Theoretical study of the optimal shape of the front profile of the lens in the eye of the scallop,Pecten

The optimal shape of the front profile of the thick lens in the eye of the scallop,Pecten is theoretically, geometric optically investigated as a function of the refractive index of the lens and the retina, as well as of the geometrical parameters of the eye. The shape of the theoretical front surfaces is compared with that of the real, experimentally determined front face of the lens. The degree of correction of the lens for spherical aberration of the reflecting spherical mirror in thePecten eye is examined. The optimal shape of the front profile of the lens depends strongly on a set of parameters, such that a certain fine tuning is required among them to assure a full correction for spherical aberration. The extreme variability of the eye parameters and the shape of the front face of the lens in the scallop is inconsistent with this fine tuning requirement. The degree of correction of thePecten lens for spherical aberration might not be as good as it could be, a possible biooptical reason for which is discussed.     

Characterization of the channel constriction allowing the access of the substrate to the active site of yeast oxidosqualene cyclase

In oxidosqualene cyclases (OSCs), an enzyme which has been extensively studied as a target for hypocholesterolemic or antifungal drugs, a lipophilic channel connects the surface of the protein with the active site cavity. Active site and channel are separated by a narrow constriction operating as a mobile gate for the substrate passage. In Saccharomyces cerevisiae OSC, two aminoacidic residues of the channel/constriction apparatus, Ala525 and Glu526, were previously showed as critical for maintaining the enzyme functionality. In this work sixteen novel mutants, each bearing a substitution at or around the channel constrictions, were tested for their enzymatic activity. Modelling studies showed that the most functionality-lowering substitutions deeply alter the H-bond network involving the channel/constriction apparatus. A rotation of Tyr239 is proposed as part of the mechanism permitting the access of the substrate to the active site. The inhibition of OSC by squalene was used as a tool for understanding whether the residues under study are involved in a pre-catalytic selection and docking of the substrate oxidosqualene.     

The dependance of the absorbance of the final chromophore formed in the Feulgen-Schiff reaction on the pH of the medium

Summary Polyacrylamide model films containing DNP were investigated for the influence of buffer rinses of various pH values and for various periods of treatment after Feulgen-Schiff staining.A citric acid/phosphate buffer of pH 5.6 as the final medium before the dehydration and embedding procedures is recommended to obtain a defined end product with a high molecular absorbance and good stability with time.     

Self-organization in the determination of the size of the axial structures in the embryogenesis of the clawed toad

Experiments were performed using X. laevis embryos during gastrulation and neurulation (stages 10, 11 1/2, 12 1/2, 13 1/2, 15 and 18). Part of presumptive epidermis and lateral plate mesoderm was removed, and embryos raised until stage 25. The size of axial structures (notochord, somite mesoderm, central nervous system) was determined using serial histological sections and compared with that of control embryos. In experimental embryos, the size of axial structures was decreased. Until a specific stage of development, close correlation was found between the volume of embryonic compartment corresponding to a particular, structure and the volume of presumptive epidermis and lateral plate mesoderm. This stage is individual for each axial organ: middle gastrula (stage 11 1/2) for notochord, late gastrula (stage 12 1/2) for somite mesoderm, and late neurula (stage 18) for central nervous system. This data suggest that differentiation pattern of ecto-mesodermal rudiment is subject to regulation during gastrulation-neurulation, and subdivision of ectoderm and mesoderm into axial and non-axial tissues is a self-organizing process.     

On the origin of the functional architecture of the cortex

The basic structure of receptive fields and functional maps in primary visual cortex is established without exposure to normal sensory experience and before the onset of the critical period. How the brain wires these circuits in the early stages of development remains unknown. Possible explanations include activity-dependent mechanisms driven by spontaneous activity in the retina and thalamus, and molecular guidance orchestrating thalamo-cortical connections on a fine spatial scale. Here I propose an alternative hypothesis: the blueprint for receptive fields, feature maps, and their inter-relationships may reside in the layout of the retinal ganglion cell mosaics along with a simple statistical connectivity scheme dictating the wiring between thalamus and cortex. The model is shown to account for a number of experimental findings, including the relationship between retinotopy, orientation maps, spatial frequency maps and cytochrome oxidase patches. The theory's simplicity, explanatory and predictive power makes it a serious candidate for the origin of the functional architecture of primary visual cortex.     

