Reconstruction of human influence during the last two centuries on two small oxbow lakes near Warsaw (Poland)

Short sediment cores from two small oxbow lakes located in the Vistula valley near Warsaw (Poland) were analysed for chemical composition and zooplankton (Cladocera) remains. The results of these analyses were evaluated using ordination techniques and the results were used to reconstruct the history of human impact of the lakes. The cores were dated using the ²¹⁰Pb method. These analyses show that the collected sediments (60 cm- and 67 cm-long-cores) were deposited during the last 150–200 years. Cladocera assemblages were different in the two lakes; however, Bosmina longirostris was dominant among subfossil Cladocera species in both lakes. The presence of this species indicates the high trophic state of the lakes. Changes in Cladocera species composition suggest that a significant increase in the lakes’ trophic levels has occurred since the 1920s. The change could be related to the construction of flood dikes along the river Vistula, the isolation of the studied lakes from the river, changes in land use, or some combination of these factors. The chemical composition of sediments, particularly the increase in phosphorus and sulphur concentrations, confirms that the construction of dikes against flood was the major factor inducing eutrophication of the oxbow lakes. This study shows that the Warsaw small water bodies are especially sensitive to local disturbances caused by human activity, mainly water management, land use changes and agriculture. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Differential expression of cell surface proteins in human bone marrow mesenchymal stem cells cultured with or without basic fibroblast growth factor containing medium

Mesenchymal stem cells (MSCs) are multipotent cells, which have the capability to differentiate into various mesenchymal tissues such as bone, cartilage, fat, tendon, muscle, and marrow stroma. However, they lose the capability of multi‐lineage differentiation after several passages. It is known that basic fibroblast growth factor (bFGF) increases growth rate, differentiation potential, and morphological changes of MSCs in vitro. In this report, we have used 2‐DE coupled to MS to identify differentially expressed proteins at the cell membrane level in MSCs growing in bFGF containing medium. The cell surface proteins isolated by the biotin–avidin affinity column were separated by 2‐DE in triplicate experiments. A total of 15 differentially expressed proteins were identified by quadrupole‐time of flight tandem MS. Nine of the proteins were upregulated and six proteins were downregulated in the MSCs cultured with bFGF containing medium. The expression level of three actin‐related proteins, F‐actin‐capping protein subunit alpha‐1, actin‐related protein 2/3 complex subunit 2, and myosin regulatory light chain 2, was confirmed by Western blot analysis. The results indicate that the expression levels of F‐actin‐capping protein subunit alpha‐1, actin‐related protein 2/3 complex subunit 2, and myosin regulatory light chain 2 are important in bFGF‐induced morphological change of MSCs.     

S100在猫小脑中的分布及其表达的年龄相关性变化

用免疫组织化学ABC法标记S100免疫阳性(S100-IR)细胞,观察S100蛋白在青年猫和老年猫小脑中的分布,探讨其表达的年龄相关变化及意义。光镜下计数颗粒层和髓质中S100-IR细胞密度及浦肯野细胞(PC)层阳性细胞线密度。结果显示,颗粒层和髓质中S100-IR细胞密度较小、分布均匀,PC层阳性细胞相对密集,分子层未见阳性反应;阳性细胞胞浆深染。与青年猫相比,老年猫小脑颗粒层、髓质和PC层中S100-IR细胞密度显著增加(P<0.01),胞体较大,阳性较强。表明S100-IR细胞在小脑中的分布具区域性差异,呈明显的年龄相关性增生,推测其增生对衰老神经元的丢失起保护作用。     

Chaoborus predation and the function of phenotypic variation in Daphnia

To investigate the role of helmet formation in defense against predation, laboratory experiments were used to analyze the effects of morphological changes in Daphnia on susceptibility to Chaoborus predation. Behavioral observations of Chaoborus preying on helmeted and non-helmeted Daphnia suggest pre-contact advantages for helmeted prey but post-contact advantages for non-helmeted prey. Helmeted Daphnia are better at evading capture by Chaoborus but may also be more easily handled by the predator. Swimming behavior of the prey, which is influenced by the presence of a tailspine, may affect Chaoborus strike distance. These results re-emphasize the potential hydromechanical importance of body shape changes in defense against predation.     

