Biomedical subjects

F Rieger

Publications and source records attributed to F Rieger.

At least 37 records · Page 2Linked to original sources

PubMed1998

[Endogenous retroviral sequences analogous to that of the new retrovirus MSRV associated with multiple sclerosis (part 1)].

Multiple sclerosis (MS) is still of unknown origin and may involve autoimmune, genetic and viral components in a pathogenic sequence whose relative importance is yet to be determined. A peptide, isolated from the cerebrospinal fluid of MS patients, is similar to a fragment of the pol protein reverse transcriptase (RT) of the newly reported MSRV retrovirus. The 700 amino acid sequence of MSRV-RT is closely related to a novel human retroviral-like sequences. We also identified a gag-like sequence upstream of this human genomic RT-like sequence, which allowed us to identify altogether 4,000 nucleotides, possibly coding for an endogenous retroviruses. Homologous sequences found in other locations in the human genome seem to characterize a new family of retroviral endogenous sequences, which may be of relevance to multiple sclerosis.

Amino Acid Sequence↗

PubMed1998

Endogenous retroviruses and multiple sclerosis. II. HERV-7q.

The search for new endogenous retroviral sequences, on the basis of sequence homologies with the pol gene of the recently reported multiple sclerosis associated retrovirus (MSRV), allowed us to identify a full length endogenous retrovirus sequence located on the long arm of human chromosome 7. This retrovirus, HERV-7q, includes in its env region, within a single 1,620 bp open reading frame, a 664 bp domain almost identical to a 3' non-coding region of the rab7 gene. Transcripts encompassing both the env and the 3' LTR regions of HERV-7q have already been identified as expressed sequence tags, suggesting that this env-like gene might code for a 538 amino acid long deduced protein.

Amino Acid Sequence↗

PubMed1998

Distinct location and prevalence of alpha-, beta-catenins and gamma-catenin/plakoglobin in developing and denervated skeletal muscle.

We studied the distribution of alpha-catenin, beta-catenin and gamma-catenin/plakoglobin in developing, adult and denervated mouse skeletal muscle. During primary myogenesis, all three catenins present a subsarcolemmal distribution within primary myotubes. During secondary myogenesis they accumulate at myotube-myotube contacts. In contrast to the other catenins, gamma-catenin is strongly expressed in the sarcoplasm. In adult muscle, all three catenins are localized on the presynaptic elements of the neuromuscular junction. In denervated muscles, alpha- and beta-catenins are upregulated like N- and M-cadherin, while the levels of gamma-catenin/plakoglobin remain unchanged. The developmental changes in localization and regulation of alpha- and beta-catenins in muscle compared to gamma-catenin/plakoglobin are suggestive of a privileged association of alpha- and beta-catenins with N- and M-cadherins, while gamma-catenin/plakoglobin appears to be expressed quite independently and must assume a different role during myogenesis.

Animals↗

PubMed1998

The peripheral nerve and the neuromuscular junction are affected in the tenascin-C-deficient mouse.

A thorough examination of the structure and plasticity of the neuromuscular system was performed in tenascin-C mutant mice deficient in tenascin-C. The study of the peripheral nerve revealed a number of abnormal features. In the motor nerve, numerous unmyelinated and myelinated fibers with degraded myelin were present. Schwann cell processes often enclosed degenerative terminals. Transgene (beta-galactosidase) expression analyzed at the ultrastructural level was found to be unequally distributed in the mutant's neuromuscular tissues. At the NMJ, preterminal disorganization was prevalent. Some axon terminals exhibited abnormal overgrowth. A surprising lack of beta-galactosidase expression at some cellular sites known to possess tenascin-C in wild type mice correlated best with marked changes in the cytoarchitecture of the peripheral nerve and NMJ. In some other -but not all- cellular sites which normally express the molecule, immunofluorescence analysis suggested the presence of significant but low levels of tenascin-C-like immunoreactivity together with beta-galactosidase expression. Messenger RNA detection by RT-PCR confirmed the presence of low amounts of tenascin-C mRNA in skeletal muscle suggesting that the mice deficient in tenascin-C are not complete knock-outs of this gene, but low-expression mutants. Following in vivo injections of botulinum type-A toxin, we observed a greatly reduced sprouting response of the motor nerves in tenascin-C mutant mice. We also observed that N-CAM and beta-catenin were overexpressed in the mutant. Our results suggest that tenascin-C is involved both in stabilization and in plasticity of the NMJ.

Animals↗

PubMed1998

Case report: DNA fragmentation in glial cells in a cerebral biopsy from a multiple sclerosis patient.

