Convergent evolution as a mechanism for pathogenic adaptation

The survival of human pathogens depends on their ability to modulate defence pathways in human host cells. This was thought to be attained mainly by pathogen specific "virulence factors". However, pathogens are increasingly being discovered that use distant homologs of the human regulatory proteins as virulence factors. We analyzed several cases of this approach, with a particular focus on virulence proteases. The analysis reveals clear cases of bacterial proteases mimicking the specificity of their human counterparts, such as strong similarities in their active and/or binding sites. With more sensitive tools for distant homology recognition, we could expect to discover many more such cases.     

Aging mechanism as the "down side" of adaptation: a network approach

Many diverse hypotheses on aging are in play. All from "aging genes" over decreasing telomere length to increased level of gene mutations has been suggested to determine an organism's lifespan, but no unifying theory exists. As part of a growing interest toward more integrative approaches in the field we propose a simplistic model based on the "use-it-or-lose-it" concept: we hypothesize that biological aging is a systemic property and the down side of adaptation in complex biological networks at various levels of organization: from brain over the immune system to specialized tissues or organs. The simple dynamical model undergoes three phases during its lifetime: (1) general plasticity (childhood), (2) optimization/adaptation to given conditions (youth and adolescence) and (3) steady state associated with high rigidity (aging). Furthermore, our model mimics recent data on the dynamics of the immune system during aging and, although simplistic, thus captures essential characteristics of the aging process. Finally, we discuss the abstract model in relation to current knowledge on aging and propose experimental setups for testing some of the theoretical predictions.     

Par force evolution as a mechanism for rapid adaptation

An important task is to reduce the cost of natural selection. The stress provides a short-term non-specific resistance to a number of factors (cross resistance); however, in the long term, it is harmful (distress). In a small population, it is more expedient to change the stress flow (prolonging the phase of cross resistance, neutralizing distress) by natural selection within a small group of stress genes than to test all mutations of genome in a search for preadaptations. This process can provoke allo- or aromorphosis.     

A brainstem integrator for self-location memory and positional homeostasis in zebrafish

1. Download : Download high-res image (296KB)
2. Download : Download full-size image

     

Dopaminergic system as the mechanism underlying personality in a beetle

Individuals in many animal species exhibit 'personality,' consistent differences in behaviour across time, situations and/or contexts. Previous work has revealed a negative genetic correlation between intensity of tonic immobility and walking activity levels in the confused flour beetle, Tribolium confusum, thus suggesting these beetles exhibit personality in activity-related traits. The present study investigated the mechanism underlying this correlation. We used individuals derived from two strains established via artificial divergent selection for duration of tonic immobility. "Long" (L) strains exhibited higher frequencies and longer durations of tonic immobility, and lower activity levels, while "Short" (S) strains exhibited lower frequencies and shorter durations of tonic immobility and higher activity levels. We found that the duration of tonic immobility, and activity level, could be altered by caffeine administration; L strains fed with caffeine exhibited decreased durations of tonic immobility and increased activity levels. We also found that brain dopamine levels were lower in L strains than in S strains. Consequently, this study demonstrates that the dopaminergic system plays an important part in controlling the genetic correlation between tonic immobility and activity levels in this species.     

Phosphorylation of rhodopsin as a possible mechanism of adaptation

Light-induced phosphorylation of rhodopsin has been extensively studied by a number of investigators from a biochemical point of view. However, little is known about the physiological function of this reaction. The slow rates measured for phosphorylation and dephosphorylation suggest that it may be involved in visual adaptation rather than in excitation. This paper presents biochemical data obtained from phosphorylation experiments in isolated photoreceptor membranes as well as in the more physiological system of whole retinas and living animals. An attempt is made to compare the phosphorylation reaction with visual adaptation hypotheses taken from the electrophysiological literature. Finally, effects of cyclic nucleotide metabolism on the sensitivity of photoreceptors are presented and discussed.Abbreviations used ATP adenosine 5-triphosphate - GTP guanosine 5-triphosphate - ROS rod outer segments - IBMX isobutylmethylxanthine - cyclic GMP guanosine 3, 5-monophosphate Presented at the EMBO-Workshop on Transduction Mechanism of Photoreceptors, Jülich, Germany, October 4–8, 1976     

