bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission of HIV in the dental clinic and elsewhere
Authors: McCarthy GM , Ssali CS , Bednarsh H , Jorge J , Wangrangsimakul K , Page‐Shafer K
Published: March 2003

This review focuses on the risk of transmission of HIV in dental practice in developed and developing countries; and as a result of oral sex, perinatal transmission and breast feeding. Postexposure prophylaxis (PEP) and practical measures to control cross‐infection with TB are also discussed. There are few data from resource‐poor countries where prevalence of HIV and risk of infection are higher – issues that deserve priority. Available information indicates that the risk of HIV transmission in the dental office is very low. Transmission of HIV from three healthcare workers to patients has been confirmed, including a dentist who infected six patients. There are >300 reports (102 confirmed) of occupational transmission to healthcare workers, including nine dental workers (unconfirmed). Exposure to HIV has been reported by 0.5% dentists/year. The risk of HIV infection after percutaneous exposure (0.3%) can be reduced by 81% with zidovudine PEP. However, risk assessment is required to assess the need and appropriate regimen. The risk of HIV transmission associated with orogenital sex exists, but is considered extremely low: barrier protection is recommended. Conversely, the proportion of babies who acquire HIV from untreated HIV‐seropositive mothers is 15–25% in developed countries and 25–45% in developing countries. The frequency of HIV transmission attributable to breastfeeding is 16%. Airborne transmission of TB can be avoided by the prompt referral of known/suspected cases of active TB for chemotherapy, deferral of elective procedures until patients are not infectious, and the use of appropriate standard/isolation precautions including adequate ventilation of treatment areas.
The discourse of dental hygiene practice in Canada
Authors: McKeown L. , Sunell S. , Wickstrom P.
Published: March 2003

Abstract:  Recently the discourse in Canada relating to dental hygiene practice has changed. While dentistry still exercises controlling power over the public's oral cavity, dental hygienists have made inroads through legislative changes. A description of Canadian dental hygiene practice is provided to set the stage for a discussion about current discourse in the dental hygiene profession. Although power is often perceived as a shifting changing set of relations, these can be frozen in abstraction. It is rather like taking a photo of a single moment or event in an ongoing activity. This moment provides a starting point, an event that can be analysed. Four such events are evident in Canadian dental hygiene practice; they include, education, recognition of dental hygienists as primary care providers, the culture of dental hygiene and self‐regulation. While all the events are important, self‐regulation is critical to the viability and development of the profession. It is the central event that provides the backdrop for effecting change. With self‐regulation comes responsibility and accountability for professional actions. It also provides possibilities for changing the discourse in oral care. As oral health care discourse is transformed through legislation and public awareness, the public will, hopefully, be able to directly access dental hygiene services, and dental hygienists themselves might increasingly recognise their importance as contributors in the health care system.
Chaperone-like activity of alpha-crystallin is enhanced by high-pressure treatment
Authors: BÖDE Csaba , TÖLGYESI Ferenc G. , SMELLER László , HEREMANS Karel , AVILOV Sergiy V. , FIDY Judit
Published: March 2003

α-Crystallin, an oligomeric protein in vertebrate eye lens, is a member of the small heat-shock protein family. Several papers pointed out that its chaperone-like activity could be enhanced by increasing the temperature. We demonstrate in the present study that structural perturbations by high hydrostatic pressures up to 300MPa also enhance this activity. In contrast with temperature-induced changes, the pressure-induced enhancement is reversible. After pressure release, the extra activity is lost with a relaxation time of 2.0±0.5h. Structural alterations contributing to the higher activity were studied with IR and fluorescence spectroscopy, and light-scattering measurements. The results suggest that while the secondary structure barely changes under pressure, the interactions between the subunits weaken, the oligomers dissociate, the area of accessible hydrophobic surfaces significantly increases and the environment of tryptophan residues becomes slightly more polar. It seems that structural flexibility and the total surface area of the oligomers are the key factors in the chaperone capacity, and that the increase in the chaperone activity does not require the increase in the oligomer size as was assumed previously [Burgio, Kim, Dow and Koretz (2000) Biochem. Biophys. Res. Commun. 268, 426—432]. After pressure release, the structure of subunits are reorganized relatively quickly, whereas the oligomer size reaches its original value slowly with a relaxation time of 33±4 h. In our interpretation, both the fast and slow structural rearrangements have an impact on the functional relaxation.
Identification of a non-canonical E-box motif as a regulatory element in the proximal promoter region of the apolipoprotein E gene
Authors: SALERO Enrique , GIMÉNEZ Cecilio , ZAFRA Francisco
Published: March 2003

