Reappraisal of the Regulation of Lactococcal l-Lactate Dehydrogenase

Lactococcal lactate dehydrogenases (LDHs) are coregulated at the substrate level by at least two mechanisms: the fructose-1,6-biphosphate/phosphate ratio and the NADH/NAD ratio. Among the Lactococcus lactis species, there are strains that are predominantly regulated by the first mechanism (e.g., strain 65.1) or by the second mechanism (e.g., strain NCDO 2118). A more complete model of the kinetics of the regulation of lactococcal LDH is discussed.     

Physiological function of alcohol dehydrogenases and long-chain (C(30)) fatty acids in alcohol tolerance of Thermoanaerobacter ethanolicus

A mutant strain (39E H8) of Thermoanaerobacter ethanolicus that displayed high (8% [vol/vol]) ethanol tolerance for growth was developed and characterized in comparison to the wild-type strain (39E), which lacks alcohol tolerance (<1.5% [vol/vol]). The mutant strain, unlike the wild type, lacked primary alcohol dehydrogenase and was able to increase the percentage of transmembrane fatty acids (i.e., long-chain C(30) fatty acids) in response to increasing levels of ethanol. The data support the hypothesis that primary alcohol dehydrogenase functions primarily in ethanol consumption, whereas secondary alcohol dehydrogenase functions in ethanol production. These results suggest that improved thermophilic ethanol fermentations at high alcohol levels can be developed by altering both cell membrane composition (e.g., increasing transmembrane fatty acids) and the metabolic machinery (e.g., altering primary alcohol dehydrogenase and lactate dehydrogenase activities).     

Physiological Function of Alcohol Dehydrogenases and Long-Chain (C30) Fatty Acids in Alcohol Tolerance of Thermoanaerobacter ethanolicus

A mutant strain (39E H8) of Thermoanaerobacter ethanolicus that displayed high (8% [vol/vol]) ethanol tolerance for growth was developed and characterized in comparison to the wild-type strain (39E), which lacks alcohol tolerance (<1.5% [vol/vol]). The mutant strain, unlike the wild type, lacked primary alcohol dehydrogenase and was able to increase the percentage of transmembrane fatty acids (i.e., long-chain C₃₀ fatty acids) in response to increasing levels of ethanol. The data support the hypothesis that primary alcohol dehydrogenase functions primarily in ethanol consumption, whereas secondary alcohol dehydrogenase functions in ethanol production. These results suggest that improved thermophilic ethanol fermentations at high alcohol levels can be developed by altering both cell membrane composition (e.g., increasing transmembrane fatty acids) and the metabolic machinery (e.g., altering primary alcohol dehydrogenase and lactate dehydrogenase activities).     

Rapid cleavage of cyclic tertiary amides of Kemp's triacid: effects of ring structure

The piperidyl and prolyl amides of Kemp's triacid (7 and 8, respectively) have been prepared and their rates of intramolecular acylolysis measured as a function of pD. The piperidyl derivative 7 reacts approximately four-times faster (e.g., t(1/2)=3 min at 20 degrees C and pD7.7) than the previously reported pyrrolidyl and methylphenethyl amide derivatives, while the prolyl derivative 8 reacts two-times more slowly (e.g., e.g., t(1/2)=30 min at 20 degrees C and pD7.8). Molecular-mechanics calculations indicate that the nonbonded interactions in the piperidyl derivative 7 are distinct from those in the prolyl, pyrrolidyl, and methylphenethyl amide derivatives, a result that supports the suggestion that ground-state pseudoallylic strain contributes to the enormous reactivity of Kemp's triacid tertiary amides. In sum, the results reported indicate that the Kemp's triacid scaffolding provides a general means of activating tertiary amide derivatives.     

