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PubMed1988

Twenty-four hour variations in subcellular structures of rat pancreatic islet B-, A- and D-cells, and of portal plasma glucose and insulin levels.

Variations in stomach weights, plasma glucose and insulin levels in the portal vein, and in subcellular structures of rat pancreatic islet B-, A- and D-cells were examined over 24 h. The variation in stomach weights paralleled plasma glucose levels, indicating that the levels may be influenced by intestinal glucose absorption. Plasma insulin levels increased from the late dark to the early light periods, whereas they decreased from the late light to the early dark periods. The variation in plasma insulin levels was in the opposite sense to that in the relative numbers of B-cell granules. The decrease in the relative numbers of A-cell granules occurred between the late dark and early light periods. The relative numbers of D-cell granules decreased before and after the decreases in B- and A-cell granules. The variation in D-cell granules appears to correspond to the inhibitory effect of somatostatin. The relative amounts of rough endoplasmic reticulum (rER) in each cell varied in a reciprocal manner to those of B-cell granules. Moreover, the variation in plasma insulin levels coincided with variations in rER of hepatocytes and pancreatic acinar cells. The changes in rER of each cell may correlate with the trophic effect of insulin.

Animals↗

PubMed2004

Variation in xylem structure from tropics to tundra: evidence from vestured pits.

Bordered pits play an important role in permitting water flow among adjacent tracheary elements in flowering plants. Variation in the bordered pit structure is suggested to be adaptive in optimally balancing the conflict between hydraulic efficiency (conductivity) and safety from air entry at the pit membrane (air seeding). The possible function of vestured pits, which are bordered pits with protuberances from the secondary cell wall of the pit chamber, could be increased hydraulic resistance or minimized vulnerability to air seeding. These functional hypotheses have to be harmonized with the notion that the vestured or nonvestured nature of pits contains strong phylogenetic signals (i.e., often characterize large species-rich clades with broad ecological ranges). A literature survey of 11,843 species covering 6,428 genera from diverse climates indicates that the incidence of vestured pits considerably decreases from tropics to tundra. The highest frequencies of vestured pits occur in deserts and tropical seasonal woodlands. Moreover, a distinctly developed network of branched vestures is mainly restricted to warm habitats in both mesic and dry (sub)tropical lowlands, whereas vestures in woody plants from cold and boreal arctic environments are usually minute and simple. A similar survey of the frequency of exclusively scalariform perforation plates illustrates that the major ecological trend of this feature is opposite that of vestured pits. These findings provide previously undescribed insights suggesting that vessels with vestured pits and simple perforation plates function as an efficient hydraulic system in plants growing in warm environments with periodical or continuous drought stress.

Cold Climate↗

PubMed2004

Periodic structures and diurnal variation in blood pressure and heart rate in relation to microgravity on space station MIR.

Four Russian crew members were studied on space station MIR, and blood pressure (BP) and heart rate (HR) data were continuously collected. BP and HR data were collected on earth 1 day before orbital flight to the space station, then at weeks 8, 16 and 24 during space flight, and again 1 or 2 days after returning to earth. Time serial data for BP and HR were analyzed by spectral analysis with the MemCalc system (Suwa Trust, Sapporo, Japan). Periodic structures of diurnal variation in systolic blood pressure (SBP), diastolic blood pressure (DBP) and HR were compared at 24-hour, 12-hour and 8-hour intervals, these being determined as the main periodic components for the assessment of BP and HR variability. The 24-h mean levels of SBP and HR during space flight were unchanged. Waking SBP was not different from pre-flight values. During sleep, in-flight changes in HR did not differ from pre-flight values. SBP during sleep in orbit increased to over pre-flight values. Waking DBP was reduced during flight. The SBP and HR phases over a 24-hour cycle were shortened with a more pronounced shortening in weeks 8 and 16 compared with pre-flight values, and at week 24 recovered to preflight values. The 12, 8-hour-cycle remained unchanged, and were similar to pre-flight values. At the space station, the astronauts' mission was carried out under strict control of sleeping and waking hours; therefore, their 24-hour schedule is an artificially constructed situation. Main periodicity structures were maintained by strict control of lifestyle during long-term space flight. The conclusions reached were as follows: 1) SBP levels during sleep in a space environment increased compared with those on earth; 2) the periodicity phase of BP and HR shifted toward to 24-hour cycle as a result of long-term space flight, even though these periods shortened after a few months compared with pre-space flight values.

