On the interrelations of the Na+-and Cl?-influxes in the pulmonate freshwater snailLymnaea stagnalis

Summary In the freshwater snailLymnaea stagnalis the influxes of Na⁺ and Cl^– were studied at different external concentrations of these ions. The characteristies of the Na⁺- and Cl^–-influxes are similar with respect to saturation kinetics,K _m (0.1 mM) and activation by low-salt adaptation. In short-term experiments the Na⁺- and Cl^–-influxes are independent. Because of the counter-ions (H⁺ and HCO ₃ ^– ) involved, this indicates a potential acid-base regulatory capacity. Low-salt adaptation, due to either Na⁺-or Cl^–-depletion, activates both the Na⁺- and the Cl^–-influx. It is suggested that under both conditions the number of active integumental pumps, involved in Na⁺- as well as in Cl^–-uptake, is increased.     

Dynamic organization of the β-heterochromatin in the Drosophila melanogaster polytene X chromosome

Region 20 of the polytene X chromosome of Drosophila melanogaster was studied in salivary glands (SG) and pseudonurse cells (PNC) of otu mutants. In SG chromosomes the morphology of the region strongly depends on two modifiers of position effect variegation: temperature and amount of heterochromatin. It is banded in XYY males at 25° C and β-heterochromatic in X0 males at 14° C, i.e. it shows dynamic transitions. In PNC chromosomes region 20 is not heterochromatic, but demonstrates a clear banding pattern. Some molecular markers of mitotic heterochromatin were localized by means of in situ hybridization on PNC chromosomes: DNA of the gene su(f) in section 20C, the nucleolar organizer and 359-bp satellite in 20F. The 359-bp satellite, which has been considered to be specific for heterochromatin of the mitotic X chromosome, was found at two additional sites on chromosome 3L, proximally to 80C. The right arm of the X chromosome in SG chromosomes was localized in the inversion In(1LR)pn2b: the telomeric HeT-A DNA and AAGAG satellite from the right arm are polytenized, having been relocated from heterochromatin to euchromatin. Received: 1 July 1998 / Accepted: 7 September 1998     

Phylogeny of the Rhizobium–Allorhizobium–Agrobacterium clade supports the delineation of Neorhizobium gen. nov.

The genera Agrobacterium, Allorhizobium, and Rhizobium belong to the family Rhizobiaceae. However, the placement of a phytopathogenic group of bacteria, the genus Agrobacterium, among the nitrogen-fixing bacteria and the unclear position of Rhizobium galegae have caused controversy in previous taxonomic studies. To resolve uncertainties in the taxonomy and nomenclature within this family, the phylogenetic relationships of generic members of Rhizobiaceae were studied, but with particular emphasis on the taxa included in Agrobacterium and the “R. galegae complex” (R. galegae and related taxa), using multilocus sequence analysis (MLSA) of six protein-coding housekeeping genes among 114 rhizobial and agrobacterial taxa. The results showed that R. galegae, R. vignae, R. huautlense, and R. alkalisoli formed a separate clade that clearly represented a new genus, for which the name Neorhizobium is proposed. Agrobacterium was shown to represent a separate cluster of mainly pathogenic taxa of the family Rhizobiaceae. A. vitis grouped with Allorhizobium, distinct from Agrobacterium, and should be reclassified as Allorhizobium vitis, whereas Rhizobium rhizogenes was considered to be the proper name for former Agrobacterium rhizogenes. This phylogenetic study further indicated that the taxonomic status of several taxa could be resolved by the creation of more novel genera.     

Patterning the dorsal–ventral axis of the wasp Nasonia vitripennis

Regulatory networks composed of interacting genes are responsible for pattern formation and cell type specification in a wide variety of developmental contexts. Evolution must act on these regulatory networks in order to change the proportions, distribution, and characteristics of specified cells. Thus, understanding how these networks operate in homologous systems across multiple levels of phylogenetic divergence is critical for understanding the evolution of developmental systems. Among the most thoroughly characterized regulatory networks is the dorsal–ventral patterning system of the fly Drosophila melanogaster. Due to the thorough understanding of this system, it is an ideal starting point for comparative analyses. Here we report an analysis of the DV patterning system of the wasp, Nasonia vitripennis. This wasp undergoes a mode of long germ embryogenesis that is superficially nearly identical to that of Drosophila, but one that was likely independently derived. We have found that while the expression of genes just prior to the onset of gastrulation is almost identical in Nasonia and Drosophila, both the upstream network responsible for generating this pattern, and the downstream morphogenetic movements that it sets in motion, are significantly diverged. From this we conclude that many network structures are available to evolution to achieve particular developmental ends.     

