells receive and implement instructions governing differentiation to diverse neuronal and glial fates. Exploration of the mechanisms generating the many cell types of the brain depends crucially on markers identifying the stem cell state. We describe a gene whose expression distinguishes the stem cells from the more differentiated cells in the neural tube. This gene was named nestin because it is specifically expressed in neuroepithelial stem cells. The predicted amino acid sequence of the nestin gene product shows that nestin defines a distinct sixth class of intermediate filament protein. These observations extend a model in which transitions in intermediate filament gene expression reflect major steps in the pathway of neural differentiation.

Amino Acid Sequence↗
PubMed1990

The Balbiani ring 3 gene in Chironomus tentans has a diverged repetitive structure split by many introns.

A set of approximately 15 secretory proteins is synthesized by the salivary gland cells in the midge Chironomus tentans. These proteins are secreted but do not form insoluble fibers until they are transported out of the gland lumen. A Balbiani ring (BR) gene family consisting of four genes (BR1, BR2.1, BR2.2 and BR6) have previously been shown to encode four of these proteins, sp-I a to d, with relative molecular weights of 1 x 10(6). Each BR gene contains an uninterrupted block in which about 100 repeats are tandemly arranged. The repeats are virtually identical and efficient homogenization mechanisms must operate within each block. Here we describe a new BR gene, the BR3 gene, which according to structural similarities may belong to the BR gene family, but at the same time exhibits a strikingly different structure. The gene encodes a 10.9 kb transcript that contains 38 introns and is spliced into a 5.5 kb mRNA. The mRNA is translated into a cysteine-rich 185 kDa major component of the gland secretion. The coding sequence in the gene is built from diverged repeats in which mainly the cysteine codons are preserved and the sequence is split by the introns into 17 to 678-bp long exons. The introns are located at defined positions in relation to the repeat structure. In sharp contrast to the uninterrupted array of identical repeats in the BR1-BR6 genes, the repeats in the BR3 gene are not efficiently homogenized and have diverged extensively from each other. We propose that the splitting of the repeat structure into variable sized exons prevents homogenizations dependent on unequal aligning of homologous sequences.

Amino Acid Sequence↗
PubMed1990

A new member of a secretory protein gene family in the dipteran Chironomus tentans has a variant repeat structure.

We describe the structure of a gene expressed in the salivary gland cells of the dipteran Chironomus tentans and show that it encodes 1 of the approximately 15 secretory proteins exported by the gland cells. This sp115,140 gene consists of approximately 65 copies of a 42-bp sequence in a central uninterrupted core block, surrounded by short nonrepetitive regions. The repeats within the gene are highly similar to each other, but divergent repeats are present in a pattern which suggests that the repeat structure has been remodeled during evolution. The 42-bp repeat in the gene is a simple variant of the more complex repeat unit present in the Balbiani ring genes, encoding four of the other secretory proteins. The structure of the sp115,140 gene suggests that related repeat structures have evolved from a common origin and resulted in the set of genes whose secretory proteins interact in the assembly of the secreted protein fibers.

Amino Acid Sequence↗