Adult↗

PubMed1984

Comparison of structural and functional variation in class I HLA molecules: the role of charged amino acid substitutions.

Functional and structural heterogeneity of HLA class I molecules was sought among five donors serologically identical for A2, A3, B7, and Bw44. Functional differences were identified by cell-mediated lympholysis (CML) after allogeneic mixed lymphocyte reaction among the five donors. Structural differences were characterized by high resolution two-dimensional electrophoretic maps of the class I HLA proteins synthesized by peripheral blood lymphocytes of these donors. Cells from three donors showed no CML-defined differences from one another; their HLA protein maps were identical. The cells of one donor recognized an A3-associated target antigen on the cells of all the other donors; her HLA map revealed a unique protein with altered isoelectric point. Another donor's cells differed by two CML-detected antigens: one was identified as a variant of Bw44 ("44.2") and the other was associated with Cw4. This donor's two-dimensional HLA map showed two novel charged proteins. By using these data, a two-dimensional map locating HLA-A2, -A3, -A3', -B7, -Bw44.1, -Bw44.2, and -Cw4 was prepared. Because each of three CML-detected antigens was correlated with a protein of distinctive charge, our results and the available published data raise the possibility that amino acid substitution producing charge variation may be a particularly important mechanism in the generation of CML-detectable HLA diversity.

Amino Acids↗

PubMed1999

[Variation of primary structure in nonstructural region 5 b of hepatitis C virus].

OBJECTIVE: To analyze the sequence variation in the nonstructural region 5 b(NS5 b) of hepatitis C virus (HCV) of China. METHODS: Complementary DNA fragments from sera of 49 Chinese patients were amplified by reverse transcription nested polymerase chain reaction (RT-nested-PCR) and the products were cloned and sequenced. RESULTS: 33 clones belonged to genotype 1 b and 16 clones were genotype 2 a. Several conserved nucleotide sites were found to be different from those of Japanese isolates though they belonged to an identical genotype. Comparison of average homology among the 33 clones of genotype 1 b and the 16 clones of genotype 2 a indicated that the average homology among genotype 2 a was lower than that among genotype 1 b. A deletion of three nucleotides and a frame-shift, resulting from the introduction of an in-frame stop codon, were firstly observed in the NS5 b region. CONCLUSION: The nucleotide sequences of different HCV isolates of a same subtype may possibly possess the characteristics for different geographical distribution and so a definite epidemic HCV strain may emerge from a definite area.

Base Sequence↗

PubMed1983

Variation in epidermal structure as function of different fixation methods. A stereological and morphological study.

Ultrastructural and volume variations in intact human epidermis due to differences in composition of the fixative have been investigated by electron microscopy and stereology. It was found that with glutaraldehyde as fixative variations in buffer osmolality in the range of 120-390 mosmol caused readily detectable changes in volume of the intercellular space and keratinocyte morphology. Also the epidermal Langerhans' cell was effected by variations in buffer osmolality. Three commonly used fixatives (glutaraldehyde, glutaraldehyde + paraformaldehyde, and osmium tetroxide) were found to result in different morphological and volume relations.

Adult↗

PubMed2003

Mutation rates: estimating phase variation rates when fitness differences are present and their impact on population structure.

