Biochemical Adaptation to the Environment

SYNOPSIS. Biochemical adaptation to environmental parameterssuch as temperature appears to involve two distinct types ofchanges in the organism's chemistry. On the one hand, the quantitiesof certain molecular species present in the cells may change.Alternatively, the actual types of molecules present may vary.Rainbow trout (Salmo gairdneri) acclimated to warm and coldtemperatures exhibit a striking example of this latter typeof adaptation. For all enzymes we have examined in this species,distinct "warm" and "cold" isozymes are present. The isozymesfound in warmacclimated (18°C) trout function well onlyat temperatures above 10–12°C. The isozymes presentin cold-acclimated (4°C) trout function optimally at 2-5°C,temperatures this species normally encounters in winter. Thesedata, plus information on comparable changes in membrane lipids,lead us to propose that adult poikilotherms may undergo a considerabledegree of "biochemical restructuring" on a seasonal basis. Thefactors which control this "restructuring," and the rates atwhich the process occurs at high and low temperatures, are topicsfor future investigation.     

冷血脊椎动物冷适应研究

环境温度是制约冷血脊椎动物分布、生存、繁殖、迁徙等活动最重要的生态因子之一.冷血脊椎动物在多种多样栖息环境中形成多种耐寒策略.本文重点从冷血脊椎动物冷适应行为生态、生理、冷冻诱导基因表达与抗冻物质获得、低温与性别决定等方面对国内外研究进展进行综述,以探讨低温生物学在冷血脊椎动物的发展趋势.     

Modelling Adaptation to Directional Motion Using the Adelson-Bergen Energy Sensor

The motion energy sensor has been shown to account for a wide range of physiological and psychophysical results in motion detection and discrimination studies. It has become established as the standard computational model for retinal movement sensing in the human visual system. Adaptation effects have been extensively studied in the psychophysical literature on motion perception, and play a crucial role in theoretical debates, but the current implementation of the energy sensor does not provide directly for modelling adaptation-induced changes in output. We describe an extension of the model to incorporate changes in output due to adaptation. The extended model first computes a space-time representation of the output to a given stimulus, and then a RC gain-control circuit (“leaky integrator”) is applied to the time-dependent output. The output of the extended model shows effects which mirror those observed in psychophysical studies of motion adaptation: a decline in sensor output during stimulation, and changes in the relative of outputs of different sensors following this adaptation.     

Crowded Cell-like Environment Accelerates the Nucleation Step of Amyloidogenic Protein Misfolding

