Experimentally produced ependymal inclusions in the brain ofXenopus laevis

Zusammenfassung Verletzungen des Endhirns beim erwachsenen Krallenfrosch (Xenopus laevis) führen zur Entstehung von Ventrikelteilen, die vollständig oder teilweise vom Ventrikelsystem des Gehirns isoliert sind. Das Ependym solcher Ventrikelteile zeigt stark Chromhämatoxylin-positive cytoplasmatische Einschlüsse (GPI), die im Perikaryon und in den Zellfortsätzen der Tanycyten lokalisiert sind. Charakter und Bedeutung der GPI werden diskutiert.     

Kinetik des Malondialdehydes im Organismus

Summary We followed the kinetics of malonyldialdehyde in vivo and we found that it is very quickly metabolized. This may result in inaccuracy in the estimation of lipoperoxidation in the organism (reaction with 2-thiobarbituric acid).     

Selection and validation of differentially expressed genes in head and neck cancer

We applied a robust combinatorial (multi-test) approach to microarray data to identify genes consistently up- or down-regulated in head and neck squamous cell carcinoma (HNSCC). RNA was extracted from 22 paired samples of HNSCC and normal tissue from the same donors and hybridized to the Affymetrix U95A chip. Forty-two differentially expressed probe sets (representing 38 genes and one expressed sequence tag) satisfied all statistical tests of significance and were selected for further validation. Selected probe sets were validated by hierarchical clustering, multiple probe set concordance, and target-subunit agreement. In addition, real-time PCR analysis of 8 representative (randomly selected from 38) genes performed on both microarray-tested and independently obtained samples correlated well with the microarray data. The genes identified and validated by this method were in comparatively good agreement with other rigorous HNSCC microarray studies. From this study, we conclude that combinatorial analysis of microarray data is a promising technique for identifying differentially expressed genes with few false positives.Received 12 February 2004; received after revision 22 March 2004; accepted 14 April 2004     

β2-integrins mediate a novel form of chemoresistance in cycloheximide-induced U937 apoptosis

In this study with cycloheximide (CHX, an inhibitor of protein synthesis) and the human leukaemic cell line U937, a novel form of chemoresistance, which we termed sudden drug resistance (SDR), was identified using Hoechst33258 staining, Western blott and DNA Ladder. CHX^high (10–100 g/ml)-induced apoptosis can spontaneously subside after 4–6 h or can be inhibited by short-term preincubation with CHXlow (2.5 g/ml). Unlike typical multidrug resistance, SDR is not caused by reduced drug accumulation or altered protein expression, and may be associated with a non-P-glycoprotein mechanism. To uncover this underlying mechanism, we focused on U937 cell aggregation promoted by CHX, because cell adhesion has been suggested to influence cell survival and prevent apoptosis. EDTA, or anti-CD18 monoclonal antibody, but not EGTA, acetylsalicylic acid or RGDS tetrapeptide, abrogated this homotypic aggregation and greatly increased CHX-induced apoptosis in a time-dependent manner, while fibrinogen and soluble intercellular adhesion molecule-1 exerted opposite effects. These results establish that ₂-integrin engagement is a key mediator of SDR, although it may be non-exclusive. This finding supplements the classical basis of chemoresistance and may provide another opportunity for improved leukemia therapy.Received 15 April 2004; received after revision 18 May 2004; accepted 21 June 2004     

The chordate amphioxus: an emerging model organism for developmental biology

The cephalochordate amphioxus is the closest living invertebrate relative of the vertebrates. It is vertebrate-like in having a dorsal, hollow nerve cord, notochord, segmental muscles, pharyngeal gill slits and a post-anal tail that develops from a tail bud. However, amphioxus is less complex than vertebrates, lacking neural crest and having little or no mesenchyme. The genetic programs patterning the amphioxus embryo are also similar to those patterning vertebrate embryos, although the amphioxus genome lacks the extensive gene duplications characteristic of vertebrates. This relative structural and genomic simplicity in a vertebrate-like organism makes amphioxus ideal as a model organism for understanding mechanisms of vertebrate development.Received 18 February 2004; received after revision 9 April 2004; accepted 19 April 2004     

