Folding Index Research Articles

Epigenetic dental variability of Israeli hares (Lepussp.): ecogenetic or phylogenetic causation?

AbstractWe examined 3747 teeth from 134 hares (Lepussp.) collected at 46 sites in Israel to test whether variation in epigenetic occlusal characters was linked to ecogenetic or phylogenetic factors. Collection sites encompassed a wide range of ecogeographical and climatic regimes. We compared data from Israeli hares with occlusal characters of 160 cape haresL. capensisfrom East Africa and 68 brown haresL. europaeusfrom central Europe. Only three teeth (I1, I2, M3) did not show occlusal variation. Thirty‐eight occlusal characters were derived from dental variants by dichotomous (0/1) scoring. Absence of association of character states among characters of single teeth indicated a lack of morphotypes. Epigenetic differentiation among hares from northern, central and southern Israel, and the two East African, and two central European samples, was revealed by pairwise C. A. B. Smith's ‘mean measures of divergence’ (MMD), based on frequencies of character states. Cluster analyses of MMD values revealed little epigenetic differentiation between northern and southern Israeli hares, but greater differentiation between central European and East African hares. Concordance of the MMD matrix with linear geographical distances among sampling regions was demonstrated by a Mantel test. No frequencies of character states exhibited significant changes across the climatic parameters among hares from northern and southern Israel. But the individual folding index, which expresses the degree of enamel on the occlusal surface, slightly decreased from north to south. Our results support a phylogenetic interpretation of occlusal character variation. Despite distinct differences in external appearance, hares from northern and southern Israel probably comprise a single species that encompasses two closely related geographical populations with a probable area of overlap. Israeli hares are intermediate between European brown hares and East African cape hares, with a slightly closer relationship to the cape hares.

Confinement of phonons in InGaAs/InP superlattices

A comparison is presented of optical mode Raman spectra of an In0.48Ga0.52As/InP superlattice, an In0.48Ga0.52As strained epilayer on InP, and bulk InP. The sharpness of the interfaces between the alloy and InP layers in the superlattice sample is confirmed through the observation of folded acoustic modes up to folding index m=6. Mixed interface modes were correspondingly not observed in the superlattice optic mode Raman spectra. The GaAs-like longitudinal optic (LO) and transverse optic and InP LO modes in the superlattice are found to decrease in frequency with respect to the corresponding strained-epilayer and bulk-InP modes. These frequency shifts arise from phonon confinement effects in the superlattice.

On a characterization of the folding of proteins

We consider a characterization of the folding of 3-D model proteins. Using as the input the geometry of molecules, we first construct a distance/distance matrix in which element i, j is given by the quotient of the Euclidean and the graph theoretical distance between the two vertices. The leading eigenvalue of the D/D matrix gives a measure of the folding of the protein structure. Using higher powers of the elements of D/D matrices, we generate the corresponding leading eigenvalue λ(k) for different exponents (k=1, 2, 3,…). So, derived invariants represent a characterization of the folding of a structure—here, model proteins. The derived invariants are analogous to the characterization of proteins based on the average distance, referred to as a protein profile. The folding index ϕ=λ/n, that is, the leading eigenvalue, is normalized to the number of “points” representing the structure. Structures that are more folded have a smaller folding index. We illustrate the use of the folding indices to measure the degree of similarity of molecules. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 1017–1026, 1999

