bluuebunny/crossref_metadata_2025 huggingface dataset:
The reproductive biology of Ptomascopus morio, a brood parasite of Nicrophorus
Authors: Trumbo Stephen T. , Kon Masahiro , Sikes Derek
Published: September 2010

Nicrophorine beetles (Nicrophorus and Ptomascopus spp.) use small carcasses as a food source for young, a breeding ecology distinct from other silphid beetles. While adaptations to the use of small carcasses are well known for Nicrophorus (emitting sex pheromone, burying, rounding and removing hair from carcasses, regulating brood size, regurgitating to young, and preventing predation), there is little information regarding its sister group, Ptomascopus. Like Nicrophorus, Ptomascopus morio males emit pheromone to attract females. In the absence of carrion competitors Ptomascopus morio parents were found to stay with a carcass and their brood for up to 10 days. We tested six hypotheses to examine whether young benefit from this long period of parent–offspring contact. (1) There was no evidence that parents buried or otherwise pre‐empted carcasses to reduce competitive pressure. (2) We found no evidence that parents influenced the decomposition of the carcass. This was supported by experimental manipulations in which brood production (number of larvae and total brood mass) was no greater on carcasses on which parents were present than on carcasses not ‘prepared’ by parents. In addition, the carcass was not rounded and little hair was removed by the adults. (3) The presence of parents benefited the brood by reducing the negative effects of competition with carrion fly larvae. This likely resulted from predatory feeding by adult beetles. (4) Females adjusted clutch size to the size of the carcass. Parents, however, did not make a second adjustment in brood size after young reached the larval stage (filial cannibalism), as occurs in Nicrophorus. (5) Although parents were observed to open feeding holes in the carcass, this was not necessary for normal larval growth and survival. Parents were not observed to feed young directly by regurgitation. (6) Lastly, parents did not reduce predation on their brood when a conspecific intruder was present. These findings suggest that after the female parent adjusts clutch size to the size of the resource, the only parental benefit is clearing the carcass of fly larvae. Other differences with Nicrophorus include an extended period of oviposition (5 days) and less pronounced changes in ovarian mass and juvenile hormone titers in response to discovery of a carcass. In a field experiment in Kyoto, Japan, 17 of 21 broods of N. concolor during August contained larvae of P. morio. Mixed Nicrophorus–Ptomascopus broods were less common at other times of the year and when N. quadripunctatus occupied carcasses. In the laboratory, P. morio was able to parasitize 19 of 20 broods of N. concolor. The pattern of oviposition, the absence of explicit parental behaviours, and the interactions with N. concolor in the field suggest that Ptomascopus morio is a brood parasite of Nicrophorus.
Functional anatomy of the ovaries of wild brush‐tailed porcupines (Atherurus africanus, Gray 1842) from Gabon
Authors: Jori Ferran , López‐Béjar Manel , Mayor Pedro , López Carlos
Published: September 2010

The brush‐tailed porcupine Atherurus africanus is an important source of meat for local people in tropical forested areas of Central Africa. Information on the biology of this species in free‐ranging conditions is scarce. Data on its reproduction and productivity are essential to establish accurate management practices in the exploitation of this rodent. In order to provide data on the reproductive physiology and to assess the prolificacy of the brush‐tailed porcupine in the wild, the structural and functional anatomy of the ovaries of free‐ranging females were studied. Twenty‐two female carcasses were obtained from various markets in Libreville, Gabon, between August 1995 and February 1997. Reproductive tracts were macroscopically examined for the presence of embryos or foetuses. The ovaries were embedded in paraffin wax or plastic and examined by light microscopy. The morphology and constituent cell types of the ovaries were similar to those described for other hystricognath rodents. All pregnant females had only one embryo or foetus and the number of corpora lutea (CL) per female was 19.9 ± 5.4 (mean diameter ±sd, 1709 ± 421 μm), including one CL of pregnancy (diameter, 4821 ± 1364 μm). Also, 8.9 ± 6.8 accessory CL per female in the pre‐implantation and embryonic stages of pregnancy (diameter, 1629 ± 463 μm) were observed. The average active luteal volume was high (115.6 ± 73.5 mm3). The mean number of antral follicles in the adult females was 24.6 ± 9.9. The study confirms that the brush‐tailed porcupine is a mono‐embryonic species, as observed in captive breeding experiences, but polyovular, suggesting important ovum mortality. This unusual reproductive feature in a mammalian species gives this rodent a low reproductive productivity. Therefore, A. africanus could be more susceptible to the effects of hunting than generally thought.
Breeding biology of high‐latitude Antarctic fulmarine petrels (Procellariidae)
Authors: Hodum Peter J.
Published: September 2010

This paper provides basic information about the breeding biology of four species of Antarctic fulmarine petrels breeding in the Rauer Islands, East Antarctica: Antarctic fulmar Fulmarus glacialoides, Antarctic petrel Thalassoica antarctica, Cape petrel Daption capense, and snow petrel Pagodroma nivea. Timing and duration of the nesting cycle, incubation and nestling periods, and timing of breeding were determined over three consecutive breeding cycles. Comparing these data with those of other populations revealed that the duration of breeding showed little interannual and spatial variation within the four species. The length of the breeding period varied between the species, with incubation period and nesting cycle length positively related to adult body mass. Nestling period length also differed between the species but was unrelated to adult body mass. Breeding period lengths for these fulmarine petrels were shorter than those for other procellarids and albatrosses. Compressed and invariant breeding cycles of Antarctic fulmarine petrels may have evolved in response to a short season which limits breeding and to opportunities presented by highly abundant food sources.
Sand‐dwellers in rocky habitats: a new species of Gerbillus (Mammalia: Rodentia) from Mali
Authors: Granjon L. , Aniskin V. M. , Volobouev V. , Sicard B.
Published: September 2010

