beta -Amyloid peptide activates alpha 7 nicotinic acetylcholine receptors expressed in Xenopus oocytes

The alpha7 nicotinic acetylcholine receptor is highly expressed in hippocampus and in cholinergic projection neurons from the basal forebrain, structures that are particularly vulnerable to the ravages of Alzheimer's disease. Previous work suggests that beta-amyloid peptide can interact with alpha7 nicotinic acetylcholine receptors, although the nature of this interaction has not been well characterized. To test whether beta-amyloid peptide can activate alpha7 nicotinic acetylcholine receptors, we expressed these receptors in Xenopus oocytes and performed two-electrode voltage clamp recordings, characterizing the response to beta-amyloid peptide 1-42 applied at concentrations ranging from 1 pm to 100 nm. In alpha7-expressing oocytes, beta-amyloid peptide 1-42 elicits inward currents at low concentrations (1-100 pm), whereas at higher concentrations (nm), less effective receptor activation is observed, indicative of receptor desensitization. Preincubation with the alpha7-selective agents, the antagonist methyllycaconatine, and the agonist 4-OH-GTS-21 blocked beta-amyloid peptide-induced receptor activation. beta-amyloid peptide 1-42 at low concentrations was able to activate the L250T mutant alpha7 receptor. The endogenous Ca(2+)-activated chloride current in Xenopus oocytes is recruited upon receptor activation since replacing Ca(2+) with Ba(2+) in the recording solution reduced current amplitude. Thus, when beta-amyloid peptide activation of alpha7 receptors occurs, these currents are comprised, at least in part, of Ca(2+).     

INK4a-deficient human diploid fibroblasts are resistant to RAS-induced senescence

The CDKN2A tumour suppressor locus encodes two distinct proteins, p16(INK4a) and p14(ARF), both of which have been implicated in replicative senescence, the state of permanent growth arrest provoked in somatic cells by aberrant proliferative signals or by cumulative population doublings in culture. Here we describe primary fibroblasts from a member of a melanoma-prone family who is homozygous for an intragenic deletion in CDKN2A. Analyses of the resultant gene products imply that the cells are p16(INK4a) deficient but express physiologically relevant levels of a frameshift protein that retains the known functions of p14(ARF). Although they have a finite lifespan, the cells are resistant to arrest by oncogenic RAS. Indeed, ectopic expression of RAS and telomerase (hTERT) results in outgrowth of anchorage-independent colonies that have essentially diploid karyotypes and functional p53. We find that in human fibroblasts, ARF is not induced demonstrably by RAS, pointing to significant differences between the proliferative barriers implemented by the CDKN2A locus in different cell types or species.     

Freshwater bryozoans (Bryozoa) of Norway III: distribution and ecology of Plumatella fruticosa

Bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of Plumatella fruticosawas evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance, and absence. According to our material P. fruticosais one of the most common bryozoan species in Norwegian fresh water, represented in samples from 251 localities. This species occurred frequently all over the country, north to 71° 06 N (the northernmost record globally). Maximum elevation above sea level was 1179 m (maximum for Northern Europe).In most studies of freshwater bryozoans from the holarctic region, Plumatella fruticosahas been reported as widely distributed, but locally rare. In Norway, however, P. fruticosa is frequently found all over the country, even far to the north. The species apparently finds an optimal climate in the cold temperate and cold regions of Norway. Plumatella fruticosapreferred lakes, avoided slow-flowing rivers and ponds, and was absent in smaller water bodies. The species preferred somewhat higher elevation (400–900 m above sea level), but avoided lakes with the lowest summer temperatures (below 11 °C). P. fruticosa also preferred oligotrophic conditions with poor aquatic vegetation, stony shores, lakes poor in calcium and magnesium (sometimes almost comparable with distilled water), where the water was clear and colourless, and slightly acidic to neutral. The species also preferred lakes surrounded by Sphagnum bogs and was absent when pH was below 5.2. P. fruticosa avoided eutrophic conditions with rich aquatic vegetation, alkaline water (pH above 7.0), lakes with a higher content of calcium and magnesium and those with strongly coloured water (above 100 mg Pt l^–1). In spite of its preference for ion-poor conditions, it was also found in a brackish water lake. For most environmental variables, the species had a wider tolerance range than reported from elsewhere.     

