Oxidative Damage to Membranes by a Combination of Aluminum and Iron in Suspension-Cultured Tobacco Cells

Aluminum (Al) and ferrous iron [Fe(II)] are separately non-toxicto cultured tobacco cells in nutrient solution. However, Aland Fe(II) together cause the peroxidation of membrane iipids,the accumulation of Al and Fe, and the loss of viability [Onoet al. (1995) Plant Cell Physiol. 36: 115]. We investigatedthe cause-and-effect relationships of these various responses.In cells exposed to Fe(TT) or Fe(III)-EDTA, both the peroxidationof ipids and the loss of viability were similarly enhanced byAlCl₃ in a dose-dependent manner. During exposure to AlCl₃,the accumulation of Al and the loss of viability became apparentrapidly and simultaneously at 8 h, whereas both the peroxidationof lipids and the accumulation of Fe occurred at later times.However, lipophilic antioxidants protected cells efficientlynot only from the peroxidation of Iipids but also from the lossof viability and the accumulation of Al and Fe. These resultssuggest that the peroxidation of Iipids in the plasma membranethat is caused by both Al and Fe leads to the accumulation ofAl and Fe and the loss of viability. (Received April 18, 1997; Accepted October 1, 1997)     

Independent differentiation of mammotropes and somatotropes in the chicken embryonic pituitary gland

It has been reported that mammotropes in a rodent pituitary gland are derived from somatotropes via somatomammotropes (SMTs), cells that produce both growth hormone (GH) and prolactin (Prl). However, no studies have been done on the transdifferentiation of somatotropes in the chicken pituitary gland. In this study, in order to determine the origin of mammotropes, we studied detail property of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs in the chicken embryonic pituitary gland. Immunohistochemical analysis revealed that GH-immunopositive (GH-ip) cells appeared on embryonic day (E) 14 and were mainly distributed in the caudal lobe, while Prl-immunopositive (Prl-ip) cells appeared in the cephalic lobe of the pituitary gland on E16. In situ hybridization (ISH) and RT-PCR analysis showed that expression of GH and Prl mRNA starts at E12 in the caudal lobe and at E14 in the cephalic lobe respectively. Pit-1 mRNA was first detected on E5 by RT-PCR, and pit-1 mRNA-expressing cells were found in the cephalic lobe on E8. Then with the ontogeny of the chicken, these cells spread into both lobes. Using a double staining method with ISH and immunohistochemistry, we could not detect the existence of SMTs in the chicken embryonic pituitary gland even in the marginal region of either lobe. These results suggest that chicken somatotropes and mammotropes independently appear in different lobes of pituitary gland and that transdifferentiation from somatotropes to mammotropes is not the central route for differentiation of mammotropes in the embryonic chicken pituitary gland.     

Photo-movement of coral larvae influences vertical positioning in the ocean

Coral Reefs - Behaviour can have profound consequences for the dispersal potential of an organism. In the marine environment, larvae rely heavily on oceanic currents to migrate from one area to...     

Monitoring of occupational exposure to cyclohexanone by diffusive sampling and urinalysis

The present study was initiated in order to identify the best marker of occupational exposure to cyclohexanone among cyclohexanone and its metabolites in urine. To examine if diffusive samplers are applicable to personal monitoring of exposure to cyclohexanone in workroom air, the performance of carbon cloth to adsorb cyclohexanone in air was studied by experimental exposure of the cloth to cyclohexanone at 5, 10, 25 or 50 ppm (i.e. 20, 40, 100 or 200 mg m-3) for up to 8 h. Cyclohexanone in the exposed cloth was extracted with carbon disulphide followed by gas chromatographic (GC) analysis. The cloth adsorbed cyclohexanone in proportion to the concentration (up to 50 ppm) and the duration (up to 8 h), and responded quantitatively to a 15 min exposure at 100 ppm. In a field survey, end-of-shift urine samples were collected from 24 factory workers occupationally exposed to cyclohexanone (up to 9 ppm) in combination with toluene and other solvents. Urine samples were also collected from 10 subjects with no occupational exposure to solvents. The urine samples were treated with acid or an enzyme preparation for hydrolysis, and extracted with dichloromethane or ethyl acetate. The extracts were analysed by GC for cyclohexanone, cyclohexanol, and trans- and cis-isomers of 1,2- and 1,4-cyclohexanediol. Both cyclohexanol and trans-1,2-cyclohexanediol in urine correlated significantly with time-weighted average intensity of exposure to cyclohexanone. Although trans -1,4-isomer was also excreted, its quantitative relation with cyclohexanone exposure could not be established, because the solvent extraction rate was low and unstable. Excretion of cis-isomers was not confirmed. The two analytes, cyclohexanol and trans-1,2-cyclohexanediol, appeared to be equally valid as exposure markers, but the latter may be superior to the former in the sense that it is sensitive enough to separate the exposed from the non-exposed at 1 ppm or less cyclohexanone exposure.     

