Metabolon formation and metabolic channeling in the biosynthesis of plant natural products

Metabolon formation and metabolic channeling in plant secondary metabolism enable plants to effectively synthesize specific natural products and to avoid metabolic interference. Channeling can involve different cell types, take advantage of compartmentalization within the same cell or proceed directly within a metabolon. New experimental approaches document the importance of channeling in the synthesis of isoprenoids, alkaloids, phenylpropanoids, flavonoids and cyanogenic glucosides. Metabolon formation and metabolic channeling in natural-product synthesis facilitate attempts to genetically engineer new pathways into plants to improve their content of valuable natural products. They also offer the opportunity to introduce new traits by genetic engineering to produce plant cultivars that adhere to the principle of substantial equivalence.     

Mice defective in the mismatch repair gene Msh2 show increased predisposition to UVB radiation-induced skin cancer

Mice defective in the mismatch repair (MMR) gene Msh2 manifest an enhanced predisposition to skin cancer associated with exposure to UVB radiation. This predisposition is further heightened if the mice are additionally defective for the nucleotide excision repair gene Xpc. To test the hypothesis that the predisposition of Msh2 mutant mice to skin cancer reflects a mutator phenotype associated with increased proliferation of skin cells following exposure to UV radiation, Msh2 mutant mice were exposed to the tumor promoter TPA. Such mice showed a robust proliferative response in the skin, but did not manifest evidence of dysplasia or neoplasia. We conclude that the predisposition of Msh2 mice to UVB radiation-induced skin cancer reflects an interaction between the processes of mismatch repair and some other excision repair mode, the exact nature of which remains to be established.     

Benthic Bacterial and Fungal Productivity and Carbon Turnover in a Freshwater Marsh

Heterotrophic bacteria and fungi are widely recognized as crucial mediators of carbon, nutrient, and energy flow in ecosystems, yet information on their total annual production in benthic habitats is lacking. To assess the significance of annual microbial production in a structurally complex system, we measured production rates of bacteria and fungi over an annual cycle in four aerobic habitats of a littoral freshwater marsh. Production rates of fungi in plant litter were substantial (0.2 to 2.4 mg C g⁻¹ C) but were clearly outweighed by those of bacteria (2.6 to 18.8 mg C g⁻¹ C) throughout the year. This indicates that bacteria represent the most actively growing microorganisms on marsh plant litter in submerged conditions, a finding that contrasts strikingly with results from both standing dead shoots of marsh plants and submerged plant litter decaying in streams. Concomitant measurements of microbial respiration (1.5 to 15.3 mg C-CO₂ g⁻¹ of plant litter C day⁻¹) point to high microbial growth efficiencies on the plant litter, averaging 45.5%. The submerged plant litter layer together with the thin aerobic sediment layer underneath (average depth of 5 mm) contributed the bulk of microbial production per square meter of marsh surface (99%), whereas bacterial production in the marsh water column and epiphytic biofilms was negligible. The magnitude of the combined production in these compartments (~1,490 g C m⁻² year⁻¹) highlights the importance of carbon flows through microbial biomass, to the extent that even massive primary productivity of the marsh plants (603 g C m⁻² year⁻¹) and subsidiary carbon sources (~330 g C m⁻² year⁻¹) were insufficient to meet the microbial carbon demand. These findings suggest that littoral freshwater marshes are genuine hot spots of aerobic microbial carbon transformations, which may act as net organic carbon importers from adjacent systems and, in turn, emit large amounts of CO₂ (here, ~870 g C m⁻² year⁻¹) into the atmosphere.     

An in silico platform for the study of epithelial pre-invasive neoplastic development

To study the possible mechanisms of epithelial preneoplastic development we developed an integrated platform using a 3D agent-based model (ABM). This platform, named idefics, allows for the implementation of normal biological rules at the cell level that interact and generate the usual homeostatic equilibrium of epithelium as well as other abnormal processes that can disrupt this equilibrium. The structure of this model is based on data from multi-scale quantitative analysis of a unique collection of preneoplastic lesions of the lung, cervix, and oral epithelium, that have been collected in our lab in the last 25 years. In this paper, we are describing the different components of this platform and will present results from different simulations generated by the model.     

