Cloning of a new aquaporin (AQP10) abundantly expressed in duodenum and jejunum

A new aquaporin (AQP10) was identified in human small intestine. This gene encoded a 264-amino-acid protein with high sequence identity with AQP3 (53%), 9 (52%), and 7 (43%). These AQPs constitute one subfamily of AQP family that is differentiated from the other subfamily of AQP (AQP0, 1, 2, 4, 5, 6, and 8) by sequence homology. Ribonuclease protection assay and Northern blotting demonstrated almost exclusive expression of AQP10 mRNA in the duodenum and jejunum. In situ hybridization localized it in absorptive jejunal epithelial cells. Xenopus oocytes expressing AQP10 exhibited an increased osmotic water permeability in a mercury-sensitive manner. Although AQP10 belongs to the AQP subfamily, which has been characterized by permeability to water and neutral solutes such as urea and glycerol, it was not permeable to urea nor glycerol. The specific expression of AQP10 suggests its contribution to the water transport in the upper portion of small intestine.     

Regulation of the cell cycle at the G1-S transition by proteolysis of cyclin E and p27Kip1

The transition from G1 phase to S phase of the mammalian cell cycle is controlled by many positive and negative regulators, among which cyclin E and p27Kip1, respectively, undergo the most marked changes in concentration at this transition. The abundance of both cyclin E and p27Kip1 is regulated predominantly by posttranslational mechanisms, in particular by proteolysis mediated by the ubiquitin-proteasome pathway. Cyclin E and p27Kip1 each bind to and undergo polyubiquitination by the same ubiquitin ligase, known as SCF(Skp2). The degradation of cyclin E and p27Kip1 is greatly impaired in Skp2-deficient mice, resulting in intracellular accumulation of these proteins. In this article, recent progress in characterization of the molecular mechanisms that control the proteolysis of cyclin E and p27Kip1 is reviewed.     

An F-box protein, FWD1, mediates ubiquitin-dependent proteolysis of beta-catenin

beta-catenin plays an essential role in the Wingless/Wnt signaling cascade and is a component of the cadherin cell adhesion complex. Deregulation of beta-catenin accumulation as a result of mutations in adenomatous polyposis coli (APC) tumor suppressor protein is believed to initiate colorectal neoplasia. beta-catenin levels are regulated by the ubiquitin-dependent proteolysis system and beta-catenin ubiquitination is preceded by phosphorylation of its N-terminal region by the glycogen synthase kinase-3beta (GSK-3beta)/Axin kinase complex. Here we show that FWD1 (the mouse homologue of Slimb/betaTrCP), an F-box/WD40-repeat protein, specifically formed a multi-molecular complex with beta-catenin, Axin, GSK-3beta and APC. Mutations at the signal-induced phosphorylation site of beta-catenin inhibited its association with FWD1. FWD1 facilitated ubiquitination and promoted degradation of beta-catenin, resulting in reduced cytoplasmic beta-catenin levels. In contrast, a dominant-negative mutant form of FWD1 inhibited the ubiquitination process and stabilized beta-catenin. These results suggest that the Skp1/Cullin/F-box protein FWD1 (SCFFWD1)-ubiquitin ligase complex is involved in beta-catenin ubiquitination and that FWD1 serves as an intracellular receptor for phosphorylated beta-catenin. FWD1 also links the phosphorylation machinery to the ubiquitin-proteasome pathway to ensure prompt and efficient proteolysis of beta-catenin in response to external signals. SCFFWD1 may be critical for tumor development and suppression through regulation of beta-catenin protein stability.     

Ecto-ATPase activity in the rat cardiac muscle: biochemical characteristics and histocytochemical localization

We used a combined biochemical and histocytochemical approach to study ecto-ATPase in the rat cardiac muscle. The reaction medium employed for histocytochemical detection was optimized in biochemical assays to achieve the highest enzyme activity and lowest inhibition by the capture agent used for visualization of the reaction product. Approximately 70% of the enzyme activity was retained in samples after the fixation procedure. Divalent cations stimulated ecto-ATPase. High activity was detectable within a wide pH range. Histocytochemical reaction was observed at sites at which extracellular ATP can potentially exert its actions on the cardiac muscle: nerve endings, plasma membranes of cardiac myocytes and capillary endothelial cells, and T-tubules. Product of the reaction was found exclusively at the outer surface of the cells. In controls, enzyme activity was abolished by diethyl pyrocarbonate and slightly stimulated by digitonin and concanavalin A, whereas sodium orthovanadate, N-ethylmaleimide, and sodium azide yielded no effect. Our results support the view that cardiac ecto-ATPase is involved in important physiological functions and suggest that its activity may be regulated by the release of ATP from nerve endings.     

Artificial life simulation of self-assembly in bacteriophage by movable finite automata

This paper presents a model which is based on biological research using the movable finite automata (MFA) on a self-assembly of T4 phage, and exhibits the results of artificial life simulation. In the previous work, Thompson and Goel [Artificial Life, Addison Weley, 1989, pp. 317-340; Biosystems 18 (1985) 23; J. Theor. Biol. 131 (1988) 351] presented the movable finite automata (MFA) which has a capability of moving on finite automata, and simulated on a computer. They were represented individual rectangular boxes, however, the results of simulation was different from real T4 phage. We propose the sphere model as a protein structure, and simulate the self-assembly of the entire structure of the T4 phage on a computer.     