The genus Gerbillus (Mammalia: Rodentia) is characterized by an important morphological homogeneity associated with an extensive karyotypic diversity. Here we describe a new species of Gerbillus from the Inner Delta of the Niger River in Mali, on the basis of morphological and chromosomal data. This new species seems to be morphologically very similar to G. campestris, another bare‐footed species known from northern Africa. Nevertheless, it can be distinguished from the latter species by a different molar pattern and a specific karyotype. The three specimens on which this description is based were caught in a rocky outcrop, and behavioural observations in captivity suggest an adaptation to life in rocky habitats. This finding is unusual as rodents of the genus Gerbillus are generally sand‐dwellers. Moreover, this new species enriches the gerbil community of this Sahelian region, in which at least nine species of the genus can be found. Finally, this description highlights the importance of chromosomal studies for the characterization of biological diversity in tropical rodents, where morphological sibling species are numerous.
Life in the slow lane? Demography and life histories of male and female sifaka (Propithecus verreauxi verreauxi)
Authors: Richard Alison F. , Dewar Robert E. , Schwartz Marion , Ratsirarson Joelisoa
Published: September 2010

A 16‐year study of wild, unprovisioned sifaka Propithecus verreauxi verreauxi at Beza Mahafaly in south‐west Madagascar provides estimates of age‐specific fertility, mortality, and dispersal in a population of 426 marked animals, and longitudinal records of individual life histories. Sifaka females give birth for the first time later and live longer, for their size, than mammals in other orders; they also give birth later and continue reproducing longer, for their size, than other primates. Theory postulates that these features, commonly referred to as bet‐hedging, evolve in unpredictable environments in association with widely varying infant survival and a trade‐off between reproductive effort and adult survival. The climate of south‐west Madagascar is highly unpredictable compared to almost all other regions in the tropics with similar average rainfall, and we argue that sifaka females are bet‐hedgers par excellence. Male sifaka, in contrast, become reproductively active at an earlier age than females, and are less likely to have long lives than females. The atypical direction of this asymmetry between males and females reflects a ‘slowing down’ of female life histories rather than a ‘speeding up’ of male life histories. Two other unusual features of sifaka biology and behaviour may be linked to the unpredictability of Madagascar's climate: intense local competition between females, and a sex ratio at birth strongly biased in favour of males in most years. In drought years, reproductive females must cope with suddenly intensified resource constraints. This, in turn, may strongly limit the number of ‘breeding slots’ available over the long‐term for females.
Rainfall, dispersal and reproductive inhibition in eusocial Damaraland mole‐rats (Cryptomys damarensis)
Authors: Molteno A. J. , Bennett N. C.
Published: September 2010

Non‐reproductive female Damaraland mole‐rats Cryptomys damarensis that were caught before a period of good rainfall (during which 90% of the average annual fell) (Group 1), exhibited a significantly lower pituitary sensitivity to gonadotrophin‐releasing hormone compared to non‐reproductive females (Group 2) caught in the same area, close to the end of the wet period. Group 2 were also significantly heavier than Group 1. Pituitary sensitivity was not significantly correlated to body mass within either group of females, nor within groups of reproductive males and non‐reproductive males from a laboratory held colony. This suggests that rainfall may have resulted in the simultaneous, but unrelated, increase in pituitary sensitivity and body mass. Larger size and reduced sexual inhibition assist dispersal and the probability of successful independent reproduction, during periods when environmental constraints on dispersal are relaxed. These findings support the hypothesis that low rainfall may be an important constraint on dispersal and an important factor promoting the evolution of reproductive inhibition, and consequently eusociality, in this species.
Gonadal development and an indication of functional protogyny in the Indian damselfish (Dascyllus carneus)
Authors: Asoh Kazue , Yoshikawa Tomoko
Published: September 2010

The objective of this study was to determine the sexual pattern of the Indian dascyllus Dascyllus carneus. After an initially undifferentiated state, gonads of D. carneus developed an ovarian lumen and primary growth stage oocytes, and subsequently cortical‐alveolus stage oocytes. From ovaries with cortical‐alveolus stage oocytes and from more developed ovaries, some gonads redifferentiated into testes. From a sample of 163 individuals, two had a gonad containing degenerating vitellogenic oocytes and proliferating spermatogenic tissue, nine had a gonad containing degenerating cortical‐alveolus stage oocytes and spermatogenic tissue, and five had a gonad with degenerating primary growth stage oocytes and spermatogenic tissue. The size of these individuals overlapped greatly with the size range of mature females, suggesting that at least in some individuals, redifferentiation toward a testis occurred after spawning as females. This indicates that D. carneus is a functional, diandric protogynous hermaphrodite. Removal of a dominant male(s) did not induce a sex change in any of the ranking females in the laboratory and field groups. There was no difference in the number of chases and signal jumps performed by the ranking female between control and experimental field groups, or before and after removal of the male. However, the sizes of the ranking females were at or beyond the size range of individuals with a mixed‐stage gonad, suggesting that the developmental window for female‐to‐male sex change may not be open ended. In 41 of 43 field groups, in which sex of fish was determined histologically or by the shape of the urogenital papilla, one to several highest size ranks were occupied by males, followed by one to several females. Mature males, however, were not limited to the highest ranks and occurred at various lower size ranks within groups. Individuals with a mixed‐stage gonad also occupied various size ranks within groups.
Variation in daily and seasonal foraging routines of non‐breeding barnacle geese (Branta leucopsis): working harder does not overcome environmental constraints
Authors: Cope David R.
Published: September 2010

