Dynamics of the sit-to-stand movement

The strategies of the sit-to-stand movement are investigated by describing the movement in terms of the topology of an associated phase diagram. Kinematic constraints are applied to describe movement sequences, thus reducing the dimension of the phase space. This dimensional reduction allows us to apply theorems of topological dynamics for two-dimensional systems to arrive at a classification of six possible movement strategies, distinguished by the topology of their corresponding phase portrait. Since movement is treated in terms of topological structure rather than specific trajectories, individual variations are automatically included, and the approach is by nature model independent. Pathological movement is investigated, and this method clarifies how subtle abnormalities in movement lead to difficulties in achieving a stable stance upon rising from a seated position. This article was processed by the author using the LAT_EX style file pljour2 from Springer-Verlag.     

A microdialysis study of the effects of the nicotinic agonist RJR-2403 on cortical release of acetylcholine and biogenic amines

Transcortical dialysis was employed to investigate the effects of subcutaneous (s.c.) injections of RJR-2403 (1.2–7.2 μmol/kg) on extracellular levels of acetylcholine (ACh), norepinephrine (NE), dopamine (DA), and serotonin (5-HT) in rat. Systemic administration of RJR-2403 produced a 90% increase of cortical extracellular ACh levels that persisted for up to 90 minutes after injection. Norepinephrine and DA release were increased 124% and 131% above basal values, respectively. Serotonin (5-HT) levels in the dialysate were also significantly elevated by RJR-2403 (3.6 μmol/kg, s.c.) 70% above baseline at 90 minutes post-injection. Comparison of these responses to those of (−)nicotine from a previous study reveals little difference between the two compounds in their ability to influence cortical neurotransmitter release following systemic administration.     

Allonia decandra: Floral remains of the tribeHamamelideae (Hamamelidaceae) from Campanian strata of southeastern USA

A single flower, detached anthers with in situ pollen grains, and isolated seeds from Campanian strata (Upper Cretaceous) of Georgia, southeastern USA, document the presence of plants assignable toHamamelidaceae in the Upper Cretaceous. The fossil flower is actinomorphic, pentacyclic and pentamerous. Irregular sepals are preserved as lobes of the floral cup, and petals are narrow, with parallel margins. The androecium has two whorls of functional stamens. Anthers are tetrasporangiate, dehisce through two valves, and have strongly elongate connective protrusions which converge over the center of the flower. The organizational and architectural features of the fossil document its affinity within subtribeLoropetalinae (Hamamelideae, Hamamelidoideae). Cladistic phylogenetic analyses using parsimony were conducted to explore the relationships between the fossil flower and extant genera of the tribeHamamelideae. The strict consensus of the four most parsimonious trees showsHamamelideae andLoropetalinae as well-supported monophyletic taxa. The fossil flower is clearly included within theLoropetalinae, and is placed as sister taxon to the southeastern Asian genusMaingaya. The occurrence of fossils assignable toLoropetalinae during the Campanian documents the existence ofHamamelidaceae with a level of floral organization and character evolution equivalent to that of extant genera, early in the evolutionary history of the family.     

Differential Expression of a Mycobacterium tuberculosis Protein Recognized by a Mouse Monoclonal Antibody

Murine monoclonal antibodies were produced against Mycobacterium tuberculosis (Mtb) using standard hybridoma procedures. By a whole cell enzyme-linked immunosorbent assay (ELISA), one monoclonal antibody (mAb), HB28, demonstrated high level specific reactivity to Mtb. Western blot analysis demonstrated reactivity to a single 65 kDa Mtb protein in the cell wall extract and culture filtrate. HB28 mAb appears to be recognizing a 65 kDa Mtb protein that is over-expressed by Mtb but not other species under certain culture conditions. Differential expression and detection of this protein by HB28 mAb may have potential for diagnostic applications.     