The vulnerability of the fetal sheep brain to hypoxemia at mid-gestation

Our aim was to test the hypothesis that a brief episode of hypoxemia near mid-gestation in fetal sheep will result in damage to the fetal brain with the extent and type of damage in any particular region being related to the developmental processes occurring at the time of the insult. Hypoxemia was induced, sufficient to reduce arterial O 2 content by approximately 50%, by restricting utero–placental blood flow in 14 chronically catheterised fetuses for 6 h or 12 h at 84 days of gestation (term 145–8 days). Age-matched fetuses ( n=14; 4 operated and 10 unoperated) were used as controls. Fetuses were killed 7 days after being exposed to hypoxemia, and brains removed for histological analysis at the light and ultrastructural levels. Body weights of hypoxemic fetuses did not differ significantly from controls but brain weights were significantly reduced both in absolute terms and when expressed in relation to body weight ( P<0.05). Most fetuses exposed to hypoxemia sustained no gross brain damage. However, in one hypoxemic fetus from a multiple pregnancy there was extensive leucomalacia in the cortical white matter; mild focal damage was seen in another 8 hypoxemic fetuses. In the cerebral cortex (frontal lobe) the surface folding index was significantly reduced ( P<0.05) in hypoxemic fetuses compared to controls suggesting that gyral formation had been delayed. In these fetuses there were also degenerating neurons in the deeper cortical layers. In the hippocampus of hypoxemic fetuses there was a delay ( P<0.05), compared to controls, in the migration of cells from the germinal layer to the pyramidal layer in the CA1 region, and decreases ( P<0.05) in the density (areal) of neurons in the pyramidal layer and in the width of stratum oriens. In the cerebellum of hypoxemic fetuses there was a decrease ( P<0.05), compared to controls, in the density (areal) of mitotic bodies in the external granule cell layer. However, there were no significant differences in the number of pyknotic cells in this layer, in the density of Purkinje cells, in their somal area, or in the width of the external granule cell or molecular layers. There was an increase ( P<0.05) in the proportion of the brain parenchyma occupied by blood vessels in both the hippocampus and cortex of hypoxemic fetuses compared to controls. This study has shown that an hypoxemic insult near mid-gestation can result, one week later, in white matter damage and in neuronal death in the hippocampus and to a lesser extent in the cerebral cortex and cerebellum. It can also retard neuronal migration and the growth of neural processes in the hippocampus where development is well established at this age. Such brain damage could result in less than optimal neuronal connectivity and could affect function postnatally.

Resonance Raman Study of Folded Acoustic Modes in StrainedInSb/In1-xAlxSb Superlattices

The folded acoustic modes in a series of InSb/In1-xAlxSb (0.2<x<0.5) strained-layer superlattices were investigated using resonance Raman spectroscopy. Folded modes up to fourth order in the folding index were observed. Analysis of the wavenumbers and intensities of these modes allowed estimates of the superlattice periods and layer thicknesses, and also the ratioP2/P1 of the photoelastic coefficients for the InSb (P1) and alloy (P2) layers at 647.1 nm. TheP2/P1 ratio remarkably changes sign forx≈0.1 under near-resonance excitation owing to the variation in the alloyE1 optical gap withx.

Resonance Raman Study of Folded Acoustic Modes in StrainedInSb/In1-xAlxSb Superlattices

The folded acoustic modes in a series of InSb/In1-xAlxSb (0.2<x<0.5) strained-layer superlattices were investigated using resonance Raman spectroscopy. Folded modes up to fourth order in the folding index were observed. Analysis of the wavenumbers and intensities of these modes allowed estimates of the superlattice periods and layer thicknesses, and also the ratioP2/P1 of the photoelastic coefficients for the InSb (P1) and alloy (P2) layers at 647.1 nm. TheP2/P1 ratio remarkably changes sign forx≈0.1 under near-resonance excitation owing to the variation in the alloyE1 optical gap withx.

Mechanical Properties and Microstructure of Drawn High-Density Polyethylene Films by Unilateral Roller Drawing Method.

The unilateral roller-drawing (URD) method was tested to prepare high-modulus and high-strength polyethylene films. Samples were heated locally for a short period during the drawing by this method, in which only the bottom-edge of a roller was soaked with a part of the film in silicone of high temperatures. The deformation aspects of macroscopic shape and microscopic structure as well as the mechanical properties of the films drawn by the URD method were studied under the various conditions of draw-temperature (Td) and draw-ratio (λ). The values of breaking stress and Young's modulus reached 1.0GPa and 40.0GPa, respectively, at Td=120°C and λ>25. The results obtained from wide-angle X-ray diffraction indicated orientations of (110) and (200) planes as well as high degrees of c-axis orientation along the draw-direction. On the basis of small-angle X-ray scattering, it was suggested that the two-phase structure composed of crystalline and amorphous regions changed into the mono-phase structure with the extended-chain crystals when λ was increased. The folding index was evaluated from IR spectra to show that chain unfolding appreciably occurred when λ was larger than 15 and Td was in the region of between 120 and 135°C. The endothermic peak in DSC caused by the melting of the sample was found to shift to the higher temperature region with increasing λ. It was confirmed from the scanning electron microscopic observation on the fractured surface that the brittle fracture occurred for the sample drawn by the URD method, while the uniaxially cold-drawn films showed the ductile-fracture appearance. It was considered from these results that the URD method was useful to prepare high-density polyethylene films with superior mechanical properties such as high-strength and high-modulus.