Wnt/β-catenin signaling induces the aging of mesenchymal stem cells through the DNA damage response and the p53/p21 pathway

Recent studies have demonstrated the importance of cellular extrinsic factors in the aging of adult stem cells. However, the effects of an aged cell-extrinsic environment on mesenchymal stem cell (MSC) aging and the factors involved remain unclear. In the current study, we examine the effects of old rat serum (ORS) on the aging of MSCs, and explore the effects and mechanisms of Wnt/β-catenin signaling on MSC aging induced by ORS treatment. Senescence-associated changes in the cells are examined with SA-β-galactosidase staining and ROS staining. The proliferation ability is detected by MTT assay. The surviving and apoptotic cells are determined using AO/EB staining. The results suggest that ORS promotes MSC senescence and reduces the proliferation and survival of cells. The immunofluorescence staining shows that the expression of β-catenin increases in MSCs of old rats. To identify the effects of Wnt/β-catenin signaling on MSC aging induced with ORS, the expression of β-catenin, GSK-3β, and c-myc are detected. The results show that the Wnt/β-catenin signaling in the cells is activated after ORS treatment. Then we examine the aging, proliferation, and survival of MSCs after modulating Wnt/β-catenin signaling. The results indicate that the senescence and dysfunction of MSCs in the medium containing ORS is reversed by the Wnt/β-catenin signaling inhibitor DKK1 or by β-catenin siRNA. Moreover, the expression of γ-H2A.X, a molecular marker of DNA damage response, p16(INK4a), p53, and p21 is increased in senescent MSCs induced with ORS, and is also reversed by DKK1 or by β-catenin siRNA. In summary, our study indicates the Wnt/β-catenin signaling may play a critical role in MSC aging induced by the serum of aged animals and suggests that the DNA damage response and p53/p21 pathway may be the main mediators of MSC aging induced by excessive activation of Wnt/β-catenin signaling.     

Is the Cu/Zn Disorder the Main Culprit for the Voltage Deficit in Kesterite Solar Cells?

Photovoltaic thin film solar cells based on kesterite Cu₂ZnSn(S_x,Se_1–x)₄ compounds (CZTSSe) have reached >12% sunlight‐to‐electricity conversion efficiency. This is still far from the >20% record devices known in Cu(In_1–y,Ga_y)Se₂ and CdTe parent technologies. A selection of >9% CZTSSe devices reported in the literature is examined to review the progress achieved over the past few years. These devices suffer from a low open‐circuit voltage (V_oc) never better than 60% of the V_{oc max}, which is expected from the Shockley‐Queisser radiative limit (S‐Q limit). The possible role of anionic (S/Se) distribution and of cationic (Cu/Zn) disorder on the V_oc deficit and on the ultimate photovoltaic performance of kesterite devices, are clarified here. While the S/Se anionic distribution is expected to be homogeneous for any ratio x, some grain‐to‐grain and other non‐uniformity over larger area can be found, as quantified on our CZTSSe films. Nevertheless, these anionic distributions can be considered to have a negligible impact on the V_oc deficit. On the Cu/Zn order side, even though significant bandgap changes (>10%) can be observed, a similar conclusion is brought from experimental devices and from calculations, still within the radiative S‐Q limit. The implications and future ways for improvement are discussed.     

High pressure effect on the main transition from the ripple gel P′β phase to the liquid crystal (Lα) phase in dipalmitoylphosphatidylcholine. Microcalorimetric study

Scanning microcalorimetry has been used to study the high pressure effect on the main transition from the ripple gel P′_β phase to the liquid crystal (L_α) phase in DPPC (dipalmitoylphosphatidylcholine). It has been demonstrated that an increase of the pressure by 200 MPa shifts the transition to higher temperatures by 36.4 degrees. The pressure increase does not affect the cooperativity of transition but reduces noticeably its enthalpy. The changes of the molar partial volume, isothermal compressibility as well as volume thermal expansibility during transition in DPPC suspension have been estimated. It has been shown that monovalent ions (Na⁺, Cl⁻) in solution slightly affect the main thermodynamic parameters of the transition. Calcium ions significantly decrease distinction in compressibility and thermal expansibility between liquid-crystal and ripple gel phases of lipid suspension, which in its turn reflects less difference in their volume fluctuations.     

