Resource productivity and availability impacts for food-chain length

Ecologists have focused on food-chain length (FCL) for the past eight decades as an index of food-web structure. Here, I review the hypotheses determining FCL with a focus on resource productivity and availability effects on FCL. First, I introduce the mainstream hypotheses to explain FCL variations: productivity, ecosystem size, and disturbance. For the existing productivity and productive space hypotheses, I stress the importance of using resource availability to estimate the productivity effect on FCL. Using a FCL dataset from 15 ponds, I tested the resource stoichiometry effect on FCL for ponds with between carbon:nitrogen ratio of primary producers and FCL. Moreover, I provide a perspective for studying resource availability and stoichiometry effects on FCL and of the alternative hypotheses of productive-space and ecosystem size. Finally, I suggest the future directions of the FCL study: a resource subsidy and climate change effects on FCL and food-web structure.     

Stomach-specific calpain, nCL-2, localizes in mucus cells and proteolyzes the beta-subunit of coatomer complex, beta-COP

Calpain is a Ca2+-regulated cytosolic protease. Mammals have 14 calpain genes, half of which are predominantly expressed in specific organ(s); the rest are expressed ubiquitously. A defect in calpains causes lethality/pathogenicity, indicating their physiological indispensability. nCL-2/calpain-8a was identified as a stomach-specific calpain, whose physiological functions are unclear. To elucidate these, we characterized nCL-2 in detail. Unexpectedly, nCL-2 was localized strictly to the surface mucus cells in the gastric epithelium and the mucus-secreting goblet cells in the duodenum. Yeast two-hybrid screening identified several nCL-2-interacting molecules. Of these, the beta-subunit of coatomer complex (beta-COP) occurs in the stomach pit cells and is proteolyzed by nCL-2 in vitro. Furthermore, beta-COP and nCL-2 co-expressed in COS7 cells co-localized in the Golgi, and Ca2+-ionophore stimulation caused the proteolysis of beta-COP near the linker region, resulting in the dissociation of beta-COP from the Golgi. These results strongly suggest novel functions for nCL-2 that involve the membrane trafficking of mucus cells via interactions with coat protein.     

Jagged1-selective notch signaling induces smooth muscle differentiation via a RBP-Jkappa-dependent pathway

The Notch signaling pathway plays a crucial role in specifying cellular fates by interaction between cellular neighbors; however, the molecular mechanism underlying smooth muscle cell (SMC) differentiation by Notch signaling has not been well characterized. Here we demonstrate that Jagged1-Notch signaling promotes SMC differentiation from mesenchymal cells. Overexpression of the Notch intracellular domain, an activated form of Notch, up-regulates the expression of multiple SMC marker genes including SMC-myosin heavy chain (Sm-mhc) in mesenchymal 10T1/2 cells, but not in non-mesenchymal cells. Physiological Notch stimulation by its ligand Jagged1, but not Dll4, directly induces Sm-mhc expression in 10T1/2 cells without de novo protein synthesis, indicative of a ligand-selective effect. Jagged1-induced expression of SM-MHC was blocked bygamma-secretase inhibitor, N-(N-(3,5-difluorophenyl)-l-alanyl)-S-phenylglycine t-butyl ester, which impedes Notch signaling. Using Rbp-jkappa-deficient cells and site-specific mutagenesis of the SM-MHC gene, we show that such an induction is independent of the myocardin-serum response factor-CArG complex, but absolutely dependent on RBP-Jkappa, a major mediator of Notch signaling, and its cognate binding sequence. Of importance, Notch signaling and myocardin synergistically activate SM-MHC gene expression. Taken together, these data suggest that the Jagged1-Notch pathway constitutes an instructive signal for SMC differentiation through an RBP-Jkappa-dependent mechanism and augments gene expression mediated by the myocardin-SRF-CArG complex. Given that Notch pathway components are expressed in vascular SMC during normal development and disease, Notch signaling is likely to play a pivotal role in such situations to modulate the vascular smooth muscle cell phenotype.     

