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At least 811 records · Page 45Linked to original sources
PubMed2004

Anatomic variations of the root canal of the rat according to age.

The mesial canal of the first lower molar of the rat has been used as an experimental model in Endodontics. The present study involves a detailed analysis of its structural variations as a function of age and thus contributes to its characterization and adequate use as an experimental model. We evaluated 60 molars of Wistar rats of different body weight: (group 1: 300-399 g, n=22; group 2: 400-499 g, n=16; group 3: 600-700 g, n=22). The samples were radiographed employing a standardized system. Total canal length and volume were measured on enlarged projections of the radiographs. Canal diameter was measured at coronary, middle and apical levels and employed to estimate the area of canal cross-section as an indicator of potential flow or metabolic interchange. From the second age group onwards, we detected radicular hypercementosis that increased canal length and resulted in the formation of a complex apical delta. The canal diameter decreased very significantly in the apical third. The estimated flow expressed in terms of the area of cross-section on the projection decreased from 1.2 mm2 in Group 1 to 0.05 mm2 in Group 2. Group 3 did not differ significantly from Group 2. The present results reveal that the spontaneous, age-related variations in canal anatomy described herein must be considered when performing experimental endodontics in rats.

Aging↗
PubMed1991

Structural systematics of bioactive peptides and their biosynthetic implications.

Structures of natural peptides have been linearized according to their biosynthetic constructions. The structural diversities of these peptides originate from highly complex enzyme systems, that are often found to be integrated to polyenzymes. Polyenzymes are constructed from similar elements or modules, and structural variations can be understood from mutational events and rearrangements at the DNA-level.

Enzymes↗
PubMed2005

Common deletions and SNPs are in linkage disequilibrium in the human genome.

Humans show great variation in phenotypic traits such as height, eye color and susceptibility to disease. Genomic DNA sequence differences among individuals are responsible for the inherited components of these complex traits. Reports suggest that intermediate and large-scale DNA copy number and structural variations are prevalent enough to be an important source of genetic variation between individuals. Because association studies to identify genomic loci associated with particular phenotypic traits have focused primarily on genotyping SNPs, it is important to determine whether common structural polymorphisms are in linkage disequilibrium with common SNPs, and thus can be assessed indirectly in SNP-based studies. Here we examine 100 deletion polymorphisms ranging from 70 bp to 7 kb. We show that common deletions and SNPs ascertained with similar criteria have essentially the same distribution of linkage disequilibrium with surrounding SNPs, indicating that these polymorphisms may share evolutionary history and that most deletion polymorphisms are effectively assayed by proxy in SNP-based association studies.

Gene Frequency↗
PubMed2005

Spermiogenesis in Psilochorus simoni (Berland, 1911) (Pholcidae, Araneae): evidence for considerable within-family variation in sperm structure and development.

A large number of characters and considerable variation among taxa make animal sperm cells promising objects for phylogenetic studies. However, our knowledge about sperm structure and development in spiders is still rudimentary. In pholcids, previous studies of two species representing different subfamily level taxa have revealed conspicuous differences. Here, we report on a representative of a third subfamily level taxon, confirming substantial variation in sperm structure and development within the family. The male genital system in Psilochorus simoni (Berland, 1911) consists of paired testes and deferent ducts which lead into a common ejaculatory duct. The somatic cells of the testes show a high secretory activity, and produce at least two different kinds of secretion. The spermatozoa show features already known from other Pholcidae as well as unique characters. The acrosomal vacuole is tube-like with a narrow subacrosomal space. The axoneme migrates deep into the nucleus and is finally located near the acrosomal vacuole. Thus, the postcentriolar elongation of the nucleus is very long. A centriolar adjunct is not present and after the coiling process the implantation fossa is completely filled with glycogen which is also found in larger amounts within the cytoplasm of the sperm cell. After the coiling process, a vesicular area is present that becomes most prominent in the periphery of the sperm cell and surrounds the axoneme and parts of the nucleus. The secretion sheath surrounding the mature spermatozoon is already formed in the lumen of the testis, possibly by a secretion present in the testis but absent in the deferent duct. Sperm are transferred as cleistospermia. Results are compared with previous studies on pholcid spermiogenesis and sperm structure.

Animals↗
PubMed2002

Low frequency ultrasonic propagation through fibre reinforced, polymer composites.

This paper concentrates upon mesoscale variations observed in the time-of-flight (TOF) area scans of shear wave propagation through 'identically processed', injection moulded, glass fibre reinforced, polypropylene plaques. The effect of these structural variations on the derived 3D stiffness constants is discussed. Hence the random measurement errors associated with the stiffness constant measurements are differentiated from the intrinsic process-induced spatial variations. Interesting correlations between TOF and received amplitudes of shear wave propagation have been found and our tentative interpretation of these data in terms of mesostructural variations in the reinforcing fibre locations and fibre orientations is presented.

