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Biomedical subjects

B Fontaine

Publications and source records attributed to B Fontaine.

At least 163 records · Page 9Linked to original sources
PubMed1990

Hyperkalemic periodic paralysis and the adult muscle sodium channel alpha-subunit gene.

Hyperkalemic periodic paralysis (HYPP) is an autosomal dominant disorder characterized by episodes of muscle weakness due to depolarization of the muscle cell membrane associated with elevated serum potassium. Electrophysiological studies have implicated the adult muscle sodium channel. Here, portions of the adult muscle sodium channel alpha-subunit gene were cloned and mapped near the human growth hormone locus (GH1) on chromosome 17. In a large pedigree displaying HYPP with myotonia, these two loci showed tight linkage to the genetic defect with no recombinants detected. Thus, it is likely that the sodium channel alpha-subunit gene contains the HYPP mutation.

Adult↗
PubMed1990

Phase I study of idarubicin administered orally on a daily x 3 schedule.

Twenty-one adult patients with refractory solid tumors were treated on a phase I study of idarubicin (4-demethoxydaunorubicin) administered daily for 3 days every 3 weeks. Nineteen of the patients had received previous chemotherapy (including 13 with prior anthracyclines), and 12 had received prior radiotherapy. Idarubicin dose levels of 10, 15, 17.5, 20, and 25 mg/m2 were explored. Hematological toxicity was dose-related. Other toxicity was acceptable. Only one patient (treated with an idarubicin dose of 17.5 mg/m2/day) developed neutropenic fever, from which he recovered. Further dose escalations beyond 25 mg/m2 were not carried out because of the increasing length of time required for recovery from granulocytopenia at higher doses. No patient experienced a major response, but minor responses were seen in 3 patients with carcinomas of the colon, breast, and kidney respectively. Further phase II studies of oral idarubicin at a starting dose of 20-25 mg/m2 daily times 3 days in patients with good bone marrow reserves are recommended. Because of the degree of neutropenia expected, patients would have to be observed carefully.

Administration, Oral↗
PubMed1990

Denervation of mouse skeletal muscle differentially affects the expression of the jun and fos proto-oncogenes.

The mRNA levels of the jun and fos proto-oncogenes, whose products are part of the transcription regulatory complex AP1, were investigated after denervation of the lower-leg muscles of adult mice. The levels of the four transcripts studied varied in a non-coordinated manner after muscle denervation. As early as 1.5 h after sciatic nerve section, c-fos mRNA reached a maximum and then returned to basal level at 6 h, while c-jun and jun-B mRNA levels increased after 24 h and remained elevated for at least 8 days. In contrast, jun-D mRNA levels did not change after denervation. In situ hybridization experiments revealed different patterns of spatial localization of the c-jun and jun-D transcripts. Labeling of dividing cells by the thymidine analog bromo-deoxyuridine demonstrated that proliferating cells were at least 40-fold less abundant than those expressing c-jun. Thus, denervation rapidly and differentially modulates the expression of genes coding for the AP1 transcription factor subunits in differentiated muscle cells. The possibility that these proto-oncogenes might be involved in the trans-synaptic regulation of muscle-specific gene expression is discussed.

Animals↗
PubMed1990

Equal parental origin of chromosome 22 losses in human sporadic meningioma: no evidence for genomic imprinting.

Inactivation of tumor suppressor genes can occur either by mutation at the gene locus or by loss of part or all of the chromosome region containing the gene. The latter is most frequently detected by DNA markers as loss of heterozygosity in the tumor tissue. In several reports, the paternal homologue was preferentially retained in embryonal tumors associated with loss of particular chromosomal regions, suggesting genomic imprinting of the corresponding tumor suppressor loci. To explore the generality of these findings and the possible role of genomic imprinting in adult tumors of the nervous system, we have determined the parental origin of chromosome 22 loss in sporadic meningioma. Of nine cases studied, five tumors retained the maternally derived chromosome 22 homologue while four retained the paternally derived chromosome 22. Thus, in contrast to the embryonal tumors, the meningioma locus on chromosome 22 is inactivated by random mutation in sporadic adult meningiomas.

Alleles↗
PubMed1989

Acetylcholine receptor expression in primary cultures of embryonic chick myotubes--I. Discoordinate regulation of alpha-, gamma- and delta-subunit gene expression by calcitonin gene-related peptide and by muscle electrical activity.

