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Biomedical subjects

F Michel

Publications and source records attributed to F Michel.

At least 163 records · Page 9Linked to original sources
PubMed1991

Incipient mitochondrial evolution in yeasts. II. The complete sequence of the gene coding for cytochrome b in Saccharomyces douglasii reveals the presence of both new and conserved introns and discloses major differences in the fixation of mutations in evolution.

We have determined the complete sequence of the mitochondrial gene coding for cytochrome b in Saccharomyces douglasii. The gene is 6310 base-pairs long and is interrupted by four introns. The first one (1311 base-pairs) belongs to the group ID of secondary structure, contains a fragment open reading frame with a characteristic GIY ... YIG motif, is absent from Saccharomyces cerevisiae and is inserted in the same site in which introns 1 and 2 are inserted in Neurospora crassa and Podospora anserina, respectively. The next three S. douglasii introns are homologous to the first three introns of S. cerevisiae, are inserted at the same positions and display various degrees of similarity ranging from an almost complete identity (intron 2 and 4) to a moderate one (intron 3). We have compared secondary structures of intron RNAs, and nucleotide and amino acid sequences of cytochrome b exons and intron open reading frames in the two Saccharomyces species. The rules that govern fixation of mutations in exon and intron open reading frames are different: the relative proportion of mutations occurring in synonymous codons is low in some introns and high in exons. The overall frequency of mutations in cytochrome b exons is much smaller than in nuclear genes of yeasts, contrary to what has been found in vertebrates, where mitochondrial mutations are more frequent. The divergence of the cytochrome b gene is modular: various parts of the gene have changed with a different mode and tempo of evolution.

Amino Acid Sequence↗
PubMed1991

A small chloroplast RNA may be required for trans-splicing in Chlamydomonas reinhardtii.

In C. reinhardtii, the mature psaA mRNA is assembled by a process involving trans-splicing of three separate transcripts encoded at three widely scattered loci of the chloroplast genome. At least one additional chloroplast locus (tscA) is required for trans-splicing of exons 1 and 2. We have mapped this gene by transformation of a deletion mutant with a particle gun. The 0.7 kb region of the chloroplast genome that is sufficient to rescue tscA function has been subjected to insertion mutagenesis, showing that it does not contain significant open reading frames. We suggest from these experiments that the product of the tscA gene may be a small chloroplast RNA that acts in trans in the first trans-splicing reaction of psaA. A model for the mode of action of this RNA is presented, in which the characteristic structure of group II introns is assembled from three separate transcripts.

Amino Acid Sequence↗
PubMed1991

Oxysterol activation of arachidonic acid release and prostaglandin E2 biosynthesis in NRK 49F cells is partially dependent on protein kinase C activity [corrected].

We previously demonstrated that the oxysterol potentiation of arachidonic acid release and prostaglandin biosynthesis induced by foetal calf serum activation of normal rat kidney (NRK) cells (fibroblastic clone 49F) was not related to a direct effect of oxysterols on cell free Ca2+ level. Since both Ca2+ variations and protein kinase C are involved in arachidonic acid release in some models, we looked for a possible modulation by protein kinase C in the oxysterol effect on arachidonic acid release. We show that when the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA), a protein kinase C activator, was added to the culture medium, the oxysterol effect on arachidonic acid release and prostaglandin synthesis clearly increased. Moreover, the effect of TPA was dose-dependent and TPA EC50 (4 x 10(-9) M) was unchanged in the presence of the oxysterol. Preincubation of cells with TPA for 24 h prevented the arachidonic acid release induced by TPA alone, whereas the oxysterol effect was decreased but not abolished. In the absence of serum, TPA and ionomycin added together induced the same noticeable (arachidonic acid) release and PGE2 synthesis as serum alone. Nevertheless, the potentiating effect of cholest-5-ene-3 beta, 25-diol was much higher when serum itself was used to activate NRK cells than it was in the present serum-mimicking experimental conditions. Thus, the presence of growth factors is probably required to obtain a full oxysterol effect. We conclude that the oxysterol effect was synergistic with, but not fully dependent on, protein kinase C and Ca2+ ion fluxes, therefore oxysterols could affect earlier events triggered by serum growth factor binding to their cell membrane receptors.

Animals↗
PubMed1991

Unmasking of visual deficits following unilateral prestriate lesions in man.

The primate visual cortex is a mosaic of different areas which are roughly organized into two major pathways, a dorsal one along an occipito-parietal channel and a ventral one along an occipito-temporal channel. It is known that visual stimuli are processed differently within these two systems and one might expect therefore that behavioral deficits would differ according to the channel damaged by cerebral lesions. Two patients with left prestriate lesions presented perceptual deficits in the right visual field. These deficits involved reading, recognition of line drawings and colour perception and would be compatible with a dysfunction of the ventral system. Magnetic resonance imaging analysis confirmed that this was the case.

Adult↗
PubMed1991

Initial staging of non-small cell lung cancer: value of routine radioisotope bone scanning.