Phase variation is a mechanism of ON-OFF switching that is widely utilized by bacterial pathogens. There is currently no standardization to how the rate of phase variation is determined experimentally, and traditional methods of mutation rate estimation may not be appropriate to this process. Here, the history of mutation rate estimation is reviewed, describing the existing methods available. A new mathematical model that can be applied to this problem is also presented. This model specifically includes the confounding factors of back-mutation and the influence of fitness differences between the alternate phenotypes. These are central features of phase variation but are rarely addressed, with the result that some previously estimated phase variation rates may have been significantly overestimated. It is shown that, conversely, the model can also be used to investigate fitness differences if mutation rates are approximately known. In addition, stochastic simulations of the model are used to explore the impact of 'jackpot cultures' on the mutation rate estimation. Using the model, the impact of realistic rates and selection on population structure is investigated. In the absence of fitness differences it is predicted that there will be phenotypic stability over many generations. The rate of phenotypic change within a population is likely, therefore, to be principally determined by selection. A greater insight into the population dynamics of mutation rate processes can be gained if populations are monitored over successive time points.

Bacteria↗

PubMed1984

A morphometric study of the variations in subcellular structures of rat hepatocytes during 24 hours.

Subcellular structures of hepatocytes in periportal and perivenous zones were examined during 24 h. The volume, surface and numerical profile densities of cytoplasmic organelles were analysed morphometrically. Most subcellular structures in periportal and perivenous hepatocytes were subject to strong circadian variations. In hepatocytes from both zones, the volume densities of smooth endoplasmic reticulum (sER), mitochondria, lysosomes, peroxisomes, polysomes and lipid droplets demonstrated peak values at 16.00 h, 20.00 h or 00.00 h; trough values were at 04.00 h, 08.00 h, or 12.00 h, except for peroxisomes (16.00 h). However, the volume densities of glycogen granules and rough endoplasmic reticulum (rER) in periportal and perivenous hepatocytes exhibited maximal values at 04.00 h, 08.00 h or 12.00 h and minimal values at 20.00 h. The surface densities of sER, mitochondria, lysosomes and peroxisomes, and the numerical profile densities of mitochondria, lysosomes and peroxisomes in periportal and perivenous hepatocytes showed similar trends. These events suggest that membranes of the rER show a partial correlation with the sER, mitochondrial and lysosomal membranes during the 24-h span. This may involve the interaction between ribosomes and rER. Almost all cytoplasmic organelles examined displayed significant differences between periportal and perivenous hepatocytes, morphometrically and in fine structure, indicating that the morphofunctional variability of hepatocytes differs depending on the location in the liver acinus.

Animals↗

PubMed2006

Accounting for structural properties and nucleotide co-variations in the quantitative prediction of binding affinities of protein-DNA interactions.

We describe a quantitative model for predicting the binding affinity of protein-DNA interactions. The described model is based on templates capable of providing a global representation of the modelled transcription factor (TF) binding sites. Templates can capture non independent nucleotide variations and structural properties present in these sites. Tests carried out on the p50p50 and p50p65 variants of the transcription factor NF-kappa B demonstrate a high correlation between the observed binding affinities and the binding affinities predicted by the templates. Only a small subset of training data spanning the space of the binding sites is required to train the templates.

Animals↗

PubMed2005

Multiunit arrector pili muscular structure as a variation observed by using computer-based three-dimensional reconstruction.

The arrector pili (AP) muscle was recently suggested to comprise one AP muscular unit inserted into all the hair follicles contained within the follicular unit (FU). This study investigated the presence of variations in AP muscular units associated with the FUs. Human cadaver scalp skin specimens were serially sectioned and stained with Masson's trichrome. Three-dimensional reconstructions of the serially sectioned images were analyzed on a computer, which revealed two types of variation in 20 FUs, one of which was the multiunit AP muscular structure, in which the AP muscular unit was inserted into two or more FUs.

Hair Follicle↗

PubMed2003

Effects of chronic variate stress on feeding behavior and on monoamine levels in different rat brain structures.