Journal Article↗
PubMed1999

Bilateral dimorphism of Loewenthal's gland in young male albino rats: an ultrastructural investigation.

This study represents a further contribution to our knowledge about the structure of Loewenthal's gland. There are several divergences in the available literature on the topic, concerning both the histological and ultrastructural findings. However, in these studies, the authors did not take into account the potential influence of a putative side-dependent dimorphism previously reported by us. We therefore carried out histological and electronmicroscopic observations specifically aimed at evaluating the importance of the gland shape for its structure. In particular, in male albino rats aged 70-120 days, we compared the structure of the left and right glands. Depending on the side undergoing morphological investigation, we observed differences in the acini, cells, nuclei, endoplasmic reticulum, Golgi apparatus and granular content. Apart from slight individual differences, we found that structural variations were most frequently observed in glands displaying a more evident macroscopic side-specific dimorphism. Our findings demonstrate that several conflicting data in the literature dealing with the structure of Loewenthal's glands might be explained by the morphofunctional side-dependent dimorphism of the organ.

Aging↗
PubMed1997

Selecting optimally diverse compounds from structure databases: a validation study of two-dimensional and three-dimensional molecular descriptors.

The efficiency of the drug discovery process can be significantly improved using design techniques to maximize the diversity of structure databases or combinatorial libraries. Here, several physicochemical descriptors were investigated to quantify molecular diversity. Based on the 2D or 3D topological similarity of molecules, the relationship between physicochemical metrics and biological activity was studied to find valid descriptors. Several compounds were selected using those descriptors from a database containing diverse templates and 55 biological classes. It was evaluated whether the obtained subsets represent all biological properties and structural variations of the original database. In addition, hierarchical cluster analyses were used to group molecules from the parent database, which should have similar biological properties. Using various sets of structurally similar molecules, it was possible to derive quantitative measures for compound similarities in relation to biological properties. A similarity radius for 2D fingerprints and molecular steric fields was estimated; compounds within this radius of another molecule were shown to have comparable biological properties. This study demonstrates that 2D fingerprints alone or in combination with other metrics as the primary descriptor allow to handle global diversity. In addition, standard atom-pair descriptors or molecular steric fields can be used to correlate structural diversity with biological activity. Hence, the latter two descriptors can be classified as secondary descriptors useful for analog library design, while 2D fingerprints are applicable to design a general library for lead discovery. Based on these findings, an optimally diverse subset containing only 38% of the entire IC93 database was generated using 2D fingerprints. Here no structure is more similar than 0.85 to any other (Tanimoto coefficient), but all biological classes were selected. This reduction of redundancy led to a child database with the same physicochemical diversity space, which contains the same information as the original database.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2003

Enantioselectivity of epoxide hydrolase catalysed oxirane ring opening: a 3D QSAR study.

A 3D QSAR analysis (quantitative structure activity relationships) of a set of 2,2-disubstituted epoxides, substrates for epoxide hydrolases originating from four different organisms, was conducted by CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis), with respect to the enantioselective ring opening to the corresponding vicinal diol. Structural variations of the substrates include alkyl chains of different lengths, unsaturated moieties ((E)- and (Z)-alkenyl, alkinyl, aryl) and electronegative groups (ether oxygens, halogen atoms) at different locations within the 2-substituent group. Generally, all four organisms, namely Rhodococcus ruber NCIMB 11216, Rhodococcus ruber DSM 43338, Rhodococcus ruber DSM 44540 and Rhodococcus ruber DSM 44539, preferentially react with the (S)-enantiomer of the epoxide. Enantioselectivities (enantiomeric ratio, In E values) show a rather large variation, ranging from almost no (ln E < 1) to nearly complete selectivity (In E > 5.3). In addition, the response of the epoxide hydrolases stemming from the four organisms towards structural modifications of the substrate is different. Models for the enantioselectivity (enantiomeric ratio, ln E values) obtained by CoMFA and CoMSIA are of different but reasonable predictive power, e.g., q2CV = 0.701 and r2 = 0.937 for the CoMFA model of Rhodococcus ruber DSM 43338. Enantiomeric ratios for the test molecules can be well predicted. Plots of steric and electrostatic CoMFA (CoMSIA) fields allow conclusions to be drawn for the choice of the most suitable organism for a specific type of substrate.

Computational Biology↗
PubMed1991

Intertissular variations in osteonectin: a monoclonal antibody directed to bone osteonectin shows reduced affinity for platelet osteonectin.