Actin binding proteins that change extent and rate of actin monomer-polymer distribution by different mechanisms

Actin binding proteins control actin assembly and disassembly by altering the critical concentration and by changing the kinetics of polymerization. All of these control mechanisms in some way or the other make use of the energy of hydrolysis of actin-bound ATP. Capping of barbed filament ends increases the critical concentration as long as ATP hydrolysis maintains a difference in the actin monomer binding constants of the two ends. A further increase in the critical concentration on adding a second cap, tropomodulin, to the other, pointed filament end also requires ATP hydrolysis as described by the model presented here. Changes in the critical concentration are amplified into much larger changes of the monomer pool by actin sequestering proteins, provided their actin binding equilibrium constants fall within a relatively narrow range around the values for the two critical concentrations of actin. Cofilin greatly speeds up treadmilling, which requires ATP hydroysis, by increasing the rate constant of depolymerization. Profilin increases the rate of elongation at the barbed filament end, coupled to a lowering of the critical concentration, only if ATP hydrolysis makes profilin binding to the barbed end independent of its binding constant for actin monomers.     

Vertical Distribution and Feeding Activity of Metamorphosing Sole, Solea Solea, Before Immigration to the Bay of Vilaine Nursery (Northern Bay of Biscay, France)

To evaluate the impact of metamorphosis on the vertical distribution and feeding activity of sole, Solea solea, larvae passing from offshore spawning grounds to the Bay of Vilaine, sampling series at fixed stations were carried out in April 1991 and April 1993 at depths from 50 to 30 m. Comparisons between plankton and bottom samplin series indicated differences in vertical distribution of larvae in pre-metamorphic and metamorphic steps. Metamorphosing larvae displayed a tendency to concentrate in the lower part of the water column, mainly during the day. Gut contents, analysed for prey identification, fullness index and carbon content, indicated that metamorphosing larvae fed mostly on plankton. Variations in fullness index were observed not only during the day, but also depended on tide and wind-induced mixing conditions. Larvae sampled in mixed spring-tide waters had highly variable carbon estimates, resulting in unclear diel activity. More larvae fed actively at neap-tide, which allowed the observation of a diurnal feeding activity through hourly changes in carbon estimates. It is concluded that immigrating sole were not yet able to settle but prepared themselves for demersal life (i) without undergoing starvation and (ii) by modifying the patterns of vertical distributions. The presence of a larval swimbladder suggests they can adjust their vertical movements, depending on tidal cycles, which could in turn favour coastal accumulation of metamorphosing larvae and pulses of new settlers entering the nursery grounds.     

pH-dependent conformational changes of ferricytochrome c induced by electrode surface microstructure

pH-dependent processes of bovine heart ferricytochrome c have been investigated by electronic absorption and circular dichroism (CD) spectra at functionalized single-wall carbon nanotubes (SWNTs) modified glass carbon electrode (SWNTs/GCE) using a long optical path thin layer cell. These methods enabled the pH-dependent conformational changes arising from the heme structure change to be monitored. The spectra obtained at functionalized SWNTs/GCE reflect electrode surface microstructure-dependent changes for pH-induced protein conformation, pK_a of alkaline transition and structural microenvironment of the ferricytochrome c heme. pH-dependent conformational distribution curves of ferricytochrome c obtained by analysis of in situ CD spectra using singular value decomposition least square (SVDLS) method show that the functionalized SWNTs can retain native conformational stability of ferricytochrome c during alkaline transition.     

