bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Modal Dynamics of Wind Turbines to Avoid Stall‐induced Vibrations
Authors: Hansen M. H.
Published: April 2003

Stall‐induced edgewise blade vibrations have occasionally been observed on three‐bladed wind turbines over the last decade. Experiments and numerical simulations have shown that these blade vibrations are related to certain vibration modes of the turbines. A recent experiment with a 600 kW turbine has shown that a backward whirling mode associated with edgewise blade vibrations is less aerodynamically damped than the corresponding forward whirling mode. In this article the mode shapes of the particular turbine are analysed, based on a simplified turbine model described in a multi‐blade formulation. It is shown that the vibrations of the blades for the backward and forward edgewise whirling modes are different, which can explain the measured difference in aerodynamic damping. The modal dynamics of the entire turbine is important for stability assessments; blade‐only analysis can be misleading. In some cases the modal dynamics may even be improved to avoid stall‐induced vibrations. Copyright © 2003 John Wiley & Sons, Ltd.
Ciliate Hitch-hikers—Nematode ecto-commensals from tropical Australian sea grass meadows
Authors: Fisher R.
Published: April 2003

The presence of suctorian ciliates attached to the cuticle of heavily ornamented free-living marine nematodes, especially the family Desmodoridae, has been reported. Observations of nematode hosts and their attached ciliates were made from samples extracted from very fine muddy sands of tropical Australian sea grass meadows. Measurements of the point of attachment of the ciliates revealed that they tend to position themselves near the anus/cloaca of the nematode host.
Presence of two new species of suctorian (Protozoa: Ciliophora) epibiont on the marine crustacean isopod Excirolana chiltoni
Authors: Fernandez-Leborans Gregorio , Hanamura Yukio , Nagasaki Keizo
Published: April 2003

Specimens of the marine isopod Excirolana chiltoni collected in Hokkaido (northern Japan) showed epibiont protozoan ciliates belonging to two species of loricate suctorian: Acineta hokkaidensis sp. nov. and Acineta excirolensis sp. nov. Acineta hokkaidensis is larger, with an elongated body covered by a lorica. The short stalk had 15–18 longitudinal striations. The contractile vacuole was located apically. The macronucleus was posterior. Two fascicles of capitate tentacles located at the edges of the apical area project through the anterior aperture of the lorica. The suctorians were found on the pereiopods and antennae of the isopod. Acineta excirolensis which is smaller and triangular in shape, showed a very wide lorica and a noticeably long stalk. At the edges of the apical region there were two lobulate actinophores, each with a fascicle of capitate tentacles. The contractile vacuole was anterior and spherical, and the macronucleus was central. These suctorians were attached as planobionts on the pereiopods of the isopod. The taxonomic position of both species was analysed in relation to other similar species previously described.
Feeding behaviour and associated sensory mechanisms of stage I–III phyllosoma of Jasus edwardsii and Jasus verreauxi
Authors: Cox Serena L. , Bruce Michael P.
Published: April 2003

The feeding behaviour of stage I–III phyllosoma of the spiny lobsters Jasus edwardsii and Jasus verreauxi was recorded to determine the sequence of events and sensory mechanisms involved in the feeding process. All phyllosoma exhibited a characteristic tumbling behaviour prior to making contact with an individual Artemia and feeding behaviour was similar between the two species. Tactile contact with pereiopods 1 or 2 was necessary to initiate a prey capture response which involved spearing of Artemia, using the terminal dactyl present on these two pereiopods and then passing the prey forward to the mouth with the maxillipeds.

Scanning electron microscopy (SEM) of the pereiopods revealed two morphologically distinct receptors present on the distal segments. These receptors are suggested to have tactile and chemoreceptive roles.
Aspects of the feeding biology of the pectinacean Bathypecten vulcani, a peri-hydrothermal vent bivalve
Authors: PENNEC Gaël LE , BENINGER Peter G. , PENNEC Marcel LE , DONVAL Anne
Published: April 2003

The feeding biology of Bathypecten vulcani, a peri-hydrothermal vent pectinacean, was investigated using histological and scanning electron microscope studies of the gills and stomach contents of specimens sampled from the 9° and 13°N sites of the East Pacific Rise. Salient characteristics were compared with those of Bathymodiolus thermophilus from the same and similar habitats. The gills of Bathypecten vulcani displayed heterogeneous organic and mineral particles on their frontal surface. The digestive tract possessed well-developed structures (whose anatomical and cytological characteristics indicated full functionality), typically found in bivalves from littoral aerobic environments, as well as in Bathymodiolus thermophilus, which is capable of suspension-feeding: oesophagus, stomach, crystalline style, digestive gland, and intestine. Observations of stomach contents revealed diverse particles from the photic zone, including debris from diatoms and coccolithophorans. In contrast to Bathymodiolus thermophilus, bacteria were rarely observed in the digestive tract, indicating a more complete reliance on surface-originating particles.
Interactions between benthic molluscs in a Sulawesi mangal, Indonesia: the cerithiid mud-creeper Cerithium coralium and potamidid mud-whelks, Terebralia spp.
Authors: BARNES R.S.K.
Published: April 2003

