Molecular Mimicry Between Protein and tRNA

Mimicry is a sophisticated development in animals, fish, and plants that allows them to fool others by imitating a shape or color for diverse purposes, such as to prey, evade, lure, pollinate, or threaten. This is not restricted to the macro-world, but extends to the micro-world as molecular mimicry. Recent advances in structural and molecular biology uncovered a set of translation factors that resembles a tRNA shape and, in one case, even mimics a tRNA function for deciphering the genetic code. Nature must have evolved this art of molecular mimicry between protein and ribonucleic acid by using different protein structures until the translation factors sat in the cockpit of a ribosome machine, on behalf of tRNA, and achieved diverse actions. Structural, functional, and evolutionary aspects of molecular mimicry will be discussed. Received: 9 January 2001 / Accepted: 22 March 2001     

Modulation of intracellular calcium changes and glutamate release by neuropeptide Y1 and Y2 receptors in the rat hippocampus: differential effects in CA1, CA3 and dentate gyrus

In the present work, we investigated the role of pre- and post-synaptic neuropeptide Y1 (NPY1) and Y2 receptors on the calcium responses and on glutamate release in the rat hippocampus. In cultured hippocampal neurones, we observed that only NPY1 receptors are involved in the modulation of intracellular free calcium concentration ([Ca(2+)](i)). In 88% of the neurones analysed, the increase in the [Ca(2+)](i), in response to depolarization with 50 mM KCl, was inhibited by 1 microM [Leu31,Pro34]NPY, whereas 300 nM NPY13-36 was without effect. However, studies with hippocampal synaptosomes showed that both NPY1 and Y2 receptors can modulate the [Ca(2+)](i) and glutamate release. The pharmacological characterization of the NPY-induced inhibition of glutamate release indicated that Y2 receptors play a predominant role, both in the modulation of Ca(2+)-dependent and -independent glutamate release. However, we could distinguish between Y1 and Y2 receptors by using [Leu31,Pro34]NPY and NPY13-36. Active pre-synaptic Y1 receptors are present in the dentate gyrus (DG) as well as in the CA3 subregion, but its activity was not revealed by using the endogenous agonist, NPY. Concerning the Y2 receptors, they are present in the three subregions (CA1, CA3 and DG) and were activated by either NPY13-36 or NPY. The present data support a predominant role for NPY2 receptors in mediating NPY-induced inhibition of glutamate release in the hippocampus, but the physiological relevance of the presently described DG and CA3 pre-synaptic NPY1 receptors remains to be clarified.     

Functional striatal hypodopaminergic activity in mice lacking adenosine A(2A) receptors.

Adenosine and caffeine modulate locomotor activity and striatal gene expression, partially through the activation and blockade of striatal A(2A) receptors, respectively. The elucidation of the roles of these receptors benefits from the construction of A(2A) receptor-deficient mice (A(2A)-R(-/-)). These mice presented alterations in locomotor behaviour and striatal expression of genes studied so far, which are unexpected regarding the specific expression of A(2A) receptor by striatopallidal neurones. To clarify the functions of A(2A) receptors in the striatum and to identify the mechanisms leading to these unexpected modifications, we studied the basal expression of immediate early and constitutive genes as well as dopamine and glutamate neurotransmission in the striatum. Basal zif268 and arc mRNAs expression was reduced in mutant mice by 60-80%, not only in the striatum but also widespread in the cerebral cortex and hippocampus. Striatal expression of substance P and enkephalin mRNAs was reduced by about 50% and 30%, respectively, whereas the expression of GAD67 and GAD65 mRNAs was slightly increased and unaltered, respectively. In vivo microdialysis in the striatum revealed a 45% decrease in the extracellular dopamine concentration and three-fold increase in extracellular glutamate concentration. This was associated with an up-regulation of D(1) and D(2) dopamine receptors expression but not with changes in ionotropic glutamate receptors. The levels of tyrosine hydroxylase and of striatal and cortical glial glutamate transporters as well as adenosine A(1) receptors expression were indistinguishable between A(2A)-R(-/-) and wild-type mice. Altogether these results pointed out that the lack of A(2A) receptors leads to a functional hypodopaminergic state and demonstrated that A(2A) receptors are necessary to maintain a basal level in immediate early and constitutive genes expression in the striatum and cerebral cortex, possibly via their control of dopamine pathways.     