To understand the role of a crowded physiological environment in the pathogenesis of neurodegenerative diseases, we report the following. 1) The formation of fibrous aggregates of the human Tau fragment Tau-(244–441), when hyperphosphorylated by glycogen synthase kinase-3β, is dramatically facilitated by the addition of crowding agents. 2) Fibril formation of nonphosphorylated Tau-(244–441) is only promoted moderately by macromolecular crowding. 3) Macromolecular crowding dramatically accelerates amyloid formation by human prion protein. A sigmoidal equation has been used to fit these kinetic data, including published data of human α-synuclein, yielding lag times and apparent rate constants for the growth of fibrils for these amyloidogenic proteins. These biochemical data indicate that crowded cell-like environments significantly accelerate the nucleation step of fibril formation of human Tau fragment/human prion protein/human α-synuclein (a significant decrease in the lag time). These results can in principle be predicted based on some known data concerning protein concentration effects on fibril formation both in vitro and in vivo. Furthermore, macromolecular crowding causes human prion protein to form short fibrils and nonfibrillar particles with lower conformational stability and higher protease resistance activity, compared with those formed in dilute solutions. Our data demonstrate that a crowded physiological environment could play an important role in the pathogenesis of neurodegenerative diseases by accelerating amyloidogenic protein misfolding and inducing human prion fibril fragmentation, which is considered to be an essential step in prion replication.Amyloid fibrils associated with neurodegenerative diseases such as Alzheimer disease, Parkinson disease, Huntington disease, and transmissible spongiform encephalopathy (TSE)³ (1–5) can be considered biologically relevant failures of the cellular protein quality control mechanisms (6) consisting of molecular chaperones and proteases (7). Up to now, about 20 different proteins with unrelated sequences and tertiary structures are known to form fibrous aggregates associated with various neurodegenerative diseases. These amyloidogenic proteins include both natively unfolded proteins, such as human Tau protein (3) and human α-synuclein (8), and folded globular proteins such as human prion protein (4). There are two faces of protein misfolding in neurodegeneration as follows: a gain of toxic function and a loss of physiological function, which can even occur in combination (9).Human Tau protein, a marker for Alzheimer disease, forms filaments in the brains of patients with Alzheimer disease (3, 10, 11). It has been found that hyperphosphorylation of Tau reduces the binding affinity between Tau and tubulin and contributes to the self-association of Tau and the formation of Tau paired helical filaments (3, 11–13). It has been proposed that glycogen synthase kinase-3β (GSK-3β) hyperphosphorylation of Tau plays an important role in Alzheimer disease (14, 15), and GSK-3β induces an Alzheimer disease-like hyperphosphorylation of Tau when overexpressed in cultured human neurons (16).A large body of data strongly suggests Creutzfeldt-Jakob disease, bovine spongiform encephalopathy, and other TSEs are caused by prions (4). Prions are infectious proteins that can transmit biological information by propagating protein misfolding and aggregation (17). The infectious agent is believed to consist entirely of the prion protein (PrP) and is devoid of nucleic acid (4, 17). Prion biogenesis is associated with the normal protease-sensitive form of the protein (cellular PrP molecule, PrP^C) undergoing structural change into an abnormal, protease-resistant, disease-causing isoform of prion protein (PrP^Sc) (4, 17). Although the mechanism by which PrP^C is converted to PrP^Sc in TSE-infected cells and in vivo is not clear, data from cell-free reactions suggest this process is akin to autocatalytic polymerization (18).Misfolding of Tau and prion proteins has been traditionally and widely studied in dilute solutions (10, 19–21). However, the physiological environment is poorly modeled by such dilute solutions, and biochemical reactions in vivo differ greatly from those in dilute solutions (22). The proteins associated with neurodegenerative diseases form fibrils in a physiological environment crowded with other background macromolecules (22–26), such as proteins, glycosaminoglycans, and proteoglycans (23). Crowding is not confined to cellular interiors but also occurs in the extracellular matrix of tissues (24) and takes place at membrane surfaces (27). For example, blood plasma contains ∼80 g/liter protein, a concentration sufficient to cause significant crowding effects (24). Polysaccharides also contribute to crowding, especially in the extracellular matrix of tissues such as collagen (23, 26). The conversion of PrP from a normal soluble conformation PrP^C to its pathogenic conformation PrP^Sc is believed to occur on the cell surface, in the endocytic vesicles, or in the crowded extracellular matrix (18). Thus, macromolecular crowding on the cell surface and in the extracellular matrix may play an important role in the conformational transition and amyloid formation of PrP in vivo, which have not been fully characterized yet. In vitro, such a crowded environment can be achieved experimentally by adding high concentrations of single or mixed nonspecific crowding agents to the system (23–31). Recently, it has been demonstrated that macromolecular crowding significantly enhances the rate of amyloid formation of α-synuclein (32, 33), amyloid-β peptides (27), and human apolipoprotein C-II (34). However, the role of the crowded physiological environment in the pathogenesis of neurodegenerative diseases is poorly understood so far.To address the contributions of crowded physiological environments on the pathogenesis of neurodegenerative diseases, we report here that macromolecular crowding dramatically accelerates fibril formation by human Tau fragment and by human prion protein under physiological conditions. Our results indicate that macromolecular crowding significantly accelerates the nucleation step of fibril formation of human Tau fragment/human prion protein/human α-synuclein by fitting the data to a sigmoidal equation (35, 36). Furthermore, macromolecular crowding causes human prion protein to form short fibrils and nonfibrillar particles with lower conformational stability and higher protease resistance activity, compared with those formed in dilute solutions.     

圆锥南芥适应高山环境极端高温的系统性耐热能力

高山生态系统的主要气候特征是温度变化幅度较大,目前研究主要集中于高山植物的抗冻机制,而很少关注其对极端高温（高于45℃）的适应性。本研究发现高山物种圆锥南芥跟拟南芥比,具有更强的基础耐热性和获得性耐热性。通过叶绿素荧光检测发现在极端高温下,圆锥南芥具有更稳定的光系统II和更有效的能量耗散机制来维持更高水平的光合效率。通过电导率和丙二醛含量的检测发现圆锥南芥的膜伤害更小,膜流动性与脂肪酸链的长度和不饱和度紧密相关,圆锥南芥脂肪酸具有更低的16∶3含量,更长的碳链,不饱和度没有明显的变化,这些可能有助于维持膜的稳定。另外,更高表达量的HSP101和HSP70可能为圆锥南芥提供了更好的保护作用。以上结果表明,圆锥南芥能利用生理生化活动的调整来适应高山环境中的极端高温,这种耐热策略与低地耐热植物相似,因此圆锥南芥具有系统性耐热能力,可以作为研究植物耐热分子机制的模式物种。     

Recombinational Rearrangements in Bacterial Genome and Bacterial Adaptation to the Environment

The rearrangement of bacterial chromosomes induced by intragenomic recombination is considered. The role of stochastic and programmed genome rearrangements in bacterial adaptation to the environment and in cell differentiation is discussed.     