The sediment surface within the Osbornia belt of a mangal on Pulau Hoga, Tukang Besi Islands, Sulawesi, Indonesia, is dominated inter alia by deposit-feeding gastropod molluscs at a mean density of some 230 ind m−2 although, unusually, species of Cerithidea do not occur. Densities of the two most numerous species, the potamidid mud-whelk Terebralia sulcata and the Cerithidea-like cerithiid mud-creeper Cerithium coralium, are inversely correlated, although the species occurred together in 42% of quadrat samples. Within and beyond the normal range of field densities of each species (C. coralium mean 153 m−2; T. sulcata mean 75 m−2) there was no evidence of intraspecific depression of feeding rate, as assessed by the production of faecal pellets, although this was significantly reduced in the occasional very high density aggregations of C. coralium (>1100 m−2). The presence of the larger T. sulcata did appear to have a strong inhibitory effect on feeding in C. coralium; the converse, however, could not be demonstrated. Abundances of Terebralia palustris and C. coralium were also inversely correlated where the two co-occurred.
Diet, prey selection and cannibalism in the hunter opisthobranch Roboastra europaea
Authors: Megina César , Cervera Juan Lucas
Published: April 2003

The diet and predatory behaviour of the nudibranch Roboastra europaea (Mollusca) is described and compared with other nudibranch-hunting opisthobranchs. The natural diet in the Strait of Gibraltar was studied by the analysis of gut contents. Roboastra europaea is a specialist predator of nudibranchs, and the diet is comprised essentially of the polycerids Polycera sp., Polycerella emertoni, Limacia clavigera and conspecific R. europaea. One or several Polycera species appeared as the most dominant prey.  The complete assemblage of potential prey of this predator—the fundamental diet—was assessed in laboratory trials that included all likely prey groups. This predator consistently rejected both non-nudibranch species and non-polycerid nudibranchs. Roboastra europaea is exclusively a predator of polycerids and previously unencountered polycerids are also potential prey items.  As most of the hunter opisthobranchs, R. europaea exhibited cannibalistic behaviour, to the extent that aggressiveness prevailed over mating in intraspecific encounters. Roboastra europaea as prey showed a complex result in laboratory trials: (a) if one individual was small enough complete ingestion proceeded; (b) if there was not enough difference in size, a cannibal attack proceeded, but if ingestion was not possible, it could result in mating behaviour.
Relationship between density and feeding frequency for reared larvae of the gastropod Crepidula fornicata
Authors: Marty Regis , Desroy Nicolas , Bureau Sophie , Retière Christian
Published: April 2003

The aim of this study is to improve rearing device of Crepidula fornicata (Mollusca: Gastropoda) reported in the literature, by determining the best arrangement between densities and feeding frequency in reared enclosures. Optimal growth (26·4 μm d−1) and survival rates (55·1%) were obtained when larvae were reared at 500 ind l−1 and fed every two days.
Lack of dietary specialization in adult Aplysia californica: evidence from stable carbon isotope composition
Authors: Korb Rebecca
Published: April 2003

Natural abundance, 13C/12C ratios (δ13C) of Californian sea hares, Aplysia californica, (Gastropoda: Opisthobranchia) were measured for comparison with the animals preferred red algal diets, Plocamium cartilagineum and Laurenciapacifica. Isotopic compositions of animals collected from around Santa Catalina Island, did not reflect those of the favoured red algal diets, nor the majority of algal species found in the field. However, animals held in seawater tanks and fed diets with a constant carbon isotopic composition exhibited δ13C values similar to their food. Fast turnover tissue, such as the muscle tissue of actively growing juveniles or egg masses laid by adults, showed δ13C values within ±2‰ of the algal diet. Slow turnover tissue, such as the muscle tissue of large adults, reflected the diet over several months. Stable carbon isotope ratios thus proved a useful tool to clarify the extent to which specialized feeding in A. californica can occur upon algae which are only moderately to rarely common.
Dietary variation of the squid Moroteuthis ingens at four sites in the Southern Ocean: stomach contents, lipid and fatty acid profiles
Authors: Phillips Katrina L. , Nichols Peter D. , Jackson George D.
Published: April 2003

Specimens of the onychoteuthid squid Moroteuthis ingens were collected from four sites in the Southern Ocean: Macquarie Island, the Falkland Islands, the Chatham Rise (New Zealand) and the Campbell Plateau (New Zealand). Spatial variations in diet among these areas were investigated using stomach contents and lipid and fatty acid profiles. Myctophid fish were prominent prey items at all sites, and the diet at New Zealand sites contained temperate myctophid species that were not identified at other sites. The diet at the Falkland Islands differed considerably from other sites due to the large proportion of cephalopod prey that had been consumed by M. ingens. This is likely to be due to the absence of key myctophids, such as Electrona carlsbergi, and the abundance of smaller squid such as Loligo gahi and juvenile M. ingens over the Patagonian Shelf. Stomach contents data could not be used effectively to determine dietary differences between the Chatham Rise and Campbell Plateau, largely due to differences in sample sizes between these sites. Lipid class and fatty acid profiles of the digestive gland indicated that the diet of M. ingens differed significantly between the Chatham Rise and Campbell Plateau, despite the relative proximity of these sites. We conclude from total lipid content that this was due to a reduction in food availability to M. ingens at the Campbell Plateau. The highly productive waters of the Subtropical Front pass over the Chatham Rise, whereas the Campbell Plateau is situated in less productive sub-Antarctic water. Differences in oceanographic conditions are likely to have driven dietary variations between these two sites.
Population biology of Octopus vulgaris on the temperate south-eastern coast of South Africa
Authors: Oosthuizen A. , Smale M.J.
Published: April 2003

