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M Laurent

Publications and source records attributed to M Laurent.

At least 217 records · Page 12Linked to original sources
PubMed1983

At least two transposed sequences are associated in the expression site of a surface antigen gene in different trypanosome clones.

The expression of several trypanosome surface antigen genes proceeds by duplication of a basic copy (BC) of the gene and transposition of the expression-linked copy (ELC) into an expression site. This site, which seems to be the same for different genes of the same repertoire, is located near a chromosome end. In the AnTat 1.1 antigen gene expression site, the ELC is found associated with another sequence that we have called the "companion." We found that this companion is the transposed copy of another sequence also located in an unstable DNA terminus, and that it is conserved in the expression site of AnTat 1.10 and AnTat 1.1B, two clones successively derived from AnTat 1.1. The companion sequence is not part of the surface antigen gene, but we may infer from extensive homologies with another ELC sequence (IoTat 1.3, J. E. Donelson, personal communication) that it represents a 5' residual fragment of a former ELC. In three other AnTat 1.1-like clones, the companion sequence was not found associated with the ELC. It is concluded that the expression-linked duplicative transposition of variable antigen genes is a flexible mechanism, which can apply to variably sized stretches of the same BC.

Animals↗
PubMed1983

Gene conversion as a mechanism for antigenic variation in trypanosomes.

Expression of the gene coding for the trypanosome AnTat 1.1 surface antigen is linked to the duplicative transposition of a basic copy (BC) of this gene to an expression site. In two trypanosome clones successively derived from AnTat 1.1 (AnTat 1.10 and AnTat 1.1B) we found evidence that gene conversions are involved in the transformation of the AnTat 1.1 transposed element into the two new surface antigen coding sequences. Although the three resultant mRNAs--AnTat 1.1, 1.10, and 1.1B--are different, they still share large homologies. Two of them, AnTat 1.1 and 1.1B, code for surface coats that are indistinguishable by conventional serological techniques, whereas AnTat 1.10 has been found different by the same methods. The three genomic rearrangements involve two of the five members of the AnTat 1.1 gene family. These two members are both located in unstable telomeric regions similar to the expression site, each in a different orientation with respect to the DNA terminus. We have concluded that the duplicative transposition is achieved by a gene conversion that may affect variable lengths of the same silent genes, and that different members of the same surface antigen gene family can contribute to the diversification of the antigen repertoire.

Amino Acid Sequence↗
PubMed1982

Alterations in glycopeptide and glycosaminoglycan biosynthesis in bovine lens epithelial cells cultured in the presence of an eye-derived growth factor.

D-[3H]glucosamine-labeled glycosaminoglycans and glycopeptides, obtained by Pronase digestion from bovine lens epithelial cells grown in the presence and in the absence of an eye-derived growth factor, were investigated comparatively in the extra- and pericellular compartments of 16-17th subcultures. Glycosaminoglycans and glycopeptides were separated on Ultrogel AcA 202 column and the retained glycopeptides were further separated by the successive application of affinity, ion-exchange and exclusion chromatographic methods. The following results were obtained: (1) the proportion of the label increased in hyaluronic acid and decreased in the glycopeptide fraction on stimulation with the growth factor: (2) the comparison of the chromatographic elution profiles of the glycopeptides from control and stimulated cells revealed that differences between the two cell groups were largely quantitative. An increase in the high molecular weight glycopeptides, as it was found in transformed cells, could not be demonstrated in eye-derived growth factor-treated cells.

Animals↗
PubMed1982

Separation and chemical differentiation of alpha and beta subunits in yeast phosphofructokinase.

The two types of subunits alpha and beta constitutive of yeast phosphofructokinase have been separated by ion-exchange chromatography under denaturating conditions. Amino acid analysis and peptide mapping were performed on the isolated subunits. The frequence of most of the amino acids significantly differs between the two types of polypeptide chains. Moreover, tryptic peptide maps of alpha and beta subunits are clearly not superimposable. These chemical differences seem sufficient to account for the distinct catalytic and regulatory functions of beta and alpha subunits in the yeast phosphofructokinase reaction.

Amino Acids↗
PubMed1982

[Intestinal bypass in the treatment of obesity. Results of 14 cases (author's transl)].

Fourteen women with severe obesity resistant to previous dietetic measures underwent intestinal bypass using Scott's method. Weight loss ranged from 1-2 kg to 50 kg (mean = 25 kg) but weas unpredictable and varied from patient to patient; most remained obese. The other results of the operation were similar to those already reported. There was a decrease in total plasma cholesterol, while HDL cholesterol remained normal. Calcaemia was in the lower range of normal values; one patient developed severe hypokaliaemia (1.8 mEq); low blood magnesium levels and steatorrhoea were common. Fibrosis of the liver was observed in one patient and probably in another. Five patients were re-operated upon for incisional hernia or intestinal occlusion. Other complications reported in the literature (pulmonary embolism, arthralgias, kidney stones and gall stones) did not occur in this series. Because of these complications we decided to stop using intestinal bypass for the treatment of severe obesity. However, in view of the potential dangers of severe obesity we feel that other surgical techniques, such as Mason's gastric bypass, should be considered in some patients.