The exclusion of bone metastases is important in the initial staging of non-small cell lung cancer, though there is debate about whether bone scans should be performed routinely or restricted to patients who present with clinical or laboratory indicators suggesting skeletal metastases. In a prospective study of 110 consecutive patients referred for initial staging of non-small cell lung cancer, we assessed the sensitivity of a group of clinical indicators (chest pain, skeletal pain, bone tenderness on physical examination, serum alkaline phosphatase, and serum calcium) for the presence of skeletal metastases as determined by bone scanning. The final staging result was validated with follow up data over at least three years. At the initial staging 37 of 110 bone scans (34%) showed areas of increased uptake, of which only nine were confirmed to be metastases (by tomography, computed tomography, or biopsy). Half the patients (55) had at least one clinical indicator suggesting skeletal metastases, including all patients with proved skeletal metastases. Thus the sensitivity of these clinical indicators was 100% and the specificity 54%. Within one year three of 27 patients with non-confirmed positive bone scans had skeletal metastases, one of which was in the area that had shown increased uptake initially. All these patients had clinical indicators for skeletal metastases and all had inoperable advanced tumours. Four of 69 patients with an initially negative bone scan developed skeletal metastases within one year. It is concluded that in non-small cell lung cancer bone scanning can be restricted to patients with clinical indicators for skeletal metastases. This approach reduces the number of bone scans and consecutive investigations without loss of sensitivity in the detection of skeletal metastases.

Adult↗
PubMed1991

Long-term oxygen therapy for cor pulmonale in patients with chronic obstructive pulmonary disease.

Besides smoking cessation, antiobstructive therapy, and the treatment of intercurrent infections, long-term oxygen therapy has had the most impressive impact on survival in patients with chronic obstructive pulmonary disease (COPD). COPD leads to a functional and anatomical obstruction of the pulmonary vascular bed, with the development of pulmonary arterial hypertension and cor pulmonale. In these patients, survival benefit from long-term oxygen therapy (LTOT) stems mainly from improved hemodynamics. However, this improvement is limited: hypoxemic COPD patients treated by LTOT have the same life expectancy as nonhypoxemic COPD patients. Practical aspects concerning the prescription and application of LTOT are discussed, with special emphasis on ambulatory oxygen and oxygen-saving techniques.

Humans↗
PubMed1990

Modelling of the three-dimensional architecture of group I catalytic introns based on comparative sequence analysis.

Alignment of the 87 available sequences of group I self-splicing introns reveals numerous instances of covariation between distant sites. Some of these covariations cannot be ascribed to historical coincidences or the known secondary structure of group I introns, and are, therefore, best explained as reflecting tertiary contacts. With the help of stereochemical modelling, we have taken advantage of these novel interactions to derive a three-dimensional model of the conserved core of group I introns. Two noteworthy features of that model are its extreme compactness and the fact that all of the most evolutionarily conserved residues happen to converge around the two helices that constitute the substrate of the core ribozyme and the site that binds the guanosine cofactor necessary for self-splicing. Specific functional implications are discussed, both with regard to the way the substrate helices are recognized by the core and possible rearrangements of the introns during the self-splicing process. Concerning potential long-range interactions, emphasis is put on the possible recognition of two consecutive purines in the minor groove of a helix by a GAAA or related terminal loop.

Animals↗
PubMed1990

Phylogenetic and genetic evidence for base-triples in the catalytic domain of group I introns.

Understanding the mechanisms by which ribozymes catalyse chemical reactions requires a detailed knowledge of their structure. The secondary structure of the group I introns has been confirmed by comparison of over 70 published sequences, by chemical protection studies, and by genetic experiments involving compensatory mutations. Phylogenetic data can also be used to identify tertiary interactions in RNA molecules. This was first done by Levitt, who predicted tertiary interactions in transfer RNA, which were subsequently confirmed by X-ray crystallography. More recently, sequence comparison data have been used to predict tertiary interactions in ribosomal RNA. We have searched a complete alignment of the core regions of group I introns for evolutionary covariations that could not be ascribed to classical Watson-Crick or wobble base pairings. Here we describe two examples of phylogenetic covariation that are most simply explained by postulating hydrogen-bonded base-triples similar to those found in tRNA. Genetic experiments with the Tetrahymena and sunY introns confirm the importance of these interactions for the structure of the ribozyme.

Animals↗
PubMed1990

Base-pairing interactions involving the 5' and 3'-terminal nucleotides of group II self-splicing introns.

By combining comparative sequence analyses and nucleotide replacements, we show that formation of the active center of group II introns rests in part on two novel long-range base-pairing interactions. (1) The last nucleotide of group II introns forms a solitary Watson-Crick base-pair with one of the nucleotides in the short sequence stretch connecting domains II and III. Formation of this base-pair is rate-limiting for the 3' cleavage and ligation step. (2) Nucleotides 3 and 4 form base-pairs with two consecutive nucleotides in a well-conserved internal loop of domain I. This interaction is involved in both the 5' and 3' cleavage steps. Possible relationships between group II and nuclear pre-mRNA introns are reassessed by taking into account these new pieces of information.

Bacteriophages↗
PubMed1990

DNA sequence analysis of the mitochondrial ND4L-ND5 gene complex from Podospora anserina. Duplication of the ND4L gene within its intron.