This study describes the changes in stored body fat in Svalbard barnacle geese Branta leucopsis over the non‐breeding period, and uses behavioural patterns to explain the variation in body fat stores. It was predicted that foraging effort would: (1) increase at low food densities; (2) increase when days were short; (3) decrease in smaller flocks; (4) be bimodally distributed throughout the day for long days, but constant for short days. Time constraints were found to be the major driving force behind foraging decisions during the shortest days of mid‐winter, whereas food density was found to drive decisions during longer days. Field observations of fat stores showed that fat was rapidly accumulated at the start and end of the non‐breeding period, but that fat stores remained constant during mid‐winter. It is suggested that day length prevented a positive fat storage rate in mid‐winter through the limitation of foraging time, even though foraging effort was high during this period. During a single day, evidence for a bimodal foraging routine was found, where feeding activity was concentrated in the early morning and late afternoon periods. This pattern was found in the full range of day lengths, which suggests that even for short days, feeding must be interrupted so that other essential activities can be conducted. It is concluded that the behavioural choices of barnacle geese were constrained by environmental conditions, and that these behavioural patterns allow the variation in fat stores to be explained.
Sequence analyses of the small subunit rRNA gene confirm the paraphyly of oligotrich ciliates sensu lato and support the monophyly of the subclasses Oligotrichia and Choreotrichia (Ciliophora, Spirotrichea)
Authors: Strüder‐Kypke Michaela C. , Lynn Denis H.
Published: September 2010

Oligotrich ciliates are an abundant and important component of planktonic food webs. Classified together, based on morphology and the arrangement of the oral ciliature, they include sensu lato halteriids, strombidiids, strobilidiids, and tintinnids. The oral ciliature of tintinnids and strobilidiids, the subclass Choreotrichia, is composed of a closed circle of external polykinetids with internal polykinetids, leading to the cytostome. Strombidiid and halteriid species, the subclass Oligotrichia, have an open circle of adoral polykinetids and separate ventral polykinetids. Previous molecular phylogenetic analyses of spirotrichs have placed Halteria grandinella among the stichotrichs. Apart from H. grandinella, only one other small subunit ribosomal RNA (SSrRNA) gene sequence of an oligotrich ciliate (Strombidium purpureum) has been published. Fourteen additional species representative of the major oligotrich orders were collected to determine their phylogenetic relationships. These SSrRNA gene sequences include two strombidiids (Strombidium spp.), one strobilidiid (Strobilidium caudatum), and 11 tintinnid species (i.e. Codonellopsis americana, Eutintinnus pectinis, Eutintinnus sp., Favella panamensis, Metacylis angulata, Metacylis sp., Rhabdonella hebe, Tintinnidium mucicola, Tintinnopsis dadayi, Tintinnopsis fimbriata and Tintinnopsis tocatinensis). The subclasses Oligotrichia (excluding Halteria) and Choreotrichia form a monophyletic group and are sister group to the subclass Stichotrichia with high nodal support. The choreotrichs are confirmed as a monophyletic subclass whereas the halteriids do not cluster with the strombidiids, but within the subclass Stichotrichia. Therefore, the family Halteriidae is transferred to the order Sporadotrichida in the subclass Stichotrichia. The strombidiids form a sister clade to the subclass Choreotrichia. Since there are no clear morphological or genetical synapomorphies for these two groups combined, the separate subclasses Choreotrichia and Oligotrichia are retained. The genetic relationships among tintinnid genera do not correspond to relationships based on lorica morphology: species with agglomerated and hyaline loricae do not form separate branches but are interrelated.
A global picture of the seasonal persistence of stratospheric ozone anomalies
Authors: Tegtmeier S. , Fioletov V. E. , Shepherd T. G.
Published: September 2010