Mechanotransduction and endothelial cell homeostasis: the wisdom of the cell

Vascular endothelial cells (ECs) play significant roles in regulating circulatory functions. Mechanical stimuli, including the stretch and shear stress resulting from circulatory pressure and flow, modulate EC functions by activating mechanosensors, signaling pathways, and gene and protein expressions. Mechanical forces with a clear direction (e.g., the pulsatile shear stress and the uniaxial circumferential stretch existing in the straight part of the arterial tree) cause only transient molecular signaling of pro-inflammatory and proliferative pathways, which become downregulated when such directed mechanical forces are sustained. In contrast, mechanical forces without a definitive direction (e.g., disturbed flow and relatively undirected stretch seen at branch points and other regions of complex geometry) cause sustained molecular signaling of pro-inflammatory and proliferative pathways. The EC responses to directed mechanical stimuli involve the remodeling of EC structure to minimize alterations in intracellular stress/strain and elicit adaptive changes in EC signaling in the face of sustained stimuli; these cellular events constitute a feedback control mechanism to maintain vascular homeostasis and are atheroprotective. Such a feedback mechanism does not operate effectively in regions of complex geometry, where the mechanical stimuli do not have clear directions, thus placing these areas at risk for atherogenesis. The mechanotransduction-induced EC adaptive processes in the straight part of the aorta represent a case of the "Wisdom of the Cell," as a part of the more general concept of the "Wisdom of the Body" promulgated by Cannon, to maintain cellular homeostasis in the face of external perturbations.     

Dosimetric analysis of the carousel setup for the exposure of rats at 1.62 GHz

The so-called carousel setup has been widely utilized for testing the hypotheses of adverse health effects on the central nervous system (CNS) due to mobile phone exposures in the frequency bands 800-900 MHz. The objectives of this article were to analyze the suitability of the setup for the upper mobile frequency range, i.e., 1.4-2 GHz, and to conduct a detailed experimental and numerical dosimetry for the setup at the IRIDIUM frequency band of 1.62 GHz. The setup consists of a plastic base on which ten rats, restrained in radially positioned tubes, are exposed to the electromagnetic field emanating from a sleeved dipole antenna at the center. Latest generation miniaturized dosimetric E field and temperature probes were used to measure the specific absorption rate (SAR) inside the brain of three rat cadavers of the Lewis strain and two rat cadavers of the Fisher 344 strain. A numerical analysis was conducted on the basis of three numerical rat phantoms with voxel sizes between 1.5 and 0.125 mm3 that are based on high resolution MRI scans of a 300 g male Wistar rat and a 370 g male Sprague-Dawley rat. The average of the assessed SAR values in the brain was 2.8 mW/g per W antenna input power for adult rats with masses between 220 and 350 g and 5.3 mW/g per W antenna input power for a juvenile rat with a mass of 95 g. The strong increase of the SAR in the brain with decreasing animal size was verified by simulations of the absorption in numerical phantoms scaled to sizes between 100 and 500 g with three different scaling methods. The study also demonstrated that current rat phantom models do not provide sufficient spatial resolution to perform absolute SAR assessment for the brain tissue. The variation of the SAR(brain)(av) due to changes in position was assessed to be in the range from +15% to -30%. A study on the dependence of the performance of the carousel setup on the frequency revealed that efficiency, defined as SAR(brain)(av) per W antenna input power, and the ratio between SAR(brain)(av) and SAR(body)(av) are optimal in the mobile communications frequency range, i.e., 0.8-3 GHz.     

Inheritance and expression of tissue-specific catalase activity during development and aging in mice

