Hypoxia-inducible factor 1α regulates branching morphogenesis during kidney development

The kidneys are exposed to hypoxic conditions during development. Hypoxia-inducible factor (HIF), an important mediator of the response to hypoxia, is believed to have an important role in development. However, the relationship between HIF and branching morphogenesis has not been elucidated clearly.     

The APC/C activator Cdh1 regulates the G2/M transition during differentiation of placental trophoblast stem cells

Differentiation of placental trophoblast stem (TS) cells to trophoblast giant (TG) cells is accompanied by transition from a mitotic cell cycle to an endocycle. Here, we report that Cdh1, a regulator of the anaphase-promoting complex/cyclosome (APC/C), negatively regulates mitotic entry upon the mitotic/endocycle transition. TS cells derived from homozygous Cdh1 gene-trapped (Cdh1^GT/GT) murine embryos accumulated mitotic cyclins and precociously entered mitosis after induction of TS cell differentiation, indicating that Cdh1 is required for the switch from mitosis to the endocycle. Furthermore, the Cdh1^GT/GT TS cells and placenta showed aberrant expression of placental differentiation markers. These data highlight an important role of Cdh1 in the G2/M transition during placental differentiation.     

Extensin Secreted into the Culture Medium by Tobacco Cells I. Purification and Some Properties

The medium of 12-day-old culturs of tobacco cells (Nicotianatabacum L., var Xanthi; line XD-6S) contain c.a. 160mg/literof protein, of which 14% of the constituent ami no acids werefound to be hydroxyproline. By sequential column chromatographiesand CsCl density-gradient centrifugation, a basic hydroxyproline-richglycoprotein was purified from the medium and found to havean amino acid composition typical of extensin; with a high levelof hydroxyproline (33mole%), tyrosine (13%), and lysine (14%).The glycoprotein contained 42% (w/w) of sugars, among whicharabinose was the major component (85%). The proportion of thisextensin in the proteins in the culture medium was estimatedto be much higher than that of arabino-galactan protein (about5 times higher) on a protein basis, with extensin comprisingbetween 25% and 41%, and probably about 37% of the proteinsin the medium. (Received September 19, 1988; Accepted December 26, 1988)     

Localization of cytochrome P-450 in the colonic mucosa of 3-methylcholanthrene-pretreated and untreated rats An immunohistochemical study

Summary Immunohistochemical localization of cytochrome P-450 in the colonic mucosa of 3-methylcholanthrene-pretreated and untreated rats was studied by indirect fluorescent antibody staining technique. A polyclonal antibody for cytochrome P-450_MC purified from hepatic microsomes of 3-methylcholanthrene-pretreated rats was used for this experiment. A strong immunofluorescence was found to be localized in the cytoplasm of the surface epithelium of the mucosa in the colon of 3-methylcholanthrene-pretreated rats. A faint immunofluorescence was also observed in the epithelium of untreated rats. 7-Ethoxycoumarin O-deethylase activity of colonic microsomes was significantly enhanced by 3-methylcholanthrene-pretreatment in parallel with an increase in the intensity of immunostaining for cytochrome P-450_MC in Western blotting analysis. This is the first report on the localization of cytochrome P-450 in the colonic mucosa.     

Stabilization of cortical microtubules by the cell wall in cultured tobacco cells

Cortical microtubules (MTs) in protoplasts prepared from tobacco (Nicotiana tabacum L.) BY-2 cells were found to be sensitive to cold. However, as the protoplasts regenerated cell walls they became resistant to cold, indicating that the cell wall stabilizes cortical MTs against the effects of cold. Since poly-l-lysine was found to stabilize MTs in protoplasts, we examined extensin, an important polycationic component of the cell wall, and found it also to be effective in stabilizing the MTs of protoplasts. Both extensin isolated from culture filtrates of tobacco BY-2 cells and extensin isolated in a similar way from cultures of tobacco XD-6S cells rendered the cortical MTs in protoplasts resistant to cold. Extensin at 0.1 mg·ml⁻¹ was as effective as the cell wall in this respect. It is probable that extensin in the cell wall plays an important role in stabilizing cortical MTs in tobacco BY-2 cells.     

Analysis of Vibrio cholerae O139 Bengal Isolated from Different Geographical Areas Using Macrorestriction DNA Analysis

Vibrio cholerae O139 isolated from different countries, as well as from different locations within a country, were examined using macrorestriction DNA analysis to determine the clonality of the O139 strains. NotI digests of genomic DNA of representative strains from Nepal, India, Bangladesh, China, Thailand, and Malaysia revealed very similar but not identical patterns. Examinations of the banding patterns generated by pulsed-field gel electrophoresis of strains isolated within countries revealed complete homogeneity. These results further reiterate the spread of an identical clone of V. cholerae O139 although it appears that genetic polymorphism among the O139 strains is becoming apparent.     