Interannual anomalies in vertical profiles of stratospheric ozone, in both equatorial and extratropical regions, have been shown to exhibit a strong seasonal persistence, namely, extended temporal autocorrelations during certain times of the calendar year. Here we investigate the relationship between this seasonal persistence of equatorial and extratropical ozone anomalies using the SAGE‐corrected SBUV data set, which provides a long‐term ozone profile time series. For the regions of the stratosphere where ozone is under purely dynamical or purely photochemical control, the seasonal persistence of equatorial and extratropical ozone anomalies arises from distinct mechanisms but preserves an anticorrelation between tropical and extratropical anomalies established during the winter period. In the 16–10 hPa layer, where ozone is controlled by both dynamical and photochemical processes, equatorial ozone anomalies exhibit a completely different behavior compared to ozone anomalies above and below in terms of variability, seasonal persistence, and especially the relationship between equatorial and extratropical ozone. Cross‐latitude‐time correlations show that for the 16–10 hPa layer, Northern Hemisphere (NH) extratropical ozone anomalies show the same variability as equatorial ozone anomalies but lagged by 3–6 months. High correlation coefficients are observed during the time frame of seasonal persistence of ozone anomalies, which is June–December for equatorial ozone and shifts by approximately 3–6 months when going from the equatorial region to NH extratropics. Thus in the transition zone between dynamical and photochemical control, equatorial ozone anomalies established in boreal summer/autumn are mirrored by NH extratropical ozone anomalies with a time lag similar to transport time scales. Equatorial ozone anomalies established in boreal winter/spring are likewise correlated with ozone anomalies in the Southern Hemisphere extratropics with a time lag comparable to transport time scales, similar to what is seen in the NH. However, the correlations between equatorial and SH extratropical ozone in the 10–16 hPa layer are weak.
Biomass burning smoke aerosol properties measured during Fire Laboratory at Missoula Experiments (FLAME)
Authors: Levin E. J. T. , McMeeking G. R. , Carrico C. M. , Mack L. E. , Kreidenweis S. M. , Wold C. E. , Moosmüller H. , Arnott W. P. , Hao W. M. , Collett J. L. , Malm W. C.
Published: September 2010

During the Fire Laboratory at Missoula Experiments (FLAME), we studied the physical, chemical, and optical properties of biomass burning smoke from the laboratory combustion of various wildland fuels. A good understanding of these properties is important in determining the radiative effects of biomass burning aerosols, with impacts on both local and regional visibility and global climate. We measured aerosol size distributions with two instruments: a differential mobility particle sizer (DMPS) and an optical particle counter (OPC). Volume size distributions from different burns varied from monomodal to multimodal, with geometric mean diameters ranging from 0.20–0.57 μm and geometric standard deviations ranging from 1.68–2.97. By reconciling the differences between the two sizing instruments, we estimated aerosol effective refractive indices with values ranging from 1.41 to 1.61. We reconstructed aerosol chemical composition for each burn using data from filters collected and analyzed with the Interagency Monitoring of Protected Visual Environments (IMPROVE) samplers and protocols. Aerosols were generally comprised of carbon with organic species accounting for the largest mass fraction in most cases. We used composition data to calculate aerosol density, which ranged from 1.22–1.92 g cm−3, and real and imaginary refractive indices, which had ranges of 1.55–1.80 and 0.01–0.50 respectively. Aerosol physical, chemical, and optical characterizations were combined to calculate dry mass scattering (MSE) and absorption (MAE) efficiencies at 532 nm. These parameters had values between 1.6–5.7 m2 g−1 and 0.04–0.94 m2 g−1.
Effect of sediment pulse grain size on sediment transport rates and bed mobility in gravel bed rivers
Authors: Venditti J. G. , Dietrich W. E. , Nelson P. A. , Wydzga M. A. , Fadde J. , Sklar L.
Published: September 2010

Sediment supply to gravel bed river channels often takes the form of episodic sediment pulses, and there is considerable interest in introducing sediment pulses in stream restorations to alter bed surface grain size distributions and bed mobility. A series of laboratory experiments was conducted in order to examine how sediment pulse grain size and volume affects the mobility of bed material in gravel bed channels. Pulses used in the experiments were composed of either the fine tail or the median of the subsurface bed material grain size distribution. Bed material refers to sediment in the channel prior to the pulse introduction exclusively. Both types of pulse were finer than the bed material surface median. Two pulse sizes were used, which were either equivalent to the volume of sediment required to cover the entire bed one median subsurface bed material grain diameter deep (full unit) or 1/4 of this volume (1/4 unit). The latter was designed to produce a transitory pulse. With the exception of the 1/4 unit coarse pulse, introduction of the sediment pulses to the channel caused dramatic increases in the bed load flux. The coarse sediment pulses fine the bed surface and coarsen the bed load. Finer pulses also fine the surface, but the bed load fines while the bed material load (that excludes pulse material) coarsens. The greatest effects on the fractional transport occurred during the full unit fine pulse where the pulse covered the greatest bed surface and effectively smoothed the bed, increasing near bed velocity and mobilizing the coarse particles. Overall, the coarse pulses were not very effective at mobilizing bed material. The large fine pulse mobilized ∼35% of the bed material surface (∼35% of its input weight) and was most effective at mobilizing the surface. However, the small fine pulse mobilized 50% of its input weight as it passed through the channel, making it the most efficient at mobilizing the bed material.
Testing statistical self‐similarity in the topology of river networks
Authors: Mantilla Ricardo , Troutman Brent M. , Gupta Vijay K.
Published: September 2010