The catalase activity in the liver, kidney, lung, and blood hemolysate was measured in newborn, 21-, 70-, 175-, and greater than 400-day-old mice from the strains BALB/c, Csb, C3H/HeSnJ, C3H/S, C57BL/6J, SW, and 129/ReJ. Catalase activity was found to be highest in the liver (approximately 0.33 U/mg protein) followed by the kidney (approximately 0.13 U/mg protein), lung (approximately 0.05 U/mg protein), and blood hemolysate (approximately 0.03 U/mg protein). ANOVA analysis indicated significant differences in enzyme activity among strains and age groups studied. The developmental profiles of enzyme activity were tissue and strain specific. Catalase activity in the blood, for example, was generally higher at birth and at old age, whereas the kidney catalase activity was low at birth and increased substantially with age. Strains could be classified as normal (129/ReJ, BALB/c, C3H/HeSnJ, C3H/S), hypocatalasemic (C57BL/6J, SW), and acatalasemic (Csb) with respect to enzyme activity and it was on this basis that the inheritance of the catalase phenotype was studied using appropriate crosses. The enzyme activity level in each tissue appears to be governed by a unique set of genetic regulators/modifiers that interact with a single structural gene (Cs) or its product to produce the catalase phenotype. Some of these (e.g., Ce-1 and Ce-2) have been previously described but based on the results of various crosses reported here, more must exist that remain still uncharacterized at the molecular level. Models proposed for the inheritance of the catalase phenotype vary in complexity from single allelic differences between strains (e.g., BALB/c x Csb; blood) to a system of multiple interacting genetic determinants (e.g., BALB/c x Csb; liver) each having dominant (e.g., C57BL/6J over BALB/c; liver) and recessive components (e.g., gene(s) conferring the acatalasemic phenotype in BALB/c x Csb; blood and kidney). Such results are important and offer an interesting model to further characterize aspects of eukaryotic gene regulation.     

Enhancement of pyruvate production by osmotic-tolerant mutant of Torulopsis glabrata

Pyruvate production by Torulopsis glabrata was used as a model to study the mechanism of product inhibition and the strategy for enhancing pyruvate production. It was found that the concentration of cell growth and pyruvate deceased with the increase of NaCl and sorbitol concentrations. To enhance the osmotic stress resistance of the strain, an NaCl-tolerant mutant RS23 was screened and selected through a pH-controlled continuous culture with 70 g/L NaCl as the selective criterion. Compared with the parent strain, mutant RS23 could grow well on the medium containing 70 g/L NaCl or 0.6 mol/L sorbitol. Pyruvate concentration by the mutant strain RS23 reached 94.3 g/L at 82 h (yield on glucose 0.635 g/g) in a 7-l fermentor with 150 g/L glucose as carbon source. Pyruvate concentration and yield of mutant RS23 were 41.1% and 11.1% higher than those of the parent strain, respectively. The strategy for enhancing pyruvate production by increasing osmotic stress resistance may provide an alternative approach to enhance organic acids production with yeast.     

He-Ne laser irradiation of folate-producing Candida utilis and optimization of culture conditions under submerged fermentation

In an attempt to obtain a microbial strain with higher yield of folate for industrial applications, we mutated the wild strain Candida utilis Y1.0 using a novel mutagenic process, i.e., irradiation by a helium–neon (He-Ne) laser with an output power of 20 mW and an exposure time of 20 min. The yield of folate in the mutated cells reached 1,102 ng/mL, which was 20.4-fold that of the wild strain. The mutant strain Y3.636 was relatively stable in terms of folate production through eight successive transfers of cultures and batch fermentation in a 3.7-L stirred-tank fermenter. Optimization further increased the yield of the mutant by 110 %, i.e., to 2,314?±?13 ng/mL. The optimal culture conditions for folate production were: cultivation in fermentation culture medium composed of 62.5 g/L glucose, 15 g/L corn liquor, 3 g/L (NH₄)₂SO₄, 3 g/L MgSO₄, and 1 g/L glutamic acid; inoculum size of 9 %; incubation at 28 °C and 196 rpm for 36 h. A time-course study of cell growth and folate production by mutant strain Y3.636 strongly suggested that folate production in C. utilis is growth-associated.     