Osteonectin, a major noncollagenous protein of bone, is also synthesized and secreted by various non-mineralized tissues and by platelets. To establish whether there are structural specificities of osteonectin according to its tissular origin, we raised 12 monoclonal antibodies against bovine bone osteonectin and screened them for their ability to recognize bone and platelet osteonectin. When hybridoma culture media were radioimmunoassayed all MAbs showed the same titer for [125I]human platelet osteonectin and for [125I]bovine bone osteonectin, except MAb 2, which poorly bound platelet osteonectin. Immunoprecipitation and immunoblotting experiments were performed on human bone protein extracts and on material secreted by human platelets upon thrombin stimulation; in these experiments MAb 2 recognized human bone osteonectin and only faintly human platelet osteonectin. A "sandwich" immunoradiometric assay was devised in which osteonectin bound to a solid phase by a first MAb was recognized by a 125I-labeled second MAb. In this assay MAb 2, used as a tracer, showed a 100-fold lower affinity for purified human platelet osteonectin than for purified human bone osteonectin. These results suggest the existence of structural variations in osteonectin obtained from bone and platelets. Whether these variations result from differences in sequence, post-translational processing, or postsecretional fate remains to be established.

Amino Acid Sequence↗
PubMed1994

Molecular evolution of SRP cycle components: functional implications.

Signal recognition particle (SRP) is a cytoplasmic ribonucleoprotein that targets a subset of nascent presecretory proteins to the endoplasmic reticulum membrane. We have considered the SRP cycle from the perspective of molecular evolution, using recently determined sequences of genes or cDNAs encoding homologs of SRP (7SL) RNA, the Srp54 protein (Srp54p), and the alpha subunit of the SRP receptor (SR alpha) from a broad spectrum of organisms, together with the remaining five polypeptides of mammalian SRP. Our analysis provides insight into the significance of structural variation in SRP RNA and identifies novel conserved motifs in protein components of this pathway. The lack of congruence between an established phylogenetic tree and size variation in 7SL homologs implies the occurrence of several independent events that eliminated more than half the sequence content of this RNA during bacterial evolution. The apparently non-essential structures are domain I, a tRNA-like element that is constant in archaea, varies in size among eucaryotes, and is generally missing in bacteria, and domain III, a tightly base-paired hairpin that is present in all eucaryotic and archeal SRP RNAs but is invariably absent in bacteria. Based on both structural and functional considerations, we propose that the conserved core of SRP consists minimally of the 54 kDa signal sequence-binding protein complexed with the loosely base-paired domain IV helix of SRP RNA, and is also likely to contain a homolog of the Srp68 protein. Comparative sequence analysis of the methionine-rich M domains from a diverse array of Srp54p homologs reveals an extended region of amino acid identity that resembles a recently identified RNA recognition motif. Multiple sequence alignment of the G domains of Srp54p and SR alpha homologs indicates that these two polypeptides exhibit significant similarity even outside the four GTPase consensus motifs, including a block of nine contiguous amino acids in a location analogous to the binding site of the guanine nucleotide dissociation stimulator (GDS) for E. coli EF-Tu. The conservation of this sequence, in combination with the results of earlier genetic and biochemical studies of the SRP cycle, leads us to hypothesize that a component of the Srp68/72p heterodimer serves as the GDS for both Srp54p and SR alpha. Using an iterative alignment procedure, we demonstrate similarity between Srp68p and sequence motifs conserved among GDS proteins for small Ras-related GTPases. The conservation of SRP cycle components in organisms from all three major branches of the phylogenetic tree suggests that this pathway for protein export is of ancient evolutionary origin.

Amino Acid Sequence↗
PubMed2006

Decrease of thalamic gray matter following limb amputation.

Modern neuroscience has elucidated general mechanisms underlying the functional plasticity of the adult mammalian brain after limb deafferentation. However, little is known about possible structural alterations following amputation and chronic loss of afferent input in humans. Using voxel-based morphometry (VBM), based on high-resolution magnetic resonance images, we investigated the brain structure of 28 volunteers with unilateral limb amputation and compared them to healthy controls. Subjects with limb amputation exhibited a decrease in gray matter of the posterolateral thalamus contralateral to the side of the amputation. The thalamic gray matter differences were positively correlated with the time span after the amputation but not with the frequency or magnitude of coexisting phantom pain. Phantom limb pain was unrelated to thalamic structural variations, but was positively correlated to a decrease in brain areas related to the processing of pain. No gray matter increase was detected. The unilateral thalamic differences may reflect a structural correlate of the loss of afferent input as a secondary change following deafferentation.

Adolescent↗
PubMed1975

Antimalarials. 7.2,8-Bis(trifluoromethyl)-4-quinolinemethanols.