We have used the yeast one-hybrid system to identify transcription factors with binding capability to specific sequences in proximal regions of the apolipoprotein E gene (APOE) promoter. The sequence between −113 and −80nt, which contains regulatory elements in various cell types, was used as a bait to screen a human brain cDNA library. Four cDNA clones that encoded portions of the human upstream-stimulatory-factor (USF) transcription factor were isolated. Electrophoretic-mobility-shift assays ('EMSAs') using nuclear extracts from various human cell lines as well as from rat brain and liver revealed the formation of two DNA—protein complexes within the sequence CACCTCGTGAC (region −101/-91 of the APOE promoter) that show similarity to the E-box element. The retarded complexes contained USF1, as deduced from competition and supershift assays. Functional experiments using different APOE promoter—luciferase reporter constructs transiently transfected into U87, HepG2 or HeLa cell lines showed that mutations that precluded the formation of complexes decreased the basal activity of the promoter by about 50%. Overexpression of USF1 in U87 glioblastoma cells led to an increased activity of the promoter that was partially mediated by the atypical E-box. The stimulatory effect of USF1 was cell-type specific, as it was not observed in hepatoma HepG2 cells. Similarly, overexpression of a USF1 dominant-negative mutant decreased the basal activity of the promoter in glioblastoma, but not in hepatoma, cells. These data indicated that USF, and probably other related transcription factors, might be involved in the basal transcriptional machinery of APOE by binding to a non-canonical E-box motif within the proximal promoter.
The catalytic domain limits the translocation of protein kinase Calpha in response to increases in Ca2+ and diacylglycerol
Authors: RAGHUNATH Arathi , LING Mia , LARSSON Christer
Published: March 2003

Translocation of protein kinase C (PKC) α, βII, Δ and ∊ fused to enhanced green fluorescent protein (EGFP) was studied in living neuroblastoma cells by confocal microscopy. Exposure to carbachol elicited transient translocation of PKCα-EGFP and βII-EGFP in most of the cells, PKCΔ-EGFP in a few cells and induced sustained translocation of PKC∊-EGFP. To monitor levels of Ca2+ and diacylglycerol and the translocation of PKC in the same cell, the Ca2+-sensitive C2 domain, diacylglycerol-sensitive C1 domains and full-length PKC were fused to red, cyan and yellow fluorescent proteins respectively. PKCα was translocated a few seconds after the C2 domain, which represents an increase in Ca2+. This delay was insensitive to removal of the pseudosubstrate in PKCα, but the isolated regulatory domain translocated simultaneously with the C2 domain. Translocation of PKC∊ coincided with the increase in diacylglycerol. Ionomycin induced translocation of PKCα and the C2 domain, whereas 1,2-dioctanoylglycerol caused translocation of the C1 domains and PKC∊, but not PKCα. Experiments with individual C1 domains showed that treatment with carbachol or phorbol 12,13-dibutyrate elicited translocation of PKCαC1a, PKC∊C1a and PKC∊C1b, whereas PKCαC1b was largely insensitive to these agents. In contrast with full-length PKCα, the regulatory domain of PKCα and pseudosubstrate-devoid PKCα responded to the carbachol-stimulated increase in diacylglycerol.
Active-site-mutagenesis study of rat liver betaine-homocysteine S-methyltransferase
Authors: GONZÁLEZ Beatriz , CAMPILLO Nuria , GARRIDO Francisco , GASSET María , SANZ-APARICIO Juliana , PAJARES María A.
Published: March 2003

A site-directed-mutagenesis study of putative active-site residues in rat liver betaine—homocysteine S-methyltransferase has been carried out. Identification of these amino acids was based on data derived from a structural model of the enzyme. No alterations in the CD spectra or the gel-filtration chromatography elution pattern were observed with the mutants, thus suggesting no modification in the secondary structure content or in the association state of the proteins. All the mutants obtained showed a reduction of the enzyme activity, the most dramatic effect being that of Glu159, followed by Tyr77 and Asp26. Changes in affinity for either of the substrates, homocysteine or betaine, were detected when substitutions were performed of Glu21, Asp26, Phe74 and Cys186. Interestingly, Asp26, postulated to be involved in homocysteine binding, has a strong effect on affinity for betaine. The relevance of these results is discussed in the light of very recent structural data obtained for the human enzyme.
Retrieval-independent localization of lysyl hydroxylase in the endoplasmic reticulum via a peptide fold in its iron-binding domain
Authors: SUOKAS Marko , LAMPELA Outi , JUFFER André H. , MYLLYLÄ Raili , KELLOKUMPU Sakari
Published: March 2003

Lysyl hydroxylase (LH) is a peripheral membrane protein in the lumen of the endoplasmic reticulum (ER) that catalyses hydroxylation of lysine residues in collagenous sequences. Previously, we have mapped its primary ER localization motif within a 40-amino acid segment at its C-terminus. Here, we have characterized this localization mechanism in more detail, and our results indicate that this segment confers ER residency in a KDEL-receptor-independent manner, and without any apparent recycling of the enzyme between the Golgi apparatus and the ER. In addition, we show that a rather long peptide region, rather than a specific peptide sequence per se, is required for efficient retention of a reporter protein in the ER. Accordingly, the minimal retention motif was found to require the last 32 C-terminal amino acids, and sequential substitution of all five charged residues within this critical segment interfered only marginally with the retention or association of the enzyme with the ER membranes. Moreover, our fold-recognition and structure-prediction analyses suggested that this critical peptide segment forms an extended loop within LH's iron-binding domain, and that this loop is exposed and readily accessible for binding. Collectively, our results define a novel retrieval-independent retention mechanism in the ER.
Generation of hepatocytes expressing functional cytochromes P450 from a pancreatic progenitor cell line in vitro
Authors: MAREK Carylyn J. , CAMERON Gary A. , ELRICK Lucy J. , HAWKSWORTH Gabrielle M. , WRIGHT Matthew C.
Published: March 2003