Recent work has demonstrated that the topological properties of real river networks deviate significantly from predictions of Shreve's random model. At the same time the property of mean self‐similarity postulated by Tokunaga's model is well supported by data. Recently, a new class of network model called random self‐similar networks (RSN) that combines self‐similarity and randomness has been introduced to replicate important topological features observed in real river networks. We investigate if the hypothesis of statistical self‐similarity in the RSN model is supported by data on a set of 30 basins located across the continental United States that encompass a wide range of hydroclimatic variability. We demonstrate that the generators of the RSN model obey a geometric distribution, and self‐similarity holds in a statistical sense in 26 of these 30 basins. The parameters describing the distribution of interior and exterior generators are tested to be statistically different and the difference is shown to produce the well‐known Hack's law. The inter‐basin variability of RSN parameters is found to be statistically significant. We also test generator dependence on two climatic indices, mean annual precipitation and radiative index of dryness. Some indication of climatic influence on the generators is detected, but this influence is not statistically significant with the sample size available. Finally, two key applications of the RSN model to hydrology and geomorphology are briefly discussed.
Tension at EMBO's Aneuploidy Workshop
Authors: De Wulf Peter , Cheeseman Iain M
Published: September 2010

The EMBO 2010 Workshop on Chromosome Segregation and Aneuploidy, held between 19 and 23 June at Edinburgh University's Royal College of Surgeons, highlighted basic mitotic mechanisms, chromosome‐based defects linked to human diseases and the processes that connect them.
Mechanisms of force generation and force transmission during interstitial leukocyte migration
Authors: Renkawitz Jörg , Sixt Michael
Published: September 2010

For innate and adaptive immune responses it is essential that inflammatory cells use quick and flexible locomotion strategies. Accordingly, most leukocytes can efficiently infiltrate and traverse almost every physiological or artificial environment. Here, we review how leukocytes might achieve this task mechanistically, and summarize recent findings on the principles of cytoskeletal force generation and transduction at the leading edge of leukocytes. We propose a model in which the cells switch between adhesion‐receptor‐mediated force transmission and locomotion modes that are based on cellular deformations, but independent of adhesion receptors. This plasticity in migration strategies allows leukocytes to adapt to the geometry and molecular composition of their environment.
Functional analysis of two isoforms of phosphatidylethanolamine N-methyltransferase
Authors: Morita Shin-ya , Takeuchi Atsuko , Kitagawa Shuji
Published: September 2010

The enzyme catalysing the conversion of PE (phosphatidylethanolamine) into PC (phosphatidylcholine), PEMT (PE N-methyltransferase), exists as two isoforms, PEMT-L (longer isoform of PEMT) and PEMT-S (shorter isoform of PEMT). In the present study, to compare the functions of the two isoforms of PEMT, we established HEK (human embryonic kidney)-293 cell lines stably expressing PEMT-L and PEMT-S. Both PEMT-L and PEMT-S were localized in the ER (endoplasmic reticulum). PEMT-L, but not PEMT-S, was N-glycosylated with high-mannose oligosaccharides. The enzymatic activity of PEMT-S was much higher than that of PEMT-L. By using novel enzymatic assays for measuring PC and PE, we showed that PEMT-L and PEMT-S expression remarkably increased the cellular PC content, whereas the PE content was decreased by PEMT-S expression, but was hardly affected by PEMT-L expression. The cellular content of phosphatidylserine was also reduced by the expression of PEMT-L or PEMT-S. MS analyses demonstrated that the expression of PEMT-S led to more increases in the molecular species of PC and PC-O (ether-linked PC) with longer polyunsaturated chains than that of PEMT-L, whereas the PC-O species with shorter chains were increased more by PEMT-L expression than by PEMT-S expression, suggesting a difference in the substrate specificity of PEMT-L and PEMT-S. On the other hand, various PE and PE-O species were decreased by PEMT-S expression. In addition, PEMT-L and PEMT-S expression promoted the proliferation of HEK-293 cells. Based upon these findings, we propose a model in which the enzymatic activity and substrate specificity are regulated by the glycosylated N-terminal region of PEMT-L localized in the ER lumen.
AHSP (α-haemoglobin-stabilizing protein) stabilizes apo-α-haemoglobin in a partially folded state
Authors: Krishna Kumar Kaavya , Dickson Claire F. , Weiss Mitchell J. , Mackay Joel P. , Gell David A.
Published: September 2010

To produce functional Hb (haemoglobin), nascent α-globin (αo) and β-globin (βo) chains must each bind a single haem molecule (to form αh and βh) and interact together to form heterodimers. The precise sequence of binding events is unknown, and it has been suggested that additional factors might enhance the efficiency of Hb folding. AHSP (α-haemoglobin-stabilizing protein) has been shown previously to bind αh and regulate redox activity of the haem iron. In the present study, we used a combination of classical and dynamic light scattering and NMR spectroscopy to demonstrate that AHSP forms a heterodimeric complex with αo that inhibits αo aggregation and promotes αo folding in the absence of haem. These findings indicate that AHSP may function as an αo-specific chaperone, and suggest an important role for αo in guiding Hb assembly by stabilizing βo and inhibiting off-pathway self-association of βh.
Saccharomyces cerevisiae glucose signalling regulator Mth1p regulates the organellar Na+/H+ exchanger Nhx1p
Authors: Mitsui Keiji , Matsushita Masafumi , Kanazawa Hiroshi
Published: September 2010