An isoflavone conjugate-hydrolyzing beta-glucosidase from the roots of soybean (Glycine max) seedlings: purification, gene cloning, phylogenetics, and cellular localization

Soybeans (Glycine max (L.) Merr.) and certain other legumes excrete isoflavones from their roots, which participate in plantmicrobe interactions such as symbiosis and as a defense against infections by pathogens. In G. max, the release of free isoflavones from their conjugates, the latent forms, is mediated by an isoflavone conjugate-hydrolyzing beta-glucosidase. Here we report on the purification and cDNA cloning of this important beta-glucosidase from the roots of G. max seedlings as well as related phylogenetic and cellular localization studies. The purified enzyme, isoflavone conjugate-hydrolyzing beta-glucosidase from roots of G. max seedling (GmICHG), is a homodimeric glycoprotein with a subunit molecular mass of 58 kDa and is capable of directly hydrolyzing genistein 7-O-(6 '-O-malonyl-beta-d-glucoside) to produce free genistein (k(cat), 98 s(-1); K(m), 25 microM at 30 degrees C, pH 7.0). GmICHG cDNA was isolated based on the amino acid sequence of the purified enzyme. GmICHG cDNA was abundantly expressed in the roots of G. max seedlings but only negligibly in the hypocotyl and cotyledon. An immunocytochemical analysis using anti-GmICHG antibodies, along with green fluorescent protein imaging analyses of Arabidopsis cultured cells transformed by the GmICHG:GFP fusion gene, revealed that the enzyme is exclusively localized in the cell wall and intercellular space of seedling roots, particularly in the cell wall of root hairs. A phylogenetic analysis revealed that GmICHG is a member of glycoside hydrolase family 1 and can be co-clustered with many other leguminous beta-glucosidases, the majority of which may also be involved in flavonoid-mediated interactions of legumes with microbes.     

Frictional properties of regenerated cartilage in vitro

Although tribological function is the most important mechanical property of articular cartilage, few studies have examined this function in tissue-engineered cartilage. We investigated changes in the frictional properties of cartilage regenerated from the inoculation of rabbit chondrocytes into fibroin sponge. A reciprocating friction-testing apparatus was used to measure the friction coefficient of the regenerated cartilage under a small load. The specimen was slid against a stainless steel plate in a water vessel filled with physiological saline. The applied load was 0.03 N, the stroke length was 20 mm, and the mean sliding velocity was 0.8 mm/s. The friction coefficient of the regenerated cartilage decreased with increasing cultivation time, because a hydrophilic layer of synthesized extracellular matrix was formed on the fibroin sponge surface. The friction coefficient of the regenerated cartilage was as low as that of natural cartilage in the early stages of the sliding tests, but it increased with increasing duration of sliding owing to exudation of interstitial water from the surface layer.     

Short-term passive smoking causes endothelial dysfunction via oxidative stress in nonsmokers

Recent studies have shown that passive smoking impairs vascular endothelial function and induces oxidative stress in humans. However, in most of the previous human data regarding tobacco-induced pathophysiology, vascular endothelial dysfunction and oxidative stress have been separately assessed. This study was designed to determine the association between the acute effect of passive smoking on vascular endothelial function and in-vivo oxidative stress status. We studied 30 healthy male Japanese volunteers (32 +/- 7 years) including 15 habitual smokers and 15 nonsmokers. After baseline echocardiographic, hemodynamic recording, and blood sampling, subjects were exposed to passive smoking for 30 min. Endothelium-dependent vasodilation was measured by using % flow-mediated vasodilation (%FMD) of the brachial artery and plasma levels of 8-isoprostane was measured by enzyme immunoassay before and after the passive smoking exposure. Baseline %FMD was lower (4.3% +/- 1.2% vs. 10.9% +/- 3.1%, p < 0.001) and baseline plasma 8-isoprostane level was higher (41.5 +/- 5.8 pg/mL vs. 26.9 +/- 5.4 pg/mL, p < 0.001) in smokers than those in nonsmokers. The %FMD and 8-isoprostane level did not change after passive smoking in smokers. In nonsmokers, however, the %FMD decreased (to 5.0% +/- 1.9%, p < 0.001) and the 8-isoprostane level increased (to 37.8 +/- 9.6 pg/mL, p < 0.001) significantly after 30 min passive smoking exposure, equivalently to the levels of smokers. Sixty corrected samples before and after passive smoking exposure in all patients showed a significant negative correlation between the % FMD and the plasma 8-isoprostane levels (n = 60, r = -0.69, p < 0.001). Even 30 min of passive smoking rapidly impairs vascular endothelial function, which is associated with oxidative stress. Our data provide the pathophysiological insight for the recent epidemiological evidence about the increased risk of coronary heart disease among nonsmokers exposed to passive smoking.     