Localization of a Trypanosome Peroxin to the Endoplasmic Reticulum

Trypanosoma brucei is the causative agent of diseases that affect 30,000–50,000 people annually. Trypanosoma brucei harbors unique organelles named glycosomes that are essential to parasite survival, which requires growth under fluctuating environmental conditions. The mechanisms that govern the biogenesis of these organelles are poorly understood. Glycosomes are evolutionarily related to peroxisomes, which can proliferate de novo from the endoplasmic reticulum or through the growth and division of existing organelles depending on the organism and environmental conditions. The effect of environment on glycosome biogenesis is unknown. Here, we demonstrate that the glycosome membrane protein, TbPex13.1, is localized to glycosomes when cells are cultured under high glucose conditions and to the endoplasmic reticulum in low glucose conditions. This localization in low glucose was dependent on the presence of a C‐terminal tripeptide sequence. Our findings suggest that glycosome biogenesis is influenced by extracellular glucose levels and adds to the growing body of evidence that de novo glycosome biogenesis occurs in trypanosomes. Because the movement of peroxisomal membrane proteins is a hallmark of ER‐dependent peroxisome biogenesis, TbPex13.1 may be a useful marker for the study such processes in trypanosomes.     

高山植物对其环境的生理生态适应性研究进展

高山林线植物(林木和草本)由于生长环境特殊而形成其独特的适应环境的生理生态特性.该文对近年来国内外有关高山植物、特别是林线林木在形态解剖结构、光合作用、养分利用和碳水化合物及抗氧化系统等方面对高山环境的生理生态适应性的研究进展进行综述,指出了林线树种生理生态适应性研究方面的不足,并提出了今后高山林线树种生理生态需要研究的方向,以期为研究气候变化下高山林线植物的应对策略和适应机制提供参考.     

Effects of Crowding and Attention on High-Levels of Motion Processing and Motion Adaptation

The motion after-effect (MAE) persists in crowding conditions, i.e., when the adaptation direction cannot be reliably perceived. The MAE originating from complex moving patterns spreads into non-adapted sectors of a multi-sector adapting display (i.e., phantom MAE). In the present study we used global rotating patterns to measure the strength of the conventional and phantom MAEs in crowded and non-crowded conditions, and when attention was directed to the adapting stimulus and when it was diverted away from the adapting stimulus. The results show that: (i) the phantom MAE is weaker than the conventional MAE, for both non-crowded and crowded conditions, and when attention was focused on the adapting stimulus and when it was diverted from it, (ii) conventional and phantom MAEs in the crowded condition are weaker than in the non-crowded condition. Analysis conducted to assess the effect of crowding on high-level of motion adaptation suggests that crowding is likely to affect the awareness of the adapting stimulus rather than degrading its sensory representation, (iii) for high-level of motion processing the attentional manipulation does not affect the strength of either conventional or phantom MAEs, neither in the non-crowded nor in the crowded conditions. These results suggest that high-level MAEs do not depend on attention and that at high-level of motion adaptation the effects of crowding are not modulated by attention.     

Adaptation of the Osmotolerant Yeast Zygosaccharomyces rouxii to an Osmotic Environment Through Copy Number Amplification of FLO11D

Copy number variations (CNVs) contribute to the adaptation process in two possible ways. First, they may have a direct role, in which a certain number of copies often provide a selective advantage. Second, CNVs can also indirectly contribute to adaptation because a higher copy number increases the so-called “mutational target size.” In this study, we show that the copy number amplification of FLO11D in the osmotolerant yeast Zygosaccharomyces rouxii promotes its further adaptation to a flor-formative environment, such as osmostress static culture conditions. We demonstrate that a gene, which was identified as FLO11D, is responsible for flor formation and that its expression is induced by osmostress under glucose-free conditions, which confer unique characteristics to Z. rouxii, such as osmostress-dependent flor formation. This organism possesses zero to three copies of FLO11D, and it appears likely that the FLO11D copy number increased in a branch of the Z. rouxii tree. The cellular hydrophobicity correlates with the FLO11D copy number, and the strain with a higher copy number of FLO11D exhibits a fitness advantage compared to a reference strain under osmostress static culture conditions. Our data indicate that the FLO gene-related system in Z. rouxii has evolved remarkably to adapt to osmostress environments.