The neuropeptide calcitonin gene-related peptide calcitonin gene-related peptide, and muscle electrical activity regulate in opposite directions the content of nicotinic acetylcholine receptor alpha-subunit mRNA in primary cultures of chick embryonic myotubes. Indeed, treating the cells with calcitonin gene-related peptide or blocking the spontaneous activity of muscle cells by tetrodotoxin (an inhibitor of sodium channels) increases, although to different levels, the content of acetylcholine receptor alpha-subunit mRNA [Fontaine B., Klarsfeld A. and Changeux J. P. (1987) J. Cell Biol. 105, 1337-1342; Klarsfeld A. and Changeux J. P. (1985) Proc. natn. Acad. Sci. U.S.A. 82, 4558-4562]. In this paper, we demonstrate that, under these in vitro culture conditions, calcitonin gene-related peptide (0.1 microM) and tetrodotoxin (0.5 microM) regulate to a smaller extent (no more than 2.5-fold above control) the levels of acetylcholine receptor gamma- and delta-subunit mRNAs. No effect of either compound on acetylcholine receptor biosynthesis was observed during the initial three days of culture. The response to calcitonin gene-related peptide was already maximal when the cells were treated between days three and four after plating (about 3-fold increase of the alpha-subunit mRNA level). The effect of tetrodotoxin resulted in a six-fold increase of the acetylcholine receptor alpha-subunit mRNA level in cells treated between days three and four, and still increased when the cells were exposed to tetrodotoxin through days six and eight (up to a maximum of 20-fold).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Acetylcholine receptor expression in primary cultures of embryonic chick myotubes--II. Comparison between the effects of spinal cord cells and calcitonin gene-related peptide.

Spinal cord cells co-cultured with primary chick myotubes caused a 1.5-3-fold increase in the number of muscle surface acetylcholine receptors assayed with [125I]alpha-bungarotoxin. This increase did not result from the metabolic stabilization of the acetylcholine receptor protein and was at least partially due to a stimulation of acetylcholine receptor biosynthesis up to the level of the accumulation of alpha-subunit mature and partially spliced precursor mRNAs. A medium conditioned by spinal cord cells also caused a rise in acetylcholine receptor number. This increase did not coincide with an augmentation of the intracellular cyclic AMP level as reported for the neuropeptide calcitonin gene-related peptide. In contrast, spinal cord cells and the medium conditioned by them potentiated the effect of calcitonin gene-related peptide on acetylcholine receptor number. Stimulation of acetylcholine receptor synthesis by the conditioned medium was blocked by the protein kinase C activator 12-O-tetradecanoyl phorbol-13-acetate and by the calcium ionophore A23187. These two compounds have already been reported to block the increase of acetylcholine receptor number produced by the voltage sensitive sodium channel antagonist tetrodotoxin which stimulates acetylcholine receptor biosynthesis by blocking spontaneous electrical activity of the cultured muscle cells. The possibility that different neural factors and second messenger systems are involved in the regulation of acetylcholine receptor biosynthesis during the development of the neuromuscular junction is discussed.

Animals↗
PubMed1989

Regulation of muscle AChR alpha subunit gene expression by electrical activity: involvement of protein kinase C and Ca2+.

Using primary cultures of chicken myotubes, we investigated the involvement of protein kinase C and Ca2+ in the repression of nicotinic acetylcholine receptor (AChR) biosynthesis by electrical activity. Treatment with the Ca2+ channel blocker verapamil or the Na+ channel blocker tetrodotoxin increased alpha subunit mRNA levels 11.5- to 15-fold. The effect of tetrodotoxin was abolished in the presence of the Ca2+ ionophore A23187. Dantrolene, which blocks Ca2+ efflux from the sarcoplasmic reticulum, caused only a 1.7-fold increase in alpha subunit mRNA levels. Down regulation of protein kinase C by prolonged exposure to the phorbol ester TPA or inhibition of protein kinase C by staurosporine led to 8- to 10-fold increases in alpha subunit mRNA levels. Mature and precursor forms of AChR alpha subunit mRNA were found to vary in parallel throughout all of these treatments, suggesting that protein kinase C and Ca2+ ions may modulate AChR alpha subunit biosynthesis at the transcriptional level.

