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Biomedical subjects

G Lefranc

Publications and source records attributed to G Lefranc.

At least 145 records · Page 8Linked to original sources
PubMed1980

Discontinuous genes and DNA sequence transposition: a model for immunoglobulin chain synthesis.

An attempt is made to account for immunoglobulin chain synthesis in terms of genetic events involving IS or controlling elements analogous to those found in bacteria, maize and drosophila. Transposition of variable and constant genes and normal immunoglobulin chain synthesis as well as qualitative and quantitative abnormalities might be explained by such regulatory elements. Intrachromosomal transpositions over short distances would be expressed as apparent hypermutability or redundancy of the variable DNA segment. The constant gene might comprise four sequences coding for the three homology domains and the hinge, separated by intervening sequences. A strong preference for short-range transposition on the same chromosome and immobilization of the controlling element in the end might account for allelic exclusion.

Alleles↗
PubMed1979

Gm, Am and Km immunoglobulin allotypes of two populations in Tunisia.

Gm, Am and Km allotypes were investigated in two Tunisian populations (236 samples from Mahdia and 142 samples from Sfax). These populations descend from immigrants and, therefore, the results were compared with those obtained in other populations living in the Near East and in North Africa. The subclass heavy chain allotypes G1m, G2m, G3m and A2m are inherited in fixed combinations. There were five main and four minor Gm-Am haplotypes that could be deduced from the phenotypes. This led to the conclusion that the populations studied are Caucasoids with some African admixture (about 10%) and a very low oriental contribution. Furthermore, there were 11 samples which showed 8 uncommon Gm-Am phenotypes. These could be explained by the assumption of five different uncommon Gm-Am haplotypes. Four of these may have arisen by equal crossing over of prevalent haplotypes. The fifth may be the result of unequal crossing over of prevalent haplotypes. The fifth may be the result of unequal crossing over, since it was proven, by family study, that more markers are transmitted together than are present in the prevalent haplotypes.

Female↗
PubMed1979

HLA markers in six Lebanese religious subpopulations.

A total of 315 normal, unrelated individuals from six of the seven principal religious communities of Lebanon have been typed for 26 alleles of the A and B loci. The gene, haplotype frequencies and delta values have been calculated. The HLA gene frequencies for loci A and B reported in this study are shown to cross Moslim-Christian lines, but generate a distinguishably different profile for the Armenian immigrant subpopulation. This first-level homogeneity which is inconsistent with results earlier reported for ABO, rhesus and Gm systems, seems to disappear when linkage disequilibrium deltas are compared.

ABO Blood-Group System↗
PubMed1978

Common and uncommon immunoglobulin haplotypes among Lebanese communities.

Allotypes of IgG1, IgG2, IgG3, and IgA2 subclasses were investigated in seven Lebanese communities (three Moslem and four Christian). The Gm-Am haplotypes found were mainly those prevalent in Caucasians with a low frequency of haplotypes usually observed in Africans and Orientals. The difference between highlanders and lowlanders as expressed by G2m(23) was highly significant and suggested a possible adaptation to selective pressure related to the gamma2 genes, possibly due to endemic malaria in the past. Exceptional Gm-Am haplotypes were unambiguously determined by family studies. Some were characterized either by a deletion or a repression or, in contrast, by a partial or total duplication of gamma genes. Two others had uncommon combinations of allotypes: Gm17;23;5,10,11,13,14 A2m1, where G1m (17) was present without G1m (1); and Gm3;23;5,14 A2m1, where the CH3 allotypes G3m (10,11,13) were lacking.

Gene Frequency↗
PubMed1977

[Cytochemical study of intestinal endocrine cells in rabbit fetuses during in vitro induced degeneration and differentiation (author's transl)].

Ontogenic differentiation of intestinal serotonin cells of 22 days old rabbit fetuses were studied in vitro. After 3 days of organotypic cultivation in solid medium, a great part of epithelial cells became necrotic and were eliminated into the lumen while a first flattened, then cuboïdal, then prismatic new growed epithelium in which FIF indicated some serotonin cells was present. Comparison of pictures obtained on the same slide by different methods was used in order to estimate correspondances between amine storage, argentaffin, argyrophilic and reductive properties. A new phase in serotonin cell differentiation was readily distinguished since young cells successively yeilded FIF, later argyrophilia, later argentaffinity. These datas, at variance with that occurs in vivo where FIF and argyrophilia appeared simultaneously, give a new criteria for differential mechanism studies, disprove the theory of an amine induced argyrophilia and enhance the hypothesis of a hyaloplasmic amine storage in very young cells.

Animals↗
PubMed1977

Improvements in electron microscopy by application of superconductivity.