Population structure and biology of Octopus vulgaris was investigated along the south-eastern coast of South Africa. Samples were collected inter- and sub-tidally as a precursor to the establishment of an experimental octopus fishery in the region. In total, 300 (intertidal) and 147 (subtidal) O. vulgaris were collected over a two year period. Females were found to dominate the intertidal area (sex ratio 2:1), while no difference was found subtidally (sex ratio 1:1). Of those collected intertidally, immature females were most prevalent while males ranged from immature to mature. Mature females were only found subtidally. A marked size difference was apparent, with the subtidal octopus being substantially larger. Although brooding females were found throughout the year, numbers peaked in summer. Individual fecundity ranged between 42,000–790,000 eggs. The total number of eggs produced and the number of eggs per egg string were correlated to female size. Diet did not vary greatly between the inter- and sub-tidal areas, with the main prey items being crustaceans, teleosts and octopus. It appears that the immature females use the intertidal area to feed and grow, before migrating to deeper areas to mature and spawn.
Seasonal changes in the biochemical composition of body components of the sea urchin, Paracentrotus lividus, in Lorbé (Galicia, north-western Spain)
Authors: Montero-Torreiro M.F. , Garcia-Martinez P.
Published: April 2003

Seasonal variations in the gonad index and the biochemical composition of gonad and gut tissue of the sea urchin, Paracentrotus lividus (Echinodermata: Echinoidea) were determined. Samples were collected from Lorbé (Galicia, north-western Spain) between November 1994 and October 1995. The gametogenic cycle of the sea urchin was annual, with a long, single spawning period from May to August 1995. Most of the biochemical components in gonad showed clear seasonal variation, which was related to the gonad cycle. The main component was protein, which ranged between 36 and 60% of the dry weight, with maximum levels coinciding with the minimum levels of glycogen. Gonad glycogen therefore seemed to be the energy source employed for protein synthesis during gametogenesis. Seasonal variation in total lipids in the gonad was less evident; the main lipidic component was triacylglycerol (around 10% of the dry weight), whereas total cholesterol accounted for less than 1%. The gut does not seem to act as a storage tissue in P. lividus and seasonal variation in biochemical components may be a consequence of fluctuations in the availability of food.
Structural dynamics of a sea-star (Marthasterias glacialis) population
Authors: Verling Emma , Crook Anne C. , Barnes David K.A. , Harrison Simon S.C.
Published: April 2003

The dynamics and feeding biology of a population of Marthasterias glacialis (Echinodermata: Asteroidea) was examined over a two-year period from 2000–2002 at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. A multivariate approach was used and both multiple factors and multiple interactions between factors were found to influence population structure. These included time of year, site, individual sea-star size, depth, and predator density. Individuals belonging to the smallest size-classes (0–50 mm and 51–100 mm) were most abundant amongst boulders in shallow water (0–1 m), while larger individuals were primarily found in water below 1 m in depth on finer grade substratum and shell debris. Dietary composition was also found to differ with depth; sea-stars in the immediate subtidal had an opportunistic diet, and fed on a variety of taxa, whilst those M. glacialis from 1–6 m were more selective and restrictive, feeding chiefly on bivalve prey. We propose that spatial partitioning of different size-classes and a generalist feeding strategy may account for the success of M. glacialis at Lough Hyne.
Feeding ecology, age, growth and sexual cycle of the Portuguese sole, Synaptura lusitanica
Authors: Cabral Henrique , Catarino Ana Isabel , Figueiredo Joana , Garcia Joana , Henriques Miguel
Published: April 2003

Portuguese sole, Synaptura lusitanica, were collected from the Portuguese coast, between April 2001 and March 2002, to examine feeding habits, age and growth, and sexual cycle. Synaptura lusitanica fed on few prey items, its diet mainly composed of polychaeta, bivalvia and cephalochordata. Significant differences were found between the proportion of prey items according to season, length class of fish and coastal area. The main differences related to fish size were the higher ingestion of bivalvia by larger fish, in the west coast area, and the increase in the important cephalochordata for fish larger than 300 mm total length, in the south coastal areas. Polychaeta presented a lower importance in the spring–summer period while bivalvia increased its values in the autumn–winter period. Cephalochordata were more important in the autumn–winter period, but only for fish larger than 300 mm total length and in the south coastal areas. Vacuity was extremely high (mean value of 52%). Ages of S. lusitanica were determined from sagittae otoliths. The length of fish analysed varied from 157 mm to 480 mm, and the oldest fish was age 8. The von Bertalanffy growth equation parameters differed little between sexes, being the asymptotic length obtained for females higher compared to males. The highest values of the gonadosomatic index were obtained in summer, which was the period when the highest percentage of individuals in the spawning stage were recorded. Therefore, the spawning season seems to be from mid-spring (May) until the end of summer (September).
Polychaete annelids in the diet of demersal fish from the southern shelf of the Bay of Biscay
Authors: Serrano Alberto , Velasco Francisco , Olaso Ignacio
Published: April 2003

Polychaete prey were studied in the diet of 16 demersal fish species caught during an evaluation survey of demersal resources in the southern part of the Bay of Biscay during autumn, year 2000. A total of 27 prey taxa belonging to 17 families (21 of them at the species level) were found. Mullus surmuletus appeared as the main polychaete specialist. The consumption of polychaetes in other species, such as Pagrus pagrus, Chelidonichthys obscurus, Raja montagui, Scyliorhinus canicula, Trachyscorpia cristulata equinata and Pagellus acarne, was also important. Four species were analysed in more detail, M. surmuletus that preyed mainly on the families Nephtyidae, Sigalionidae and Goniadidae, P. acarne on Sigalionidae, R. montagui, on Sigalionidae, Arabellidae, Glyceridae and Aphroditidae, and S. canicula on Arenicolidae, Nephtyidae and Arabellidae. The most frequent species found in the stomachs were Nephtys hombergii, Aponuphis bilineata, Labioleanira yhleni, Arabella iricolor and Laetmonice filicornis. The predators had a clear preference for errant and carnivorous polychaete species, probably due to the more active behaviour of these prey, and also as a result of trawl fishing.
Interactions between ophiuroids and beaugregory damselfish
Authors: Payne Adam G. , Smith Carl , Campbell Andrew C.
Published: April 2003