Animals↗
PubMed1989

Localization of nicotinic acetylcholine receptor alpha-subunit transcripts during myogenesis and motor endplate development in the chick.

In 15-d-old chick latissimi dorsi muscles, the nicotinic acetylcholine receptor (AChR) alpha-subunit mRNA is densely accumulated at the level of subsynaptic nuclei of the motor endplate (Fontaine et al., 1988). In this paper, using in situ hybridization with genomic probes, we further show that the expression of the AChR alpha-subunit gene in the embryo, revealed by the accumulation of mature mRNAs, starts in myotomal cells and persists during the first stages of muscle development in a majority of muscle nuclei. Subsequently, the distribution of AChR alpha-subunit mRNAs becomes restricted to the newly formed motor endplates as neuromuscular junctions develop. To assess the transcriptional activity of individual nuclei in developing muscles, a strictly intronic fragment of the AChR alpha-subunit gene was used to probe in situ the level of unspliced transcripts. AChR alpha-subunit unspliced transcripts accumulate around a large number of sarcoplasmic nuclei at embryonic day 11, but can no longer be detected at their level after embryonic day 16 in the embryo. A similar decrease in the accumulation of AChR alpha-subunit transcripts is observed between day 4 and day 6 in primary cultures of muscle cells. On the other hand, in vivo denervation and in vitro blocking of muscle electrical activity by the sodium channel blocker tetrodotoxin results in an increase in the labeling of muscle nuclei. Yet, only 6% of the muscle nuclei appear labeled by the strictly intronic probes after denervation. The possible significance of such heterogeneity of muscle nuclei during motor endplate formation in AChR gene expression is discussed.

Actins↗
PubMed1989

[Possible trophic role on the neuromuscular junction of a neuropeptide co-existing with acetylcholine in motor neurons of the spinal cord].

The Calcitonin-Gene Related Peptide (CGRP), a neuropeptide present in chick spinal cord motoneurons, increases the levels of surface acetylcholine receptor (AChR) and of the AChR alpha-subunit mRNA in cultured chick myotubes. Cholera toxin (CT), an activator of adenylate cyclase, produces a similar effect which does not add up with that of CGRP. Consistent with this observation, CGRP increases the content of cyclic AMP in chick muscle cells in culture. Tetrodotoxin (TTX), a blocker of voltage-sensitive Na+ channels, elevates the levels of AChR and of AChR alpha-subunit mRNA. This effect is additive with that of CGRP or CT. TPA (12-O-tetradecanoyl phorbol-13-acetate), an activator of protein kinase C, decreases the level of AChR but has no effect on the level of AChR alpha-subunit mRNA. Interestingly, TPA inhibits the increase of AChR alpha-subunit mRNA caused by TTX without affecting that produced by CGRP or CT. These data suggest that CGRP, which coexists with acetylcholine in spinal cord motoneurons, could be one of the anterograde factors (or a model of such factor) responsible for the enhanced expression of the genes coding for AChR subunits in subneural nuclei, via the activation of adenylate cyclase. Muscle electrical activity would then inhibit the expression of the same genes in extrajunctional nuclei, via another intracellular pathway.

Animals↗
PubMed1988

Detection of the nicotinic acetylcholine receptor alpha-subunit mRNA by in situ hybridization at neuromuscular junctions of 15-day-old chick striated muscles.

In adult vertebrate striated muscle, the nicotinic acetylcholine receptor (AChR) is almost exclusively localized in the postsynaptic membrane of the neuromuscular junction. Using in situ hybridization, we show that, in two different chicken muscles [the slow multi-innervated anterior latissimus dorsi (ALD) and the fast singly innervated posterior latissimus dorsi (PLD)], the AChR alpha-subunit mRNA is detected at discrete regions on myofibres and that these regions co-localize (80% correspondence) with neuromuscular junctions identified by histochemical staining for acetylcholinesterase. Moreover, autoradiographic grains densely accumulate on and around subsynaptic nuclei. In contrast, hybridization with an actin probe results in a strong signal distributed over the entire length of the myofibres. Denervation increases the level of AChR alpha-subunit mRNA both in the PLD and to a lesser extent in the ALD. By in situ hybridization we observe that, although a perinuclear pattern is maintained, the labelled nuclei appear randomly distributed among approximately 10% of the nuclei. These results are discussed in a model of AChR gene expression in vertebrate striated muscle fibres.

