Mechanism of buffy coat migration inhibition test

Résumé La présence de lymphocytes et la synthèse de la protéine sont nécessaires à la production du MIF (migration inhibition factor). Pour le test de migration des leucocytes du sang périphérique, nous avons pu montrer en utilisant un antigène soluble (PPD) et du sérum de cheval, qu'il n'y a point d'inhibition de migration en l'absence des lymphocytes ou en présence de puromycine. Quand le milieu contient du sérum de sujet testé, l'inhibition n'est que partiellement sensible à la puromycine.

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Supported by a grant from the New York Chapter of the Arthritis Foundation.

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Post-doctoral Fellow, National Institute of Arthritis and Metabolic disease.     

A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way

Many galaxies are thought to have supermassive black holes at their centres-more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray emission have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 +/- 1.5) x 10(6) solar masses (M(*)). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.     

Competence to replicate in the unfertilized egg is conferred by Cdc6 during meiotic maturation

Meiotic maturation, the final step of oogenesis, is a crucial stage of development in which an immature oocyte becomes a fertilizable egg. In Xenopus, the ability to replicate DNA is acquired during maturation at breakdown of the nuclear envelope by translation of a DNA synthesis inducer that is not present in the oocyte. Here we identify Cdc6, which is essential for recruiting the minichromosome maintenance (MCM) helicase to the pre-replication complex, as this inducer of DNA synthesis. We show that maternal cdc6 mRNA but not protein is stored in the oocyte. Cdc6 protein is synthesized during maturation, but this process can be blocked by degrading the maternal cdc6 mRNA by oligonucleotide antisense injections or by translation inhibition. Rescue experiments using recombinant Cdc6 protein show that Cdc6 is the only missing replication factor whose translation is necessary and sufficient to confer DNA replication competence to the egg before fertilization. The licence to replicate is given by Cdc6 at the end of meiosis I, but the cytostatic factor (CSF) pathway, which maintains large amounts of active Cdc2/Cyclin B2, prevents the entry into S phase until fertilization.