A 15 kb region of the 100 kb mitochondrial genome of Podospora anserina has been mapped and sequenced (1 kb = 10(3) base-pairs). The genes for ND4L and ND5 are identified as contiguous genes with overlapping termination and initiation codons. In race A (101 kb) the gene for ND4L (4.3 kb) has a gene duplication within an intron including a second subgroup IC intron. Race s (95 kb) lacks this second gene complex. Each intron has the identical 5' exon boundary. Secondary structure analysis showed that the closest relative of the second intron is the first intron itself. The open reading frames of the two introns are also closely related to each other as well as to their counterpart in the ND4L gene of Neurospora crassa. The 9.9 kb ND5 gene starts immediately at the termination codon of ND4L and is split by two group IB introns, one group IC intron and one group II intron. The group II intron is closely related to other group II introns although its open reading frame sequence similarity with retroviral reverse transcriptase appears to be more divergent. The similarities in secondary structure and open reading frames for these six introns are discussed.

Amino Acid Sequence↗
PubMed1990

Mitochondrial DNA sequence analysis of the cytochrome oxidase subunit II gene from Podospora anserina. A group IA intron with a putative alternative splice site.

A 5 kb region of the 95 kb mitochondrial genome of Podospora anserina race s has been mapped and sequenced (1 kb = 10(3) base-pairs). This DNA region is continuous with the sequence for the ND4L and ND5 gene complex in the accompanying paper. We show that this sequence contains the gene for cytochrome oxidase subunit II (COII). This gene is 4 kb in length and is interrupted by a subgroup IB intron (1267 base-pairs (bp) in length) and a subgroup IA intron (1992 bp in length). This group IA intron has a long open reading frame (ORF; 472 amino acid residues) discontinuous with the upstream exon sequence. A putative alternative splice site is present, which brings the ORF into phase with the 5' exon sequence. The 5'- and 3'-flanking regions of the COII gene contain G + C-rich palindromic sequences that resemble similar sequences flanking many Neurospora crassa mitochondrial genes.

Amino Acid Sequence↗
PubMed1990

[Psychiatric complications of corticotherapy].

Corticosteroid therapy may induce numerous psychiatric disorders. Minor changes of the euphoric mood type are observed in 75% of the patients under treatment. Major adverse effects are encountered in not more than about 5% of the cases. They consist of acute polymorphous psychotic manifestations which may be manic or depressive or, when high doses of corticosteroids are taken, of the organic confusion type. Such manifestations are particularly frequent in women and in some diseases such as lupus erythematosus or pemphigus. In the vast majority of cases they follow a favourable course when corticosteroids are reduced or discontinued and a symptomatic treatment with neuroleptic drugs is prescribed. Psychic dependence on corticosteroids and withdrawal syndromes have also been reported.

Adrenal Cortex Hormones↗
PubMed1990

Mechanism of 3' splice site selection by the catalytic core of the sunY intron of bacteriophage T4: the role of a novel base-pairing interaction in group I introns.

The catalytic core of the sunY intron of bacteriophage T4 is separated from its 3' exon by 837 nucleotides, most of which are part of an open reading frame (ORF). Here, we report that transcripts truncated within the sunY ORF self-splice in vitro to a variety of sites in the segment immediately 3' of the core. Recognition of these proximal splice sites is shown to depend on (1) the presence on the intron side of a terminal G, which must not be part of a secondary structure; and (2) the ability of the penultimate intron nucleotide to base-pair with a 3' splice site-binding sequence (3'SSBS) located within the core. The counterpart of the 3'SSBS can be identified in most group I introns. The possible significance of such alternative splicing events for in vivo expression of intron-encoded proteins is discussed.

Base Composition↗
PubMed1990

Distribution of the MHC antigens after liver transplantation: relationship with biochemical and histological parameters.

The aim of this study was to analyse the change in tissue distribution of HLA class I and class II molecules in patients during the course of liver transplantation. Sixty-one liver biopsies were analysed in 24 patients with or without rejection (acute or chronic) episode. In 93% of cases with chronic rejection and in 48% of cases with acute rejection episodes, HLA class I antigens are expressed in the membrane and/or the cytoplasm of hepatocytes. The expression of these molecules was significantly correlated with the ASP (aspartate amino transferase), AP (alkaline phosphatase), the bile duct damage and the centrolobular lesions. In contrast, the expression of HLA class II molecules is not correlated with either the type of rejection, the biological or histological findings. A strong expression of HLA class I antigen on hepatocytes after day 60 may be one of the best signs of chronic rejection.

Graft Rejection↗
PubMed1990

[Report of a case of malignant vesical pheochromocytoma. Diagnosis and therapy].

Bladder pheochromocytoma is a rare, usually benign bladder tumor. An exceptionally malignant bladder pheochromocytoma is reported with more than 5 years follow-up. The study of our case, and the review of 15 other cases reported in the literature show that surgery is the only effective therapy. Partial cystectomy with regional lymphadenectomy, when feasible is the treatment of choice. Because metastatic occurrence may be late, we emphasize the importance of long term follow-up.

Adrenal Gland Neoplasms↗