Lipid peroxidation as molecular mechanism of liver cell injury during reperfusion after ischemia

The pathophysiological importance of reactive oxygen species has been extensively documented in the pathogenesis of hepatic ischema-reperfusion injury. Kupffer cells and neutrophils were identified as the dominant sources of the postischemic oxidant stress. To test the hypothesis that a direct free radical-mediated injury mechanism (lipid peroxidation; LPO) may be involved in the pathogenesis, highly sensitive and specific parameters of LPO, i.e., hydroxy-eicosatetraenoic acids (HETES), and F₂-isoprostanes, were determined by gas chromatographic-mass spectrometric analysis in liver tissue and plasma during 45 min of hepatic ischemia and up to 24 h of reperfusion. A significant 60–250% increase of F₂-isoprostane levels in plasma was found at all times during reperfusion; the HETE content increased only significantly at 1 h of reperfusion and in severely necrotic liver tissue at 24 h with increases between 90–320%. On the other hand, in a model of LPO-induced liver injury (infusion of 0.8 μmol tert-butylhydroperoxide/min/g liver), the hepatic HETE content increased two to fourfold over baseline values at 45 min, i.e., before liver injury. A further increase to 12- to 30-fold of baseline was observed during moderate liver injury. Based on these quantitative comparisons of LPO and liver injury, it seems highly unlikely that LPO is the primary mechanism of parenchymal cell injury during reperfusion, although it cannot be excluded that LPO may be important as a damaging mechanism in a limited compartment of the liver, e.g., endothelial cells, close to the sources of reactive oxygen, e.g., Kupffer cells and neutrophils.     

Relationship of strain magnitude to morphological variation in the primate skull

In a comparative study of variation in primate skulls, Wood and Lieberman ([ 2001 ] Am. J. Phys. Anthropol. 116:13–25) proposed that a predictable relationship exists between in vivo bone‐strain magnitudes and the extent of morphological variation in skeletal structures. They hypothesized that regions subject to high strains are prone to enhanced levels of variation. Three questions are posed with respect to the plausibility of this hypothesis. First, does the proposed relationship hold at different levels of analysis (e.g., for more restricted anatomical regions in which large strain gradients are present)? Second, is the biomechanical rationale for the hypothesis sound, given the current understanding of bone biology? Third, is the hypothesis obviated by consideration of the functional matrix concept of skull development, in which osseous growth is posited to be governed by surrounding soft tissues (e.g., muscle and tendon) and developing spaces (e.g., the nasal capsule)? The different perspectives explored by these questions suggest that the validity of the hypothesis, despite having a defensible theoretical rationale, is likely to be context‐specific. A direct role for strain magnitude in conditioning morphological variation is difficult to demonstrate either comparatively or theoretically, and it is unlikely that a single strain threshold or interval can be directly associated with elevated variation in the skeleton. The conceptual framework of the functional matrix (which allows for independent growth among different regions of the skull) conceivably contravenes the premise of a uniform relationship of strain magnitude to morphological variability. Am J Phys Anthropol, 2003. © 2003 Wiley‐Liss, Inc.     

Stapled NRPS enhances the production of valinomycin in Escherichia coli

Nonribosomal peptides (NRPs) are a large family of secondary metabolites with notable bioactivities, which distribute widely in natural resources across microbes and plants. To obtain these molecules, heterologous production of NRPs in robust surrogate hosts like Escherichia coli represent a feasible approach. However, reconstitution of the full biosynthetic pathway in a host often leads to low productivity, which is at least in part due to the low efficiency of enzyme interaction in vivo except for the well-known reasons of metabolic burden (e.g., expression of large NRP synthetases—NRPSs with molecular weights of >100 kDa) and cellular toxicity on host cells. To enhance the catalytic efficiency of large NRPSs in vivo, here we propose to staple NRPS enzymes by using short peptide/protein pairs (e.g., SpyTag/SpyCatcher) for enhanced NRP production. We achieve this goal by introducing a stapled NRPS system for the biosynthesis of the antibiotic NRP valinomycin in E. coli. The results indicate that stapled valinomycin synthetase (Vlm1 and Vlm2) enables higher product accumulation than those two free enzymes (e.g., the maximum improvement is nearly fourfold). After further optimization by strain and bioprocess engineering, the final valinomycin titer maximally reaches about 2800 µg/L, which is 73 times higher than the initial titer of 38 µg/L. We expect that stapling NRPS enzymes will be a promising catalytic strategy for high-level biosynthesis of NRP natural products.     