C-peptide stimulates Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase via activation of ERK1/2 MAP kinases in human renal tubular cells

Proinsulin-connecting peptide (C-peptide) exerts physiological effects partially via stimulation of Na⁺, K⁺-ATPase. We determined the molecular mechanism by which C-peptide stimulates Na⁺, K⁺-ATPase in primary human renal tubular cells (HRTCs). Incubation of the cells with 5 nM human C-peptide at 37°C for 10 min stimulated ⁸⁶Rb⁺ uptake by 40% (p<0.01). The carboxy-terminal pentapeptide was found to elicit 57% of the activity of the intact molecule. In parallel with ouabain-sensitive ⁸⁶Rb⁺ uptake, C-peptide increased subunit phosphorylation and basolateral membrane (BLM) abundance of the Na⁺, K⁺-ATPase ₁ and ₁ subunits. The increase in BLM abundance of the Na⁺, K⁺-ATPase ₁ and ₁ subunits was accompanied by depletion of ₁ and ₁ subunits from the endosomal compartments. C-peptide action on Na⁺, K⁺-ATPase was ERK1/2-dependent in HRTCs. C-peptide-stimulated Na⁺, K⁺-ATPase activation, phosphorylation of ₁-subunit and translocation of ₁ and ₁ subunits to the BLM were abolished by a MEK1/2 inhibitor (20 M PD98059). C-peptide stimulation of ⁸⁶Rb⁺ uptake was also abolished by preincubation of HRTCs with an inhibitor of PKC (1 M GF109203X). C-peptide stimulated phosphorylation of human Na⁺, K⁺-ATPase subunit on Thr-Pro amino acid motifs, which form specific ERK substrates. In conclusion, C-peptide stimulates sodium pump activity via ERK1/2-induced phosphorylation of Thr residues on the subunit of Na⁺, K⁺-ATPase.Received 15 June 2004; received after revision 14 September 2004; accepted 14 September 2004     

Mechanoelectrical transduction of adult outer hair cells studied in a gerbil hemicochlea

Sensory receptor cells of the mammalian cochlea are morphologically and functionally dichotomized. Inner hair cells transmit auditory information to the brain, whereas outer hair cells (OHC) amplify the mechanical signal, which is then transduced by inner hair cells. Amplification by OHCs is probably mediated by their somatic motility in a mechanical feedback process. OHC motility in vivo is thought to be driven by the cell's receptor potential. The first steps towards the generation of the receptor potential are the deflection of the stereociliary bundle, and the subsequent flow of transducer current through the mechanosensitive transducer channels located at their tips. Quantitative relations between transducer currents and basilar membrane displacements are lacking, as well as their variation along the cochlear length. To address this, we simultaneously recorded OHC transducer currents (or receptor potentials) and basilar membrane motion in an excised and bisected cochlea, the hemicochlea. This preparation permits recordings from adult OHCs at various cochlear locations while the basilar membrane is mechanically stimulated. Furthermore, the stereocilia are deflected by the same means of stimulation as in vivo. Here we show that asymmetrical transducer currents and receptor potentials are significantly larger than previously thought, they possess a highly restricted dynamic range and strongly depend on cochlear location.     

Copper oxide superconductors: sharp-mode coupling in high-Tc superconductors

In conventional superconductivity, sharp phonon modes (oscillations in the crystal lattice) are exchanged between electrons within a Cooper pair, enabling superconductivity. A critical question in the study of copper oxides with high critical transition temperature (Tc) is whether such sharp modes (which may be more general, including, for example, magnetic oscillations) also play a critical role in the pairing and hence the superconductivity. Hwang et al. report evidence that sharp modes (either phononic or magnetic in origin) are not important for superconductivity in these materials, but we show here that their conclusions are undermined by the insensitivity of their experiment to a crucial physical effect.