The interactions between beaugregory damselfish and ophiuroids, potential damselfish egg predators, were investigated using several field studies. A survey of back reef areas showed that the two most common ophiuroid species, Ophiocoma echinata and Ophioderma appressum, were significantly associated with the territories of beaugregory males within the coral rubble habitat where both ophiuroids and beaugregory's can be found. Feeding experiments showed that three ophiuroid species (Ophiocoma echinata, Ophioderma appressum and Ophiocoma wendtii) and Echinometra viridis consumed late development stage beaugregory eggs, whereas earlier stages were only consumed by Ophioderma appressum and Echinometra viridis. Manipulation of ophiuroid densities had no significant effect on the survival of beaugregory eggs and had no measurable impact on female mate choice. The aggressive response of male beaugregory damselfish towards three ophiuroid and one echinoid species showed significant differences among species but were lower than those shown to bluehead wrasse, Thallasoma bifasciatum; the principal daylight predator of eggs. The intensity of attacks by male beaugregory damselfish towards Thallasoma bifasciatum increased significantly if males were guarding eggs, but did not appear to change for the four echinoderm species. Male habitat selection was shown to be unaffected by the presence of ophiuroids.
What drives the diel vertical migrations of Antarctic midwater fish?
Authors: Robison Bruce H.
Published: April 2003

Like their counterparts at lower latitudes, many Antarctic midwater fish make extensive, diel vertical migrations. However, Antarctic species make these migrations in the absence of two of the three selective advantages generally ascribed to this behaviour. Because the water column is nearly isothermal, there is no metabolic bonus to be gained from thermal differences in habitat depth. Likewise, because their prey do not perform significant vertical migrations, the fish migrations act to diminish rather than enhance their feeding opportunities. For Antarctic midwater fish, the sole advantage of these migrations appears to be the avoidance of visually-cued predators in the upper part of the water column. An evaluation of the relative importance of the three selective factors supports the suggestion that predator avoidance may also be the principal driver of diel vertical migrations for midwater fish at lower latitudes.
Effects of zooplankton density and diel period on surface-swimming duration of basking sharks
Authors: Sims D.W. , Southall E.J. , Merrett D.A. , Sanders J.
Published: April 2003

The surface-swimming duration of basking sharks (Cetorhinus maximus) was determined in the western English Channel from May to July over a five-year period. Surface duration showed marked variation from 0·17 to 1·45 h over the short time period from late May to mid-June. Stepwise multiple regression was used to identify any relationships between surface-swimming duration and time of day, daily sea surface temperature (SST), and zooplankton density. There was no support for any effects of SST or two measures of zooplankton density (median and maximum densities). However, there were significant relationships for surface duration with time of day and minimum zooplankton density (r2=0·50) indicating basking sharks respond to the abundance of prey and its temporal availability. This suggests that the probability of sighting sharks at the surface will vary depending on the diel period and the surface abundance of zooplankton.
Review of Data on Diets of Beaked Whales: Evidence of Niche Separation and Geographic Segregation
Authors: MacLeod C.D. , Santos M.B. , Pierce G.J.
Published: April 2003

This study reviewed published data on dietary preferences of beaked whales (Ziphiidae) from stomach contents analysis. Detailed data were only available for three of the six beaked whale genera (Hyperoodon, Mesoplodon and Ziphius). Stomach samples of these three beaked whale genera primarily contained cephalopod and fish remains, although some also contained crustaceans. Mesoplodon spp. were found to contain the most fish, with some species containing nothing but fish remains, while the southern bottlenose whale (Hyperoodon planifrons) and Cuvier's beaked whale (Ziphius cavirostris) rarely, if ever, contained fish. Of cephalopods identified, Histioteuthid, Gonatid, Cranchiid and Onychoteuthid species usually contributed most to prey numbers and biomass for all beaked whale genera. There was a wide range of species and families of cephalopods recorded from stomach contents, with no obvious preference for bioluminescent prey species, vertical migrating prey species or prey species with specific body compositions. Whales of the genus Mesoplodon generally contained smaller prey, such as cephalopods under 500 g in weight, compared with other beaked whales. Hyperoodon and Ziphius frequently contained much larger cephalopods with many important prey species having a mean weight of over 1000 g. This suggests that Mesoplodon occupies a separate dietary niche from Hyperoodon and Ziphius, which may be an example of niche segregation. In contrast, Hyperoodon and Ziphius appear to occupy very similar dietary niches but have geographically segregated distributions, with Hyperoodon occupying cold-temperate to polar waters and Ziphius occupying warm-temperate to tropical waters.
Mitochondrial targeting and a novel transmembrane arrest of Alzheimer's amyloid precursor protein impairs mitochondrial function in neuronal cells
Authors: Anandatheerthavarada Hindupur K. , Biswas Gopa , Robin Marie-Anne , Avadhani Narayan G.
Published: April 2003

