Reversible change in thiol redox status of the insulin receptor alpha-subunit in intact cells

In this study, we used maleimidobutyrylbiocytin to examine possible alteration that may occur in the redox state of the insulin receptor (IR) sulfhydryl groups in response to reduced glutathione (GSH) or N-acetyl-L-cysteine (NAC). Short-term treatment of intact cells expressing large numbers of IR with GSH or NAC led to a rapid and reversible reduction of IR alpha-subunit disulfides, without affecting the receptor beta-subunit thiol reactivity. The overall integrity of the oligomeric structure of IR was maintained, indicating that neither class I nor class II disulfides were targeted by these agents. Similar findings were obtained in cells transfected with IR mutants lacking cysteine524, one of the class I disulfides that link the two IR alpha-subunits. Membrane-associated thiols did not participate in GSH- or NAC-mediated reduction of IR alpha-subunit disulfides. No difference in insulin binding was observed in GSH-treated cells; however, ligand-mediated increases in IR autophosphorylation, tyrosine phosphorylation of cellular substrates, and dual phosphorylation of the downstream target mitogen-activated protein kinase were inhibited at concentrations of GSH (10 mM or greater) that yielded a significant increase in IR alpha-subunit thiol reactivity. GSH did not affect IR signaling in the absence of insulin. Our results provide the first evidence that the IR alpha-subunit contains a select group of disulfides whose redox status can be rapidly altered by the reducing agents GSH and NAC.     

Swelling activation of transport pathways in erythrocytes: effects of Cl-, ionic strength, and volume changes

If swelling of acell is induced by a decrease in external medium tonicity, theregulatory response is more complex than if swelling of similarmagnitude is due to salt uptake. The present results provide anexplanation. In fish erythrocytes, two distinct transport pathways wereswelling activated: a channel of broad specificity and aK⁺-Clcotransporter. Each was activated by a specific signal: the channel bya decrease in intracellular ionic strength and theK⁺-Clcotransporter by cell enlargement. A decrease in ionic strength alsoaffectedK⁺-Clcotransport activity, but by acting as a negative modulator of thecotransport. Thus cells swollen by salt accumulation respond byactivating exclusively theK⁺-Clcotransport, leading to aCl-dependentK⁺ loss. By contrast, cellsswollen by electrolyte dilution respond by activating both pathways,leading to a reduced loss of electrolytes and a large loss of taurine.Thus two swelling-sensitive pathways, differently regulated, wouldallow control of the ionic composition of a cell exposed to differentvolume perturbations.

     

Trapping radioactive carbon dioxide during cellular metabolic assays under standard culture conditions: description of a unique gas-capturing device

Measurement of carbon dioxide levels has been employed to follow cellular metabolic reactions for quite some time. By radio-labeling substrate molecules and evaluating the radioactivity levels of the carbon dioxide released, insight into metabolic pathways can be gleaned. Currently, no carbon dioxide capturing device is available that can be used with large volume cell monolayers growing under standard conditions within a regular commercially available culture flask. In this note we describe a simple device for collecting radio-labeled carbon dioxide from a standard culture flask. The device is independent of the culture flask, but can be attached for metabolic measurements allowing cells to be grown under standard conditions prior to study. The presented design permits convenient transfer of the device between flasks without contaminating or disturbing cells growing within the flasks. Data are presented demonstrating the reproducibility of measurements made with multiple devices with different substrate concentrations and varying periods of time, ranging up to 3 h.     

Milking of microalgae

The low productivity of algal cultures in the production of high-value compounds is the most significant bottleneck for commercialization of this technology. Cultures in which cell mass is reused for continuous production are proposed as a solution to overcome this problem. Recently, a method was developed in which beta-carotene was harvested from the microalga Dunaliella salina grown in a two-phase bioreactor. This raises the question of whether this technique could also be used in the mass production of secondary metabolites. Understanding the mechanism of the milking process and its relationship to the product formation pathway should reveal whether other products can be milked from various species of microalgae.     

Autoclave method for rapid preparation of bacterial PCR-template DNA

An autoclave method for preparing bacterial DNA for PCR template is presented, it eliminates the use of detergents, organic solvents, and mechanical cellular disruption approaches, thereby significantly reducing processing time and costs while increasing reproducibility. Bacteria are lysed by rapid heating and depressurization in an autoclave. The lysate, cleared by microcentrifugation, was either used directly in the PCR reaction, or concentrated by ultrafiltration. This approach was compared with seven established methods of DNA template preparation from four bacterial sources which included boiling Triton X-100 and SDS, bead beating, lysozyme/proteinase K, and CTAB lysis method components. Bacteria examined were Enterococcus and Escherichia coli, a natural marine bacterial community and an Antarctic cyanobacterial-mat. DNAs were tested for their suitability as PCR templates by repetitive element random amplified polymorphic DNA (RAPD) and denaturing gradient gel electrophoresis (DGGE) analysis. The autoclave method produced PCR amplifiable template comparable or superior to the other methods, with greater reproducibility, much shorter processing time, and at a significantly lower cost.     