Organelle-localized NHEs (Na+/H+ exchangers) are found in cells from yeast to humans and contribute to organellar pH regulation by exporting H+ from the lumen to the cytosol coupled to an H+ gradient established by vacuolar H+-ATPase. The mechanisms underlying the regulation of organellar NHEs are largely unknown. In the present study, a yeast two-hybrid assay identified Mth1p as a new binding protein for Nhx1p, an organellar NHE in Saccharomyces cerevisiae. It was shown by an in vitro pull-down assay that Mth1p bound to the hydrophilic C-terminal half of Nhx1p, especially to the central portion of this region. Mth1p is known to bind to the cytoplasmic domain of the glucose sensor Snf3p/Rgt2p and also functions as a negative transcriptional regulator. Mth1p was expressed in cells grown in a medium containing galactose, but was lost (possibly degraded) when cells were grown in medium containing glucose as the sole carbon source. Deletion of the MTH1 gene increased cell growth compared with the wild-type when cells were grown in a medium containing galactose and with hygromycin or at an acidic pH. This resistance to hygromycin or acidic conditions was not observed for cells grown with glucose as the sole carbon source. Gene knockout of NHX1 increased the sensitivity to hygromycin and acidic pH. The increased resistance to hygromycin was reproduced by truncation of the Mth1p-binding region in Nhx1p. These results implicate Mth1p as a novel regulator of Nhx1p that responds to specific extracellular carbon sources.
Virtual mitochondrion: towards an integrated model of oxidative phosphorylation complexes and beyond
Authors: Mazat Jean-Pierre , Fromentin Jonathan , Heiske Margit , Nazaret Christine , Ransac Stéphane
Published: September 2010

The modelling of OXPHOS (oxidative phosphorylation) in order to integrate all kinetic and thermodynamic aspects of chemiosmotic theory has a long history. We briefly review this history and show how new ways of modelling are required to integrate a local model of the individual respiratory complexes into a global model of OXPHOS and, beyond that, into a reliable overall model of central metabolism.
Signal integration in budding yeast
Authors: Waltermann Christian , Klipp Edda
Published: September 2010

A complex signalling network governs the response of Saccharomyces cerevisiae to an array of environmental stimuli and stresses. In the present article, we provide an overview of the main signalling system and discuss the mechanisms by which yeast integrates and separates signals from these sources. We apply our classification scheme to a simple semi-quantitative model of the HOG (high-osmolarity glycerol)/FG (filamentous growth)/PH (pheromone) MAPK (mitogen-activated protein kinase) signalling network by perturbing its signal integration mechanisms under combinatorial stimuli of osmotic stress, starvation and pheromone exposure in silico. Our findings include that the Hog1 MAPK might act as a timer for filamentous differentiation, not allowing morphological differentiation before osmo-adaptation is sufficiently completed. We also see that a mutually exclusive decision-making between pheromone and osmo-response might not be taken on the MAPK level and transcriptional regulation of MAPK targets. We conclude that signal integration mechanisms in a wider network including the cell cycle have to be taken into account for which our framework might provide focal points of study.
Glycobiomimics and glycobiosensors
Authors: Gerlach Jared Q. , Cunningham Stephen , Kane Marian , Joshi Lokesh
Published: September 2010

Following steady advances in analytical technologies, our knowledge in glycomics is now increasing rapidly. Over the last decade, specific glycans have been described that are associated with a range of diseases, such as cancer and inflammation, with host–pathogen interactions and with various stages during stem cell development and differentiation. Simultaneously, deeper structural insight has been gained on glycosylated biopharmaceutical protein therapeutics manufactured in CHO (Chinese-hamster ovary) and other cell systems. This glycomic information is highly relevant for clinicians and biomanufacturing industries as a new class of glycobiomarkers emerges. However, current methods of glycoanalysis are primarily research tools and are not suitable for point-of-care on-site detection and analysis, or sensor devices. Lectin-based glycan detection provides the most promising approach to fill these gaps. However, the limited availability of lectins with high specificity and sensitivity for specific glycan motifs presents one of the main challenges in building reliable glycobiosensors. Recent reports have demonstrated the use of recombinant protein engineering, phage display and aptamer technologies in the production of lectin mimics, as well as the construction of biosensors that are capable of rapidly detecting glycan motifs at low levels in both a labelled and label-free manner. These are primarily proof-of-principle reports at this stage, but some of the approaches, either alone or in combination, will lead to functional glycobiosensors in the coming years which will be valuable tools for the clinical, biopharmaceutical and life science research communities.
Exploring the LPS/TLR4 signal pathway with small molecules
Authors: Peri Francesco , Piazza Matteo , Calabrese Valentina , Damore Gaetana , Cighetti Roberto
Published: September 2010

The identification of the bacterial endotoxin receptors for innate immunity, most notably TLR4 (Toll-like receptor 4), has sparked great interest in therapeutic manipulation of the innate immune system. In the present mini-review, several natural and synthetic molecules that modulate the TLR4-mediated LPS (lipopolysaccharide) signalling in animals and humans are considered, and their mechanisms of action are discussed. The process of LPS sensing and signal amplification in humans is based on the sequential action of specific receptors situated in the extracellular side of the innate immunity cells, which bind and transfer LPS to TLR4: LBP (LPS-binding protein), CD14, MD-2 (myeloid differentiation protein 2). We classified the compounds active on TLR4 pathway depending on the specific molecular targets (LPS, LBP, CD14, MD-2 or TLR4). Small molecules developed by our group are described that inhibit LPS-stimulated TLR4 activation by selectively targeting the LPS–CD14 interaction. These compounds have an interesting antiseptic shock, anti-inflammatory and anti-neuropathic pain activity in vivo.
Optical and structural characterization of AlInN layers for optoelectronic applications
Authors: Aschenbrenner T. , Dartsch H. , Kruse C. , Anastasescu M. , Stoica M. , Gartner M. , Pretorius A. , Rosenauer A. , Wagner Thomas , Hommel D.
Published: September 2010