Alzheimer's amyloid precursor protein 695 (APP) is a plasma membrane protein, which is known to be the source of the toxic amyloid β (Aβ) peptide associated with the pathogenesis of Alzheimer's disease (AD). Here we demonstrate that by virtue of its chimeric NH2-terminal signal, APP is also targeted to mitochondria of cortical neuronal cells and select regions of the brain of a transgenic mouse model for AD. The positively charged residues at 40, 44, and 51 of APP are critical components of the mitochondrial-targeting signal. Chemical cross-linking together with immunoelectron microscopy show that the mitochondrial APP exists in NH2-terminal inside transmembrane orientation and in contact with mitochondrial translocase proteins. Mutational studies show that the acidic domain, which spans sequence 220–290 of APP, causes the transmembrane arrest with the COOH-terminal 73-kD portion of the protein facing the cytoplasmic side. Accumulation of full-length APP in the mitochondrial compartment in a transmembrane-arrested form, but not lacking the acidic domain, caused mitochondrial dysfunction and impaired energy metabolism. These results show, for the first time, that APP is targeted to neuronal mitochondria under some physiological and pathological conditions.
Prostaglandin F2α stimulates growth of skeletal muscle cells via an NFATC2-dependent pathway
Authors: Horsley Valerie , Pavlath Grace K.
Published: April 2003

Skeletal muscle growth requires multiple steps to form large multinucleated muscle cells. Molecules that stimulate muscle growth may be therapeutic for muscle loss associated with aging, injury, or disease. However, few factors are known to increase muscle cell size. We demonstrate that prostaglandin F2α (PGF2α) as well as two analogues augment muscle cell size in vitro. This increased myotube size is not due to PGF2α-enhancing cell fusion that initially forms myotubes, but rather to PGF2α recruiting the fusion of cells with preexisting multinucleated cells. This growth is mediated through the PGF2α receptor (FP receptor). As the FP receptor can increase levels of intracellular calcium, the involvement of the calcium-regulated transcription factor nuclear factor of activated T cells (NFAT) in mediating PGF2α-enhanced cell growth was examined. We show that NFAT is activated by PGF2α, and the isoform NFATC2 is required for PGF2α-induced muscle cell growth and nuclear accretion, demonstrating the first intersection between prostaglandin receptor activation and NFAT signaling. Given this novel role for PGF2α in skeletal muscle cell growth, these studies raise caution that extended use of drugs that inhibit PG production, such as nonsteroidal antiinflammatory drugs, may be deleterious for muscle growth.
RAF1-activated MEK1 is found on the Golgi apparatus in late prophase and is required for Golgi complex fragmentation in mitosis
Authors: Colanzi Antonino , Sutterlin Christine , Malhotra Vivek
Published: April 2003

Amitotically activated mitogen-activated protein kinase 1 (MEK1) fragments the pericentriolar Golgi stacks in mammalian cells. We show that activated MEK1 is found on the Golgi apparatus in late prophase. The fragmented and dispersed Golgi membranes in prometaphase and later stages of mitosis do not contain activated MEK1. MEK1-dependent Golgi complex fragmentation is through activation by RAF1 and not MEK1 kinase 1. We propose that a RAF1-dependent activation of MEK1 and its presence on the Golgi apparatus in late prophase is required for Golgi complex fragmentation.
Postnatal NG2 proteoglycan–expressing progenitor cells are intrinsically multipotent and generate functional neurons
Authors: Belachew Shibeshih , Chittajallu Ramesh , Aguirre Adan A. , Yuan Xiaoqing , Kirby Martha , Anderson Stacie , Gallo Vittorio
Published: April 2003

Neurogenesis is known to persist in the adult mammalian central nervous system (CNS). The identity of the cells that generate new neurons in the postnatal CNS has become a crucial but elusive issue. Using a transgenic mouse, we show that NG2 proteoglycan–positive progenitor cells that express the 2′,3′-cyclic nucleotide 3′-phosphodiesterase gene display a multipotent phenotype in vitro and generate electrically excitable neurons, as well as astrocytes and oligodendrocytes. The fast kinetics and the high rate of multipotent fate of these NG2+ progenitors in vitro reflect an intrinsic property, rather than reprogramming. We demonstrate in the hippocampus in vivo that a sizeable fraction of postnatal NG2+ progenitor cells are proliferative precursors whose progeny appears to differentiate into GABAergic neurons capable of propagating action potentials and displaying functional synaptic inputs. These data show that at least a subpopulation of postnatal NG2-expressing cells are CNS multipotent precursors that may underlie adult hippocampal neurogenesis.
Myosin and the PAR proteins polarize microfilament-dependent forces that shape and position mitotic spindles in Caenorhabditis elegans
Authors: Severson Aaron F. , Bowerman Bruce
Published: April 2003

In Caenorhabditis elegans, the partitioning proteins (PARs), microfilaments (MFs), dynein, dynactin, and a nonmuscle myosin II all localize to the cortex of early embryonic cells. Both the PARs and the actomyosin cytoskeleton are required to polarize the anterior-posterior (a-p) body axis in one-cell zygotes, but it remains unknown how MFs influence embryonic polarity. Here we show that MFs are required for the cortical localization of PAR-2 and PAR-3. Furthermore, we show that PAR polarity regulates MF-dependent cortical forces applied to astral microtubules (MTs). These forces, which appear to be mediated by dynein and dynactin, produce changes in the shape and orientation of mitotic spindles. Unlike MFs, dynein, and dynactin, myosin II is not required for the production of these forces. Instead, myosin influences embryonic polarity by limiting PAR-3 to the anterior cortex. This in turn produces asymmetry in the forces applied to MTs at each pole and allows PAR-2 to accumulate in the posterior cortex of a one-cell zygote and maintain asymmetry.
Integrin-specific signaling pathways controlling focal adhesion formation and cell migration
Authors: Mostafavi-Pour Zohreh , Askari Janet A. , Parkinson Scott J. , Parker Peter J. , Ng Tony T.C. , Humphries Martin J.
Published: April 2003