Genetic and morphological variation in the venus clam Cyclina?sinensis along the coast of China

Six geographic samples of Cyclina sinensis were collected from the coast along China and analyzed to reveal morphological and genetic variation by using nine allozyme loci and 11 morphological variables. The discriminant function analysis (DFA) of morphology suggested a clear separation between the southern and northern populations. Polymorphism was detected at nine loci across all six populations. The mean allele number ranged from 2.44 to 2.78, and the mean observed heterozygosity ranged from 0.218 to 0.296. High level of genetic differentiation was found between three northern populations and three southern populations. The marked genetic differentiation can be explained by the upwelling of the Zhejiang province and the freshwater outflow of Yangtze River. The results obtained in this study indicate that the northern and southern populations of C. sinensis should be treated as separate units for conservation management.     

Is hypothermia necessary for the winter survival of the GoldcrestRegulus regulus?

Summary The Goldcrest is an interesting species for studies of physiological and behavioural adaptions to cold, since it is the smallest species present in Europe. Although many small birds have to lower their metabolic rate and enter hypothermia in order to make their energy reserves last throughout the night, our measurements of oxygen consumption of five Goldcrests suggest that these birds may be able to balance their nocturnal energy budget during the winter at normothermic body temperatures, provided that the available food supply is adequate. These results are in agreement with those of another small bird, the Common Bushtit, which, like the Goldcrest, reduce nocturnal heat loss by contact roosting. Since the energy saved by hypothermia decreases with decreasing ambient temperature and also decreasing body weight, this strategy might not be such an advantage for the smallest birds living at very low ambient temperatures.

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Zusammenfassung Am Wintergoldhähnchen als dem kleinsten europäischen Vogel interessieren besonders seine physiologischen und Verhaltens-Anpassungen an niedere Temperaturen. Viele Kleinvögel senken ihre Stoffwechselaktivität und verfallen in Hypothermie, um mit ihren Energie-Reserven während der langen Winternächte auszukommen. Unsere Untersuchungen über den O₂-Verbrauch von 5 Wintergoldhähnchen legen jedoch nahe, daß sich das nächtliche Energie-Budget auch im Tiefwinter auf Normalniveau bewegt und daß sie bei ausreichendem Nahrungsangebot ihre normale Körpertemperatur auch nachts beibehalten. Ähnliche Befunde liegen von den vergleichbaren kleinen amerikanischen Buschmeisen vor, die wie Goldhähnchen den nächtlichen Wärmeverlust durch Schlafen auf engem Gefiederkontakt reduzieren. Es ist anzunehmen, daß die Hypothermie als Überwinterungsstrategie für unsere kleinsten Vögel garnicht so vorteilhaft wäre: Die durch Hypothermie eingesparte Energie geht mit abnehmender Umgebungstemperatur und mit geringerer Körpergröße wieder verloren.

     

Land Use/Cover Change and the Terrestrial Carbon Cycle in the Asia-Pacific Region

Current atmospheric CO_2 concentrations are the highest on record in the last half a millionyears and are expected to reach between 540 and 970 ppm over the next one hundred years. Thisunprecedented increase is linked to human activities including fossil fuel combustion anddeforestation. The increase in CO_2 concentrations, and to a lesser extent in other greenhouse gases,is linked to changes in climate patterns and variability, and to an average global warming of 0.6℃during the 20th Century (IPCC 2001). Changes in land use and cover are critical controls of the distribution and strength of carbon     

Will the invasive mussel Mytilus galloprovincialis Lamarck replace the indigenous Perna perna L. on the south coast of South Africa?

The mussel Mytilus galloprovincialis is invasive worldwide, has displaced indigenous species on the west coast of South Africa and now threatens Perna perna on the south coast. We tested the hypothesis that Mytilus will replace Perna by examining changes in their distribution on shores where they co-exist. Total cover, adult density, recruit density, recruit/adult correlations and mean maximum lengths of both species were measured in 2001 at two contrasting sites (Plettenberg Bay and Tsitsikamma) 70 km apart, each including two locations 100 m apart. Cover and density were measured again in 2004. Total mussel abundance was significantly lower in Tsitsikamma, and recruit density was only 17% that of Plettenberg Bay. Abundance and cover increased upshore for Mytilus, but decreased for Perna, giving Mytilus higher adult and recruit density and total cover than Perna in the upper zones. Low shore densities of recruits and adults were similar between species but cover was lower for Mytilus, reflecting its smaller size, and presumably slower growth or higher mortality there. Thus, mechanisms excluding species differed among zones. Recruitment limitation delays invasion at Tsitsikamma and excludes Perna from the high shore, while Mytilus is excluded from the low shore by post-recruitment effects. Recruitment limitation also shapes population structure. Recruit/adult correlations were significant only where adult densities were low, and this effect was species-specific. Thus, at low densities, larvae settle or survive better near adult conspecifics. After 3 years, these patterns remained strongly evident, suggesting Mytilus will not eliminate Perna and that co-existence is possible through partial habitat segregation driven by recruitment limitation of Perna on the high shore and post-settlement effects on Mytilus on the low shore.     