Resolution tests on amorphous carbon foils were carried out in an electron microscope with a superconducting system containing 4 lenses including a shielding lens at 200 kV beam voltage. Due to the mechanical and electrical stability of the system and the absence of contamination of the specimen the highest space frequencies transferred at vertically incident beam were 6 nm-1 corresponding to a resolution of 0.17 nm, a value which approaches the theoretical resolving power of the electron optical system. It should also be feasible to apply such a lens system for microprobe analysis without strongly reducing the theoretical resolution limit, if the construction of the shielding lens is slightly changed.

Carbon↗
PubMed1977

Recombination, mutation, or constitutive expression at a Gm locus and familial hypergammaglobulinemia.

In a hypercholesterolemic Lebanese family, an uncommon Gm haplotype carrying an unexpected C gamma 1 gene was inherited by only one of 10 siblings. A new recombination during the maternal or paternal meiosis could explain its formation. According to this hypothesis, our data would be informative for the linkage relationship between the gamma-cistrons and the alpha 2-cistron. The latter might be located near the N-terminal side of the gamma-cistron linkage group, and the sequence of genes would be alpha 2, gamma 4, gamma 3, and gamma 1. A mutation could also effect the change from G1m(17) (codons AAA and AAG) TO G1m(3) (codons AGA and AGG). Another alternative is to postulate a constitutive expression of a C gamma 1 structural gene which, normally, would not be expressed. The uncommon derepression could be the consequence of uncommon cellular response to environmental, pathological or metabolic perturbation of a regulatory mechanism.

Adolescent↗
PubMed1976

[De novo trisomy 4p by 4p isochromosome].

A new example of trisomy 4p is reported, due in this case to formation of an isochromosome i(4p). The long arm of chromosome 4 was translocated onto the short arm of chromosome 1.

Child, Preschool↗
PubMed1976

Evidence for "deleted" or "silent" genes homozygous at the locus coding for the constant region of the gamma3 chain.

Three uncommon stable Gm haplotypes, Gm3;23;--, Gm1,2,17;..;-- and Gm1,17;..;-- have been transmitted through 3 generations of two related Lebanese and Syrian families. No pathological consequence was noted in seven individuals, aged 14--65, whose sera were deficient for all the allotypes carried by the IgG3 chains. Among the different genetic events which could have produced these haplotypes (alteration of a regulatory gene, point mutation, gene hybridization, gene deletion), it appears that a structural deletion is the most probable explanation. The observed data can be explained by either a partial or a total deletion of the constant portion of the IgG3 heavy chain.

Adolescent↗
PubMed1976

[Coexistence of reactive and nonreactive endocrine cells in the fundal mucosa in the rabbit].

Whether the same endocrine like cells are reactive towards different staining methods has been examined in normal and L-Dopa treated rabbits for distinction of cell types. Correlation with electron microscopy is proposed. It seems likely that SM cells (poorly reactive with Sevier-Munger technic) include two cell types: cells having around medium size and dense granules; cells having small round dense granules (D1?). X cells may correspond to a well defined group at the electron or photonic microscopic level. Insertion of D cells (according to Solcia and coworkers nomenclature) is not satisfactory but true non Apud cells are described. The signification of Jt (dim yellow) cells remains unknown.

Animals↗
PubMed1975

[Ultrastructural and cytochemical study of the endocrine serotonin secreting cells of the fetal and adult rabbit intestinal mucosa].

Endocrine cells of intestinal mucosa have been studied in rabbit fetuses and adults. The problem of an ultrastructural identification of "preargentaffin" serotonin cells has been elucidated comparing cytochemical and ultrastructural datas. Since all cells exhibiting a yellow formaldehyde-induced fluorescence reacted with Sevier-Munger method and since all impregnated cells were fluorescent it has been concluded that impregnated cells at the electron microscope level are serotonin cells; these cells had generally small and round granules. Another cell type with small round granules showing deposition of silver grains on the outer rim has been identified as granular S cells.

Animals↗
PubMed1975

[Quantitative study of serotonin-containing cells in fetal rabbit duodenum].

In order to attempt identification in vitro of parameters involved in the cellular differenciation, it was necessary to possess a standard material with identical content and distribution of serotonin cells; these two properties are investigated in this paper. Falck's technic is the only sensitive and specific method in demonstrating serotonin young cells devoid of argentaffinity. From 21, 22, 23 and 25 days old rabbit foetuses, 10 mm length duodenal pieces were treated according to Falck and sections serially cut at 8 microns. Some of these specimens were divided prior to Falck treatment in two pieces 3 mm away from the pylorus and in each piece 200 paraffin sections were cut at 8 microns beginning by adjacent ends and progressing in opposite direction. The number of EC sections in 400 whole transverse sections were determined for each foetus. Great variations were observed from one foetus to another, along the intestine, with weight and age. The Student-Fisher test applied to two consecutive pieces of the same duodenum gathering foetuses in groups of 5 animals did not show significative differences from a group to another. Thus, this material can be employed for comparisons under experimental conditions.

Animals↗