Multiple sclerosis is characterized by myelin destruction and oligodendrocyte loss. The neuropathological hallmark of the disease is the presence of demyelinated plaques in the central nervous system. We have recently found a gliotoxic factor in MS cerebrospinal fluid which induces programmed cell death in vitro, in glial cells. Here we show DNA fragmentation and glial cell death in biopsy samples, obtained from a patient who underwent surgery with suspicion of tumor, and whose disease record, including brain autopsy, demonstrated an active multiple sclerosis. We used the in situ TUNEL technique, a method which sensitively detects the DNA fragmentation accompanying programmed cell death in tissue sections, and compatible with classical fixation techniques. We found intense DNA fragmentation in nuclei of glial cells at-or very near-to the site of demyelination. A double labeling technique showed that glial fibrillary associated protein positive astrocytes may undergo programmed cell death in multiple sclerosis.

Astrocytes↗

PubMed1998

An endogenous retrovirus with nucleic acid sequences similar to those of the multiple sclerosis associated retrovirus at the human T-cell receptor alpha, delta gene locus.

Retroviruses are suspected to be involved in the pathogenesis of autoimmune diseases, such as multiple sclerosis (MS). Here, we describe a complete cartography of a novel human endogenous retroviral sequence with a pol domain which shares a high homology with the pol sequence of the multiple sclerosis associated retrovirus (MSRV). Since this new endogenous retroviral sequence is located in the close vicinity of the locus of the human gene coding for the T-cell receptor (TcR) alpha and delta chains on chromosome 14, it could be of potential interest for the understanding of MS pathogenesis.

Amino Acid Sequence↗

PubMed1997

Brain-derived neurotrophic factor fails to arrest neuromuscular disorders in the paralysé mouse mutant, a model of motoneuron disease.

Several new neurotrophic factors have been recently identified and shown to prevent motoneuron death in vitro and in vivo. One such agent is brain-derived neurotrophic factor (BDNF). In this study, we tested BDNF on an animal model of early-onset motoneuron disease: the paralysé mouse mutant, characterized by a progressive skeletal muscle atrophy and the loss of 30-35% of spinal lumbar motoneurons between the first and second week post-natal. The results show that subcutaneous injections of 1 or 10 mg/kg BDNF did not have any significant effect in increasing the mean survival time of mutant mice or in preventing the loss of motor function and total body weight in paralysé mice. The weight and choline acetyltransferase activity of specific muscles and the number of motoneurons in the spinal cords were identical in BDNF-treated and placebo-injected paralysé mice. These results suggest that BDNF does not act on the disease process in paralysé mice in the conditions we used. By contrast, BDNF has previously been shown to partially prevent the loss of motor function in the wobbler mouse, a suggested model of later-onset motoneuron disease. Taken together these findings suggest that BDNF acts differently on early and late-onset motoneuron diseases. It is however possible that treatment of paralysé mice with BDNF or combinations of different neurotrophic factors prior to the phenotypical expression of the paralysé mutation may prevent the loss of motor function and motoneurons in mutant mice.

Animals↗

PubMed1997

Gliotoxicity, reverse transcriptase activity and retroviral RNA in monocyte/macrophage culture supernatants from patients with multiple sclerosis.

In investigating a possible link between a novel retroviral agent (provisionally called MSRV), recently characterised in multiple sclerosis (MS), and the neuropathology of MS, it was found that there was a significant correlation between gliotoxicity and reverse transcriptase activity in monocyte/macrophage culture supernatants (MMCS) unique to MS patients. MMCS from healthy controls and patients with other neurological diseases did not display either gliotoxicity or reverse transcriptase activity. The observed gliotoxic effect was an initial, intermediate filament network disorganization and subsequent cell death which was specific to astrocytes and oligodendrocytes. The reverse transcriptase activity and MSRV-specific RNA were observed during the first 2 weeks of culture in MMCS from patients with active MS. The further elucidation of the molecular form(s) of this gliotoxic factor and its original source may be crucial in elucidating important etiopathogenic mechanisms in MS.

Animals↗

PubMed1997

Mouse-chick chimera: a developmental model of murine neurogenic cells.