Foliation of the cerebellar vermis in trisomy 19 mice

The development of the folial pattern was studied in the cerebellar vermis of 32 trisomy 19 (Ts19) mice aged 1–16 days postpartum and their euploid littermates. In the Ts 19 cerebellum, fissures were formed in the regular sequence observed in control littermates, but their appearance was delayed by about 2 days. Fissure number increased until day 6 in euploid controls and in Ts19 mice, remaining constant thereafter. In Ts19 cerebella, fissure number and fissure depth were reduced significantly; there were 30% fewer Purkinje cells and the cross-sectional areas of the external germinal layer and of the total cerebellar vermis were decreased, reflecting a permanent hypoplasia. Both in Ts19 and control mice, a temporal and quantitative relationship was observed between fissure formation and the expansion of the external germinal layer, whereas the increase in fissure depth was found to correlate with the growth of the whole cerebellar vermis. Determination of the surface folding index revealed that only during fissure formation, the expansion of the cerebellar surface exceeded that of the cerebellar volume. The present study does not give any indication that foliation and histogenesis of the cerebellum are differentially affected by trisomy.

Relationships between microvascular function and capillary structure in diabetic and nondiabetic human skin.

Despite the commonly held view that abnormalities in capillary morphology, in particular thickening of the capillary basement membrane, are partly responsible for diabetic ischemia, few studies have correlated anatomic and hemodynamic variables in the same diabetic subjects. In a previous study of 24 type II (non-insulin-dependent) diabetic subjects and 24 age-matched control subjects, we showed that a standard finger exercise vasodilated cutaneous forearm vessels nearly equally (51%), but the postarteriolar flow responded differently between groups. Nondiabetic subjects increased flow by recruitment of capillaries, whereas diabetic subjects did so by capillary flow augmentation. Moreover, resting permeability-surface area product (PS) to pentetic acid was 85% higher in diabetic than nondiabetic subjects. In this study, these same subjects had their forearm skin biopsied and examined morphometrically by electron microscopy for capillary radius, basement membrane thickness, endothelial cell density, and a folding index of luminal membrane reduplication. All morphological variables were correlated stepwise in a saturated, analysis of covariance model with the physiological results. The correlations were sparse and specifically excluded basement membrane thickness. The highest r2 value was .432 between resting PS and a ratio of capillary density to endothelial cell number per capillary. These studies show little evidence that diabetic microvascular physiological variables are tightly connected to morphometric changes except for minor permeability changes, which rise with capillary density and decrease with endothelial cell number. Because PS to pentetic acid is increased in diabetic subjects at any level of capillary density, it seems reasonable that permeability may be increased above that of nondiabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

CEREBELLAR FOLIATION IN RATS

The effects of maternal malnutrition on the formation of cerebellar fissures was studied in foetal rats. The rats were given a diet containing either 14 (normal) or 7 (protein-deprived) per cent protein by weight from two weeks before conception and throughout gestation. The first day with a sperm-positive vaginal smear was designated as Embryonic day 1 (E 1). Foetuses were examined on days E 19 to 22. In seventy-five foetuses, a sagittal slice of the cerebellum, 3-4 mm thick was embedded in Sorvall embedding medium. Sagittal sections, 2 micron thick were cut at levels 100 micron apart through the specimen. Sixty-three foetuses were examined for presence of cerebellar fissures only after filling their vascular system with ink-gelatin and cutting serial sagittal frozen sections, 100 micron thick. A morphological comparison of the foliation in normal and malnourished foetuses suggested a slight delay in the malnourished ones, albeit the earliest fissures were visible on the same day as in normal foetuses. The existence of a developmental alteration due to malnutrition was demonstrated by a decrease in the length of the pial surface and a surface folding index day on E 22. The alteration is discussed in relation to previously reported changes in cerebellar development during malnutrition, such as delayed Purkinje cell formation and alterations in proliferation/differentiation in the EGL.