Evaluation of dog owners' perceptions concerning radiation therapy

Background  

External radiation therapy (RT) has been available for small animals in Sweden since 2006. This study was designed to obtain information on owner experiences and perceptions related to RT of cancer in their dogs. Another survey was used to determine the attitudes about use of RT in a group of Swedish veterinarians. Their responses were analyzed and compared to their level of knowledge of oncology and RT.     

Pain following stroke: a population-based follow-up study

Background and Purpose

Chronic pain is increasingly recognized as a consequence of stroke. This study aimed to describe the prevalence and pain types of new onset chronic pain (“novel pain”) in patients with stroke compared with a randomly selected reference group from the general population and to identify factors associated with pain development in stroke patients.

Methods

In a population-based follow-up design, development of chronic pain after stroke was assessed by a questionnaire sent to consecutive stroke patients, registered in a Danish national stroke database, two years after their stroke. A randomly selected sex- and age-matched reference group from the same catchment area received a similar questionnaire about development of new types of chronic pain in the same time period. A total of 608 stroke patients and 519 reference subjects were included in the study.

Results

Development of novel pain was reported by 39.0% of stroke patients and 28.9% of reference subjects (OR 1.57, CI 1.21-2.04), and was associated with low age and depression in a multivariate model. Daily intake of pain medication for novel pain was reported by 15.3% and 9.4% of the stroke and reference population, respectively. Novel headache, shoulder pain, pain from increased muscle stiffness, and other types of novel pain were more common in stroke patients, whereas joint pain was equally common in the two groups.

Conclusions

Development of chronic pain is more common in stroke patients compared with sex- and age-matched reference subjects. Evaluation of post-stroke pain should be part of stroke follow-up.     

Construction of implantable optical fibers for long-term optogenetic manipulation of neural circuits

In vivo optogenetic strategies have redefined our ability to assay how neural circuits govern behavior. Although acutely implanted optical fibers have previously been used in such studies, long-term control over neuronal activity has been largely unachievable. Here we describe a method to construct implantable optical fibers to readily manipulate neural circuit elements with minimal tissue damage or change in light output over time (weeks to months). Implanted optical fibers readily interface with in vivo electrophysiological arrays or electrochemical detection electrodes. The procedure described here, from implant construction to the start of behavioral experimentation, can be completed in approximately 2-6 weeks. Successful use of implantable optical fibers will allow for long-term control of mammalian neural circuits in vivo, which is integral to the study of the neurobiology of behavior.     

Elevated ammonium levels: differential acute effects on three glutamate transporter isoforms

Increased ammonium (NH(4)(+)/NH(3)) in the brain is a significant factor in the pathophysiology of hepatic encephalopathy, which involves altered glutamatergic neurotransmission. In glial cell cultures and brain slices, glutamate uptake either decreases or increases following acute ammonium exposure but the factors responsible for the opposing effects are unknown. Excitatory amino acid transporter isoforms EAAT1, EAAT2, and EAAT3 were expressed in Xenopus oocytes to study effects of ammonium exposure on their individual function. Ammonium increased EAAT1- and EAAT3-mediated [(3)H]glutamate uptake and glutamate transport currents but had no effect on EAAT2. The maximal EAAT3-mediated glutamate transport current was increased but the apparent affinities for glutamate and Na(+) were unaltered. Ammonium did not affect EAAT3-mediated transient currents, indicating that EAAT3 surface expression was not enhanced. The ammonium-induced stimulation of EAAT3 increased with increasing extracellular pH, suggesting that the gaseous form NH(3) mediates the effect. An ammonium-induced intracellular alkalinization was excluded as the cause of the enhanced EAAT3 activity because 1) ammonium acidified the oocyte cytoplasm, 2) intracellular pH buffering with MOPS did not reduce the stimulation, and 3) ammonium enhanced pH-independent cysteine transport. Our data suggest that the ammonium-elicited uptake stimulation is not caused by intracellular alkalinization or changes in the concentrations of cotransported ions but may be due to a direct effect on EAAT1/EAAT3. We predict that EAAT isoform-specific effects of ammonium combined with cell-specific differences in EAAT isoform expression may explain the conflicting reports on ammonium-induced changes in glial glutamate uptake.