The proliferating AR42J-B13 pancreatic cell line is known to respond to glucocorticoid treatment by producing foci of cells that express the liver-specific albumin gene. We demonstrate that this cell line also expresses liver-specific or liver-enriched functional cytochrome P450 proteins when stimulated to trans-differentiate into hepatocytes by glucocorticoid. These data suggest that this cell line has an unusual ability to trans-differentiate into functional hepatocytes and that it could be possible to generate a limitless supply of functional hepatocyte-like cells in vitro.
Recombinantly expressed isoenzymic aminopeptidases from Helicoverpa armigera (American cotton bollworm) midgut display differential interaction with closely related Bacillus thuringiensis insecticidal proteins
Authors: RAJAGOPAL R. , AGRAWAL Neema , SELVAPANDIYAN Angamuthu , SIVAKUMAR S. , AHMAD Suhail , BHATNAGAR Raj K.
Published: March 2003

Several investigators have independently identified membrane-associated aminopeptidases in the midgut of insect larvae as the initial interacting ligand to the insecticidal crystal proteins of Bacillus thuringiensis. Though several isoenzymes of aminopeptidases have been identified from the midgut of an insect and their corresponding cDNA cloned, only one of the isoform has been expressed heterologously and studied for its binding to Cry toxins. Here we report the cloning and expression of two aminopeptidases N from Helicoverpa armigera (American cotton bollworm) (HaAPNs). The full-length cDNA of H. armigera APN1 (haapn1) is 3205bp in size and encodes a 1000-amino-acid protein, while H. armigera APN2 (haapn2) is 3116bp in size and corresponds to a 1012-amino-acid protein. Structurally these proteins show sequence similarity to other insect aminopeptidases and possess characteristic aminopeptidase motifs. Both the genes have been expressed in Trichoplusia ni (cabbage looper) cells using a baculovirus expression vector. The expressed aminopeptidases are membrane-associated, catalytically active and glycosylated. Ligand-blot analysis of both these aminopeptidases with bioactive Cry1Aa, Cry1Ab and Cry1Ac proteins displayed differential interaction. All the three toxins bound to HaAPN1, whereas only Cry1Ac interacted with HaAPN2. This is the first report demonstrating differential Cry-toxin-binding abilities of two different aminopeptidases from a susceptible insect.
Sexually Dimorphic Activation of Galanin Neurones in the Ferret's Dorsomedial Preoptic Area/Anterior Hypothalamus after Mating
Authors: Bakker J. , Woodley S. K. , Kelliher K. R. , Baum M. J.
Published: March 2003

Male ferrets in breeding condition possess three times as many galanin‐immunoreactive (IR) neurones as oestrous females in the sexually dimorphic dorsomedial preoptic area/anterior hypothalamus (dmPOA/AH). Using Fos‐IR as a marker of activation, we investigated whether mating with intromission differentially activates this sexually dimorphic group of galanin‐IR neurones in male and female ferrets. Male ferrets that intromitted had a significantly greater percentage of galanin‐IR neurones in the dmPOA/AH that were colabelled with nuclear Fos‐IR than oestrous females that received an intromission. Intromissive stimulation augmented Fos‐IR in an equal percentage of galanin‐IR neurones in both sexes in the medial amygdala (MA) and bed nucleus of the stria terminalis (BNST). Peripheral anosmia induced by bilateral occlusion of males' nares did not reduce the mating‐induced activation of galanin‐IR neurones in the dmPOA/AH, and there was a significant correlation among individual males between intromission duration and the percentage of dmPOA/AH galanin‐IR neurones colabelled with Fos‐IR. Exposure of castrated, testosterone propionate‐treated male ferrets to either soiled bedding or to volatile odours from oestrous females failed to induce nuclear Fos‐IR in galanin‐IR neurones located in the dmPOA/AH, BNST or MA, suggesting that the mating‐induced activation of galanin‐IR forebrain neurones in male ferrets depends more on genital‐somatosensory than on olfactory inputs. The observed sex dimorphism in the mating‐induced activation of galanin‐IR neurones in the dmPOA/AH raises the possibility that these neurones perform a mating‐dependent function that occurs only in males.
Vulnerability to cavitation of leaf minor veins: any impact on leaf gas exchange?
Authors: Salleo S. , Lo Gullo M. A. , Raimondo F. , Nardini A.
Published: March 2003

Vulnerability to cavitation of leaf minor veins and stems of Laurus nobilis L. was quantified together with that of leaflets, rachides and stems of Ceratonia siliqua L. during air‐dehydration of 3‐year‐old branches. Embolism was estimated by counting ultrasound acoustic emissions (UAE) and relating them to leaf water potential (ΨL). The threshold ΨL for cavitation was less negative in L. nobilis than in C. siliqua according to the known higher drought resistance of the latter species. Leaf minor vein cavitation was also quantified by infiltrating leaves with fluorescein at different dehydration levels and observing them under microscope. Distinct decreases in the functional integrity of minor veins were observed during leaf dehydration, with high correlation between the two variables. The relationship between leaf conductance to water vapour (gL) and ΨL showed that stomata of L. nobilis closed in response to stem and not to leaf cavitation. However, in C. siliqua, gL decreased in coincidence to the leaf cavitation threshold, which was, nevertheless, very close to that of the stem. The hypothesis that stem cavitation acts as a signal for stomatal closure was confirmed, while the same role for leaf cavitation remains an open problem.
Molecular and biochemical responses of perennial forage crops to oxygen deprivation at low temperature
Authors: Bertrand A. , Castonguay Y. , Nadeau P. , Laberge S. , Rochette P. , Michaud R. , Bélanger G. , Benmoussa M.
Published: March 2003