A mechanistic model on methane oxidation in a rice rhizosphere

A mechanistic model is presented onthe processes leading to methane oxidation inrice rhizosphere. The model is driven byoxygen release from a rice root into anaerobicrice soil. Oxygen is consumed by heterotrophicand methanotrophic respiration, described bydouble Monod kinetics, and by iron oxidation,described by a second order reaction.Substrates for these reactions – ferrous iron,acetate and methane – are produced by anexponential time dependent organic mattermineralisation in combination with modifiedMichaelis Menten kinetics for competition foracetate and hydrogen. Compounds diffusebetween rhizosphere, root and atmosphere. Adiffusion resistance between the rice root andshoot is included. Active transport across theroot surface occurs for root exudation andplant nutrient uptake. Iron adsorption isdescribed dependent on pH. The model predictswell root oxygen release, compound gradientsand compound concentrations in a ricerhizosphere. Methane oxidation estimates arecomparable to experimental estimates. Asensitivity analysis showed however thatmethane oxidation is highly dependent on modelinitialisation and parameterisation, which ishighly dependent on the history of therhizosphere and root growth dynamics.Equilibrium is not obtained within the periodthat a single root influences a soil micrositeand results in a large change in methanestorage. Equilibrium is moreover dependentupon the diffusion resistance across the rootsurface. These factors make methane oxidationdynamics highly variable in space and time anddependent on root dynamics. The increasedunderstanding of methane oxidation does notdirectly lead to increased predictiveabilities, given this high variability and theuncertainties involved in rhizospheredynamics.     

Secondary Metabolites as Plant Traits: Current Assessment and Future Perspectives

Referee: Dr. Peter B. Kaufman, Dept. of Biology, University of Michigan, Ann Arbor, MI 48109-1048 Traditionally, secondary metabolites in plants have been investigated by phytochemists. Originally classified as waste products, these compounds more recently have been investigated extensively by ecologists and pharmacologists, and many complex biological functions have been discovered. Secondary metabolites occur nearly in all living organisms, within bacteria as well as in mammals, and are especially prominent in those organisms lacking an immune system. Functions of plant secondary metabolites comprise attractants, such as color pigments and scents, repellents such as antifeedants against insects and mammals, or toxins that affect growth and development of animal and microbial predators. Conversely, insects can employ plant-synthesized compounds to their own advantage, such as signals for feeding and oviposition and location of prey. Microbes also use secondary metabolites as carbon sources, and bacteria utilize them for quorum-sensing, an aspect recently discovered. Despite the diversity of recognized functions, the biochemical processes underlying these interactions are few. Primarily, they relate to the ability of these small molecules to bind to receptor regions of various proteins such as keys into locks. This review attempts a summary of current knowledge of secondary plant metabolism with focus on history of discovery, development of analytical techniques, theories of origin and function, signal pathways, biosynthesis, and assessment of biological activities. Outlined is current utilization by, and future perspectives in, different disciplines, such as chemosystematics, chemical ecology, and agricultural biotechnology. Examples illustrate the strong potential of research in secondary metabolism, particularly in comparison to more established disciplines such as developmental biology and physiology.     

Allium ampeloprasum var. babingtonii (Alliaceae): an isoclonal plant found across a range of habitats in S.W. England

Despite the widespread distribution and common habitat dominance of clonal plant species the mechanisms for their ecological success often remain uncertain. Allium ampeloprasum var. babingtonii is a sterile plant that reproduces with physiologically independent asexual propagules. The variety is found mainly in the S.W. of England over a wide habitat range including sea cliffs and open woodlands and displays an autumn-spring phenology in common with its close Mediterranean relatives. The role of population genetic structure in the remarkable habitat distribution of the variety is not known. Genetic variation in A. ampeloprasum var. babingtonii was analysed using RAPD markers in single individuals of var. babingtonii from 16 distinct populations and five further individuals from a single population. This analysis revealed no polymorphism suggesting that all sampled individuals are part of a single clone. We offer the conjecture that in the absence of genetic variation an ecological release, due to temporal separation from competing species, may contribute to the ability of var. babingtonii to exploit heterogeneous environmental conditions.     

Changes in the Glutamate Release and Uptake of Cerebellar Cells in Perinatally Nicotine-Exposed Rat Pups

Cerebellar granule and glial cells were cultured from 7 day-old rat pups after pre- and post-natal nicotine treatment. Ten days later, the basal release of glutamate in the granule cells prepared from the pre- and post-natally nicotine-exposed pups was higher and lower than the controls, respectively. The N-methyl-D-aspartate-induced release of glutamate was higher in the granule cells of post-natal nicotine exposed rats. However, the nicotine-induced glutamate release was either unchanged or was lower in the granule cells of all nicotine-treated pups. The basal glutamate uptake was higher in the glial cells from those exposed pre-natally and lower in the continuously nicotine-exposed pups. The sensitivities of L-trans-pyrrolidine-2,4-dicarboxylic acid on glutamate uptake were higher in all nicotine treated groups. There was a higher number of specific [³H]dizocilpine binding sites in the pre- or continuously nicotine-exposed group. These results suggest that the cerebellar cell properties are altered after perinatal nicotine exposure and that the development of an excitatory amino acid system might be affected differently depending on the nicotine exposure time.     

家蝇对拟除虫菊酯抗性机理研究进展

本文概述了家蝇对拟除虫菊酯的抗性机制 ,特别是结合我国室内培育的抗拟除虫菊酯家蝇品系 (Dec R和 2Cl R) ,探讨了Na+通道、神经递质释放、ATPase、蛋白质磷酸化等与家蝇Kdr抗性的关系 ,从多方面证明了神经敏感性降低是家蝇对拟除虫菊酯产生抗性的重要机制。