Binding-protein-dependent glucose transport by Agrobacterium radiobacter grown in glucose-limited continuous culture

Agrobacterium radiobacter NCIB 11883 was grown in glucose-limited continuous culture at low dilution rate. Whole cells transported glucose using an energy-dependent mechanism which exhibited an accumulation ratio greater than 2000. Three major periplasmic proteins were purified and their potential role as glucose-binding proteins (GBP) were investigated using equilibrium dialysis. Two of these, GBP1 (Mr 36,500) and GBP2 (Mr 33,500), bound D-glucose with high affinity (KD 0.23 and 0.07 microM respectively), whereas the third protein (Mr 30,500) showed no binding ability. Competition experiments using various analogues showed that those which differed from glucose at C-6 (e.g. 6-chloro-6-deoxy-D-glucose and 6-deoxy-D-glucose) variably decreased the binding of glucose to both GBP1 and GBP2, whereas those which differed at C-4 (e.g. D-galactose) were only effective with GBP1. The rate of glucose uptake and the concentration of the glucose-binding proteins increased in parallel during prolonged growth under glucose-limitation due to the emergence of new strains in which GBP1 (e.g. strain AR18) or GBP2 (e.g. strain AR9), but not both, was hyperproduced and accounted for at least 27% of the total cell protein. It is concluded that A. radiobacter synthesizes two distinct periplasmic binding proteins which are involved in glucose transport, and that these proteins are maximally derepressed during growth under glucose limitation.     

A genome shuffling-generated <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> isolate that ferments xylose and glucose to produce high levels of ethanol

Genome shuffling is an efficient approach for the rapid improvement of industrially important microbial phenotypes. This report describes optimized conditions for protoplast preparation, regeneration, inactivation, and fusion using the Saccharomyces cerevisiae W5 strain. Ethanol production was confirmed by TTC (triphenyl tetrazolium chloride) screening and high-performance liquid chromatography (HPLC). A genetically stable, high ethanol-producing strain that fermented xylose and glucose was obtained following three rounds of genome shuffling. After fermentation for 84 h, the high ethanol-producing S. cerevisiae GS3-10 strain (which utilized 69.48 and 100% of the xylose and glucose stores, respectively) produced 26.65 g/L ethanol, i.e., 47.08% higher than ethanol production by S. cerevisiae W5 (18.12 g/L). The utilization ratios of xylose and glucose were 69.48 and 100%, compared to 14.83 and 100% for W5, respectively. The ethanol yield was 0.40 g/g (ethanol/consumed glucose and xylose), i.e., 17.65% higher than the yield by S. cerevisiae W5 (0.34 g/g).     

Selection for the transfer of phenotypically nonselectable chromosomal mutations to recombinant plasmids through introduction of an altered restriction site

We describe a simple method to select for transfer of mutant alleles from the Escherichia coli chromosome to a plasmid which formerly carried the wild-type (wt) allele. The wt allele on the plasmid is modified by introduction of a unique restriction site (e.g., XhoI) and transformed into a rec ⁺ strain carrying the mutant allele on the chromosome. Upon homogenotization, the efficiency of which was increased by UV irradiation of the transforming plasmid [Chattoraj et al., Gene 27 (1982) 213–222], plasmids carrying the mutant allele are formed which are resistant to XhoI. These plasmids are selected from the population by resistance to XhoI digestion coupled with the low transformation efficiency of linear DNA molecules in recA⁻ strain. The method is efficient and rapid and has particular advantages in situations where the mutant allele is difficult to detect by its phenotype.     