Chimeras were prepared by transplanting fragments of neural primordium from 8- to 8.5- and 9-day postcoital mouse embryos into 1.5- and 2-day-old chick embryos at different axial levels. Mouse neuroepithelial cells differentiated in ovo and organized to form the different cellular compartments normally constituting the central nervous system. The graft also entered into the development of the peripheral nervous system through migration of neural crest cells associated with mouse neuroepithelium. Depending on the graft level, mouse crest cells participated in the formation of various derivatives such as head components, sensory ganglia, orthosympathetic ganglionic chain, nerves and neuroendocrine glands. Tenascin knockout mice, which express lacZ instead of tenascin and show no tenascin production (Saga, Y., Yagi, J., Ikawa, Y., Sakakura, T. and Aizawa, S. (1992) Genes and Development 6, 1821-1838), were specifically used to label Schwann cells lining nerves derived from the implant. Although our experiments do not consider how mouse neural tube can participate in the mechanism required to maintain myogenesis in the host somites, they show that the grafted neural tube behaves in the same manner as the chick host neural tube. Together with our previous results on somite development (Fontaine-Pérus, J., Jarno, V., Fournier Le Ray, C., Li, Z. and Paulin, D. (1995) Development 121, 1705-1718), this study shows that chick embryo constitutes a privileged environment, facilitating access to the developmental potentials of normal or defective mammalian cells. It allows the study of the histogenesis and precise timing of a known structure, as well as the implication of a given gene at all equivalent mammalian embryonic stages.

Animals↗

PubMed1996

Mouse G2-GPI AChE is processed as a membrane-bound ectoenzyme in transfected mouse sarcoma cells but is not a homophilic adhesion molecule.

Acetylcholinesterase (AChE) is mainly involved in synaptic transmission by hydrolyzing acetylcholine in the synaptic cleft. It has been suggested that it could also be involved in other functions such as cell-cell adhesion. In this study, we have expressed mouse G2-GPI AChE at the membrane surface of S180 cells. We obtained a transfected cell line which permanently expresses high levels of AChE at the cell surface. However, transfected cells behave as single cells in culture. We performed cell aggregation and adhesion tests and found no significant aggregation or adhesion, which suggests that AChE is not a homophilic adhesion molecule.

Acetylcholinesterase↗

PubMed1996

Involvement of the dihydropyridine receptor and internal Ca2+ stores in myoblast fusion.

The process of myoblast fusion during skeletal myogenesis is calcium regulated. Both dihydropyridine receptor and ryanodine receptor are already present on muscle precursors, at the prefusional stage, before they are required for excitation-contraction coupling. Previous pharmacological studies have shown the need for a special pool of Ca2+ associated with the membrane for the fusion process to occur. We hypothesized that this pool of Ca2+ is mobilized via a machinery similar to that involved in excitation-contraction coupling. The process of fusion in rat L6 muscle precursors was either totally or partially abolished in the presence of the L-type calcium channel inhibitors SR33557 and nifedipine (half inhibition towards 2 microM), respectively. The inhibition was reversible and dose-dependent. Drugs able to deplete internal calcium stores (caffeine, ryanodine, and thapsigargin) were also tested on the fusion. Both caffeine and thapsigargin drastically inhibited fusion whereas ryanodine had no effect. This suggests that fusion may be controlled by internal pools of Ca2+ but that its regulation may be insensitive to ryanodine. We presumed that an early form of the ryanodine receptor may exist, with different pharmacological properties than the adult forms. Indeed, Western blot analysis of pre- and postfusional L6 cells demonstrated the presence, at the prefusional stage, of a transient form of the ryanodine receptor protein with an apparent molecular weight slightly different from those of the classical skeletal and cardiac forms. Taken together, these results support the hypothesis that the fusion process is driven by a mechanism involving both the dihydropyridine receptor (alpha1 subunit of the L-type Ca2+ channel) and the internal stores of Ca2+. The machinery underlying this mechanism might consist of slightly different forms of the classic molecules that in adult muscle ensure excitation-contraction coupling. It remains to be seen, however, whether the mobilization of the internal pool of Ca2+ is triggered by the type of mechanism already described in skeletal muscle.

Animals↗

PubMed1996

The paralysé mouse mutant: a new animal model of anterior horn motor neuron degeneration.