The fibronectin (FN)-binding integrins α4β1 and α5β1 confer different cell adhesive properties, particularly with respect to focal adhesion formation and migration. After analyses of α4+/α5+ A375-SM melanoma cell adhesion to fragments of FN that interact selectively with α4β1 and α5β1, we now report two differences in the signals transduced by each receptor that underpin their specific adhesive properties. First, α5β1 and α4β1 have a differential requirement for cell surface proteoglycan engagement for focal adhesion formation and migration; α5β1 requires a proteoglycan coreceptor (syndecan-4), and α4β1 does not. Second, adhesion via α5β1 caused an eightfold increase in protein kinase Cα (PKCα) activation, but only basal PKCα activity was observed after adhesion via α4β1. Pharmacological inhibition of PKCα and transient expression of dominant-negative PKCα, but not dominant-negative PKCδ or PKCζ constructs, suppressed focal adhesion formation and cell migration mediated by α5β1, but had no effect on α4β1. These findings demonstrate that different integrins can signal to induce focal adhesion formation and migration by different mechanisms, and they identify PKCα signaling as central to the functional differences between α4β1 and α5β1.
Synapse formation is regulated by the signaling adaptor GIT1
Authors: Zhang Huaye , Webb Donna J. , Asmussen Hannelore , Horwitz Alan F.
Published: April 2003

Dendritic spines in the central nervous system undergo rapid actin-based shape changes, making actin regulators potential modulators of spine morphology and synapse formation. Although several potential regulators and effectors for actin organization have been identified, the mechanisms by which these molecules assemble and localize are not understood. Here we show that the G protein–coupled receptor kinase–interacting protein (GIT)1 serves such a function by targeting actin regulators and locally modulating Rac activity at synapses. In cultured hippocampal neurons, GIT1 is enriched in both pre- and postsynaptic terminals and targeted to these sites by a novel domain. Disruption of the synaptic localization of GIT1 by a dominant-negative mutant results in numerous dendritic protrusions and a significant decrease in the number of synapses and normal mushroom-shaped spines. The phenotype results from mislocalized GIT1 and its binding partner PIX, an exchange factor for Rac. In addition, constitutively active Rac shows a phenotype similar to the GIT1 mutant, whereas dominant-negative Rac inhibits the dendritic protrusion formation induced by mislocalized GIT1. These results demonstrate a novel function for GIT1 as a key regulator of spine morphology and synapse formation and point to a potential mechanism by which mutations in Rho family signaling leads to decreased neuronal connectivity and cognitive defects in nonsyndromic mental retardation.
The conformational state of Tes regulates its zyxin-dependent recruitment to focal adhesions
Authors: Garvalov Boyan K. , Higgins Theresa E. , Sutherland James D. , Zettl Markus , Scaplehorn Niki , Köcher Thomas , Piddini Eugenia , Griffiths Gareth , Way Michael
Published: April 2003

The function of the human Tes protein, which has extensive similarity to zyxin in both sequence and domain organization, is currently unknown. We now show that Tes is a component of focal adhesions that, when expressed, negatively regulates proliferation of T47D breast carcinoma cells. Coimmunoprecipitations demonstrate that in vivo Tes is complexed with actin, Mena, and vasodilator-stimulated phosphoprotein (VASP). Interestingly, the isolated NH2-terminal half of Tes pulls out α-actinin and paxillin from cell extracts in addition to actin. The COOH-terminal half recruits zyxin as well as Mena and VASP from cell extracts. These differences suggest that the ability of Tes to associate with α-actinin, paxillin, and zyxin is dependent on the conformational state of the molecule. Consistent with this hypothesis, we demonstrate that the two halves of Tes interact with each other in vitro and in vivo. Using fibroblasts lacking Mena and VASP, we show that these proteins are not required to recruit Tes to focal adhesions. However, using RNAi ablation, we demonstrate that zyxin is required to recruit Tes, as well as Mena and VASP, but not vinculin or paxillin, to focal adhesions.
Calcium signaling in a low calcium environment
Authors: Gazarini Marcos L. , Thomas Andrew P. , Pozzan Tullio , Garcia Célia R.S.
Published: April 2003

Malaria parasites, Plasmodia, spend most of their asexual life cycle within red blood cells, where they proliferate and mature. The erythrocyte cytoplasm has very low [Ca2+] (<100 nM), which is very different from the extracellular environment encountered by most eukaryotic cells. The absence of extracellular Ca2+ is usually incompatible with normal cell functions and survival. In the present work, we have tested the possibility that Plasmodia overcome the limitation posed by the erythrocyte intracellular environment through the maintenance of a high [Ca2+] within the parasitophorous vacuole (PV), the compartment formed during invasion and within which the parasites grow and divide. Thus, Plasmodia were allowed to invade erythrocytes in the presence of Ca2+ indicator dyes. This allowed selective loading of the Ca2+ probes within the PV. The [Ca2+] within this compartment was found to be ∼40 μM, i.e., high enough to be compatible with a normal loading of the Plasmodia intracellular Ca2+ stores, a prerequisite for the use of a Ca2+-based signaling mechanism. We also show that reduction of extracellular [Ca2+] results in a slow depletion of the [Ca2+] within the PV. A transient drop of [Ca2+] in the PV for a period as short as 2 h affects the maturation process of the parasites within the erythrocytes, with a major reduction 48 h later in the percentage of schizonts, the form that re-invades the red blood cells.
Abnormal neurofilament transport caused by targeted disruption of neuronal kinesin heavy chain KIF5A
Authors: Xia Chun-Hong , Roberts Elizabeth A. , Her Lu-Shiun , Liu Xinran , Williams David S. , Cleveland Don W. , Goldstein Lawrence S.B.
Published: April 2003

