Comptes rendus de l'Academie des sciences. Serie III, Sciences de la vie最新文献

This note aims to given an interpretation of the "paradoxical" increase of dizygotic twin pregnancies (and more generally of multiple pregnancies) according to maternal age, when in parallel the number of growing follicles decreases strongly. From the analysis, through an allometric model, of the relative variations with age of the size of the various ovarian follicular compartments, it reinforces the hypothesis of the existence of an inhibition factor, whose level would depend on the size of the residual stock of follicles and which would act on one or several phases of the follicular development. It brings evidence for the major role that this factor might play in the regulation of the whole reproductive life of women (and probably other mammals).

Certain morphological data, obtained in studies of the ultrastructure of centrioles and basal bodies in cells of metazoa and protists, lead us to think that the cartwheel represents of the most appropriate organization for a self-reproducing and transmissible centriolar organizer. Centrioles and basal bodies might then not be simply the centres of replication of those organizers, but also reservoirs containing several superposed centriolar organizers, which are released depending on the requirements of the cell. As an isolated cartwheel is extremely unlikely to be detected, either in conventional electron microscopy or in immunocytochemistry, it is thus the reservoir which has so far been under consideration. Such a hypothesis would permit the explanation that biogenesis de novo and biogenesis in proximity to preexisting organelles may differ only in terms of the number of morphogenetic units involved.

The aim of this work was to investigate possible inhibitory effects of Ca+ and different cyclosporins (Cs) on the rat brain mitochondrial respiratory control ratio (RCR) and whether or not these effects could be antagonized by trimetazidine (TMZ). The RCR was evaluated as the state 3/state 4 ratio of oxidative phosphorylation. CsA, D, and G inhibited about 10% of RCR in a concentration-dependent manner with EC50 of 57, 19 and 7 nM, respectively, whereas CsH did not modify RCR. TMZ was able to fully antagonize this inhibitory effect in a concentration-dependent manner with EC50 of 5,200, 180, and 1 nM, respectively. The Ca2+ added to the mitochondrial preparation decreased RCR in a concentration-dependent manner with a maximal effect of 46% obtained with 100 microM Ca2+. In the presence of TMZ (100 microM), the inhibitory effect of Ca2+ was partly reversed (9%). TMZ alone showed no inhibitory or stimulant effect on RCR. These results show that restoration of RCR by TMZ is due to a Ca(2+)-dependent mechanism, promoting Ca2+ efflux from the mitochondrial matrix. However, Ca2+ efflux is only partial in case of Ca2+ overload. These data suggest that TMZ may restore ATP synthesis in circumstances where neither Ca2+ overload, nor a prooxidant have generated a RCR decrease.

An experimental system allowing the observation of 2 active organizing centers during zebrafish development is described. It was achieved by injection into a single marginal cell at the 16-cell stage of TARAM-A-D mRNA. TARAM-A-D was previously described as the mutated constitutive form of a type I receptor for transforming growth factor beta. In 80% of the injected embryos, 2 distinct organizers were observed at the onset of gastrulation. At the end of gastrulation, these embryos showed duplicated axial structures. Nevertheless, only 25% of the injected embryos displayed a recognizable axis duplication after 1 day of development. This paradox is taken as an evidence for suppressive effects exerted in a reciprocal manner when more than 1 organizing center is present.

The method of neural networks was tested for its ability to assign individuals on the basis of their multilocus genotypes, using a data collection of 430 honeybees and 8 microsatellite loci. This data set includes various taxonomical levels (populations within the same subspecies, various subspecies belonging to the same evolutionary lineage, and the 3 lineages of the species). Qualitative genotypic data have been submitted to 2 types of transformation (simple coding and coding plus factorial correspondence analysis), and they have been partitioned in 2 sets, a training set of 300 individuals and a testing set of 103 individuals. Two procedures ("leave one out" and "hold out") were applied to evaluate the quality of prediction. Compared to discriminant analysis, neural networks performed better in terms of correctly classified individuals at any taxonomical level. For instance, with the simple coding and the hold out procedure, the proportions of correctly assigned individuals from the testing set were 66.2%, 82.3% and 100% at the populations, subspecies and lineage level, respectively. The potential use of neural networks in populations genetics is discussed.