The survival and morphometric characteristics of lumbar spinal motoneurons were examined in the paralysé mouse mutant. Affected (par/par) mice can be first recognized at approximately postnatal day (PN) 7 to 8 and are characterized by their smaller-than-normal body size, a progressive generalized muscle weakness, and lack of coordination. Mutant mice die by PN16-18, when they have become almost completely paralyzed. Previously, we have shown that this mutation involves alteration of several developmental aspects of the neuromuscular system. However, whether ventral (or anterior) horn motoneurons degenerate and die during the course of the disease was unknown. We report here that at the time the mutant phenotype can be first identified (i.e. approximately PN8), lumbar motoneuron numbers in the lateral motor column of the spinal cord of paralysé mice were not significantly different from those of control littermates. In contrast, by PN14, there was a significant (30 to 35%) decrease in motoneuron numbers in mutant compared to control mice. Furthermore, motoneuron (nuclear and soma) sizes were significantly decreased in the mutants at both stages examined, i.e. PN8 and PN14. These results show that the paralysé mutation involves atrophy and subsequent death of anterior horn motoneurons. Together with the rapid progression and the severity of the disease, these results suggest that the paralysé mouse may represent a good animal model for studying early-onset human motor neuron diseases such as spinal muscular atrophy.

Animals↗

PubMed1996

M-cadherin distribution in the mouse adult neuromuscular system suggests a role in muscle innervation.

M-cadherin belongs to the Ca(2+)-dependent cadherin family of cell adhesion molecules and was first isolated from a mouse muscle cell line cDNA library. It is specifically expressed in muscle tissue during development and is supposed to play an important role in secondary myogenesis. In the present study the expression of M-cadherin mRNA and protein and its localization were investigated in adult mouse skeletal muscle and peripheral nerve. The mRNA was abundant in embryonic legs from embryonic day (E)14 to E18. It remained expressed in new-born and adult muscles. In the adult muscle M-cadherin immunoreactivity was only detected at the neuromuscular junction, associated with perijunctional mononucleated cells and on intramuscular nerves. Peripheral nerves were also M-cadherin-positive. The molecule was found at the surface of myelinated nerve fibres where it was concentrated at the node of Ranvier. When a nerve was crushed and allowed to regenerate, M-cadherin was over-expressed at the site of nerve injury and in the distal stump. M-cadherin was also upregulated on the sarcolemma of denervated muscle fibres. Taken together, these observations point toward a much wider tissue distribution of M-cadherin than previously thought. M-cadherin might be involved not only in specific steps of myogenesis but also in some aspects of synaptogenesis, axon/Schwann cell interactions and node of Ranvier structural maintenance.

Amino Acid Sequence↗

PubMed1996

[Gliotoxic factor and multiple sclerosis].

Multiple sclerosis in a disease of the central nervous system characterized by perivascular and periventricular lesions of the myelin and immune cell infiltrates and increased permeability of the blood-brain barrier. We have found a cytotoxic factor of the cerebrospinal fluid (CSF) specific for multiple sclerosis patients which has 2 main characteristic effects in vitro on primary or immortalized astrocyte cultures: (1) disruption of the gliofilament network of the cells; and (2) apoptotic cell death induction. Moreover, in vivo, intraventricular injections of minute amounts of partially purified gliotoxic factor in adult rats have striking effects on both the morphology and general organization of astrocytes in the entire brain and the permeability characteristics of the blood brain barrier, which becomes leaky to immunoglobulins. These pathological effects are strongly similar to some of the neuropathological findings reported during the course of MS--They suggest an entirely new hypothesis to explain the active stage of the disease: the presence of a new factor of unknown extrinsic (viral) or intrinsic (cellular) origin, able to disorganize the glial cytoskeleton and glial cell differentiation. This factor is then able to provoke glial cell death. Such glial cell death may result in both demyelination and increased blood brain barrier permeability. Both in vitro and in vivo studies strongly support the idea that this gliotoxic factor plays a central role in the pathogenesis of MS, making its full identification a critical theme for MS research.

Animals↗

PubMed1996

Expression and localization of RAP1 proteins during myogenic differentiation.

The RAP1 subfamily of small GTPases has been involved in various differentiation programs. In skeletal muscle, several lines of evidence suggest that various small GTPases could be implicated in muscle development. This raised the question of whether the RAP1 proteins (RAP1A and/or RAP1B) could be involved in myogenesis. In the present study, we report on the regulation of RAP1 transcripts and proteins during myogenic differentiation. Northern blot analysis performed with differentiated and undifferentiated C2 myogenic cells pointed out that both genes undergo specific regulation during myogenesis in vitro since differentiation of C2 cells was accompanied by a down-regulation of RAP1B gene transcription and continuous expression of the RAP1A mRNA. In addition, immunofluorescence experiments revealed the accumulation of the RAP1 proteins in differentiated C2 cells and in primary culture of mouse myotubes. Investigation of the intracellular location of RAP1 proteins in undifferentiated and differentiated C2 cells showed that the proteins were associated with the late endocytic compartments. To verify that the build-up of RAP1 proteins had a relevance for developmental mechanisms in vivo, we studied their expression and localization at different stages of skeletal muscle development. We found that RAP1 proteins accumulated in specialized muscle cell domains undergoing important modifications during early and late myogenesis: these were the neuromuscular and myotendinous junctions, respectively. Altogether, our data indicate that RAP1 proteins are regulated during myogenic differentiation.