Anaerobic conditions developing under ice cover affect winter survival and spring regrowth of economically important perennial crops. Our objective was to assess interspecific differences in the resistance to anaerobic conditions at low temperature, and to relate those differences to plant metabolism. Four perennial forage species, alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), timothy (Phleum pratense L.) and orchardgrass (Dactylis glomerata L.), were subjected to a progressively developing anoxic stress by enclosing potted plants in gas‐tight bags in late autumn and exposing them to simulated winter conditions in an unheated greenhouse. Near‐anaerobic conditions were reached after 60 d of enclosure for orchardgrass, alfalfa and red clover, and after 80 d for timothy. The sensitivity of the species to anaerobic conditions, based on plant regrowth, was: red clover and orchardgrass > alfalfa > timothy. The concentration of ethanol increased in response to oxygen deprivation, and reached the highest value in the sensitive red clover, whereas its concentration was the lowest in timothy. The expression of the alcohol dehydrogenase (ADH) gene was markedly lower in timothy than in the other three species for which the expression was equivalent. We conclude that the greater resistance of timothy to anaerobic conditions at low temperature is associated with a slower glycolytic metabolism.
Acclimation of tropical tree seedlings to excessive light in simulated tree‐fall gaps
Authors: Krause G. H. , Koroleva O. Y. , Dalling J. W. , Winter K.
Published: March 2003

Acclimation to periodic high‐light stress was studied in tree seedlings from a neotropical forest. Seedlings of several pioneer and late‐succession species were cultivated under simulated tree‐fall gap conditions; they were placed under frames covered with shade cloth with apertures of different widths that permitted defined periods of daily leaf exposure to direct sunlight. During direct sun exposure, all plants exhibited a marked reversible decline in potential photosystem II (PSII) efficiency, determined by means of the ratio of variable to maximum Chl a fluorescence (Fv/Fm). The decline in Fv/Fm under full sunlight was much stronger in late‐succession than in pioneer species. For each gap size, all species exhibited a similar degree of de‐epoxidation of violaxanthin in direct sunlight and similar pool sizes of xanthophyll cycle pigments. Pool sizes increased with increasing gap size. Pioneer plants possessed high levels of β‐carotene that also increased with gap size, whereas α‐carotene decreased. In contrast to late‐succession plants, pioneer plants were capable of adjusting their Chl a/b ratio to a high value in wide gaps. The content of extractable UV‐B‐absorbing compounds was highest in the plants acclimated to large gaps and did not depend on the successional status of the plants. The results demonstrate a better performance of pioneer species under high‐light conditions as compared with late‐succession plants, manifested by reduced photoinhibition of PSII in pioneer species. This was not related to increased pool size and turnover of xanthophyll cycle pigments, nor to higher contents of UV‐B‐absorbing substances. High β‐carotene levels and increased Chl a/b ratios, i.e. reduced size of the Chl a and b binding antennae, may contribute to photoprotection in pioneer species.
Ultrastructural and immunohistochemical study of the basal apparatus of solitary cilia in the human oviduct epithelium
Authors: Hagiwara Haruo , Harada Shinsuke , Maeda Sakae , Aoki Takeo , Ohwada Nobuo , Takata Kuniaki
Published: March 2003

The basal apparatus of the solitary cilium is composed of the basal body, an associated centriole and the basal body‐associated structures. To see the connection between the basal body and the centriole, we studied the basal apparatus of solitary cilia in human oviductal secretory cells by electron microscopy and immunohistochemistry. A single centriole was present in the vicinity of the basal body of a solitary cilium. The basal body and the single centriole were interconnected by one or two bundles of thin filaments with a few periodic striations. We have called these bundles the striated connector. The periodicity of striations in the striated connector measured 55 ± 6 nm, about 15 nm shorter than that of striated rootlets. The striated connector was immunolabelled with R67 antibody specific to striated rootlets, indicating that they are composed of common molecule(s). Although the true function of the connector is unknown as yet, it could play an important role for stabilising the basal body in the apical cytoplasm.
Modelling the masticatory biomechanics of a pig
Authors: Langenbach G. E. J. , Zhang F. , Herring S. W. , Hannam A. G.
Published: March 2003

The relationships between muscle tensions, jaw motions, bite and joint forces, and craniofacial morphology are not fully understood. Three‐dimensional (3‐D) computer models are able to combine anatomical and functional data to examine these complex relationships. In this paper we describe the construction of a 3‐D dynamic model using the anatomical (skeletal and muscle form) and the functional (muscle activation patterns) features of an individual pig. It is hypothesized that the model would produce functional jaw movements similar to those recordable in vivo. Anatomical data were obtained by CT scanning (skeletal elements) and MR imaging (muscles). Functional data (muscle activities) of the same animal were obtained during chewing by bipolar intramuscular electrodes in six masticatory muscles and combined with previously published EMG data. The model was driven by the functional data to predict the jaw motions and forces within the masticatory system. The study showed that it is feasible to reconstruct the complex 3‐D gross anatomy of an individual's masticatory system in vivo. Anatomical data derived from the 3‐D reconstructions were in agreement with published standards. The model produced jaw motions, alternating in chewing side, typical for the pig. The amplitude of the jaw excursions and the timing of the different phases within the chewing cycle were also in agreement with previously published data. Condylar motions and forces were within expected ranges. The study indicates that key parameters of the pig's chewing cycle can be simulated by combining general biomechanical principles, individual‐specific data and a dynamic modelling approach frequently used in mechanical engineering.
Gender difference in benefits of twinning in pre‐industrial humans: boys did not pay
Authors: Lummaa Virpi , Jokela Jukka , Haukioja Erkki
Published: March 2003