The activities of 18 enzymes involved in the intermediary and energy metabolism were measured in certain widely-spread peracarid crustaceans: 3 hypogean (Niphargus virei, Niphargus rhenorhodanensis and Stenasellus virei) and 2 epigean (Gammarus fossarum and Asellus aquaticus) ones. The activities of numerous enzymes were correlated with the known metabolic rates of the 5 species. Such rates are reduced in hypogean organisms: levels of enzymatic activity in subterranean species were 1.2 to 8.6 times lower than in epigean species for the main key regulatory enzymes involved in the Krebs cycle and glycolysis (phosphofructokinase, pyruvate kinase, hexokinase and citrate synthetase). The relative activities of phosphofructokinase, glycogen phosphorylase and hexokinase clearly indicated that glycogen was the main fuel oxidized in both epigean and hypogean organisms. A higher glycogen phosphorylase/hexokinase ratio in hypogean than in epigean crustaceans showed that subterranean species had a greater ability to function anaerobically. The presence of high activities of glutamate-pyruvate transaminase and lactate dehydrogenase in all species (and of malate dehydrogenase and fumarase in hypogean species) was indicative of a coupled fermentation of glycogen and glutamate during anaerobiosis, with lactate and alanine as end-products (as well as succinate in hypogean species). A low fructose-1,6-bisphosphatase/phosphofructokinase ratio, associated with a low level of phosphoenolpyruvate carboxykinase activity, indicated that the glycolytic pathway was active and that gluconeogenic ability was limited in epigean crustaceans. In contrast, in hypogean species, association of a higher ratio and a high level of phosphoenolpyruvate carboxykinase activity suggested a low glycolytic activity and a high gluconeogenic ability.

In order to determine the origin of cellulases in the gut of the earthworm Eisenia fetida andrei, the wall tissues of the different parts of the disinfected gut are cultured in vitro. Enzymatic activities (FPase: filter paper activity; CMCase: carboxymethycellulase, cellobiase) were measured both in the tissues and in the culture medium: the following activities were found, carboxymethycellulase (CMCase), filter paper activity (FPase). The first located in the crop, gizzard and midgut wall, the second in the foregut and midgut wall. The cellobiase was detected only in the crop and gizzard tissues, whereas it is present in each part of the gut of holoxenic worms. This fact indicates that this enzyme is mainly produced by microorganisms ingested. These results allow us to propose the hypothesis of the existence of synergy, for the cellulose hydrolysis between tissular enzymes and cellulolytic microorganisms.

The high concentrations of molecules immunologically related to salmon calcitonin (CT) and/or to human calcitonin gene-related peptide (CGRP) in the oesophagus of the norway lobster Nephrops norvegicus have been examined. In the present study. We report the purification of these molecules by means of a specific radioimmunoassay for calcitonin and calcitonin gene related peptide. The immunoreactive molecules were tested for their functional similarities with CT and CGRP. This was investigated by measuring their ability to interact with CGRP and CT radioreceptor assays and to stimulate the adenylate cyclase activity in rat liver and kidney membranes, respectively. In addition, the purified product was injected in young rats in order to check for a CT-like biological activity of these molecules. The combination of these tests led us to purify a molecular form of 33 kDa. N-terminal sequence analysis of this protein revealed a considerable homology with the lobster cysteine proteases and the human cathepsin L. Control experiments performed with the highly purified American lobster cysteine protease I showed that crustacean cysteine proteases given in vivo to rats induce a fall in the plasma calcium and phosphate levels. This study therefore adds further documentation for a common ancestral origin of CT, CGRP and the much large cysteine proteases from invertebrates.

The cystic fibrosis transmembrane conductance regulator (CFTR) is a transmembrane protein that is expressed in several epithelia, including kidney tubules. Mutations in CFTR (a PKA-chloride channel and/or regulator of other epithelial channels) give rise to the clinical manifestation of cystic fibrosis, and result in the synthesis of mutated proteins responsible for altering ion transport across secretory epithelia. The low abundance of endogenous CFTR makes a difficult to purify enough of the native protein to prepare anti-CFTR antibodies. We have used differential centrifugation to prepare cortical brush border membrane vesicles from pig kidney, cBBMV, and developed a method for the partial purification of CFTR. This is the first step in the isolation of native CFTR. The results show that CFTR is present in cBBMV. The purified protein will provide a clearer picture of the biophysical and biochemical properties of native CFTR.

In order to better understand the role of the immunodominant V3 loop in the type-specific immune response and also to determine if this sequence has a role in AIDS pathogenesis, notably in the induction of apoptosis in CD4+ cells, we have introduced 2 modifications in the env gene from pNL4-3: a partial deletion in the V3 loop, keeping only the conserved tip of the loop GPGRAF consensus sequence (env delta V3-GPGRAF) and, secondly, a complete deletion of V3 sequence plus 43 nucleotides in C3 (env delta V3+). These constructions as well as the non-modified env gene, were cloned and expressed in a baculovirus system. Western blot analysis has shown that both modified env gene products reacted with a reference anti-HIV-1 serum to the same extent as the non-modified gp 160. However, in contrast to the non-modified env-protein and to env delta V3-GPGRAF, the env delta V3+ protein failed to bind to CD4 molecule, although V3 is not directly involved in receptor binding. These modified and non-modified recombinant proteins will be very useful to determine the potential of the partially or totally V3-deleted gp 160 to induce broadly reactive neutralizing antibodies and also to determine if V3 has a role in certain aspects of HIV-induced pathogenesis, notably apoptosis.