To test the hypothesis that fast anterograde molecular motor proteins power the slow axonal transport of neurofilaments (NFs), we used homologous recombination to generate mice lacking the neuronal-specific conventional kinesin heavy chain, KIF5A. Because null KIF5A mutants die immediately after birth, a synapsin-promoted Cre-recombinase transgene was used to direct inactivation of KIF5A in neurons postnatally. Three fourths of such mutant mice exhibited seizures and death at around 3 wk of age; the remaining animals survived to 3 mo or longer. In young mutant animals, fast axonal transport appeared to be intact, but NF-H, as well as NF-M and NF-L, accumulated in the cell bodies of peripheral sensory neurons accompanied by a reduction in sensory axon caliber. Older animals also developed age-dependent sensory neuron degeneration, an accumulation of NF subunits in cell bodies and a reduction in axons, loss of large caliber axons, and hind limb paralysis. These data support the hypothesis that a conventional kinesin plays a role in the microtubule-dependent slow axonal transport of at least one cargo, the NF proteins.
Malaria parasites solve the problem of a low calcium environment
Authors: Camacho Patricia
Published: April 2003

The parasite responsible for malaria, Plasmodium falciparum, spends much of its life in the RBC under conditions of low cytosolic Ca2+. This poses an interesting problem for a parasite that depends on a Ca2+ signaling system to carry out its vital functions. This long standing puzzle has now been resolved by a clever series of experiments performed by Gazarini et al. (2003). Using advances in fluorescent Ca2+ imaging (Grynkiewics, G., M. Poenie, and R.Y. Tsien. 1985. J. Biol. Chem. 260:3440–3450; Hofer, A., and T. Machen. 1994. Am. J. Physiol. 267:G442–G451; Hofer, A.M., B. Landolfi, L. Debellis, T. Pozzan, and S. Curci. 1998. EMBO J. 17:1986–1995), these authors have elucidated the source of the Ca2+ gradient that allows the accumulation of intracellular Ca2+ within the parasite.
Systems of diagonal Diophantine inequalities
Authors: Freeman Eric
Published: April 2003

We treat systems of real diagonal forms

F
1

(

x

)
,

F
2

(

x

)
,
…
,

F
R

(

x

)

F_1(\mathbf {x}), F_2(\mathbf {x}), \ldots , F_R(\mathbf {x})

of degree

k
k

, in

s
s

variables. We give a lower bound

s
0

(
R
,
k
)

s_0(R,k)

, which depends only on

R
R

and

k
k

, such that if

s
≥

s
0

(
R
,
k
)

s \geq s_0(R,k)

holds, then, under certain conditions on the forms, and for any positive real number

ϵ
\epsilon

, there is a nonzero integral simultaneous solution

x

∈

Z

s

\mathbf {x} \in \mathbb {Z}^s

of the system of Diophantine inequalities

|

F
i

(

x

)

|

>
ϵ

|F_i(\mathbf {x})| > \epsilon

for

1
≤
i
≤
R

1 \leq i \leq R

. In particular, our result is one of the first to treat systems of inequalities of even degree. The result is an extension of earlier work by the author on quadratic forms. Also, a restriction in that work is removed, which enables us to now treat combined systems of Diophantine equations and inequalities.
Algorithms for nonlinear piecewise polynomial approximation: Theoretical aspects
Authors: Karaivanov Borislav , Petrushev Pencho , Sharpley Robert
Published: April 2003

In this article algorithms are developed for nonlinear

n
n

-term Courant element approximation of functions in

L
p

L_p

(

0
>
p
≤
∞

0 > p \le \infty

) on bounded polygonal domains in

R

2

\mathbb {R}^2

. Redundant collections of Courant elements, which are generated by multilevel nested triangulations allowing arbitrarily sharp angles, are investigated. Scalable algorithms are derived for nonlinear approximation which both capture the rate of the best approximation and provide the basis for numerical implementation. Simple thresholding criteria enable approximation of a target function

f
f

to optimally high asymptotic rates which are determined and automatically achieved by the inherent smoothness of

f
f

. The algorithms provide direct approximation estimates and permit utilization of the general Jackson-Bernstein machinery to characterize

n
n

-term Courant element approximation in terms of a scale of smoothness spaces (

B
B

-spaces) which govern the approximation rates.
Taylor expansion of an Eisenstein series
Authors: Yang Tonghai
Published: April 2003

In this paper, we give an explicit formula for the first two terms of the Taylor expansion of a classical Eisenstein series of weight

2
k
+
1

2k+1

for

Γ

0

(
q
)

\Gamma _{0}(q)

. Both the first term and the second term have interesting arithmetic interpretations. We apply the result to compute the central derivative of some Hecke

L
L

-functions.
On the canonical rings of covers of surfaces of minimal degree
Authors: Gallego Francisco , Purnaprajna Bangere
Published: April 2003

In one of the main results of this paper, we find the degrees of the generators of the canonical ring of a regular algebraic surface

X
X

of general type defined over a field of characteristic

0
0

, under the hypothesis that the canonical divisor of

X
X

determines a morphism

φ
\varphi

from

X
X

to a surface of minimal degree

Y
Y

. As a corollary of our results and results of Ciliberto and Green, we obtain a necessary and sufficient condition for the canonical ring of

X
X

to be generated in degree less than or equal to

2
2

. We construct new examples of surfaces satisfying the hypothesis of our theorem and prove results which show that many a priori plausible examples cannot exist. Our methods are to exploit the