Exo-oligosaccharides of Rhizobium sp. strain NGR234 are required for symbiosis with various legumes

Rhizobia are nitrogen-fixing bacteria that establish endosymbiotic associations with legumes. Nodule formation depends on various bacterial carbohydrates, including lipopolysaccharides, K-antigens, and exopolysaccharides (EPS). An acidic EPS from Rhizobium sp. strain NGR234 consists of glucosyl (Glc), galactosyl (Gal), glucuronosyl (GlcA), and 4,6-pyruvylated galactosyl (PvGal) residues with beta-1,3, beta-1,4, beta-1,6, alpha-1,3, and alpha-1,4 glycoside linkages. Here we examined the role of NGR234 genes in the synthesis of EPS. Deletions within the exoF, exoL, exoP, exoQ, and exoY genes suppressed accumulation of EPS in bacterial supernatants, a finding that was confirmed by chemical analyses. The data suggest that the repeating subunits of EPS are assembled by an ExoQ/ExoP/ExoF-dependent mechanism, which is related to the Wzy polymerization system of group 1 capsular polysaccharides in Escherichia coli. Mutation of exoK (NGROmegaexoK), which encodes a putative glycanase, resulted in the absence of low-molecular-weight forms of EPS. Analysis of the extracellular carbohydrates revealed that NGROmegaexoK is unable to accumulate exo-oligosaccharides (EOSs), which are O-acetylated nonasaccharide subunits of EPS having the formula Gal(Glc)5(GlcA)2PvGal. When used as inoculants, both the exo-deficient mutants and NGROmegaexoK were unable to form nitrogen-fixing nodules on some hosts (e.g., Albizia lebbeck and Leucaena leucocephala), but they were able to form nitrogen-fixing nodules on other hosts (e.g., Vigna unguiculata). EOSs of the parent strain were biologically active at very low levels (yield in culture supernatants, approximately 50 microg per liter). Thus, NGR234 produces symbiotically active EOSs by enzymatic degradation of EPS, using the extracellular endo-beta-1,4-glycanase encoded by exoK (glycoside hydrolase family 16). We propose that the derived EOSs (and not EPS) are bacterial components that play a crucial role in nodule formation in various legumes.     

Reactions of Nitric Oxide with Nitronyl Nitroxides and Oxygen: Prediction of Nitrite and Nitrate Formation by Kinetic Simulation

Nitric oxide reacts with nitronyl nitroxides (NNO) to form imino nitroxides (INO) and this transformation can be monitored using electron spin resonance spectroscopy. Recently, Akaike et al., reported that NNO such as 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO) and its derivatives (e.g., carboxy-PTIO) react with nitric oxide (·NO) in a 1:1 stoichiometry forming 2-phenyl-4,4,5,5-tetra-methylimidazoline-1-oxyl (PTI) or the respective product (e.g., carboxy-PTI) together with nitrite and nitrate (Akaike et al., Biochemistry 32, 827-832, 1993). In this paper, we reevaluate their results and show that the stoichiometry of the reaction between PTIO and ·NO is 0.63 ± 0.06:1.0. The reason for this discrepancy is due to an erroneous assumption by Akaike et al., that the stoichiometry for the reaction between ·NO and O₂ is 2:1 in aqueous solution. If the data reported by Akaike et al., were recalculated using a 4:1 stoichiometry established for the aqueous oxidation of ·NO, the reaction between ·NO and PTIO would give a stoichiometry of 0.5:1.0 in closer agreement with our data. We propose a mechanism for the reaction between PTIO and ·NO in aqueous solution. This mechanism predicts that the stoichiometry between carboxy-PTIO and ·NO is dependent on the rate of generation of ·NO and is 1:1 only at low rates of ·NO generation (i.e., 10^-13 M/s). However the stoichiometry approaches 0.5:1.0 at higher rates of ·NO production or when it is added as a bolus. The ratio between nitrite and nitrate also varies as a function of the rate of generation of ·NO. The model agrees with previous experimental observations that the aqueous oxidation of ·NO in air saturated solutions will exclusively form nitrite and predicts that ·NO will only generate substantial amounts of nitrate if it is released at a rate less than 10^-17 M/s. This may have important consequences in cellular systems where the concentration of ·NO is typically measured from nitrite production.     

