Action de deux polybases sur la charge et l'agrégation des plaquettes

Summary The action of two polybases (polybren and DEAE Dextran) on the electrophoretic mobility of platelets is studied. These two substances induce a decrease of the mobility. An investigation of the aggregability with the help of a photometric test shows a correlation between the charge decrease and platelet aggregation.

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Ce travail a été réalisé avec l'aide de la D.R.M.E. (section Biologie), Contrat No. 71.34.010.00.480.75.01.     

Polarity of meiotic gene conversion in fungi: Contrasting views

The frequency of meiotic gene conversion often varies linearly from one end of the gene to the other. This phenomenon has been called polarity. In this review, we will primarily discuss studies of polarity that have been done in the yeastSaccharomyces cerevisiae (ARG4 and HIS4 loci) and inAscobolus (b2 locus) with an emphasis on possible mechanisms. The genetic and physical data obtained at these hotspots of recombination strongly suggests that the formation of a polarity gradient reflects both the frequency of heteroduplex formation and the processing of this recombination intermediate by mismatch-repair-dependent processes.This article is dedicated to the memory of Seymour Fogel.     

Oligopotent stem cells are distributed throughout the mammalian ocular surface

The integrity of the cornea, the most anterior part of the eye, is indispensable for vision. Forty-five million individuals worldwide are bilaterally blind and another 135 million have severely impaired vision in both eyes because of loss of corneal transparency; treatments range from local medications to corneal transplants, and more recently to stem cell therapy. The corneal epithelium is a squamous epithelium that is constantly renewing, with a vertical turnover of 7 to 14 days in many mammals. Identification of slow cycling cells (label-retaining cells) in the limbus of the mouse has led to the notion that the limbus is the niche for the stem cells responsible for the long-term renewal of the cornea; hence, the corneal epithelium is supposedly renewed by cells generated at and migrating from the limbus, in marked opposition to other squamous epithelia in which each resident stem cell has in charge a limited area of epithelium. Here we show that the corneal epithelium of the mouse can be serially transplanted, is self-maintained and contains oligopotent stem cells with the capacity to generate goblet cells if provided with a conjunctival environment. Furthermore, the entire ocular surface of the pig, including the cornea, contains oligopotent stem cells (holoclones) with the capacity to generate individual colonies of corneal and conjunctival cells. Therefore, the limbus is not the only niche for corneal stem cells and corneal renewal is not different from other squamous epithelia. We propose a model that unifies our observations with the literature and explains why the limbal region is enriched in stem cells.     

Resequencing of 200 human exomes identifies an excess of low-frequency non-synonymous coding variants

Targeted capture combined with massively parallel exome sequencing is a promising approach to identify genetic variants implicated in human traits. We report exome sequencing of 200 individuals from Denmark with targeted capture of 18,654 coding genes and sequence coverage of each individual exome at an average depth of 12-fold. On average, about 95% of the target regions were covered by at least one read. We identified 121,870 SNPs in the sample population, including 53,081 coding SNPs (cSNPs). Using a statistical method for SNP calling and an estimation of allelic frequencies based on our population data, we derived the allele frequency spectrum of cSNPs with a minor allele frequency greater than 0.02. We identified a 1.8-fold excess of deleterious, non-syonomyous cSNPs over synonymous cSNPs in the low-frequency range (minor allele frequencies between 2% and 5%). This excess was more pronounced for X-linked SNPs, suggesting that deleterious substitutions are primarily recessive.     

Life's Greatest Secret: The Race to Crack the Genetic Code

In response to the Lisbon earthquake of 1 November 1755, and the subsequent seismic activity in Europe, Kant wrote several articles on earthquakes and volcanic phenomena. Full translations of the most important parts of these articles are presented, and summaries for the remainder. Kant developed a carefully worked out theory to account for seismic activity, based on his reading of the scientific literature, the reports received in Königsberg of the Lisbon earthquake and associated events, and his general theory of the origin of the Earth's crust, as presented in his Allgemeine Naturgeschichte of 1755. Following Lémery, Kant supposed that volcanic action was due to the subterranean combination of sulphur and iron, and he rejected the suggestion that earthquakes might be due to the gravitational pull of heavenly bodies. Kant's theory was naturalistic, but his account was not wholly divorced from physicotheological considerations.