Effect of Cryptobia salmositica-induced anorexia on feeding behavior and immune response in juvenile rainbow trout Oncorhynchus mykiss

At 10 degrees C, rainbow trout Oncorhynchus mykiss (n = 13 per group) infected with Cryptobia salmositica Katz, 1951 became anorexic at 3 wk post-infection (w.p.i.), with feed-intake decreasing significantly from 1.33 to 0.94% body weight (b.w.). Anorexia was most severe at 4 w.p.i. (0.80% b.w.), coinciding with peak parasitemia (9.2 x 10(6) parasites ml blood(-1)) and anemia. At 8 w.p.i., fish had recovered their appetite although they still had contained detectable parasites (6.8 x 10(5) parasites ml(-1)) and were anemic (pack cell volume, PCV, of 24.4%). However at 5 degrees C, anorexia occurred at 5 w.p.i. (0.81% b.w.), and was most severe at 7 w.p.i. (0.40% b.w.). At 8 w.p.i. (0.43% b.w.), fish displayed high parasitemia (4.6 x 10(6) parasites ml(-1)) and low PCV (10.8%). Fish at 5 degrees C had lower gastric evacuation (GE) rates (GE48h) than 10 degrees C fish, however there were no differences between infected and naive fish at both temperatures. Before anorexia, there was no significant correlation between mean share of meal (MSM, a measure of how food was partitioned within a group) and coefficient of variation in feeding but this became significant during anorexia (p = 0.02 and p = 0.0002 at 10 and 5 degrees C respectively). Significant correlations were detected between b.w. and MSM before onset of anorexia at 10 degrees C (p = 0.005) and 5 degrees C (p = 0.02); this was maintained at 10 degrees C (p = 0.001) but not at 5 degrees C (p = 0.98). Fish on an anorexic diet (0.93% b.w.) responded well at 10 degrees C to a live C. salmositica vaccine; this could partly be due to constant antigenic stimulation by the live vaccine.     

Domain movements of elongation factor eEF2 and the eukaryotic 80S ribosome facilitate tRNA translocation

An 11.7-A-resolution cryo-EM map of the yeast 80S.eEF2 complex in the presence of the antibiotic sordarin was interpreted in molecular terms, revealing large conformational changes within eEF2 and the 80S ribosome, including a rearrangement of the functionally important ribosomal intersubunit bridges. Sordarin positions domain III of eEF2 so that it can interact with the sarcin-ricin loop of 25S rRNA and protein rpS23 (S12p). This particular conformation explains the inhibitory action of sordarin and suggests that eEF2 is stalled on the 80S ribosome in a conformation that has similarities with the GTPase activation state. A ratchet-like subunit rearrangement (RSR) occurs in the 80S.eEF2.sordarin complex that, in contrast to Escherichia coli 70S ribosomes, is also present in vacant 80S ribosomes. A model is suggested, according to which the RSR is part of a mechanism for moving the tRNAs during the translocation reaction.     

Stem cells: cross-talk and developmental programs

The thesis advanced in this essay is that stem cells-particularly those in the nervous system-are components in a series of inborn 'programs' that not only ensure normal development, but persist throughout life so as to maintain homeostasis in the face of perturbations-both small and great. These programs encode what has come to be called 'plasticity'. The stem cell is one of the repositories of this plasticity. This review examines the evidence that interaction between the neural stem cell (as a prototypical somatic stem cell) and the developing or injured brain is a dynamic, complex, ongoing reciprocal set of interactions where both entities are constantly in flux. We suggest that this interaction can be viewed almost from a 'systems biology' vantage point. We further advance the notion that clones of exogenous stem cells in transplantation paradigms may not only be viewed for their therapeutic potential, but also as biological tools for 'interrogating' the normal or abnormal central nervous system environment, indicating what salient cues (among the many present) are actually guiding the expression of these 'programs'; in other words, using the stem cell as a 'reporter cell'. Based on this type of analysis, we suggest some of the relevant molecular pathways responsible for this 'cross-talk' which, in turn, lead to proliferation, migration, cell genesis, trophic support, protection, guidance, detoxification, rescue, etc. This type of developmental insight, we propose, is required for the development of therapeutic strategies for neurodegenerative disease and other nervous system afflictions in humans. Understanding the relevant molecular pathways of stem cell repair phenotype should be a priority, in our view, for the entire stem cell field.