Cell-type-specific replication initiation programs set fragility of the FRA3B fragile site

Common fragile sites have long been identified by cytogeneticists as chromosomal regions prone to breakage upon replication stress. They are increasingly recognized to be preferential targets for oncogene-induced DNA damage in pre-neoplastic lesions and hotspots for chromosomal rearrangements in various cancers. Common fragile site instability was attributed to the fact that they contain sequences prone to form secondary structures that may impair replication fork movement, possibly leading to fork collapse resulting in DNA breaks. Here we show, in contrast to this view, that the fragility of FRA3B--the most active common fragile site in human lymphocytes--does not rely on fork slowing or stalling but on a paucity of initiation events. Indeed, in lymphoblastoid cells, but not in fibroblasts, initiation events are excluded from a FRA3B core extending approximately 700 kilobases, which forces forks coming from flanking regions to cover long distances in order to complete replication. We also show that origins of the flanking regions fire in mid-S phase, leaving the site incompletely replicated upon fork slowing. Notably, FRA3B instability is specific to cells showing this particular initiation pattern. The fact that both origin setting and replication timing are highly plastic in mammalian cells explains the tissue specificity of common fragile site instability we observed. Thus, we propose that common fragile sites correspond to the latest initiation-poor regions to complete replication in a given cell type. For historical reasons, common fragile sites have been essentially mapped in lymphocytes. Therefore, common fragile site contribution to chromosomal rearrangements in tumours should be reassessed after mapping fragile sites in the cell type from which each tumour originates.     

The knockout mouse project

Mouse knockout technology provides a powerful means of elucidating gene function in vivo, and a publicly available genome-wide collection of mouse knockouts would be significantly enabling for biomedical discovery. To date, published knockouts exist for only about 10% of mouse genes. Furthermore, many of these are limited in utility because they have not been made or phenotyped in standardized ways, and many are not freely available to researchers. It is time to harness new technologies and efficiencies of production to mount a high-throughput international effort to produce and phenotype knockouts for all mouse genes, and place these resources into the public domain.     

Immunization against cobra venom

Zusammenfassung Durch Behandlung mit Glutardialdehyd wirdNaja-naja-Gift weitgehend entgiftet. Einzeldosen bis zu 20 mg pro Kaninchen können ohne Nebenwirkungen injiziert werden. Durch Immunisierung von Kaninchen wird eine gute Antikörperbildung gegenNajanaja-Gift — und vor allem auch gegen die niedermolekularen Toxine — erzielt.     

Fringe is a glycosyltransferase that modifies Notch

Notch receptors function in highly conserved intercellular signalling pathways that direct cell-fate decisions, proliferation and apoptosis in metazoans. Fringe proteins can positively and negatively modulate the ability of Notch ligands to activate the Notch receptor. Here we establish the biochemical mechanism of Fringe action. Drosophila and mammalian Fringe proteins possess a fucose-specific beta1,3 N-acetylglucosaminyltransferase activity that initiates elongation of O-linked fucose residues attached to epidermal growth factor-like sequence repeats of Notch. We obtained biological evidence that Fringe-dependent elongation of O-linked fucose on Notch modulates Notch signalling by using co-culture assays in mammalian cells and by expression of an enzymatically inactive Fringe mutant in Drosophila. The post-translational modification of Notch by Fringe represents a striking example of modulation of a signalling event by differential receptor glycosylation and identifies a mechanism that is likely to be relevant to other signalling pathways.     

Beeinflussung der Antennendifferenzierung durch Colchicin bei derDrosophilamutanteAristopedia

Summary A decrease in growth rate of the antennal bud by means of colchicine deflects the differentiation of theAristopedia antenna towards an arista.

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DieDrosophilamutanteAristopedia unterscheidet sich von der Wildform durch die Umwandlung der Fühlergeißel (=Arista) in einen Fuß.     

Tissue-specific activation of a cloned alpha-fetoprotein gene during differentiation of a transfected embryonal carcinoma cell line

To identify cis-acting DNA elements involved in the activation of the alpha-fetoprotein gene during differentiation, modified copies of the gene were introduced into murine F9 embryonal carcinoma cells. The differentiation of the transformants to either parietal or visceral endoderm was accompanied by induction of the exogenous template in a manner qualitatively, but not quantitatively, identical to that of the endogenous alpha-fetoprotein gene.     

Retarded enzymatic degradation of heterologous eledoisin sequences

Zusammenfassung Analoge des Eledoisin-Oktapeptides 4–11, die Hydrazid-Komponenten enthalten, sind durch Aminopeptidasen nur bis zur Heterobindung abbaubar. Sie werden wesentlich langsamer als die native Sequenz bzw. nicht durch Organhomogenate inaktiviert, wenn die Substitution im N-terminalen Bereich erfolgt. Mögliche sterische Veränderungen des Peptids durch eingebaute Fremdbausteine sind diskutiert.     

C19- and C18-steroids in cerebrospinal fluid,plasma and urine after intravenous administration of 7α-3H-DHEA35S-sulphate

Zusammenfassung Nach i.v. Injektion von 7-H-DHEA-³⁶S-sulfat wurden Liquor, Plasma und 24-Stundenharn eines Mannes auf freie und konjugierte, markierte C₁₉- und C₁₈-Steroide untersucht. Es zeigte sich, dass schon 30 Minuten nach Versuchsbeginn im Liquor fast nur doppelt-markierte Steroid-sulfatide mit praktisch unverändertem Isotopenverhältnis³H/³⁵S enthalten waren. Da weiterhin DHEA und seine Metaboliten im Liquor eine weitaus niedrigere spezifische³H-Aktivität besassen als die entsprechenden Verbindungen im Plasma, ist anzunehmen, dass der Übertritt von lipophilen Steroid-sulfatiden zwar verhältnismässig rasch, aber nur in begrenztem Umfang erfolgte.