O

Y

\mathcal {O}_{Y}

-algebra structure on

φ

∗

O

X

\varphi _{*}\mathcal {O}_{X}

. These methods have other applications, including those on Calabi-Yau threefolds. We prove new results on homogeneous rings associated to a polarized Calabi-Yau threefold and also prove some existence theorems for Calabi-Yau covers of threefolds of minimal degree. These have consequences towards constructing new examples of Calabi-Yau threefolds.
Integration by parts formulas involving generalized Fourier-Feynman transforms on function space
Authors: Chang Seung , Choi Jae , Skoug David
Published: April 2003

In an upcoming paper, Chang and Skoug used a generalized Brownian motion process to define a generalized analytic Feynman integral and a generalized analytic Fourier-Feynman transform. In this paper we establish several integration by parts formulas involving generalized Feynman integrals, generalized Fourier-Feynman transforms, and the first variation of functionals of the form
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper F left-parenthesis x right-parenthesis equals f left-parenthesis mathematical left-angle alpha 1 comma x mathematical right-angle comma ellipsis comma mathematical left-angle alpha Subscript n Baseline comma x mathematical right-angle right-parenthesis">

F
(
x
)
=
f
(
⟨

α

1

,
x
⟩
,
…
,
⟨

α

n

,
x
⟩
)

F(x)=f(\langle \alpha _{1} , x\rangle , \dots , \langle \alpha _{n} , x\rangle )

where

⟨

α
,
x

⟩

\langle {\alpha ,x}\rangle

denotes the Paley-Wiener-Zygmund stochastic integral

∫

0

T

α
(
t
)
d
x
(
t
)

\int _{0}^{T} \alpha (t) d x(t)

.
Strongly indefinite functionals and multiple solutions of elliptic systems
Authors: De Figueiredo D. , Ding Y.
Published: April 2003

We study existence and multiplicity of solutions of the elliptic system\[<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartLayout Enlarged left-brace 1st Row 1st Column minus normal upper Delta u equals upper H Subscript u Baseline left-parenthesis x comma u comma v right-parenthesis 2nd Column a m p semicolon in normal upper Omega comma 2nd Row 1st Column minus normal upper Delta v equals minus upper H Subscript v Baseline left-parenthesis x comma u comma v right-parenthesis 2nd Column a m p semicolon in normal upper Omega comma u left-parenthesis x right-parenthesis equals v left-parenthesis x right-parenthesis equals 0 on partial-differential normal upper Omega comma EndLayout">{−Δu=Hu(x,u,v)amp;in Ω,−Δv=−Hv(x,u,v)amp;in Ω,u(x)=v(x)=0on ∂Ω,\begin {cases} -\Delta u =H_u(x,u,v) & \text {in $\Omega $}, \\ -\Delta v =-H_v(x,u,v) & \text {in $\Omega $}, \quad u(x) = v(x) = 0 \quad \text {on $\partial \Omega $}, \end {cases}\]whereΩ⊂RN,N≥3\Omega \subset \mathbb {R}^N, N\geq 3, is a smooth bounded domain andH∈C1(Ω¯×R2,R)H\in \mathcal {C}^1(\bar {\Omega }\times \mathbb {R}^2, \mathbb {R}). We assume that the nonlinear term\[<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper H left-parenthesis x comma u comma v right-parenthesis tilde StartAbsoluteValue u EndAbsoluteValue Superscript p Baseline plus StartAbsoluteValue v EndAbsoluteValue Superscript q Baseline plus upper R left-parenthesis x comma u comma v right-parenthesis with limit Underscript StartAbsoluteValue left-parenthesis u comma v right-parenthesis EndAbsoluteValue right-arrow normal infinity Endscripts StartFraction upper R left-parenthesis x comma u comma v right-parenthesis Over StartAbsoluteValue u EndAbsoluteValue Superscript p Baseline plus StartAbsoluteValue v EndAbsoluteValue Superscript q Baseline EndFraction equals 0 comma">H(x,u,v)∼|u|p+|v|q+R(x,u,v)  with  lim|(u,v)|→∞R(x,u,v)|u|p+|v|q=0,H(x,u,v)\sim |u|^p + |v|^q + R(x,u,v) \ \ \text {with} \ \ \lim _{|(u,v)|\to \infty }\frac {R(x,u,v)}{|u|^p+|v|^q}=0,\]wherep∈(1, 2∗)p\in (1, \ 2^*),2∗:=2N/(N−2)2^*:=2N/(N-2), andq∈(1, ∞)q\in (1, \ \infty ). So some supercritical systems are included. Nontrivial solutions are obtained. WhenH(x,u,v)H(x,u,v)is even in(u,v)(u,v), we show that the system possesses a sequence of solutions associated with a sequence of positive energies (resp. negative energies) going toward infinity (resp. zero) ifp>2p>2(resp.p>2p>2). All results are proved using variational methods. Some new critical point theorems for strongly indefinite functionals are proved.
Formality in an equivariant setting
Authors: Lillywhite Steven
Published: April 2003

We define and discuss

G
G

-formality for certain spaces endowed with an action by a compact Lie group. This concept is essentially formality of the Borel construction of the space in a category of commutative differential graded algebras over

R
=

H
∙

(
B
G
)

R=H^\bullet (BG)

. These results may be applied in computing the equivariant cohomology of their loop spaces.
Thermodynamic formalism for countable to one Markov systems
Authors: Yuri Michiko
Published: April 2003

For countable to one transitive Markov systems we establish thermodynamic formalism for non-Hölder potentials in nonhyperbolic situations. We present a new method for the construction of conformal measures that satisfy the weak Gibbs property for potentials of weak bounded variation and show the existence of equilibrium states equivalent to the weak Gibbs measures. We see that certain periodic orbits cause a phase transition, non-Gibbsianness and force the decay of correlations to be slow. We apply our results to higher-dimensional maps with indifferent periodic points.