We studied how differences in the cost of producing male and female offspring in humans affected the productivity of twin vs. singleton deliveries in two ecologically different areas of pre‐industrial (1752–1850) Finland. Given the higher energy requirements of male infants, we predicted sons to suffer more from increased litter size and food scarcity than daughters.

 We found that the number of offspring surviving to adulthood from a twin delivery differed between the archipelago and mainland areas of rural Finland. On the mainland areas, where crop failures and subsequent famines were common throughout the centuries, twin deliveries were much less successful than in the south‐west archipelago, where food conditions were traditionally more stable and survival was ensured by fishing.

 Productivity of twin deliveries was modified by the gender composition of the twins; female–female twin births were generally most successful and male–male births least successful.

 On the mainland, giving birth to twins of any gender composition never increased the mothers’ reproductive success beyond giving birth to either a male or female singleton, whereas in the archipelago mothers could increase their reproductive output by producing twins. This was because in the archipelago female–female twin deliveries contributed on average more than one adult offspring to the breeding population, whereas a singleton delivery of either gender produced only about 0·7 adults.

 Our results show that increases in litter size and variability of food conditions increased male mortality. High female twin survival in the archipelago led to higher fitness of twinning mothers in relation to mothers with only singletons. Twinning has traditionally been significantly more common in the archipelago as compared to the mainland, but contrary to the prediction, there were no apparent differences in the frequency of male–male and female–female twins being born.
Effect of land cover, habitat fragmentation and ant colonies on the distribution and abundance of shrews in southern California
Authors: Laakkonen Juha , Fisher Robert N. , Case Ted J.
Published: March 2003

Because effects of habitat fragmentation and anthropogenic disturbance on native animals have been relatively little studied in arid areas and in insectivores, we investigated the roles of different land covers, habitat fragmentation and ant colonies on the distribution and abundance of shrews, Notiosorex crawfordi and Sorex ornatus, in southern California.

 Notiosorex crawfordi was the numerically dominant species (trap‐success rate 0·52) occurring in 21 of the 22 study sites in 85% of the 286 pitfall arrays used in this study. Sorex ornatus was captured in 14 of the sites, in 52% of the arrays with a total trap‐success rate of 0·2. Neither of the species was found in one of the sites.

 The population dynamics of the two shrew species were relatively synchronous during the 4–5‐year study; the peak densities usually occurred during the spring. Precipitation had a significant positive effect, and maximum temperature a significant negative effect on the trap‐success rate of S. ornatus.

 Occurrence and abundance of shrews varied significantly between sites and years but the size of the landscape or the study site had no effect on the abundance of shrews. The amount of urban edge had no significant effect on the captures of shrews but increased edge allows invasion of the Argentine ants, which had a highly significant negative impact on the abundance of N. crawfordi.

 At the trap array level, the percentage of coastal sage scrub flora had a significant positive, and the percentage of other flora had a significant negative effect on the abundance of N. crawfordi. The mean canopy height and the abundance of N. crawfordi had a significant positive effect on the occurrence of S. ornatus.

 Our study suggests that the loss of native coastal sage scrub flora and increasing presence of Argentine ant colonies may significantly effect the distribution and abundance of N. crawfordi. The very low overall population densities of both shrew species in most study sites make both species susceptible to extinction in isolated habitat fragments due to environmental stochasticity, and anthropogenic disturbance.
Canopy and substratum heterogeneity influence recruitment of the mangrove Avicennia marina
Authors: Minchinton Todd E.
Published: March 2003

Mangrove forests are structurally complex with canopy gaps generated by physical disturbances such as storms and mounds created on the forest floor by biotic disturbances such as crabs excavating burrows.

I studied how variations in canopy cover and substratum topography influence the recruitment and demography of the mangrove Avicennia marina in a temperate forest in New South Wales, Australia.

Surveys showed that mounds covered up to 44% of the forest floor and were larger and covered more of the substratum under the canopy than in gaps. Propagules and new seedlings (i.e. the most recently established cohort) were more abundant under the canopy than in gaps and on flat areas than on mounds.

A field experiment tested whether the observed spatial distribution of new seedlings was due to differences in the secondary dispersal of propagules or in the establishment or early survivorship of seedlings. Propagules were supplied in equal densities on mounds and flats under the canopy and in gaps and then monitored for 10 months.

Four times as many propagules were dispersed away from mounds as from flats, and this difference was greater under the canopy than in gaps. In contrast, seedlings established more successfully on mounds, particularly in gaps, suggesting that this is an important microhabitat for recruitment. Seedling survival to 9 months was independent of habitat structure.

The influence of mounds on dispersal was, however, much greater than on establishment, so that densities of new seedlings 9 months after establishment were greater on flats. Patterns of seedling abundance in the mangrove forest are thus primarily driven by the influence of habitat structure on the supply of propagules.