Genome sequence of Symbiobacterium thermophilum, an uncultivable bacterium that depends on microbial commensalism

Symbiobacterium thermophilum is an uncultivable bacterium isolated from compost that depends on microbial commensalism. The 16S ribosomal DNA-based phylogeny suggests that this bacterium belongs to an unknown taxon in the Gram-positive bacterial cluster. Here, we describe the 3.57 Mb genome sequence of S.thermophilum. The genome consists of 3338 protein-coding sequences, out of which 2082 have functional assignments. Despite the high G + C content (68.7%), the genome is closest to that of Firmicutes, a phylum consisting of low G + C Gram-positive bacteria. This provides evidence for the presence of an undefined category in the Gram-positive bacterial group. The presence of both spo and related genes and microscopic observation indicate that S.thermophilum is the first high G + C organism that forms endospores. The S.thermophilum genome is also characterized by the widespread insertion of class C group II introns, which are oriented in the same direction as chromosomal replication. The genome has many membrane transporters, a number of which are involved in the uptake of peptides and amino acids. The genes involved in primary metabolism are largely identified, except those that code several biosynthetic enzymes and carbonic anhydrase. The organism also has a variety of respiratory systems including Nap nitrate reductase, which has been found only in Gram-negative bacteria. Overall, these features suggest that S.thermophilum is adaptable to and thus lives in various environments, such that its growth requirement could be a substance or a physiological condition that is generally available in the natural environment rather than a highly specific substance that is present only in a limited niche. The genomic information from S.thermophilum offers new insights into microbial diversity and evolutionary sciences, and provides a framework for characterizing the molecular basis underlying microbial commensalism.     

Anti-fungal sesquiterpenoid from the root exudate of Solanum abutiloides

The Solanum abutiloides plant is highly resistant to soil-borne pathogens such as Fusarium oxysporum f. sp. melongenae, Verticillium dahliae, and Ralstonia solanacearum. This species is utilized as a mating source of resistant cultivars and is also used as a rootstock. The root exudate of Solanum abutiloides was extracted from a soil system composed of charcoal and vermiculite. Anti-fungal activity was found in the extract, and an active ingredient was isolated. The chemical structure of the active compound was determined to be 3-beta-acetoxysolavetivone, a new sesquiterpenoid. The anti-fungal activity of 3-beta-acetoxysolavetivone examined by the inhibition of spore germination of Fusarium oxysporum was close to that of lubimin, and higher than that of solavetivone.     

Hes genes regulate size, shape and histogenesis of the nervous system by control of the timing of neural stem cell differentiation

Radial glial cells derive from neuroepithelial cells, and both cell types are identified as neural stem cells. Neural stem cells are known to change their competency over time during development: they initially undergo self-renewal only and then give rise to neurons first and glial cells later. Maintenance of neural stem cells until late stages is thus believed to be essential for generation of cells in correct numbers and diverse types, but little is known about how the timing of cell differentiation is regulated and how its deregulation influences brain organogenesis. Here, we report that inactivation of Hes1 and Hes5, known Notch effectors, and additional inactivation of Hes3 extensively accelerate cell differentiation and cause a wide range of defects in brain formation. In Hes-deficient embryos, initially formed neuroepithelial cells are not properly maintained, and radial glial cells are prematurely differentiated into neurons and depleted without generation of late-born cells. Furthermore, loss of radial glia disrupts the inner and outer barriers of the neural tube, disorganizing the histogenesis. In addition, the forebrain lacks the optic vesicles and the ganglionic eminences. Thus, Hes genes are essential for generation of brain structures of appropriate size, shape and cell arrangement by controlling the timing of cell differentiation. Our data also indicate that embryonic neural stem cells change their characters over time in the following order: Hes-independent neuroepithelial cells, transitory Hes-dependent neuroepithelial cells and Hes-dependent radial glial cells.     

Acute and chronic effects of FR-149175, a beta 3-adrenergic receptor agonist, on energy expenditure in Zucker fatty rats

Clinical therapies for both obesity and obese non-insulin-dependent diabetes mellitus require maintenance of reduced body weight after the initial successful reduction resulting from calorie control, exercise, or medication. Although beta(3)-adrenergic receptor (beta(3)-AR) agonists have been shown to stimulate whole body energy expenditure and lipid mobilization, whether stimulatory effects on oxygen consumption and lipolysis are influenced by chronic exposure to agonists has not been fully characterized. We therefore examined the acute and chronic effects of FR-149175, a selective beta(3)-AR agonist, on whole body oxygen consumption in genetically obese Zucker fatty rats. Chronic treatment with FR-149175 caused a decrease in both body weight gain and white fat pad weight at doses that induced lipolysis in acute treatment (1 and 3.2 mg/kg p.o.). Single administration of FR-149175 (0.1, 1, and 3.2 mg/kg p.o.) dose dependently increased whole body oxygen consumption. Repetitive administration did not cause attenuation of the thermogenic response at lower doses (0.1 and 1 mg/kg 2 times daily), whereas the highest dose (3.2 mg/kg 2 times daily) induced a progressive increase in oxygen consumption. PCR analyses of retroperitoneal white adipose tissue indicated little or no change in beta(3)-AR mRNA levels. Uncoupling protein 1 gene expression increased at 1 mg/kg, and drastic upregulation was detected at 3.2 mg/kg. FR-149175 also increased HSL mRNA levels in a dose-related manner, whereas there was no effect on genes involved in beta-oxidation. These results support that the thermogenic effect of beta(3)-AR agonists is not attenuated by chronic exposure to agonists.