Al 1 − x In x N layers with an indium content between x=10.5% and x=24% were grown by metal-organic vapor-phase epitaxy and characterized concerning their optical, structural and morphological properties with regard to the realization of optoelectronic devices. The indium content and the strain of these layers were measured by high resolution x-ray diffraction. Ellipsometric measurements were used to determine the optical constants [refractive index n(λ) and extinction coefficient κ(λ)] in dependence of wavelength and indium content. The values determined for the electronic bandgaps are in good agreement with theoretical predictions and previous publications on this topic but are more focused on AlInN layers which are pseudomorphically grown on GaN. A bowing parameter of b=10.3±0.1 was determined for fully strained layers with an indium content between 13% and 24%. In order to investigate the suitability of these layers for use in distributed Bragg reflectors, the surface morphology is characterized with respect to the indium content. Furthermore, the influence of an annealing step which often is necessary during device growth, was studied. The influence of this annealing step on the roughness was analyzed by atomic force microscopy, while structural features are monitored by high resolution secondary electron microscopy images. Based on these results distributed Bragg reflectors for the green spectral region with up to 40 pairs and a peak reflectivity of 97% have been realized. Transmission electron microscopic analysis of the layer interfaces are in good agreement with the atomic force and secondary electron microscopy images of the single layer surfaces.
Composition dependence of magnetic and magnetotransport properties in C60–Co granular thin films
Authors: Sugai Isamu , Sakai Seiji , Matsumoto Yoshihiro , Naramoto Hiroshi , Mitani Seiji , Takanashi Koki , Maeda Yoshihito
Published: September 2010

Composition dependence of magnetic and magnetotransport properties in C60Cox thin films exhibiting large magnetoresistance (MR) effect was investigated in the Co composition range of x=8–20, where x denotes the number of Co atoms per C60 molecule. From the superparamagnetic magnetization curves observed, the average diameter (dave) of Co nanoparticles dispersed in the matrix phase was evaluated to be approximately 1 nm for the sample of x=8, and increased with the Co composition, x. By analyzing the temperature (T) dependence of resistivity based on the model by Abeles et al. [Adv. Phys. 24, 407 (1975)], the average charging energies (⟨ÊC⟩) of Co nanoparticles were evaluated to be 2–9 meV for the samples of x=8–17 while the considerably weak temperature dependence suggested much smaller values of ⟨ÊC⟩ for the samples of x>17. The composition dependence of dave and ⟨ÊC⟩ revealed a structural transition from well-defined granular structures in the range of x=8–17 to magnetically and electronically coupled states of Co nanoparticles over x∼17. As a result of the structural change, the MR behavior became different between the two composition regions separated at x∼17. In particular, for the samples of x=8–17, the bias-voltage (V) dependence of the MR ratio in the low-V region fits well with an unusual exponential form of MR=MR0 exp(−V/Vc) at T<20 K, and it is most remarkable that the zero-bias MR ratio (MR0) is in proportion to ⟨ÊC⟩ and also that the fitting parameter Vc is closely correlated with ⟨ÊC⟩. These results indicate that the charging effect of Co nanoparticles plays an important role in the anomalously large MR effect of C60–Co granular films. In addition, the power-law dependence of MR on T (MR∝T−α,α∼2) was also observed at relatively high temperature range T≥10 K in the wide range of the composition.
A physical model of exchange bias in [Pd/Co]5/FeMn thin films with perpendicular anisotropy
Authors: Lin Lin , Thiyagarajah Naganivetha , Joo Ho Wan , Heo Jang , Lee Ky Am , Bae Seongtae
Published: September 2010

A physical model of perpendicular exchange bias (PEB) has been established based on the total energy equation per unit area of an exchange bias system by assuming coherent rotation of the magnetization. The anisotropy energy of antiferromagnetic (AFM) layer, KAFM×tAFM, as well as ferromagnetic (FM) multilayers, KFM,eff×tFM, and the interfacial exchange coupling energy, Jex were considered as primary physical parameters in building up the physical model of PEB phenomenon. It was proposed that the PEB is a result of the energy competition between KAFM×tAFM, KFM,eff×tFM, and Jex; where KAFM×tAFM≥Jex, is a critical condition to observe exchange bias in the system. In particular, it was revealed that Jex is directly relevant to the net magnetization of FM and AFM spin structure, Jex∝cos αAFM×cos βFM, in the perpendicular direction rather than the magnetization angle difference observed in an in-plane system. The physical role of perpendicular anisotropy energy, KFM,eff×tFM was also found to be significant to enhance the PEB. These physical characteristics are completely different from those are observed from an exchange bias system with in-plane anisotropy. The physical validity of the proposed PEB model was confirmed using different structures of exchange biased [Pd/Co]5/FeMn thin films with perpendicular anisotropy. The experimentally analyzed results demonstrated that the physical model of PEB proposed in this work is agreed well with the experimentally observed PEB phenomenon. Furthermore, the proposed model was found to be effective to design and to predict a new PEB system for the advanced spintronics applications.
Ab initio studies of ultrafast x-ray scattering of the photodissociation of iodine
Authors: Debnarova Andrea , Techert Simone , Schmatz Stefan
Published: September 2010