3T3 Cells↗

PubMed1995

The motoneuron degeneration in the wobbler mouse is independent of the overexpression of a Bcl2 transgene in neurons.

The wobbler mouse mutation, an autosomal recessive mutation, leads to motoneuron degeneration in early post-natal development. Transgenic mice in which neurons overexpress human bcl2 transgene have been generated: the overexpression of bcl2 reduces the neuron loss during naturally occurring and experimentally-induced cell deaths. In the present study, we generate mice co-expressing the wobbler mutant gene and the bcl2 transgene in order to determine the effects of Bcl2 overexpression on the neurodegenerative disorders of the wobbler mouse. The clinical signs of the disease (weakness, tremor, small size) as well as biochemical and histological parameters (choline acetyltransferase (ChAT) activity in muscles, gliosis in spinal cord) are similar in bcl2 positive and negative wobbler mice. These results point to the fact that the neuron-specific expression of the human bcl2 transgene does not correct the effects of the wobbler mutation.

Animals↗

PubMed1995

Astrocytosis in wobbler mouse spinal cord involves a population of astrocytes which is glutamine synthetase-negative.

Mice affected by the wobbler mutation are characterized by a muscular atrophy associated with motoneuron degeneration. As soon as the first clinical signs of the disease appear, reactive astrocytes, strongly glial fibrillary acidic protein (GFAP)-positive, are observed in the spinal cord grey matter. They become prevalent at all levels with disease progression. Immunostaining of glutamine synthetase (GS) shows that these reactive astrocytes are never GS-positive. The activity and protein amounts of GS remain normal in wobbler spinal cord although astrocytosis develops. Thus, gliosis in the wobbler mouse seems to involve a subpopulation of astrocytes, which is strongly GFAP-positive but GS-negative.

Animals↗

PubMed1995

Myotube driven myogenic recruitment of cells during in vitro myogenesis.

Muscular dysgenesis (mdg) is a recessive lethal mutation in the mouse which drastically affects skeletal muscle development during embryonic life. Physiologically, the disease is characterized by a complete paralysis resulting from a lack of excitation-contraction coupling. Existing electrophysiological, biochemical, and genetic evidence shows that mdg/mdg mice express a basic alteration of L-type voltage-sensitive Ca2+ channels in skeletal muscle. Studies on mdg/mdg myotubes in primary culture have shown that +/+ fibroblasts or +/+ Schwann cells may fuse with them and correct their functional deficiency by genetic complementation. As the spontaneous formation of heterocaryons is thought to be an exclusive property of myoblasts, we asked whether fibroblasts may have changed their properties before fusion occurred. We used primary cells issued from sciatic nerves dissected from newborn transgenic mice carrying the pHuDes1-nls-LacZ transgene (Des-LacZ cells) as non-muscle cells. These cells were mainly fibroblasts (80%) positive for Thy1.1 and Schwann cells positive for S100. The cultures were negative for myogenic markers (desmin, troponin T), did not form myotubes long-term, and did not display significant activation of the muscle reporter gene (pHuDes1-nls-LacZ). After a few days in coculture with dysgenic or normal myotubes, the muscle reporter gene (beta-galactosidase) was detected both within dysgenic myotubes, correlating with the restoration of normal contractile activity, and normal myotubes. As well as confirming that fusion takes place, this shows that Des-LacZ cells nuclei incorporated into recipient myotubes express their own myogenic genes. Moreover, individual mononucleated Des-LacZ cells expressing beta-galactosidase were observed, indicating that myogenic genes were being expressed before fusion. This suggests a mechanism of myotube driven myogenic recruitment of cells during the in vitro myogenesis. Analysis of the distribution of the induced Des-LacZ cells (positive for beta-galactosidase) in compartmentalized muscle cocultures showed that in the presence of dysgenic myotubes, these cells were equally distributed in both myotube free and enriched areas, whereas in the presence of normal myotubes, the positive cells remained in close vicinity of the myotubes. This difference could be explained by the fact that the dysgenic phenotype might include release of the induction process from its normal controls. Our results are consistent with the idea of a transcellular mechanism triggering myogenic differentiation in non-muscle cells, and that myotubes themselves are able to drive myogenic recruitment of cells during the in vitro myogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