Cascading effects of larval Crucian carp introduction on phytoplankton and microbial communities in a paddy field: top-down and bottom-up controls

Effects of fish predation propagate through aquatic food webs, where the classical grazing food chain and microbial loop are interwoven by trophic interactions. The overall impact on aquatic food webs is further complicated because fish may also exert bottom-up controls through nutrient regeneration. Yet, we still have limited information about cascading effects among fish, zooplankton, phytoplankton, and microbes. In this study, we performed a mesocosm experiment to evaluate effects of fish introduction on plankton communities. Six plots were set in factorial combination with fish introduction and rice straw plowing in a paddy field, and the experiment was continued for 4 weeks. Introduction of fish significantly increased chlorophyll a concentrations in smaller size fractions (<15 μm) and abundances of filamentous bacteria (>5 μm in length) and heterotrophic nanoflagellates in 3–15 μm fraction. Microbes in 0.8–3 μm fraction showed increasing but not significant trends in response to fish introduction. These results indicate cascading effects of fish predation operating via two pathways, one through grazing food chain and the other through microbial food web. Phytoplankton community compositions shifted in similar fashion in all plots until 1 week after fish introduction, and then diverged between plots with and without fish thereafter. Bottom-up effects of fish introduction were suggested by increases of total chlorophyll a and inedible phytoplankton species in response to fish introduction. This study provides an example of how fish predation regulates biomass and structure of phytoplankton and microbial communities.     

Increased Expression of 15-Hydroxyprostaglandin Dehydrogenase in Spinal Astrocytes During Disease Progression in a Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset, progressive, and fatal neurodegenerative disease caused by selective loss of motor neurons. Both ALS model mice and patients with sporadic ALS have increased levels of prostaglandin E2 (PGE2). Furthermore, the protein levels of microsomal PGE synthase-1 and cyclooxygenase-2, which catalyze PGE2 biosynthesis, are significantly increased in the spinal cord of ALS model mice. However, it is unclear whether PGE2 metabolism in the spinal cord is altered. In the present study, we investigated the protein level of 15-hydroxyprostaglandin dehydrogenase (15-PGDH), a key enzyme in prostaglandin metabolism, in ALS model mice at three different disease stages. Western blotting revealed that the 15-PGDH level was significantly increased in the lumbar spinal cord at the symptomatic stage and end stage. Immunohistochemical staining demonstrated that 15-PGDH immunoreactivity was localized in glial fibrillary acidic protein (GFAP)-positive astrocytes at the end stage. In contrast, 15-PGDH immunoreactivity was not identified in NeuN-positive large cells showing the typical morphology of motor neurons in the anterior horn. Unlike 15-PGDH, the level of PGE2 in the spinal cord was increased only at the end stage. These results suggest that the significant increase of PGE2 at the end stage of ALS in this mouse model is attributable to an imbalance of the synthetic pathway and 15-PGDH-dependent scavenging system for PGE2, and that this drives the pathogenetic mechanism responsible for transition from the symptomatic stage.     

Formaldehyde Fixation Contributes to Detoxification for Growth of a Nonmethylotroph, Burkholderia cepacia TM1, on Vanillic Acid

During bacterial degradation of methoxylated lignin monomers, such as vanillin and vanillic acid, formaldehyde is released through the reaction catalyzed by vanillic acid demethylase. When Burkholderia cepacia TM1 was grown on vanillin or vanillic acid as the sole carbon source, the enzymes 3-hexulose-6-phosphate synthase (HPS) and 6-phospho-3-hexuloisomerase (PHI) were induced. These enzymes were also expressed during growth on Luria-Bertani medium containing formaldehyde. To understand the roles of these enzymes, the hps and phi genes from a methylotrophic bacterium, Methylomonas aminofaciens 77a, were introduced into B. cepacia TM1. The transformant strain constitutively expressed the genes for HPS and PHI, and these activities were two- or threefold higher than the activities in the wild strain. Incorporation of [¹⁴C]formaldehyde into the cell constituents was increased by overexpression of the genes. Furthermore, the degradation of vanillic acid and the growth yield were significantly improved at a high concentration of vanillic acid (60 mM) in the transformant strain. These results suggest that HPS and PHI play significant roles in the detoxification and assimilation of formaldehyde. This is the first report that enhancement of the HPS/PHI pathway could improve the degradation of vanillic acid in nonmethylotrophic bacteria.     

A new technique to co-localise membrane proteins with Homer/vesl

The minimal requirements were defined as necessary for cluster formation of the group 1 metabotropic glutamate receptor (mGluR), which is regulated by the Homer/vesl family of scaffolding proteins [Curr. Opin. Neurobiol. 10 (2000) 370]. Cluster formation of G-protein-coupled receptors (GPCRs) plays a fundamental role in signal transduction, particularly at the neuronal synapse. To understand the interaction of mGluR with PSD-Zip45, a Homer/vesl family member, we designed a series of chimeric receptor proteins, consisting of C-terminal mGluR1alpha sequences that were fused to endothelin B receptors (ET(B)Rs). In vitro and in vivo studies revealed that an extended 20 amino acid long C-terminal mGluR1alpha peptide, including the proline-rich core motif PPXXF, is sufficient to induce clustering of chimeric ET(B)R/mGluR1alpha receptors by PSD-Zip45. This result is especially important because it constitutes the basis for a new approach to form two-dimensional crystals of membrane proteins in situ, which may render unstable membrane proteins amenable to electron crystallographic structure determination.