Transcription factor Sp1 is essential for early embryonic development but dispensable for cell growth and differentiation.

Transcription factor Sp1 has been implicated in the expression of many genes. Moreover, it has been suggested that Sp1 is linked to the maintenance of methylation-free CpG islands, the cell cycle, and the formation of active chromatin structures. We have inactivated the mouse Sp1 gene. Sp1-/- embryos are retarded in development, show a broad range of abnormalities, and die around day 11 of gestation. In Sp1-/- embryos, the expression of many putative target genes, including cell cycle-regulated genes, is not affected, CpG islands remain methylation free, and active chromatin is formed at the globin loci. However, the expression of the methyl-CpG-binding protein MeCP2 is greatly reduced in Sp1-/- embryos. MeCP2 is thought to be required for the maintenance of differentiated cells. We suggest that Sp1 is an important regulator of this process

Establishment of Histone Modifications after Chromatin Assembly

Every cell has to duplicate its entire genome during S-phase of the cell cycle. After replication, the newly synthesized DNA is rapidly assembled into chromatin. The newly assembled chromatin ‘matures’ and adopts a variety of different conformations. This differential packaging of DNA plays an important role for the maintenance of gene expression patterns and has to be reliably copied in each cell division. Posttranslational histone modifications are prime candidates for the regulation of the chromatin structure. In order to understand the maintenance of chromatin structures, it is crucial to understand the replication of histone modification patterns. To study the kinetics of histone modifications in vivo, we have pulse-labeled synchronized cells with an isotopically labeled arginine (15N4) that is 4 Da heavier than the naturally occurring 14N4 isoform. As most of the histone synthesis is coupled with replication, the cells were arrested at the G1/S boundary, released into S-phase and simultaneously incubated in the medium containing heavy arginine, thus labeling all newly synthesized proteins. This method allows a comparison of modification patterns on parental versus newly deposited histones. Experiments using various pulse/chase times show that particular modifications have considerably different kinetics until they have acquired a modification pattern indistinguishable from the parental histones

L’intertextualité dans le théâtre de Samuel Beckett ou l’écriture du Tout au Rien

Notre époque a été largement marquée par un effritement du "je" et on en est venu à se demander qui parle quand on dit "je". Le "je", comme réalité inexpugnable avait déjà reçu de sérieux avertissements : ceux de Schopenhauer qui met son crédit en doute par la théorie de la représentation ; ceux de Nietzsche, ensuite, qui, dans le Livre du philosophe, conteste la notion de personne car il y voit une valeur périmée et mensongère, typique de l’occident. Pour lui, le véritable sujet n’est pas l’..

Épidémiologie de l'infection au virus West Nile

CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

An Eph-related receptor protein tyrosine kinase gene segmentally expressed in the developing mouse hindbrain

This article has been corrected. See http://hdl.handle.net/10261/167777In search of genes possibly involved in the regulation of hindbrain segmentation, we have isolated mouse cDNA clones corresponding to putative protein kinase genes by polymerase chain reaction amplification of cDNA from 9.5-day-old embryo hindbrains. In situ hybridization analysis revealed that one of these genes, Sek, was expressed in an alternating segment-restricted pattern in the developing hindbrain. Isolation and analysis of Sek cDNAs covering the entire coding sequence indicated that Sek encoded a putative receptor protein tyrosine kinase, belonging to the Eph family. These data are consistent with a role of the Sek gene product in a signal transduction process involved in pattern formation in the hindbrain.Peer reviewe