Augmentation of innate immunity by low-dose irradiation

The effect of low-dose irradiation on the immune system was investigated in mice. When a 0.2 Gy dose of X-ray irradiation was administered every other day for a total of four times, the number of lymphocytes yielded by the liver, spleen and thymus decreased at the initial stage (around day 10). At this stage, NK cells, extrathymic T cells and NKT cells were found to be radioresistant. In other words, conventional lymphocytes were radiosensitive, even in the case of low-dose irradiation. However, the number of lymphocytes in all tested immune organs increased beyond the control level at the recovery stage (around day 28). Enumeration of the absolute number of lymphocyte subsets showed that the most prominently expanding populations were NK cells, extrathymic T cells and NKT cells, especially in the liver where primordial lymphocytes are primarily present. Functional and phenotypic activation of these populations also occurred at the recovery stage. It raised a possibility that an initial activation of macrophages by low-dose irradiation then mediated the present phenomenon. These results suggest that low-dose irradiation eventually has the potential to induce a hormesis effect on the immune system.     

The stabilization of beta-catenin leads to impaired primordial germ cell development via aberrant cell cycle progression

Primordial germ cells (PGCs) are germ cell precursors that are committed to sperm or oocytes. Dramatic proliferation during PGC development determines the number of founder spermatogonia and oocytes. Although specified to a germ lineage, PGCs produce pluripotent embryonic germ (EG) cells in vitro and testicular teratomas in vivo. Wnt/beta-catenin signaling regulates pluripotency and differentiation in various stem cell systems, and dysregulation of this signaling causes various human cancers. Here, we examined the role of Wnt/beta-catenin signaling in PGC development. In normal PGC development, Wnt/beta-catenin signaling is suppressed by the GSK3beta-mediated active degradation of beta-catenin and the low expression of canonical Wnt molecules. The effects of aberrant activation of Wnt/beta-catenin signaling in PGCs were analyzed using mice carrying a deletion of the exon that encodes the GSK3beta phosphorylation sites in the beta-catenin locus. Despite the potential activity of Wnt/beta-catenin signaling in stem cell maintenance and carcinogenesis in various cell lineages, teratomas were not induced in the mice expressing the nuclear-localized beta-catenin in PGCs. Instead, the mutant mice showed germ cell deficiency caused by the delayed cell cycle progression of the proliferative phase PGCs. Our results show that the suppression of Wnt/beta-catenin signaling is a prerequisite for the normal development of PGCs.     

Ionizing radiation suppresses FAP-1 mRNA level in A549 cells via p53 activation

Ionizing radiation (IR) is known to upregulate cell surface Fas through p53 activation in various cells. However, the signaling pathway intermediating between p53 activation and cell surface Fas upregulation remains to be elucidated. Recently, Fas-associated phosphatase-1 (FAP-1) has been reported to associate with Fas and inhibit cell surface Fas expression. We evaluated the expression of FAP-1 mRNA following IR in A549 cells. Ionizing radiation inhibited the expression of FAP-1 mRNA. Pretreatment with p53 inhibitor pifithrin alpha cancelled the IR-induced downregulation of FAP-1 mRNA. These results suggest that IR-induced p53 activation may upregulate cell surface Fas via the down-modulation of FAP-1.     

In vitro reconstitution of monogalactosyldiacylglycerol (MGDG) synthase regulation by thioredoxin

Monogalactosyldiacylglycerol (MGDG), a major membrane lipid of chloroplasts, is synthesized by MGDG synthase (MGD) localized in chloroplast envelope membranes. We investigated whether MGD activity is regulated in a redox-dependent manner using recombinant cucumber MGD overexpressed in Escherichia coli. We found that MGD activity is reversibly regulated by reduction and oxidation in vitro and that an intramolecular disulfide bond(s) is involved in MGD activation. Because thioredoxin efficiently reduced disulfide bonds to enhance MGD activity in vitro, MGD is potentially an envelope-bound thioredoxin target protein in higher plants.