EEG pattern as an instrument for evaluation of neurophysiological mechanisms underlying adaptation disorders

The method of statistical evaluation of probable interaction between the main constituents of bioelectrical activity of the brain (BEA) enables to reveal the character of intercentral relations both under normal conditions and at adaptation disorders of different severance. Several types of statistic interactions have been revealed between EEG components (SSIC) correlating with normal interrelations between cortex and subcortex, level of preferential involvement of non-specific brain formations (cortex, thalamic, hypothalamic and brain-stem) into the process, and the degree of instability of neuro-dynamic processes. The findings obtained have shown the degree of expression of adaptation disorders to be connected with gradual destruction of "functional nuclear" within alpha-range, amplification of statistical interrelations with beta-EEG and teta-EEG components and formation of pathological nuclear structures within the ranges aforesaid.     

Phosphorylation of rhodopsin as a possible mechanism of adaptation.

Light-induced phosphorylation of rhodopsin has been extensively studied by a number of investigators from a biochemical point of view. However, little is known about the physiological function of this reaction. The slow rates measured for phosphorylation and dephosphorylation suggest that it may be involved in visual adaptation rather than in excitation. This paper presents biochemical data obtained from phosphorylation experiments in isolated photoreceptor membranes as well as in the physiological system of whole retinas and living animals. An attempt is made to compare the phosphorylation reaction with visual adaptation hypotheses taken from the electrophysiological literature. Finally, effects of cyclic nucleotide metabolism on the sensitivity of photoreceptors are presented and discussed.     

A test of Metabolic Theory as the mechanism underlying broad-scale species-richness gradients

Aim To test whether the temperature dependence of individuals’ metabolic rates is the mechanism shaping broad‐scale species‐richness gradients as proposed in the Metabolic Theory of Ecology recently proposed by Allen, Gillooly and Brown. Location North America, north of Mexico. Methods Metabolic Theory predicts that the natural logarithm of species richness will be a linear function of environmental temperature ((kT)⁻¹, where k is Boltzmann's constant and T is temperature in K) with a slope of −0.78. We tested these predictions using the broad‐scale variation in richness of amphibians, reptiles, trees, tiger beetles, butterflies and blister beetles. We tested whether the temperature–richness relationship was linear or curvilinear, and determined the range of temperature values (and geographical area) where the instantaneous slope of the curvilinear temperature–richness relationship was statistically indistinguishable from −0.78, after correcting for spatial autocorrelation. Results We found that for all taxa, temperature–richness relationships were curvilinear. Moreover, for five of six taxa, the slope of this relationship was close to the predicted value for only a narrow range of temperatures. Blister beetles displayed the widest temperature range that is consistent with the Metabolic Theory, covering 45% of the study's geographical area. For the remaining taxa, the geographical range in which the slope is consistent with the predicted value amounts to only 10–20% of North America. Main conclusions For a wide array of taxa in North America, temperature–richness relationships deviate from the pattern predicted by Metabolic Theory. These results demonstrate that the temperature dependence of individuals’ metabolic rates is not the sole cause of broad‐scale diversity gradients. Even in areas where factors other than temperature do not influence productivity, the data do not suggest that richness patterns are determined by the temperature dependence of metabolic rate.     

Gene duplication as a mechanism of genomic adaptation to a changing environment

A subject of extensive study in evolutionary theory has been the issue of how neutral, redundant copies can be maintained in the genome for long periods of time. Concurrently, examples of adaptive gene duplications to various environmental conditions in different species have been described. At this point, it is too early to tell whether or not a substantial fraction of gene copies have initially achieved fixation by positive selection for increased dosage. Nevertheless, enough examples have accumulated in the literature that such a possibility should be considered. Here, I review the recent examples of adaptive gene duplications and make an attempt to draw generalizations on what types of genes may be particularly prone to be selected for under certain environmental conditions. The identification of copy-number variation in ecological field studies of species adapting to stressful or novel environmental conditions may improve our understanding of gene duplications as a mechanism of adaptation and its relevance to the long-term persistence of gene duplications.     