Chronic variate stress was seen to decrease the ingestion of sweet food when compared to control rats. Brain monoamines are known to be involved in the control of food intake, serotonin appears to be involved in the mechanisms of satiety, and dopamine in mediating appetite or approach behaviors triggered by incentive stimuli associated with rewards. The effect of chronic variate stress on cerebral levels of monoamines was also studied in rats. Increased levels of DOPAC were observed in the frontal cortex and in the hippocampus and an increased 5-HIAA/5-HT ratio was also observed in this latter structure. In the hypothalamus, levels of HVA and DOPAC were decreased, as well as the DOPAC/DA ratio, while no difference was found in amygdala. During the treatment, there were no differences in the consumption of water and regular food between stressed and control animals. An increase in the adrenal weight was observed at the end of the treatment. The results suggest that emotional changes, such as exposure to stress situations can influence feeding behavior, chronic variate stress causes decreased ingestion of sweet food and decreased dopaminergic neurotransmission in hypothalamus. Increased dopamine metabolite levels in the cortex and hippocampus were also observed and some of these modifications may be related to alterations in feeding behavior.

Animals↗

PubMed2003

Variations of multifractal structure in the fetal heartbeats.

Several procedures for evaluating fetal well-being are in clinical use. The cardiotocograph is mostly used as a non-invasive procedure to measure fetal well-being in clinical settings. The cardiotocograph displays the fetal heartbeat counts that vibrate. This variation has been classified into 2 categories. We investigated this variation by a novel method, in which we analyzed the change of structure of the attractors in the phase spaces according to the time course. We adopted the global spectrum, which means the distribution of fractal dimensions, for that structure. In this procedure, we discovered a new variation in which the cycle is much longer than the 2 types of known variabilities. Although loud noises such as white noises with a magnitude 1/4 times as large as the standard deviation of the original data were added to the original data, the variations were still detected. The variation is very difficult to detect by Fourier or wavelet transformation, however, because it changes very slowly. Through this new way of analyzing the vibration phenomena, we obtained a new perspective on the biological information available.

Cardiotocography↗

PubMed1982

Role of non-histones in chromosome structure. Cell cycle variations in protein synthesis.

As part of a study of the role of non-histone proteins in chromosome structure, the synthesis of non-histones associated with interphase chromatin was investigated. Synchronized suspension cultures of HeLa cells were pulse-labeled with [35S]methionine, and chromatin was prepared by mild micrococcal nuclease digestion. Two-dimensional polyacrylamide gel electrophoresis, in addition to one-dimensional electrophoresis, was used to resolve the patterns of incorporation of radioactive label. Significant variations in non-histone synthesis were seen during the cell cycle. A strong correlation was not found between DNA synthesis in mid-S phase and variations in non-histone synthesis. The non-histone proteins of purified metaphase chromosomes were also characterized by two-dimensional gel electrophoresis and compared to the proteins of interphase chromatin. The pattern of non-histones is not identical with that of interphase chromatin, although a number of major species may be shared by interphase chromatin and metaphase chromosomes. The HeLa nuclear scaffold, the framework that maintains the overall morphology of the interphase nucleus, shows relatively few proteins on two-dimensional gels. The synthesis of nuclear scaffold proteins was quantitated by excising each of 19 proteins from two-dimensional gels and determining the incorporated radioactivity by scintillation counting. Substantial variations in protein synthesis were found, with several species showing changes of about 2-fold in the percentage of incorporation.