Adult↗
PubMed1982

[Comparison of data from exercise tests and continuous electrocardiographic recording in patients with ventricular extrasystole. Apropos of 131 cases].

A series of 131 patients aged from 4 to 70 years old with significant ventricular arrhythmias corresponding to at least Grade 2 of Lown's classification underwent exercise stress testing and continuous 24 hour electrocardiography. There were two objectives: to compare exercise electrocardiography and Holter monitoring in the detection and assessment of the seriousness of the arrhythmia, and to assess the arrhythmia's modifications on exercise. The patients were divided into 4 types: "chronic coronary insufficiency", "mitral valve prolapse", "other cardiac disease" and "idiopathic" arrhythmias. The maximum grade of arrhythmia corresponded to salvos of ventricular extrasystoles in 44 cases (33,5 p. 100), doublets in 44 cases (33,5 p. 100), polymorphic extrasystoles in 10 cases (7,6 p. 100) and monomorphic extrasystoles in 33 cases (25,2 p. 100). A significant arrhythmia was found in 90,8 p. 100 of cases by Holter and in 82,4 p. 100 of cases on exercise stress testing. The maximum grade of arrhythmia was also better appreciated on Holter monitoring (84,7 p. 100) compared to exercise stress testing (46,5 p. 100). The difference being more clear cut for repetitive forms. The superiority of Holter monitoring for assessing the grade of arrhythmia was obvious in the "idiopathic", "other cardiac disease" and "coronary" groups (79,4 p. 100 compared to 41,2 p. 100) but was not significant in the mitral valve prolapse group (73,9 p. 100 compared to 65,2 p. 100). Aggravation of the arrhythmia on exercise defined as a large increase, even transient of the number of extrasystoles (7 cases) or changing to a higher grade (59 cases) was significantly less common (p less than 0,01) in the idiopathic group (30 p. 100) than in the other groups (64,1 p. 100 in the coronary, 65,2 p. 100 in the mitral valve prolapse group). Aggravation of the arrhythmia in the coronary group was not observed more often in positive than in negative exercise electrocardiography. Complete regression of extrasystoles in the last two minutes was observed in 50 cases and significantly more often in idiopathic arrhythmias (p less than 0,01). There was no correlation between the behavior of the arrhythmia on exercise and the presence of salvos of extrasystoles, previous syncope or electrical cardioversion. Important individual differences were observed in all groups of patients. These observations suggest that the statistical superiority of Holter monitoring is debatable and imply that it is often necessary to request both investigations for the exact diagnosis of the arrhythmia and for the eventual therapeutic management of the patient and his mode of life.

Adolescent↗
PubMed1982

[Morphologic features of tumor stage lesions of mycosis fungoïdes (author's transl)].

A morphological analysis was carried out on a series of five patients, with tumor stage lesions of mycosis fungoides. The histological findings of skin, lymph nodes, spleen, liver and bone marrow were investigated. Histologically the cutaneous infiltrate consisted of large cells (mycosis cells) and small atypical lymphoid cells (Lutzner cells). Among the large cells, which predominated in number, two principal types of cell could be distinguished: lymphoid cells comparable to the Lutzner cells because of their nuclear configuration, and poorly differentiated basophilic and pyroninophilic cells with irregular nucleus ("reticulum" cells?) or regular nucleus ("T-immunoblasts"?). Ultrastructural data of cutaneous lesion obtained for study from only one patient, were consistent with these findings. Lesions of lymph nodes and viscera consisted of a cellular composition which closely resembled that of cutaneous lesions. In particular, the large so-called mycosis cells were always found and represented a supportive histologic feature in identifying this disease.

Adult↗
PubMed1981

Effects of retinal growth factor and of the increase of the number of subcultures on sulfated glycosaminoglycans of bovine lens epithelial cells.

Sulfated glycosaminoglycans of cultured bovine lens epithelial cells grown in the presence and in the absence of a retinal growth factor were investigated comparatively. The newly formed [35S]sulfate-labeled glycosaminoglycans were analysed in the extra-, peri- and intracellular compartments of early (4--5th) and late 17--18 h) subcultures. The following results were obtained: (1) Cultured lens epithelial cells grown in the presence or in the absence of the growth factor synthesize chondroitin 4- and 6-sulfates and dermatan sulfate, with heparan sulfate as the main component, the pericellular compartments were particularly rich in heparan sulfate; (2) The distribution pattern of the glycosaminoglycans changes during successive subcultures; the proportion of heparan sulfate increases in the pericellular compartment, the dermatan sulfate to chondroitin sulfate ratio increases in all three compartments; (3) IN contrast to the drastic decrease in the fibronectin levels in the presence of growth factor in the early subcultures, only minor differences were found between the glycosaminoglycan patterns of the treated and non-treated cells.

Animals↗