Techniques de recherche des polymorphismes génétiques

Sequencing the human genome has allowed the discovery of millions of DNA sequence variants. Sequence variations in human DNA are mainly present asSingle Nucleotide Polymorphisms (SNPs); this common form of variation is found about once every 1,000 bases in the human genome and 1.8 million SNPs have now been identified and located. The accessibility of databases of SNPs opens the possibility of studying the influence of these polymorphisms on disease risks as well as on drug responses. Numerous approaches have been set up for the identification of SNPs. In this review we describe the main techniques used for the identification of these polymorphisms. They rely on two major consequences of sequence variations: the apparition or the disappearance of restriction enzyme sites or the alteration of DNA strand hybridization due to the presence of a mismatch. Southern blotting and restriction endonucleases have allowed the development of the technique ofrestriction fragment length polymorphisms (RFLPs), now performed on PCR products. Several other approaches such as denaturing high-performance liquid chromatography or real-time PCR can detect allele differences upon re-hybridization and heteroduplex formation. However, DNA sequencing remains the obligate step for the positive identification of known or unknown SNPs. At last, the development of high-throughput methods allows a large increase in the rate of discovery of SNPs likely.     

Bryophytes du tardiglaciaire würmien de la zone nord-pyrénéenne des pyrénées occidentales françaises

Study of well-preserved macroscopic moss remains (stems, branches and leaves) present in a level of the Würm lateglacial (13 860 20 yr BP), from a section in a Sphagnum bog at the Estarrès (Ossau valley, Atlantic Pyrenees, France). Pollen analysis of the level shows that an hygrophilous and hydrophilous vegetation with Poaceae, Apiaceae, Ranunculus, Thalictrum, Sparganium, Potamogeton, Betula and Salix occurred in the lake depression of the Estarrès. Bryum neodamense, Calliergon giganteum, Scorpidium scorpioides, Calliergonella cuspidata, Drepanocladus aduncus and Philonotis sp. probably lived in fens at the lakeside (or even immerged in the lake in the case of the first three species). The occurrence of Eurhynchium speciosum indicates the existence of very moist and shaded habitats, whereas Palustriella commutata and Tortella tortuosa grew either on rocks or on bare calcareous soils that were respectively damp or dry. According to the French phytoecological data bank “Sophy”, Bryum neodamense and Scorpidium scorpioides are ecologically very similar to Calliergon giganteum. The three species are presently no longer found at the site of the Estarrès and are so far unknown from the Ossau valley and the Basque country, where the climatic conditions should however be suitable for them. Furthermore, these mosses are very rare in the Pyrenees. Finally, Sphagna, which are nowadays abundant at the Estarrès, are absent from the studied level.     

Fréquences de la mutation Δ32 du gène du corécepteur CCR5 dans les différentes régions françaises

We studied the frequency of the coreceptor CCR5 gene Δ32 mutation on 1836 DNA samples originating from ten French regions. This mutation confers, in the homozygous state, resistance to HIV-1 infection. For the whole territory, the mean percentage presence of the Δ32 mutation is 9.2 %. The mutation is statistically more frequent in the north (11.2 %) than in the south (6.3 %) of the country; this différenciation corresponds probably to a gradient of decreasing frequencies of the Δ32 mutation in Europe.     

Ecologie des coléoptères saproxyliques dans les forêts de l’étage montagnard des Alpes du nord françaises

Ecology of the saproxylic beetles in mountain forests of the northern French Alps. Both saproxylic beetles and deadwood stocks were studied in order to detect special deadwood features important for these organisms, and to better understand their ecology. A total of 37 window traps were used in ten stations covering four mountain forests in the French northern Alps. In the same time, the deadwood stocks were inventoried in the ten stations. 181 m³ of deadwood (1219 fragments) were measured and 4268 individuals belonging to 235 saproxylic species were trapped. The deadwood volume ranges from 21.1 to 233.6 m³/ha and the number of beetle species from 27 to 113. A positive relation was observed between the stand age, the whole volume of deadwood and the species richness of saproxylic beetles. However, in some deadwood rich sites the beetle diversity is not as high as expected. This was explained by the negative influence of the management history of the forest. The compositions of saproxylic communities depend also of some characteristics of the deadwood stocks. Xylophagous and zoophagous species prefer “not lying and recently dead softwood” while the mycophagous and saproxylophagous species are strongly dependent on fungi growing on hardwood, respectively under “large surfaces of barks” and in “large woody debris”. Surprisingly, the majority of the saproxylic beetles living on softwood does not depend on the most represented resinous deadwood type: the “decayed and lying softwood”.