Escherichia coli adenylate kinase dynamics: comparison of elastic network model modes with mode-coupling (15)N-NMR relaxation data

The dynamics of adenylate kinase of Escherichia coli (AKeco) and its complex with the inhibitor AP(5)A, are characterized by correlating the theoretical results obtained with the Gaussian Network Model (GNM) and the anisotropic network model (ANM) with the order parameters and correlation times obtained with Slowly Relaxing Local Structure (SRLS) analysis of (15)N-NMR relaxation data. The AMPbd and LID domains of AKeco execute in solution large amplitude motions associated with the catalytic reaction Mg(+2)*ATP + AMP --> Mg(+2)*ADP + ADP. Two sets of correlation times and order parameters were determined by NMR/SRLS for AKeco, attributed to slow (nanoseconds) motions with correlation time tau( perpendicular) and low order parameters, and fast (picoseconds) motions with correlation time tau( parallel) and high order parameters. The structural connotation of these patterns is examined herein by subjecting AKeco and AKeco*AP(5)A to GNM analysis, which yields the dynamic spectrum in terms of slow and fast modes. The low/high NMR order parameters correlate with the slow/fast modes of the backbone elucidated with GNM. Likewise, tau( parallel) and tau( perpendicular) are associated with fast and slow GNM modes, respectively. Catalysis-related domain motion of AMPbd and LID in AKeco, occurring per NMR with correlation time tau( perpendicular), is associated with the first and second collective slow (global) GNM modes. The ANM-predicted deformations of the unliganded enzyme conform to the functional reconfiguration induced by ligand-binding, indicating the structural disposition (or potential) of the enzyme to bind its substrates. It is shown that NMR/SRLS and GNM/ANM analyses can be advantageously synthesized to provide insights into the molecular mechanisms that control biological function.     

Molecular motions and conformational changes of HPPK

6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) belongs to a class of catalytic enzymes involved in phosphoryl transfer and is a new target for the development of novel antimicrobial agents. In the present study, the fundamental consideration is to view the overall structure of HPPK as a network of interacting residues and to extract the most cooperative collective motions that define its global dynamics. A coarse-grained model, harmonically constrained according to HPPK's crystal structure is used. Four crystal structures of HPPK (one apo and three holo forms with different nucleotide and pterin analogs) are studied with the goal of providing insights about the function-dynamic correlation and ligand induced conformational changes. The dynamic differences are examined between HPPK's apo- and holo-forms, because they are involved in the catalytic reaction steps. Our results indicate that the palm-like structure of HPPK is nearly rigid, whereas the two flexible loops: L2 (residues 43-53) and L3 (residues 82-92) exhibit the most concerted motions for ligand recognition and presumably, catalysis. These two flexible loops are involved in the recognition of HPPKs nucleotide and pterin ligands, whereas the rigid palm region is associated with binding of these cognate ligands. Six domains of collective motions are identified, comprised of structurally close but not necessarily sequential residues. Two of these domains correspond to the flexible loops (L2 and L3), whereas the remaining domains correspond to the rigid part of the molecule.     

Fluctuation of the zooplankton community in Lake Biwa during the 20th century: a paleolimnological analysis

Detailed zooplankton records from a 26-cm sediment core with a time resolution of approximately 3–10 years were obtained from Lake Biwa, Japan, to examine the historical variations in the zooplankton community during the 20th century. In the sediments, selected zooplankton remains have fluctuated over the years. Daphnia – large zooplankton herbivores – did not occur from 1900 to 1920, and formed a very minor component of the zooplankton community in the following 30 years, while Bosmina – small zooplankton herbivores – were common during this period. In the mid-1960s, however, when eutrophication was noticeable in this lake, Daphnia numbers increased dramatically and became the dominant zooplankton thereafter. In contrast, Difflugia brevicolla and D. biwae, two amoeboid protozoans that live in connection with the lake bottom environment, occurred abundantly until the late 1950s, but gradually decreased after the mid-1960s. In particular, D. biwae, a species peculiar to this lake, was not found in sediment dated after 1980, suggesting its extinction. These results indicate that the zooplankton community structure changed greatly in the 1960s, and suggest that the eutrophication occurring at this time altered the relative strength of top-down and bottom-up forces on the zooplankton community in Lake Biwa.