In contrast, saplings were most abundant on mounds in gaps. Thus, there is a shift in the spatial distribution of the population from the early to the later stages of life history in relation to habitat structure. Long‐term survival of seedlings and their development into saplings may depend both on light availability in gaps and on sediment disturbance resulting from the creation of mounds. The causative agent, crabs, may therefore be critical for regeneration of mangrove forests.
The regulation of ecosystem functions by ecotypic variation in the dominant plant: a Spartina alterniflora salt‐marsh case study
Authors: Seliskar Denise M. , Gallagher John L. , Burdick David M. , Mutz Laurie A.
Published: March 2003

Genetic differences among populations of a keystone species may affect ecosystem functional properties. We tested this by planting Spartina alterniflora from different geographical regions in a newly created salt marsh in Delaware, USA.

Spartina alterniflora plants from morphologically distinct short‐form (back marsh) populations were originally collected from Massachusetts (41°34′ N), Delaware (38°47′ N), and Georgia (31°25′ N) in the USA and vegetatively propagated for 6 years in a salt water‐irrigated common garden in Delaware before transfer to a newly created salt marsh.

The magnitude of the expression of marsh functions in the created marsh, measured over 5 years, remained distinct in patches of each ecotype. End of season aerial biomass, below‐ground biomass, root and rhizome distribution, canopy height, stem density, and carbohydrate reserves were closer to values reported for the plants’ native sites than to those typical of Delaware. Thus, many of the plant features characteristic of particular latitudes appear to be under genetic control. Such ecotypic differentiation influences ecosystem function through keystone resource and keystone modifier activities.

Respiration of the microbial community associated with either dead shoots or the soil varied with plant ecotype in the created wetland and the patterns reflected those reported for their native sites. High edaphic respiration under the Massachusetts ecotype was correlated with the high percentage of sugar in the rhizomes. Edaphic chlorophyll was greater under the canopies of the Massachusetts and Delaware ecotypes than under the Georgia canopy and exhibited a relationship similar to that of algal production rates reported for the native sites. Larval fish were most abundant in pit traps in the Massachusetts ecotype.
Accurately ageing trees and examining their height‐growth rates: implications for interpreting forest dynamics
Authors: Gutsell S. L. , Johnson E. A.
Published: March 2003

We examined the validity of classifying tree species as early, mid‐, or late‐successional based on age and height‐growth rates, by comparing the age and height‐growth rates of trees in the boreal forest.

Age was first examined using the traditional method of coring 30 cm above the root collar; then dendrochronology was used to locate the root collar and missing annual growth rings. Traditional ageing differentially underestimates tree age; species classified as early successional (Populus tremuloides, Betula papyrifera, and Pinus banksiana) are less severely underestimated than those classified as mid‐ and late‐successional (Picea glauca, Picea mariana, and Abies balsamea) (0–11 vs. 0–43 years), and also have relatively fewer locally missing growth rings. Ageing at the root collar shows that all tree species recruit within 5–10 years after fire and age cannot therefore be used to determine successional status.

Mean time taken to grow to each 1‐m increment from the root collar was estimated for each species. Species classified as early successional have relatively higher growth rates between the root collar and the first metre; they are therefore less severely underestimated when aged above the root collar, explaining why they often appear older than species classified as mid‐ and late‐successional. The lack of species differences above 1 m means that height‐growth rates cannot be used to classify these tree species as early, mid‐, or late‐successional.

In the boreal forest of Saskatchewan, the rapid recruitment of all tree species after fire, and the short fire cycle mean that the forest dynamics between catastrophic wildfires are driven primarily by the mortality rates of each species.
Citicoline: neuroprotective mechanisms  in cerebral ischemia
Authors: Rao Muralikrishna Adibhatla  , Hatcher J. F. , Dempsey R. J.
Published: March 2003

Cytidine‐5′‐diphosphocholine (citicoline or CDP‐choline), an intermediate in the biosynthesis of phosphatidylcholine (PtdCho), has shown beneficial effects in a number of CNS injury models and pathological conditions of the brain. Citicoline improved the outcome in several phase‐III clinical trials of stroke, but provided inconclusive results in recent clinical trials. The therapeutic action of citicoline is thought to be caused by stimulation of PtdCho synthesis in the injured brain, although the experimental evidence for this is limited. This review attempts to shed some light on the properties of␣citicoline that are responsible for its effectiveness. Our studies in transient cerebral ischemia suggest that citicoline might enhance reconstruction (synthesis) of PtdCho and sphingomyelin, but could act by inhibiting the destructive processes (activation of phospholipases). Citicoline neuroprotection may␣include: (i) preserving cardiolipin (an exclusive inner mitochondrial membrane component) and sphingomyelin; (ii)␣preserving the arachidonic acid content of PtdCho and phosphatidylethanolamine; (iii) partially restoring PtdCho levels; (iv) stimulating glutathione synthesis and glutathione reductase activity; (v) attenuating lipid peroxidation; and (vi)␣restoring Na+/K+‐ATPase activity. These observed effects␣of citicoline could be explained by the attenuation of␣phospholipase A2 activation. Based on these findings, a singular unifying␣mechanism has been hypothesized. Citicoline also provides choline for synthesis of neurotransmitter acetylcholine, stimulation of tyrosine hydroxylase activity and dopamine release.
Up‐regulation of tissue‐type transglutaminase after traumatic  brain injury
Authors: Tolentino Paul J. , DeFord S. Michelle , Notterpek Lucia , Glenn Christopher C. , Pike Brian R. , Wang Kevin K. W. , Hayes Ronald L.
Published: March 2003