Based on the high antilalarial activity of alpha-(2-piperidyl)-2,8-bis(trifluoromethyl)-4-quinolinemethanol, ten additional 2,8-bis(trifluoromethyl)-4-quinolinemethanols were prepared in which the amino alcohol side chain was structurally varied. Synthesis of the compounds is described and antimalarial activity data against Plasmodium berghei are presented and discussed in terms of the structure variations.

Animals↗
PubMed1971

Cochlea of the dolphin, Tursiops truncatus: the basilar membrane.

In the dolphin Tursiops truncatus, the basilar membrane over its course its course from basal to apical ends shows a systematic variation in width and in the manner and rigidity of its suspension. The suspension is by bony laminae on both the outer and inner edges in the basal region, and by progressively less rigid attachments in the more apical regions, until near the apex the membrane is held only by connective tissue. The basilar membrane shows an unusual variation in width of 14 times, ranging from an astonishingly small value of 25 mum at the basal end to a value toward the apex of about 350 mum. This structural variation is in harmony with the extension of sensitivity of the dolphin ear into the very high frequencies, and suggests unusual capabilities of pitch discrimination in this high range.

Animals↗
PubMed2006

Application of genome-wide single nucleotide polymorphism typing: simple association and beyond.

The International HapMap Project and the arrival of technologies that type more than 100,000 SNPs in a single experiment have made genome-wide single nucleotide polymorphism (GW-SNP) assay a realistic endeavor. This has sparked considerable debate regarding the promise of GW-SNP typing to identify genetic association in disease. As has already been shown, this approach has the potential to localize common genetic variation underlying disease risk. The data provided from this technology also lends itself to several other lines of investigation; autozygosity mapping in consanguineous families and outbred populations, direct detection of structural variation, admixture analysis, and other population genetic approaches. In this review we will discuss the potential uses and practical application of GW-SNP typing including those above and beyond simple association testing.

Chromosomes, Human↗
PubMed2004

Acoustic communication in the Red-vented Bulbul Pycnonotus cafer.

This paper deals with acoustic communication in the Red-vented Bulbul Pycnonotus cafer. This species emits a high variety of vocal signals that can be classified on the basis of their acoustical features and context of production. Individuals sang throughout the year and most songs were discrete and stereotyped. The songs were composed of strophes (phrases) with minor structural variations of elements that were preceded and followed by a temporal gap (3 to 12 s). Most strophes were composed of 2 to 6 elements that were often dissimilar in structure and ranging from 0.98 to 4.5 kHz. The biological function of the song appeared to be to maintain pair bonds and to synchronize breeding activities. Different types of context-specific calls were identified. Individuals produced Type-I alarm calls (fast and wide-band, 1.03 to 6.36 kHz) under low predation pressure andType-II calls (narrow frequency range, 1.37 to 3.39 kHz) under high predation pressure. Roosting calls were fast and wide-band signals phonetically similar to Type-I alarm calls. Three types of begging/contact calls were recorded in nestlings/fledglings. Greeting calls and flight calls were composed of complex phrases, like song, but were short and used for proximate functions.

Acoustics↗
PubMed2001

TEM and SEM observations on the extracellular matrix of the developing murine centra.

TEM and SEM application demonstrated that the shift from chondrification to ossification in the developing murine centra from day 15 to day 18 of gestational age is marked by typical structural variations of the extracellular matrix (ECM). During day 15 GA, typical matrix vesicles with crystalline contents appeared, as followed by single and fusing pleomorphic aggregates of a more regular crystalline structure. During days 17/18 GA, these structures disappeared, and the ECM now exhibited a network of collagen fibrils that had been less conspicuous before. During the time period studied, the ECM switched from a more acid (proteoglycans) to a rather neutral (glycoproteins) milieu.

Animals↗
PubMed1983

Genetic evidence that the multiple apolipoprotein A-1 isoforms are encoded by a common structural gene.

We have used a genetic structural variation of apolipoprotein A-I in mice to examine the origin of the multiple charge isoforms of the plasma protein. Apolipoprotein A-I translated in vitro from hepatic or enteric mRNA revealed that the genetic variation simultaneously alters the charge of the protein produced by both tissues. The variation also shifted the charge of the entire family of isoforms found in plasma or translated in vitro. These results indicate that the protein produced by different tissues as well as the multiple isoforms are all derived from a common structural gene by processing.

Animals↗
PubMed1987

Course and extent of variation of equine infectious anemia virus during parallel persistent infections.

Comparisons of peptide and oligonucleotide maps of glycoproteins and RNA from nine isolates of equine infectious anemia virus (EIAV) that were generated during parallel infections of two Shetland ponies revealed that each isolate was structurally unique. Each EIAV isolate contained a unique subset of variant peptides, oligonucleotides, or both, indicating that structural variation in EIAV is a random and noncumulative process and that a large spectrum of possible EIAV variants can be generated in infected animals.

Animals↗