Selective production of two diastereomers of disaccharide sugar alcohol, mannosylerythritol by Pseudozyma yeasts

Mannosylerythritol (ME) is the hydrophilic backbone of mannosylerythritol lipids as the most promising biosurfactants produced by different Pseudozyma yeasts, and has been receiving attention as a new sugar alcohol. Different Pseudozyma yeasts were examined for the sugar alcohol production using glucose as the sole carbon source. P. hubeiensis KM-59 highly produced a conventional type of ME, i.e., 4-O-β-d-mannopyranosyl-d-erythritol (4-ME). Interestingly, P. tsukubaensis KM-160 produced a diastereomer of 4-ME, i.e., 1-O-β-d-mannopyranosyl-d-erythritol (1-ME). In shake flask culture with 200 g/l of glucose, strain KM-59 produced 4-ME at a yield of 33.2 g/l (2.2 g/l/day of the productivity), while strain KM-160 produced 1-ME at 30.0 g/l (2.0 g/l/day). Moreover, the two strains were found to produce ME from glycerol; the maximum yields of 4-ME and 1-ME from 200 g/l of glycerol were 16.1 g/l (1.1 g/l/day) and 15.8 g/l (1.1 g/l/day), respectively. The production of 1-ME as the new diastereomer was further investigated in fed batch culture using a 5-l jar-fermenter. Compared to the flask culture, strain KM-160 gave three times higher productivity of 1-ME at 38.0 g/l (6.3 g/l/day) from glucose and at 31.1 g/l (3.5 g/l/day) from glycerol, respectively. This is the first report on the selective production of two diastereomers of ME, and should thus facilitate the functional development and application of the disaccharide sugar alcohol in the food and relative industries.     

Ultrasonic measurement of scleral cross-sectional strains during elevations of intraocular pressure: method validation and initial results in posterior porcine sclera

Background. Scleral biomechanical properties may be important in the pathogenesis and progression of glaucoma. The goal of this study is to develop and validate an ultrasound method for measuring cross-sectional distributive strains in the sclera during elevations of intraocular pressure (IOP). Method of Approach. Porcine globes (n?=?5) were tested within 24 hs postmortem. The posterior scleral shells were dissected and mounted onto a custom-built pressurization chamber. A high-frequency (55-MHz) ultrasound system (Vevo660, VisualSonics Inc., Toronto) was employed to acquire the radio frequency data during scans of the posterior pole along both circumferential and meridian directions. The IOP was gradually increased from 5 to 45?mmHg. The displacement fields were obtained from correlation-based ultrasound speckle tracking. A least-square strain estimator was used to calculate the strains in both axial and lateral directions. Experimental validation was performed by comparing tissue displacements calculated from ultrasound speckle tracking with those induced by an actuator. Theoretical analysis and simulation experiments were performed to optimize the ultrasound speckle tracking method and evaluate the accuracy and signal-to-noise ratio (SNR) in strain estimation. Results. Porcine sclera exhibited significantly larger axial strains (e.g., -5.1?±?1.5% at 45?mmHg, meridian direction) than lateral strains (e.g., 2.2?±?0.7% at 45?mmHg, meridian direction) during IOP elevations (P's?相似文献   

Centriolar Mechanisms of Differentiation and Replicative Aging of Higher Animal Cells

The centrosome (centriole) and the cytoskeleton produced by it are structures, which probably determine differentiation, morphogenesis, and switching on the mechanism of replicative aging in all somatic cells of multicellular animals. The mechanism of such programming of the events seems to include cytoskeleton influences and small RNAs related to the centrosome. 1) If these functions are really related with centrioles, the multicellular organism's cells which: a) initially lack centrioles (e.g., higher plant cells and also zygote and early blastomeres of some animals) or cytoskeleton (e.g., embryonic stem cells); or b) generate centrioles de novo (e.g., zygote and early blastomeres of some animals), will be totipotent and lack replicative aging. Consequently, the absence (constant or temporary) of the structure determining the counting of divisions also means the absence of counting of differentiation processes. 2) Although a particular damage to centrioles or cytoskeleton (e.g., in tumor cells) fails to make the cells totipotent (because the morphogenetic status of these cells, as differentiated from that of totipotent ones, is not zero), but such a transformation can suppress the initiation of the aging mechanism induced by these structures and, thus, make such cells replicatively "immortal".