Tissue‐type transglutaminase (tTG, EC 2.3.2.13) has been implicated in various disease paradigms including neurodegenerative disease. In these studies, tTG induction after traumatic brain injury was studied using a rat cortical impact model. Using western blots, two forms of tTG protein expression were identified – a ∼79‐kDa primary form (tTG‐L) and a less abundant ∼70‐kDa form (tTG‐S). Both forms of tTG protein were elevated after injury. In ipsilateral cortex, peak induction of tTG‐L protein [561% ± 80% of control (n = 5)] was observed five days after injury, with expression remaining elevated after two weeks. Peak induction of tTG‐S protein [302% ± 81% of control (n = 5)] was observed three days after injury. Lesser tTG protein induction was observed in hippocampus. Northern blot analysis demonstrated two tTG transcripts in the ipsilateral cortex with peak induction of tTG‐L mRNA three days after injury. However, tTG‐S mRNA was not identified in control samples and only faintly detected in injured tissue. To facilitate analysis of low abundance transcripts in smaller tissue samples, a semiquantitative real‐time PCR strategy was used. Semi‐quantitative PCR analysis of tTG‐L mRNA induction in ipsilateral cortex (peak after three days; 414% ± 21% of control, n= 3) confirmed tTG‐L mRNA induction determined by northern blot (410% of control).
Dietary restriction enhances neurotrophin expression and neurogenesis in the hippocampus of adult mice
Authors: Lee Jaewon , Seroogy Kim B. , Mattson Mark P.
Published: March 2003

The adult brain contains small populations of neural precursor cells (NPC) that can give rise to new neurons and glia, and may play important roles in learning and memory, and recovery from injury. Growth factors can influence the proliferation, differentiation and survival of NPC, and may mediate responses of NPC to injury and environmental stimuli such as enriched environments and physical activity. We now report that neurotrophin expression and neurogenesis can be modified by a change in diet. When adult mice are maintained on a dietary restriction (DR) feeding regimen, numbers of newly generated cells in the dentate gyrus of the hippocampus are increased, apparently as the result of increased cell survival. The new cells exhibit phenotypes of neurons and astrocytes. Levels of expression of brain‐derived neurotrophic factor (BDNF) and neurotrophin‐3 (NT‐3) are increased by DR, while levels of expression of high‐affinity receptors for these neurotrophins (trkB and trkC) are unchanged. In addition, DR increases the ratio of full‐length trkB to truncated trkB in the hippocampus. The ability of a change in diet to stimulate neurotrophin expression and enhance neurogenesis has important implications for dietary modification of neuroplasticity and responses of the brain to injury and disease.
Glucose deprivation and hypoxia increase the expression of the GLUT1 glucose transporter via a specific mRNA cis‐acting regulatory element
Authors: Boado Ruben J. , Pardridge William M.
Published: March 2003

The expression of the glucose transporter type‐1 (GLUT1) gene is up‐regulated in hypoxia and glucose deprivation. A 10 nucleotide (nt) cis‐acting regulatory element (CAE), which is located within nt 2181–2190 of the GLUT1 3′‐untranslated region (CAE2181−2190), increases the expression of a GLUT1‐luciferase reporter gene and decreases its mRNA decay. The present study investigated the role of the GLUT1 CAE2181−2190 in glucose deprivation and hypoxia using stable transfectants. Glucose and O2 deprivation produced a marked increase in the expression of the GLUT1 reporter gene carrying the CAE2181−2190, and this effect was additive. Glucose deprivation and/or hypoxia induced no significant changes in the expression of the reporter gene wherein the GLUT1 CAE2181−2190 was site‐directed deleted. Data presented here suggest that the GLUT1 CAE2181−2190 participates in the increase of GLUT1 gene expression in glucose deprivation and hypoxia.
Interaction between metabotropic glutamate receptor 7 and alpha tubulin
Authors: Saugstad Julie A. , Yang Sufang , Pohl Jan , Hall Randy A. , Conn P. Jeffrey
Published: March 2003

Metabotropic glutamate receptors (mGluRs) mediate a variety of responses to glutamate in the central nervous system. A primary role for group‐III mGluRs is to inhibit neurotransmitter release from presynaptic terminals, but the molecular mechanisms that regulate presynaptic trafficking and activity of group‐III mGluRs are not well understood. Here, we describe the interaction of mGluR7, a group‐III mGluR and presynaptic autoreceptor, with the cytoskeletal protein, alpha tubulin. The mGluR7 carboxy terminal (CT) region was expressed as a GST fusion protein and incubated with rat brain extract to purify potential mGluR7‐interacting proteins. These studies yielded a single prominent mGluR7 CT‐associated protein of 55 kDa, which subsequent microsequencing analysis revealed to be alpha tubulin. Coimmunoprecipitation assays confirmed that full‐length mGluR7 and alpha tubulin interact in rat brain as well as in BHK cells stably expressing mGluR7a, a splice variant of mGluR7. In addition, protein overlay experiments showed that the CT domain of mGluR7a binds specifically to purified tubulin and calmodulin, but not to bovine serum albumin. Further pull‐down studies revealed that another splice variant mGluR7b also interacts with alpha tubulin, indicating that the binding region is not localized to the splice‐variant regions of either mGluR7a (900–915) or mGluR7b (900–923). Indeed, deletion mutagenesis experiments revealed that the alpha tubulin‐binding site is located within amino acids 873–892 of the mGluR7 CT domain, a region known to be important for regulation of mGluR7 trafficking. Interestingly, activation of mGluR7a in cells results in an immediate and significant decrease in alpha tubulin binding. These data suggest that the mGluR7/alpha tubulin interaction may provide a mechanism to control access of the CT domain to regulatory molecules, or alternatively, that this interaction may lead to morphological changes in the presynaptic membrane in response to receptor activation.
Symbiotic nitrogen fixation research in the postgenomics era
Authors: Colebatch G. , Trevaskis B. , Udvardi M.
Published: March 2003