We computationally examine various aspects of the reaction dynamics of the photodissociation and recombination of molecular iodine. We use our recently proposed formalism to calculate time-dependent x-ray scattering signal changes from first principles. Different aspects of the dynamics of this prototypical reaction are studied, such as coherent and noncoherent processes, features of structural relaxation that are periodic in time versus nonperiodic dissociative processes, as well as small electron density changes caused by electronic excitation, all with respect to x-ray scattering. We can demonstrate that wide-angle x-ray scattering offers a possibility to study the changes in electron densities in nonperiodic systems, which render it a suitable technique for the investigation of chemical reactions from a structural dynamics point of view.
Spin-transport selectivity upon Co adsorption on antiferromagnetic graphene nanoribbons
Authors: Cocchi Caterina , Prezzi Deborah , Calzolari Arrigo , Molinari Elisa
Published: September 2010

We investigate from first principles the electronic and transport properties of zigzag graphene nanoribbons in the presence of Co adatoms. Comparing different adsorption sites across the width, we find that the Co–C coupling is rather sensitive to the local environment. While a net spin polarization appears in all cases, the spin filtering effect is significantly enhanced when the Co adatom is at the edge, where the adsorption energy is maximized and a partial suppression of edge-associated transport channels occurs. We also probe the magnetic interaction in the nonbonding regime, for Co-graphene nanoribbon (GNR) distances ranging from adsorption to π-π typical configurations. Our results indicate that Co-GNR coupling is still appreciable in an intermediate range, whereas it becomes vanishingly small in the limit of π-π distances.
Stabilization of surface spin glass behavior in core-shell Fe67Co33–CoFe2O4 nanoparticles
Authors: Hassnain Jaffari G. , Rizwan Ali S. , Hasanain S. K. , Güntherodt Gernot , Ismat Shah S.
Published: September 2010

Magnetic properties of Co33Fe67–CoFe2O4 (core-shell) nanoparticles are presented. Both dc magnetization and ac susceptibility measurements indicate a spin glass (SG) like transition occurring at TF∼175 K. The SG nature of the transition is also confirmed by the field dependence of the freezing temperature (TF(H)) following the well known Almeida–Thouless line, δTF∼H2/3. Additionally, the particles exhibit a large exchange bias (HEB∼1357 Oe) arising from the core-shell (ferromagnetic-SG) coupling. The unusually high SG transition temperature and large exchange bias effects are attributed to a combination of several factors including the thickness of the amorphous oxide shell and large values of the exchange and anisotropy constants associated with the CoFe2O4 shell.
The statistical shift of the chemical potential causing anomalous conductivity in hydrogenated microcrystalline silicon
Authors: Lof R. W. , Schropp R. E. I.
Published: September 2010

The behavior of the electrical conductivity in hydrogenated microcrystalline silicon (μc-Si:H) that is frequently observed is explained by considering the statistical shift in the chemical potential as a function of the crystalline fraction (Xc), the dangling bond density (Ndb), and the doping density (Nd). Our model shows that temperature dependent dc conductivity measurements above room temperature can be very well explained by (unintentional) micro doping of μc-Si:H. It is shown that the statistical shift in the chemical potential (μ) is influenced mostly by the ratio between Nd and Ndb. It is concluded that the anomalous dependence of the apparent activation energy (Ea) and the apparent exponential prefactor (σ0) on Xc can be explained by behavior of μ, that can be induced by a change in this ratio between Nd and Ndb. We used an effective medium approximation for the electron density of states (DOS) of μc-Si:H. The DOS is calculated as a weighted sum of the DOS of c-Si and the DOS of a-Si:H, parameterized by Xc, Ndb, and Nd. The conductivity is deduced assuming a single dominant conduction path above the conduction edge of a-Si:H.
Chemical stability of lanthanum germanate passivating layer on Ge upon high-k deposition: A photoemission study on the role of La in the interface chemistry
Authors: Tsoutsou D. , Panayiotatos Y. , Sotiropoulos A. , Mavrou G. , Golias E. , Galata S. F. , Dimoulas A.
Published: September 2010

The chemical stability of La-containing passivating layers /high-k gate stacks on Ge substrates is investigated by x-ray photoelectron spectroscopy. It is found that upon exposure to oxygen, a La-covered Ge surface spontaneously converts to a stable LaGeOx passivating layer. However, in the presence of overlying metal layers such as Al and Hf or upon deposition of high-k metal oxide cap layers such as Al2O3 and HfO2, the LaGeOx layer strongly reacts with the overlayers forming LaAlOz and LaHfOz compounds. In the case of Al or Al2O3, the LaGeOx is completely dissociated, while in the case of Hf or HfO2, LaGeOx remains although with a change in composition. The results are interpreted in terms of oxygen densification according to which the strongly electropositive La drives the reaction toward the formation of oxides with the highest oxygen density. The results suggest that HfO2 has a better chemical compatibility with LaGeOx making it more suitable for the gate stack.