Suppressive subtractive hybridization detects extensive genomic diversity in Thermotoga maritima

Comparisons between genomes of closely related bacteria often show large variations in gene content, even between strains of the same species. Such studies have focused mainly on pathogens; here, we examined Thermotoga maritima, a free-living hyperthermophilic bacterium, by using suppressive subtractive hybridization. The genome sequence of T. maritima MSB8 is available, and DNA from this strain served as a reference to obtain strain-specific sequences from Thermotoga sp. strain RQ2, a very close relative (approximately 96% identity for orthologous protein-coding genes, 99.7% identity in the small-subunit rRNA sequence). Four hundred twenty-six RQ2 subtractive clones were sequenced. One hundred sixty-six had no DNA match in the MSB8 genome. These differential clones comprise, in sum, 48 kb of RQ2-specific DNA and match 72 genes in the GenBank database. From the number of identical clones, we estimated that RQ2 contains 350 to 400 genes not found in MSB8. Assuming a similar genome size, this corresponds to 20% of the RQ2 genome. A large proportion of the RQ2-specific genes were predicted to be involved in sugar transport and polysaccharide degradation, suggesting that polysaccharides are more important as nutrients for this strain than for MSB8. Several clones encode proteins involved in the production of surface polysaccharides. RQ2 encodes multiple subunits of a V-type ATPase, while MSB8 possesses only an F-type ATPase. Moreover, an RQ2-specific MutS homolog was found among the subtractive clones and appears to belong to a third novel archaeal type MutS lineage. Southern blot analyses showed that some of the RQ2 differential sequences are found in some other members of the order Thermotogales, but the distribution of these variable genes is patchy, suggesting frequent lateral gene transfer within the group.     

Constitutive expression of the beta-ketothiolase gene in transgenic plants. A major obstacle for obtaining polyhydroxybutyrate-producing plants

Polyhydroxybutyrate (PHB) is a member of a class of thermoelastic polymers called polyhydroxyalkanoates that serve many bacteria as intracellular storage molecules for carbon and energy. Transgenic plants provide a potential means of producing this polymer cost-effectively. To date, however, few reports of the successful production of this polymer have been published, with the exception of work with transgenic Arabidopsis. Using a variety of chimeric constructs, we have determined that the constitutive, chloroplast-localized expression of one of the genes involved in PHB production-the beta-ketothiolase (phbA) gene-is detrimental to the efficient production of transgenic PHB. The alternate use of either inducible or somatically activated promoters allowed the construction of transgenic PHB-producing potato (Solanum tuberosum) and tobacco (Nicotiana tabacum) plants, although the amount of PHB formed was still rather low. Taking advantage of an inducible promoter, the maximal amount of PHB produced in transgenic potato was 0.09 mg g(-1) dry weight. In transgenic tobacco using a somatically activated promoter, up to 3.2 mg g(-1) dry weight was accumulated. In Arabidopsis, the formation of high levels of PHB had previously been shown to be accompanied by severe negative effects on growth and development of the plant. Phasins are proteins known from PHB-producing bacteria speculated to serve as protectants against the highly hydrophobic surface of the PHB granules in the bacterial intracellular milieu. Co-expression of the phasin gene in parallel with the PHB synthesis genes, however, did not lead to reduced symptom development.     

Activity-dependent synaptogenesis in the adult Mammalian cortex

Recent electron microscopic studies provide evidence that the adult cortex generates new synapses in response to sensory activity and that these structural changes can occur rapidly, within 24 hr of sensory stimulation. Together with progress imaging synapses in vivo, the stage appears set for advances in understanding the dynamics and mechanisms of experience-dependent synaptogenesis.     

PKC epsilon is associated with myosin IIA and actin in fibroblasts

Proteins coimmunoprecipitating with protein kinase C (PKC) epsilon in fibroblasts were identified through matrix-assisted laser desorption/ionisation time of flight mass spectrometry (MALDI TOF m/s). This method identified myosin IIA in PKC epsilon immunoprecipitates, as well as known PKC epsilon binding proteins, actin, beta'Cop and cytokeratin. Myosin is not a substrate for PKC epsilon. Immunofluorescence analysis showed that PKC epsilon is colocalised with actin and myosin in actomyosin stress fibers in fibroblasts. Inhibitors of PKC and myosin ATPase activity, as well as microfilament-disrupting drugs, all inhibited spreading of fibroblasts after passage, suggesting a role for a PKC epsilon-actin-myosin complex in cell spreading.     

Multiple developmental roles of Ahnak are suggested by localization to sites of placentation and neural plate fusion in the mouse conceptus

Ahnak is a gigantic (700 kD) phosphoprotein with a unique structure whose expression and cellular localization are dynamically regulated during cell cycle progression. Here, we report that Ahnak is localized to sites of major morphogenesis during mouse placentation and neurulation. Ahnak was found in: (i) derivatives of trophectoderm, including chorionic ectoderm prior to and during union with the ectoplacental cone, presumptive syncytiotrophoblast cells in the chorionic labyrinth, and giant cells at the trophoblast-uterine interface; (ii) the allantois prior to, during, and after union with the chorion; and (iii) the tips of the neural plate during formation of the neural tube. On the basis of these observations, we suggest that Ahnak may play heretofore unrecognized roles in tissue union during normal mouse development.