Nitrogen‐fixing symbioses between legumes and rhizobia are important for sustainable agriculture and contribute significantly to the global nitrogen cycle. The genomes of two rhizobial species, Mesorhizobium loti and Sinorhizobium meliloti have now been completely sequenced. Hundreds of thousands of expressed sequence tags representing tens of thousands of different genes from three major legume species; soybean, Medicago truncatula and Lotus japonicus have also been deposited in the public domain. Lotus japonicus recently became the focus of a genome project that aims to sequence one third of the entire genome over the next 5 yr. With this as a backdrop, the stage is set for a renaissance in symbiosis research, which will provide new insight into the complex molecular interplay that underpins symbiotic nitrogen fixation. This review considers how functional genomics might contribute to this renaissance.
Dry matter content as a measure of dry matter concentration in plants and their parts
Authors: Shipley Bill , Vu Thi‐Tam
Published: March 2003

This study compared the predictive ability of dry matter content (DMC, dry mass per fresh mass) of leaves, stems, roots and entire plants in relation to dry matter concentration (D, dry mass per volume of plant organ). Data came from 28 species of field‐collected plants (woody and herbaceous) and 17 species of herbaceous plants grown in hydroponic sand culture. Specific leaf areas were also measured.

 Dry matter content of the herbaceous plants grown in sand culture varied more between tissue types than did dry matter concentration but the correlation among plant parts was stronger when using DMC. Means and standard errors for DMC (g g−1) were 0.212 ± 0.009 (leaves), 0.176 ± 0.012 (support tissues) and 0.170 ± 0.021 (roots); for D (g cm−3) the values were 0.158 ± 0.010 (leaves), 0.168 ± 0.017 (support tissues) and 0.153 ± 0.013 (roots).

 Leaf DMC provided approximate estimates of leaf D (r = 0.76) for the field‐collected plants but sclerophyllous leaves from shrubs restricted to acidic bogs proved to be outliers. The relationship between these two variables was stronger in the herbaceous species grown in sand culture, especially so for whole plant estimates (r = 0.91).

 Dry matter content and dry matter concentration were equally good predictors of specific leaf area.
Genetic evidence for natural hybridization between the Dutch elm disease pathogens Ophiostoma novo‐ulmi ssp. novo‐ulmi and O. novo‐ulmi ssp. americana
Authors: Konrad H. , Kirisits T. , Riegler M. , Halmschlager E. , Stauffer C.
Published: March 2003

The Dutch elm disease pathogen Ophiostomanovo‐ulmi is separated into subspecies novo‐ulmi, formerly known as the Eurasian (EAN) race, and subspecies americana, formerly known as the North American (NAN) race. Both subspecies occur in Europe, and hybrids between them are suspected to have emerged in parts of Europe where their ranges overlap. Authenticated isolates of both subspecies were examined in order to determine whether fixed mutations occur in the cerato‐ulmin (cu) and in the colony type gene (col1). One and six mutations were detected between subspp. novo‐ulmi and americana in cu and col1, respectively. The mutation in cu and one mutation in col1 proved to be located within restriction sites, and were used for PCR‐RFLP. This method provides a quick and reliable diagnostic method to differentiate the two subspecies. Seven isolates of O.novo‐ulmi from Austria were suspected to be hybrids between subspp. novo‐ulmi and americana, and were tested by PCR‐RFLP of their cu and col1 genes. Two of the suspected hybrids from Austria (isolates AT73 and AT146) had the cu PCR‐RFLP profile of ssp. americana and the col1 PCR‐RFLP profile of ssp. novo‐ulmi. Furthermore, a ssp. novo‐ulmi tester isolate from Poland (P150) showed a similar hybrid pattern. This is the first evidence revealing recombination between two genes and thus hybridization between the two subspecies of O. novo‐ulmi in nature.
Load Testing of Floor Slabs in a Full‐scale Reinforced Concrete Building
Authors: Scott R. H. , Gilbert S. G. , Moss R. M.
Published: March 2003

A series of short and long term service load tests were undertaken on the sixth floor of the full‐scale, seven storey, reinforced concrete building at the Large Building Test Facility of the Building Research Establishment at Cardington. By using internally strain gauged reinforcing bars cast into an internal and external floor bay during the construction process it was possible to gain a detailed record of slab strains resulting from the application of several arrangements of test loads. Short term tests were conducted in December 1998 and long term monitoring then ensued until April 2001. This paper describes the test programmes and presents results to indicate slab behaviour for the various loading regimes.