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PubMed1997

Structure and spatial pattern of the sensilla of the body segments of insect larvae.

We describe the types and patterns of sensilla present on the thorax and abdomen of newly hatched larvae of representative species of several insect orders, among them Saltatoria, Mantodea, Blattaria, Heteroptera, Lepidoptera, and Diptera. Sensilla of non-Dipteran species almost exclusively comprise mechanoreceptive hairs or bristles (trichoid sensilla) of various sizes and numbers. In higher Dipterans, peg sensilla (sensilla basiconica, sensilla coeloconica) and so-called papilla sensilla predominate. The pattern of early larval sensilla falls into three main classes, which can be described as 1) fixed pattern, 2) variable pattern, and 3) variable pattern with fixed elements. In larvae exhibiting a fixed sensillum pattern (found in all Dipteran species investigated), sensilla are invariant in number; they are precisely placed in relationship to each other and typically form a single row behind the middle of each segment. A variable pattern (common in most insect groups) typically consists of several rows of relatively evenly spaced sensilla encircling the middle of each segment. In animals with a variable pattern including fixed elements, some sensilla, recognizable by their size or shape, are precisely placed, whereas other sensilla surrounding them are variable.

Animals↗
PubMed1991

Empirical Bayes estimates of cancer mortality rates using spatial models.

We give results of empirical Bayes (EB) estimation of mortality rates designed to smooth observed SMR when random fluctuation of the observed deaths is important. We have specially studied the case where the prior distributions of the EB method have a spatial structure. The need for spatial modelling of cancer mortality rates in France is first shown with testing autocorrelation and fitting autoregressive spatial models, conditional (CAR) or simultaneous (SAR). A positive autocorrelation of the rates is shown for most cancer sites studied. As expected, EB estimates of mortality rates for common tumours are similar to SMRs. For rare tumours, the EB method identifies the extreme rates more clearly than SMRs by smoothing the SMRs with large variances. CAR or SAR models are adequate prior distributions for autocorrelated rates and produce quite similar rate estimates.

Bayes Theorem↗
PubMed1994

Chemical induction of quadruple and octuple chromosomes in Chinese hamster CHO-K1 cells and relationship between their three-dimensional structure and spatial distribution of BrdU-labeled chromatids.

Double endoreduplication of Chinese hamster CHO-K1 cells that exhibited quadruple chromosomes at metaphase was induced by a combination of rotenone and ammonium vanadate treatments. Analysis of sister chromatid differential staining patterns (using 5-bromo-2'-deoxyuridine) revealed that approximately 50% of the quadruple chromosomes did not keep the scheme of "outside replication" of DNA. Based on the ratio of the staining patterns observed, we suggest that the two diplochromosomes forming a quadruple chromosome are held together by a physical link connecting the two original chromatids. Metaphases with octuple chromosomes were also produced by the same treatment. Each chromosome constituting an octuple chromosome was longer and thinner than ordinary metaphase chromosomes. This suggests incomplete chromosome condensation at metaphase. The majority of octuple chromosomes showed the eight constituent chromosomes to be so enmeshed that a planar alignment could not be observed in air-dried preparations.

Aneuploidy↗
PubMed1984

The effect of phase structures on spatial phase discrimination.

This study was concerned with the discrimination of multifrequency gratings which differed only in the relative phase of one sinewave component (the test frequency) relative to the other components (the background frequencies). The dependent variable was the contrast of the test frequency required to discriminate between the two gratings. This study found that increasing the test frequency's relative phase difference from 10 to 90 deg significantly increased an observer's contrast sensitivity. However, no overall change in contrast thresholds was measured for test gratings having a relative phase difference between 90 to 180 deg. Moreover, when the mean relative phase was changed from 0 to 45 deg, contrast thresholds did not change when discriminating between gratings having a 90 deg relative phase difference. The type of processing most likely to account for these results in discussed.

Discrimination, Psychological↗
PubMed1980

The material science of calcium phosphate ceramics.

Tricalcium, tetracalcium phosphate and hydroxyapatite ceramics exhibit distinct differences in their chemical and structural composition. Only hydroxyapatite ceramic is identical with the original bone mineral. Different preparation methods lead to compact hydroxyapatite ceramic or to porous material with interconnecting macropores as structural equivalents of the spatial structure of cancellous bone. Concerning the behaviour in a biological environment, high crystallinity and large material density result in resistance to dissolution and long lasting stability. Amorphous ultrastructure and porous formation enhance interface activity and bone ingrowth, but also biological degradation of the ceramic implant material.

Biomechanical Phenomena↗
PubMed1988

Structure and spatial conformation of the iron-binding sites of transferrins.

Transferrins are iron-binding glycoproteins involved in iron metabolism and antibacterial defense mechanisms. Since the discovery of transferrins, many studies have attempted to characterize the iron ligands and to establish the conformation of the iron-binding sites. From chemical and spectroscopic studies, it was generally accepted that iron was hexacoordinated to Tyr and His residues, to a water molecule and to a (bi)carbonate ion, electrostatically linked to an Arg residue. On the basis of these studies, on the one hand, and on the basis of the homologies between the amino acid sequences of transferrins, on the other hand, predicted data have been provided about the number and location of the iron ligands. Recent X-ray crystallography studies of human lactotransferrin have partially confirmed the above-mentioned predicted data and have brought invaluable information about the nature of the ligands and the conformation of the iron-binding site. On the basis of the obtained results, a scheme has been proposed in which the iron is coordinated to 2 Tyr, 1 His and 1 Asp residues, to a (bi)carbonate linked to an Arg residue and probably to a water molecule. The iron-binding site is located at the interface between the two domains which constitute each lobe of the transferrins.