Acetylcholinesterase↗
PubMed1987

Characterization of a factor from the U937 cell line that enhances the toxicity of human eosinophils to Schistosoma mansoni larvae.

A factor produced by lipopolysaccharide-stimulated human monocytes, monocyte-derived eosinophil cytotoxicity-enhancing factor (M-ECEF), increases the ability of human eosinophils to kill larvae of Schistosoma mansoni. In order to purify this monokine, a continuous cell line was sought as a generator of source material. It was found that high titers of an ECEF-like activity could be obtained from the U937 cell line cultured in serum-free medium. Production of this activity was optimal when cells were cultured with PMA for 2 days and were further treated with LPS for 2 days. PMA and LPS alone did not enhance eosinophil cytotoxicity and could be separated completely from U937-ECEF activity by reversed-phase HPLC. Thus, the activity was not due to carry-over of these two stimuli. U937-ECEF was compared with M-ECEF by a number of analytical methods. ECEF from both sources was resistant to several denaturing treatments but was sensitive to proteases or to reduction and alkylation. U937-ECEF exhibited activity profiles similar, if not identical, to those of M-ECEF when subjected to molecular sizing HPLC in the presence of 8 M urea, isoelectric focusing, and reversed-phase HPLC. The activity has apparent m.w. of 17,000 and 32,000, isoelectric points ranging from 3.8 to 5.1, and one or more reversed-phase HPLC retention times, depending on the method of sample preparation. These results demonstrate certain physical characteristics of M-ECEF, show that the U937 cell line is an appropriate source for the purification of M-ECEF, and provide information that will allow the design of a purification strategy. Although it appears that tumor necrosis factor (TNF) or a TNF-like molecule is a component of M-ECEF, a major component of M-ECEF is different from TNF as judged by the 1) physical characteristics of M-ECEF, 2) low direct toxicity of M-ECEF to L929 cells, 3) comparative stability of M-ECEF to heat treatment, and 4) inability of an anti-TNF monoclonal antibody to remove M-ECEF activity.

Cell Line↗
PubMed1987

Calcitonin gene-related peptide and muscle activity regulate acetylcholine receptor alpha-subunit mRNA levels by distinct intracellular pathways.

In cultured chicken myotubes, calcitonin gene-related peptide (CGRP), a peptide present in spinal cord motoneurons, increased by 1.5-fold the number of surface acetylcholine receptors (AChRs) and by threefold AChR alpha-subunit mRNA level without affecting the level of muscular alpha-actin mRNA. Cholera toxin (CT), an activator of adenylate cyclase, produced a similar effect, which did not add up with that of CGRP. In contrast, tetrodotoxin, a blocker of voltage-sensitive Na+ channels, elevated the level of AChR alpha-subunit mRNA on top of the increase caused by either CGRP or CT. 12-O-Tetradecanoyl phorbol-13-acetate (TPA), an activator of protein kinase C, markedly decreased the cell surface and total content of [125I]alpha BGT-binding sites and reduced the rate of appearance of AChR at the surface of the myotubes without reducing the level of AChR alpha-subunit mRNA. Moreover, TPA inhibited the increase of AChR alpha-subunit mRNA caused by tetrodotoxin without affecting that produced by CGRP or CT. Under the same conditions, TPA decreased the level of muscular alpha-actin mRNA and increased that of nonmuscular beta- and gamma-actins mRNA. These data suggest that distinct second messengers are involved in the regulation of AChR biosynthesis by CGRP and muscle activity and that these two pathways may contribute to the development of different patterns of AChR gene expression in junctional and extrajunctional areas of the muscle fiber.

Actins↗
PubMed1986

Calcitonin gene-related peptide, a peptide present in spinal cord motoneurons, increases the number of acetylcholine receptors in primary cultures of chick embryo myotubes.

Using immunohistochemical methods we show that calcitonin gene-related peptide (CGRP, a peptide encoded by the calcitonin gene) is present in chick spinal cord motoneurons. When added to cultured chicken myotubes, CGRP caused an average 1.5-fold increase in levels of surface acetylcholine receptors. Moreover, the effect of CGRP was independent of the one produced by tetrodotoxin, a blocker of membrane electrical activity but not of that caused by cholera toxin, an activator of adenylate cyclase.

Animals↗