Substance P and neurokinin A metabolism by cultured human skeletal muscle myocytes and fibroblasts

A recent study determined that cultured human skeletal muscle adult myoblasts, myotubes, and fibroblasts degraded angiotensins and kinins via neutral endopeptidase-24.11 (NEP-24.11; EC 3.4.24.11) and aminopeptidase N (APN; EC 3.4.11.2). Due to the possible importance of other peptides to skeletal muscle blood flow and function, the present study looked specifically at the metabolism of the neurokinins substance P (SP) and neurokinin A (NKA) by skeletal muscle peptidases. The results show that SP is degraded not only by NEP-24.11, but also sequentially by dipeptidyl(amino)peptidase IV (DAP IV; EC 3.4.14.5)/APN. NKA is unaffected by DAP IV but is metabolized by NEP-24.11 and APN. NEP-24.11 was inhibited by phosphoramidon (IC₅₀ = 80 nM), thiorphan and ZINCOV, DAP IV by diprotin A (IC₅₀ = 8 μM), and APN by amastatin (IC₅₀ = 50 nM) and bestatin (IC₅₀ = 100 μM). Skeletal muscle myocyte and fibroblast metabolism of SP and NKA may regulate local skeletal muscle vascular and extravascular functions including SP- and NKA-mediated nerve-induced vasodilation. Inhibition of both NEP-24.11 and DAP IV/APN may increase skeletal muscle blood flow and decrease peripheral vascular resistance via potentiation of local neurokinin levels.     

Immunodetection of cytoskeletal structures and the Eg5 motor protein on deep-etch replicas of Xenopus egg cortices isolated during the cortical rotation

Summary— We have developed a new method for immunogold detection on deep-etch replicas of isolated Xenopus egg cortices in order to examine the interactions of different cortical elements in three dimensions at high resolution. We have applied this technique to vegetal cortices isolated during the second half of the first cell cycle. The vegetal cortical region at this time is the site of cellular machinery responsible for the ‘cortical rotation’. The entire cortex translocates with respect to the inner cytoplasm, relocating dorsalising determinants to the future dorsal side of the egg. The aligned microtubules in the shear zone between cytoplasm and cortex, implicated in the cortical rotation, were found to be organised as interweaving loose bundles. Interleaved amongst these aligned microtubules were extensive sheets of ER lying in layers parallel to the egg surface. Cytokeratin filaments were found to associate closely with the microtubules over short stretches. Putative actin filaments were present in the shear zone and in the cortex. Eg5, an abundant kinesin-related microtubule motor protein, and candidate for a role in generating cortical rotation movement, showed an almost exclusive localisation to microtubules. Immunofluorescence studies of cortices treated with detergent to disrupt ER or cold to depolymerise microtubules confirmed that Eg5 associates primarily with microtubules. We propose revised models for the mechanism of cortical rotation based on these observations and conclude that Eg5 is unlikely to move ER relative to microtubules during the cortical rotation.     

Grass species and soil type effects on microbial biomass and activity

We evaluated plant versus soil type controls on microbial biomass and activity by comparing microbial biomass C, soil respiration, denitrification potential, potential net N mineralization and nitrification in different soils supporting four grass species, and by growing a group of 10 different grass species on the same soil, in two experiments respectively. In the first experiment, none of the microbial variables showed significant variation with grass species while all variables showed significant variation with soil type, likely due to variation in soil texture. In the second experiment, there were few significant differences in microbial biomass C among the 10 grasses but there were significant relationships between variation in microbial biomass C and potential net N mineralization (negative), soil respiration (positive) and denitrification (positive). There was no relationship between microbial biomass C and either plant yield or plant N concentration. The results suggest that 1) soil type is a more important controller of microbial biomass and activity than grass species, 2) that different grass species can create significant, but small and infrequent, differences in microbial biomass and activity in soil, and 3) that plant-induced variation in microbial biomass and activity is caused by variation in labile C input to soil.     