α-Glucosidase at the tip of the contact chemosensory seta of the blowfly, Phormia regina

α-Glucosidase activity was detected at the tip of the labellar contact chemosensory hair of the blowfly, Phormia regina. The enzyme split about 1 pmole of sucrose per hr per hair on average and the Michaelis constant for sucrose was about 50 mM. The activity of the enzyme was not solubilized into the incubation solution, but stuck stably to the tip of the sensory hair. From the cut end of the sensory hair a high activity of α-glucosidase eluted out. But its Michaelis constant was smaller by far than the one at the tip, suggesting that different types of α-glucosidase isozymes exist in the hair. The possibility that the enzyme at the tip of the sensory hair could be the sugar receptor is discussed.     

Inositol pyrophosphates and Akt/PKB: Is the pancreatic β-cell the exception to the rule?

The inositol pyrophosphate, diphosphoinositol pentakisphosphate (IP₇), is thought to negatively regulate the critical insulin signaling protein Akt/PKB. Knockdown of the IP₇-generating inositol hexakisphosphate kinase 1 (IP6K1) results in a concomitant increase in signaling through Akt/PKB in most cell types so far examined. Total in vivo knockout of IP6K1 is associated with a phenotype resistant to high-fat diet, due to enhanced Akt/PKB signaling in classic insulin regulated tissues, counteracting insulin resistance. In contrast, we have shown an important positive role for IP6K1 in insulin exocytosis in the pancreatic β-cell. These cells also possess functional insulin receptors and the feedback loop following insulin secretion is a key aspect of their normal function. Thus we examined the effect of silencing IP6K1 on the activation of Akt/PKB in β-cells. Silencing reduced the glucose-stimulated increase in Akt/PKB phosphorylation on T308 and S473. These effects were reproduced with the selective pan-IP6K inhibitor TNP. The likely explanation for IP₇ reduction decreasing rather than increasing Akt/PKB phosphorylation is that IP₇ is responsible for generating the insulin signal, which is the main source of Akt/PKB activation. In agreement, insulin receptor activation was compromised in TNP treated cells. To test whether the mechanism of IP₇ inhibition of Akt/PKB still exists in β-cells, we treated them at basal glucose with an insulin concentration equivalent to that reached during glucose stimulation. TNP potentiated the Akt/PKB phosphorylation of T308 induced by exogenous insulin. Thus, the IP₇ regulation of β-cell Akt/PKB is determined by two opposing forces, direct inhibition of Akt/PKB versus indirect stimulation via secreted insulin. The latter mechanism is dominant, masking the inhibitory effect. Consequently, pharmacological strategies to knock down IP6K activity might not have the same positive output in the β-cell as in other insulin regulated tissues.     

Elite swimmers and the D allele of the ACE I/D polymorphism

A polymorphism of the human angiotensin-1-converting enzyme (ACE) gene has been identified in which the presence (insertion, I allele) of a 287-bp fragment rather than the absence (deletion, D allele) is associated with lower ACE activity. Several recent studies have shown an association of the I allele with endurance performance, it being found with excess frequency in elite distance runners, rowers and mountaineers. Other workers using heterogeneous cohorts of athletes from mixed sporting disciplines have found no such association. An increasing linear trend of I allele frequency with the distance run amongst Olympic runners and an excess of the D allele amongst sprinters led us to examine whether the ratio of I and D alleles in swimmers competing over different distances would also vary. Swimmers (n=120) from the European and Commonwealth championships and an American college team had their ACE genotype determined and their gene and allele frequencies compared with several control groups, the most closely age-matched of which were 1,248 military recruits. Of the 103 Caucasians, there was a significant excess of the D allele compared with this control group only in the truly elite swimmers of the European and Commonwealth championships (P=0.004). This association remained in those competing over shorter distances (P=0.005 for 400 m and below) but not in the longer events. These findings were confirmed in three further large control groups. A population association study testing whether a genetic marker (the ACE I/D polymorphism) occurs more frequently in cases (elite athletes) than in controls therefore requires a homogeneous cohort of subjects from the same sporting discipline.