Amino Acid Sequence↗
PubMed1985

Analysis of the structure and spatial distribution of ultraviolet-induced DNA repair patches in human cells made in the presence of inhibitors of replicative synthesis.

The repair of ultraviolet-induced damage in the presence of hydroxyurea or hydroxyurea and arabinosylcytosine was investigated in confluent human fibroblasts at the level of DNA loops attached to the nuclear matrix. Estimation of single-strand break frequencies based on the release of DNA from the DNA-nuclear matrix complex after incubation with nuclease S1 revealed the occurrence of multiple incision events per DNA loop in the presence of inhibitors. When both inhibitors were employed, over 90% of the repair-labelled DNA was not ligated within 2 h post-incubation. In the absence of ligation of repair patches, we observed a preferential release of repair-labelled DNA from the nuclear matrix by nuclease S1 compared to prelabelled DNA, regardless of the period of post-UV incubation. The results suggest that repair events are clustered to some extent in a certain area of a DNA loop. However, the position of these clusters relative to the attachment sites of DNA loops at the nuclear matrix is random. The data are discussed in terms of denaturation of a putative repair complex in the presence of hydroxyurea resulting in an excess of incisions over repaired sites.

Cell Line↗
PubMedDate not supplied

Determination of protein structures from nuclear magnetic resonance data using a restrained molecular dynamics approach: the lac repressor DNA binding domain.

A procedure is described to determine from NMR data the three-dimensional structure of biomolecules. This procedure combines model building with a restrained Molecular Dynamics algorithm, in which distance information from NOEs is incorporated in the form of pseudo potentials. The method has been applied to the N-terminal DNA-binding domain or "headpiece" (amino acids 1-51) of the lac repressor from E. coli, for which no crystal structure is available. The spatial structure of the headpiece is discussed in terms of known physical and biochemical data and of its DNA binding properties.

Binding Sites↗
PubMed1997

Anatomical variants of brain structure: confused spatial relationship of the fornix to the corpus callosum and anterior commissure.

How the developing nerve fibers are guided to and able to find their target is currently a matter of research. As examples of the false guidance of axons, anatomical variants of the spatial relationship of the columna fornicis to the corpus callosum and the anterior commissure are demonstrated. In a 60 year-old female patient, some of the fibers of the genu corporis callosi were found to be entrapped by a fornix fiber bundle. The brain of a 20 year-old man showed that the unilateral anterior commissure ran posterior to the columna fornicis. These changes were clinically insignificant.

Adult↗
PubMed1997

Structure and spatial expression of the Manduca sexta MSCP14.6 cuticle gene.

The genomic and cDNA sequences of the MSCP14.6 gene section, which encodes a Manduca sexta cuticle protein, have been determined. The genomic sequence presented here includes 1428 N of 5' flanking DNA, 1587 N of transcribed DNA, and 465 N of 3' flanking DNA. The intron/exon boundaries mapped by comparison of these sequences were confirmed by primer extension and SI nuclease mapping. Prior work showed that the RNA produced by this gene is regulated both temporally and spatially during larval, pupal, and adult development, and also showed that both 20-hydroxyecdysone (20E) and juvenile hormone (JH) are important in controlling the amount of RNA present in the epidermis (Riddiford et al., 1986). In situ hybridizations show that MSCP14.6 is expressed throughout the epidermis in larvae and is spatially restricted in pharate pupal and pharate adult stages. The results presented here delimiting the transcription unit and 5' flanking DNA of the MSCP14.6 gene will facilitate further research to determine the DNA elements necessary for regulation of gene expression.

Amino Acid Sequence↗
PubMed2004

Control of protein adsorption: molecular level structural and spatial variables.

The adsorption of fibrinogen (Fb) and bovine serum albumin onto polycrystalline Au coated with HS(CH2)3O(CH2CH2O)5CH3 was determined by surface plasmon resonance from bare Au (0% coverage) to the complete ( approximately 100% coverage) self-assembled monolayer (SAM). Both proteins exhibit similar adsorption curves with common onset ( approximately 60% coverage) and range ( approximately 60% to 80% coverage) of minimal protein adsorption. Reflection-absorption infrared spectroscopic data show that widespread order is not present in the films over this range of coverage, indicating loosely packed, bound oligomers that are uniformly distributed and fully screen the underlying substrate. On the basis of our data, we propose a mechanism of protein rejection by oligo(ethylene oxide) (OEO)-modified surfaces in terms of changes in free energy (DeltaGsystem; system = protein + surface) due to oligomer conformational constriction over an area greater than the contact area. Minimal protein adsorption corresponds to the maximum DeltaGsystem for a given compression. This controlled study of protein adsorption provides insights into the molecular level understanding of protein adsorption unavailable from previous polymer and comparative SAM studies.

Adsorption↗
PubMed2004

Computed energetics of nucleotides in spatial ribozyme structures: an accurate identification of functional regions from structure.

Ribozymes are functionally diverse RNA molecules with intrinsic catalytic activity. Multiple structural and biochemical studies are required to establish which nucleotide bases are involved in the catalysis. The relative energetic properties of the nucleotide bases have been analyzed in a set of the known ribozyme structures. It was found that many of the known catalytic nucleotides can be identified using only the structure without any additional biochemical data. The results of the calculations compare well with the available biochemical data on RNA stability. Extensive in silico mutagenesis suggests that most of the nucleotides in ribozymes stabilize the RNA. The calculations show that relative contribution of the catalytic bases to RNA stability observably differs from contributions of the noncatalytic bases. Distinction between the concepts of "relative stability" and "mutational stability" is suggested. As results of prediction for several models of ribozymes appear to be in agreement with the published data on the potential active site regions, the method can potentially be used for prediction of functional nucleotides from nucleic sequence.

Catalytic Domain↗