Typing of Verotoxins by DNA Colony Hybridization with Poly- and Oligonucleotide Probes,a Bead-Enzyme-Linked Immunosorbent Assay,and Polymerase Chain Reaction

To identify the type of Verotoxins (VT) produced by Verocytotoxin-producing Escherichia coli (VTEC), a sensitive bead-enzyme-linked immunosorbent assay and polymerase chain reaction with common and specific primers to various VTs (VT1, VT2, VT2vha, VT2vhb, and VT2vp1) were developed. Together with colony hybridization tests with oligo- and polynucleotide probes, these methods were applied to VTEC isolates to type the VT produced. The toxin types of 26 of 37 strains were identified, but the reaction profiles in assays of the remaining 11 strains suggested the existence of new VT2 variants. The application of these identification procedures may be useful as a tool for clinical and epidemiological studies of VTEC infection.     

Improvement of serum amino acid profile in hepatic failure with the bioartificial liver using multicellular hepatocyte spheroids

We designed a bioartificial liver support system in which encapsulated multicellular spheroids of rat hepatocytes were utilized as a bioreactor in a hollow fiber cartridge. The spheroids, formed in a positively charged polystyrene dish that contained hormonally defined medium, were encapsulated into microdroplets of agarose that contained about 9 x 10(7) rat hepatocytes. The medium, including 150 mL reservoir volume, was circulated in a closed circuit in which the cartridge was inserted. The pH and levels of dissolved oxygen were monitored and automatically regulated so that they were maintained within a constant range for 72 h. Albumin accumulated in the circuit at the rate of 2.0 mg/L/h in this system. When the bioreactor cells in the system were replaced with Hep G2 cells, a human hepatoblastoma cell line, albumin accumulated at the rate of 0.15 mg/L/h. The spheroids of primary culture hepatocytes had 13 times higher albumin-producing capacity than the aggregates of Hep G2. The serum of a patient with fulminant hepatic failure was circulated in this system with the spheroids of primary culture hepatocytes. The concentration of branched amino acid (BCAA) in the circuit significantly increased during the 48 h circulation, while the concentration of aromatic amino acid (AAA) and methionine decreased. The ratio of BCAA/AAA increased from 0.640 to 0.772, indicating that the hepatocyte spheroids had improved the imbalance of the amino acid profile in the serum. These findings indicate that this system may be a useful model for an artificial liver support. (c) 1996 John Wiley & Sons, Inc.     

Purification and properties of a novel enzyme,N-acylamino acid racemase,from Streptomyces atratus Y-53

A novel enzyme, N-acylamino acid racemase, was purified to homogeneity from Streptomyces atratus Y-53 and characterized. This enzyme catalyzes the interconversion of optically active N-acylamino acids. The relative molecular mass (M_r) of the enzyme was estimated to be about 41 000 and 244 000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration, respectively, indicating that the enzyme is composed of six subunits with an equal M_r. The enzyme showed a broad substrate specificity toward N-acylamino acids, such as N-acetylmethionine, N-chloroacetylphenylalanine and N-chloroacetylvaline. The apparent Michaelis constant (K_m) values for N-acetyl-l-methionine and N-acetyl-d-methionine were calculated to be 15.2 and 5.6 mm, respectively. Enzyme activity was markedly enhanced by divalent metal ions, such as Co²⁺, Mg²⁺ and Mn²⁺, and was inhibited by metal-chelating reagent, indicating that the enzyme is a metalloenzyme. We propose to name the enzyme N-acylamino acid racemase (acylamino acid racemase). Correspondence to: S. Tokuyama     

Global bifurcation structure of a Bonhoeffer-van der Pol oscillator driven by periodic pulse trains

The Bonhoeffer-van der Pol (BVP) oscillator is a valuable dynamical system model of pacemaker neurons. Isochrons, phase transition curves (PTC), and two dimensional bifurcation diagrams served to analyze the neuron's response to periodic pulse stimuli. Responses are described and explained in terms of the nonlinear dynamical system theory. An important issue in the generation of spikes by pacemaker neurons is the existence of both slow and fast dynamics in the state point's trajectory in the phase plane. It is this feature in particular that makes the BVP oscillator a faithful model of living pacemaker neurons. Comparison of the model's responses with those of a living pacemaker was based also on return maps of interspike intervals. Analyzed in detail were the complex discharges called stammering which involve interspike intervals that arise unpredictably and exhibit histograms with several modes separated by the equal intervals.Supported by Trent H. Wells Jr. Inc.