Cell Cycle↗

PubMed1999

Fine-scale genetic structure and clinal variation in silene acaulis despite high gene flow

We investigated whether the distribution of genes reflects the patchy distribution of individuals of Silene acaulis on Pennsylvania Mountain in central Colorado. Five polymorphic protein loci were analysed using both F-statistics and spatial autocorrelation. Low thetaPOP (FST) indicated little genetic differentiation between populations approximately 1 km apart. This indicates high gene flow within our study site, perhaps as a result of long-distance pollen dispersal. Despite little differentiation between populations, there was clinal variation at the 6-Pgd-1 locus and significant within-population genetic structure (indicated by both thetaPATCH and spatial autocorrelation). We infer that this fine-scale genetic structure is the result of limited seed dispersal combined with genetic drift. The level of genetic structure varied markedly among populations, with the greatest genetic structure (highest Moran's I and thetaPATCH values) in two low-altitude, small, low-density populations. Intensive sampling such as used in this study may reveal similar patterns of fine-scale genetic differentiation in other patchily distributed plant species, particularly those with limited seed dispersal.

Journal Article↗

PubMed2003

Classification of exemplars with single- and multiple-feature manifestations: the effects of relevant dimension variation and category structure.

Most classification research focuses on cases in which each abstract feature has the same surface manifestation whenever it is presented. Previous research finds that people have difficulty learning to classify when each abstract feature has multiple surface manifestations. These studies created multiple manifestations by varying aspects of the stimuli irrelevant to the abstract feature dimension. In this article, multiple manifestations were created by varying aspects of the stimuli relevant to the abstract feature dimension. People given categories with the family resemblance category structure often used in psychology experiments had difficulty learning to classify when multiple manifestations were present, even though the variation was relevant. This effect was reversed when a family resemblance structure with nondiagnostic values was used.

Humans↗

PubMed1989

DNA determinants of structural and regulatory variation within the murine beta-glucuronidase gene complex.

The murine beta-glucuronidase (GUS) gene complex, [Gus], encompasses the GUS structural element, Gus-s, and a set of regulatory elements which serve to modulate Gus-s expression. Three common GUS haplotypes representing virtually all inbred strains of laboratory mice have been compared with respect to GUS mRNA sequence. Results of such comparisons revealed sequence variations which target the location of one of the GUS regulatory elements to sequences within Gus-s and which account for known electrophoretic and heat stability differences among GUS allozymes of the three common GUS haplotypes.

Alleles↗

PubMed1992

Nucleotide variation and molecular structure of the heterochromatic repetitive AluI DNA in the brine shrimp Artemia franciscana.

It has been suggested that DNA bending could play a role in the regulation of gene expression, chromosome segregation, specific recombination and/or DNA packaging. We have previously demonstrated that an AluI DNA family of repeats is the major component of constitutive heterochromatin in the brine shrimp A. franciscana. By the analysis of cloned oligomeric (monomer to hexamer) heterochromatic fragments we verified that the repetitive AluI DNA shows a stable curvature that determines a solenoidal geometry to the double helix. This particular structure could be of relevant importance in conferring the characteristic heterochromatic condensation. In this paper we evaluate how the point mutations that occurred during the evolution of the AluI sequence of A. franciscana could influence the sequence-dependent tridimensional conformation. The obtained data underline that, in spite of the high sequence mutation frequency (10%) of the repetitive DNA, the general structure of the heterochromatic DNA is not greatly influenced, but rather there is a substantial variation of the copy number of the repetitive AluI fragment. This variation could be responsible for the hypothetical function of the constitutive heterochromatin.

Animals↗

PubMed2006

Structure and shape variations in intermediate-size copper clusters.

Using extensive, unbiased searches based on density-functional theory, we explore the structural evolution of Cu(n) clusters over the size range n=8-20. For n=8-16, the optimal structures are plateletlike, consisting of two layers, with the atoms in each layer forming a trigonal bonding network similar to that found in smaller, planar clusters (n<or=6). For n=17 and beyond, there is a transition to compact structures containing an icosahedral 13-atom core. The calculated ground-state structures are significantly different from those predicted earlier in studies based on empirical and semiempirical potentials. The evolution of the structure and shape of the preferred configuration of Cu(n), n<or=20, is shown to be nearly identical to that found for Na clusters, indicating a shell-model-type behavior in this size range.

Journal Article↗