Integrin shedding as a mechanism of cellular adaptation during cardiac growth

Integrin-mediated cell-extracellular matrix (ECM) interactions are essential for multiple cellular processes; however, little is known regarding integrin turnover during these events. Recent studies have demonstrated shedding of cell surface molecules and suggested this as a potential mechanism for integrin turnover. Confocal microscopy of mouse hearts under different physiological conditions demonstrated the presence of beta(1)-integrin-immunoreactive material in the interstitium. Culture media from neonatal rat cardiac myocytes and fibroblasts contained a 55-kDa fragment of beta(1)-integrin. Attachment to ECM components, response to phorbol 12-myristate 13-acetate stimulation, and matrix metalloproteinase inhibition assays demonstrated that fibroblasts responded differently to the fragment compared with myocytes. The beta(1)-integrin fragment stimulated myocyte attachment to collagen and the fragment itself bound a variety of ECM proteins. These studies indicate that as myocytes and fibroblasts change size and shape, cellular contacts with the ECM are altered, resulting in the liberation of a beta(1)-integrin fragment from the cell surface. Integrin shedding may represent a novel mechanism of rapidly modifying cell-ECM contacts during various cellular processes.     

The role of calmodulin as a signal integrator for synaptic plasticity

Excitatory synapses in the brain show several forms of synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), which are initiated by increases in intracellular Ca(2+) that are generated through NMDA (N-methyl-D-aspartate) receptors or voltage-sensitive Ca(2+) channels. LTP depends on the coordinated regulation of an ensemble of enzymes, including Ca(2+)/calmodulin-dependent protein kinase II, adenylyl cyclase 1 and 8, and calcineurin, all of which are stimulated by calmodulin, a Ca(2+)-binding protein. In this review, we discuss the hypothesis that calmodulin is a central integrator of synaptic plasticity and that its unique regulatory properties allow the integration of several forms of signal transduction that are required for LTP and LTD.     

Soil memory as a potential mechanism for encouraging sustainable plant health and productivity

1. Download : Download high-res image (96KB)
2. Download : Download full-size image

     

Transcription: a mechanism for short-term memory

Yeast growing for a considerable time in glucose 'remember' a previous exposure to galactose, the inducer of its galactose-utilization (GAL) genes. This memory is conveyed by a cytoplasmically transmitted galactokinase working as a signal transducer.     

Purinergic signaling as a new mechanism underlying physical exercise benefits: a narrative review

In the last years, it has become evident that both acute and chronic physical exercise trigger responses/adaptations in the purinergic signaling and these adaptations can be considered one important mechanism related to the exercise benefits for health improvement. Purinergic system is composed of enzymes (ectonucleotidases), receptors (P1 and P2 families), and molecules (ATP, ADP, adenosine) that are able to activate these receptors. These components are widely distributed in almost all cell types, and they respond/act in a specific manner depending on the exercise types and/or intensities as well as the cell type (organ/tissue analyzed). For example, while acute intense exercise can be associated with tissue damage, inflammation, and platelet aggregation, chronic exercise exerts anti-inflammatory and anti-aggregant effects, promoting health and/or treating diseases. All of these effects are dependent on the purinergic signaling. Thus, this review was designed to cover the aspects related to the relationship between physical exercise and purinergic signaling, with emphasis on the modulation of ectonucleotidases and receptors. Here, we discuss the impact of different exercise protocols as well as the differences between acute and chronic effects of exercise on the extracellular signaling exerted by purinergic system components. We also reinforce the concept that purinergic signaling must be understood/considered as a mechanism by which exercise exerts its effects.