Molecular-cytogenetic characterization of a higher plant centromere/kinetochore complex

The centromeric region of a telocentric field bean chromosome that resulted from centric fission of the metacentric satellite chromosome was microdissected. The DNA of this region was amplified and biotinylated by degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR)/linker-adapter PCR. After fluorescence in situ hybridization (FISH) the entire chromosome complement of Vicia faba was labelled by these probes except for the nucleolus organizing region (NOR) and the interstitial heterochromatin, the chromosomes of V. sativa and V. narbonensis were only slightly labelled by the same probes. Dense uniform labelling was also observed when a probe amplified from a clearly delimited microdissected centromeric region of a mutant of Tradescantia paludosa was hybridized to T. paludosa chromosomes. Even after six cycles of subtractive hybridization between DNA fragments amplified from centromeric and acentric regions no sequences specifically located at the field bean centromeres were found among the remaining DNA. A mouse antiserum was produced which detected nuclear proteins of 33 kDa and 68 kDa; these were predominantly located at V. faba kinetochores during mitotic metaphase. DNA amplified from the chromatin fraction adsorbed by this serum out of the sonicated total mitotic chromatin also did not cause specific labelling of primary constrictions. From these results we conclude: (1) either centromere-specific DNA sequences are not very conserved among higher plants and are — at least in species with large genomes — intermingled with complex dispersed repetitive sequences that prevent the purification of the former, or (2) (some of) the dispersed repeats themselves specify the primary constrictions by stereophysical parameters rather than by their base sequence.     

Use of the additive main effects and multiplicative interaction model in QTL mapping for adaptation in barley

The additive main effects and multiplicative interaction (AMMI) model has emerged as a powerful analytical tool for genotype x environment studies. The objective of the present study was to assess its value in quantitative trait locus (QTL) mapping. This was done through the analysis of a large two-way table of genotype-by-environment data of barley (Hordeum vulgare L.) grain yields, where the genotypes constituted a genetic population suitable for mapping studies. Grain yield data of 150 doubled haploid lines derived from the Steptoe x Morex cross, and the two parental lines, were taken by the North American Barley Genome Mapping Project (NABGMP) at 16 environments throughout the barley production areas of the USA and Canada. Four regions of the genome were responsible for most of the differential genotypic expression across environments. They accounted for approximately 50% of the genotypic main effect and 30% of the genotype x environment interaction (GE) sums of squares. The magnitude and sign of AMMI scores for genotypes and sites facilitate inferences about specific interactions. The parallel use of classification (cluster analysis of environments) and ordination (principal component analysis of GE matrix) techniques allowed most of the variation present in the genotype x environment matrix to be summarized in just a few dimensions, specifically four QTLs showing differential adaptation to four clusters of environments. Thus, AMMI genotypic scores, when the genotypes constituted a population suitable for QTL mapping, could provide an adequate way of resolving the magnitude and nature of QTL x environment interactions.Ignacio Romagosa was on sabbatical leave from the University of Lleida and the Institut de Recerca i Tecnologia Agroalimentàries, Lleida, Spain, when this study was conducted     

A Familial Factor Independent of CAG Repeat Length Influences Age at Onset of Machado-Joseph Disease

Machado-Joseph disease (MJD) is a late-onset, progressive, neurodegenerative disorder caused by the expansion of an unstable trinucleotide (CAG) repeat sequence in a novel gene (MJD1) on chromosome 14. Previous studies showed that age at onset is negatively correlated with the number of CAG repeat units, but only part of the variation in onset age is explained by CAG repeat length. Ages at onset and CAG repeat lengths of 136 MJD patients from 23 kindreds of Portuguese descent were analyzed, to determine whether familial factors independent of CAG repeat length modulate age at onset of MJD. Correlation among sibs for onset age adjusted for CAG repeat length was .43, which indicates that an environmental or genetic factor common to sibs influences onset age. Positive correlations were also observed for avuncular (r = .22) and first-cousin pairs (r = .28), which supports the hypothesis that a genetic factor is influencing age at onset. Commingling analysis of onset ages adjusted for CAG repeat length identified three distributions in this population of affected individuals. Further studies of a much larger sample are needed to determine whether these distributions represent the influence of a genetic or environmental factor.