On the origin of the Hirudinea and the demise of the Oligochaeta

The phylogenetic relationships of the Clitellata were investigated with a data set of published and new complete 18S rRNA gene sequences of 51 species representing 41 families. Sequences were aligned on the basis of a secondary structure model and analysed with maximum parsimony and maximum likelihood. In contrast to the latter method, parsimony did not recover the monophyly of Clitellata. However, a close scrutiny of the data suggested a spurious attraction between some polychaetes and clitellates. As a rule, molecular trees are closely aligned with morphology-based phylogenies. Acanthobdellida and Euhirudinea were reconciled in their traditional Hirudinea clade and were included in the Oligochaeta with the Branchiobdellida via the Lumbriculidae as a possible link between the two assemblages. While the 18S gene yielded a meaningful historical signal for determining relationships within clitellates, the exact position of Hirudinea and Branchiobdellida within oligochaetes remained unresolved. The lack of phylogenetic signal is interpreted as evidence for a rapid radiation of these taxa. The placement of Clitellata within the Polychaeta remained unresolved. The biological reality of polytomies within annelids is suggested and supports the hypothesis of an extremely ancient radiation of polychaetes and emergence of clitellates.     

Study of the deglycosylation of various antibiotics of the vancomycin group

Conditions for deglycosylation of a number of antibiotics belonging to the vancomycin group were studied. A two-stage process including methanolysis followed by acidolysis in a mixture of trifluoracetic acid and HC1 in the presence of nucleophile was shown optimal for formation of a biologically active aglycone of ristomycin A while for formation of the vancomycin aglycone a one-stage process (trifluoracetic acid/HC1--acidolysis) was optimal. A scheme for isolation and purification of the aglycones of ristomycin A and vancomycin is presented.     

Reversal of the effect of the allosteric ligands of dCMP-aminohydrolase and stabilization of the enzyme in the T form

The 5-mercury derivative of dCMP is a substrate of deoxycytidylate aminohydrolase in the presence of mercaptoethanol. With this substrate a reversal of the effect of the allosteric ligands of the enzyme is observed. dCTP, which is an allosteric activator for aminohydrolysis of dCMP, becomes an inhibitor for the mercury substrate, whilst dTTP, an allosteric inhibitor for dCMP, becomes an activator for the mercury substrate.This observation has been interpreted by assuming that dCMP-Hg-S-CH₂-CH₂-OH is a substrate of the T form of the enzyme. By reacting dCMP-aminohydrolase in the T form (in the presence of dTTP) with glutaraldehyde, an enzyme has been isolated that is no longer active with dCMP, while it is fully active with the mercurated analog. Gel electrophoresis demonstrated that glutaraldehyde does not produce intermolecular crosslinks, but fixes 95% of the enzyme in a stable hexameric form by intramolecular crosslinks. The data are explained by assuming that glutaraldehyde stabilizes the enzyme in the T conformation.     

Frequency of the stages in the cycle of the seminiferous epithelium in the rat

This study determined the optimum number of tubules to be counted per testis cross section, and the number of animals per treatment group, when changes in stage frequencies in the cycle of the seminiferous epithelium are criteria for assessing effects of treatment on spermatogenesis. A data base of 9,672 observed and staged tubules was collected from testicular cross sections of 15 Sprague-Dawley rats. A significant variation between animals was found for the frequencies of Stages I, II, IV, VI, VIII, and XIII. Computer simulation was used to randomly select different combinations of animal and tubule numbers from the observed data. Stage frequency means from each simulation experiment were compared statistically to observed mean frequencies. A model that used data from all 14 stages was analyzed. The following conclusions were made: a) a minimum of 200 tubule cross sections/testis is recommended for estimating stage frequencies; b) for a fixed number of tubules scored, the number of animals sampled is more important than the number of tubules per animal in reducing variance; c) to detect a difference of 2 standard deviations from the mean with a 2% error rate and examining 200 tubules/testis, at least 12 animals must be used per group when assessing all 14 stages; d) when individual stages are examined using 10 animals per group, only Stage VII has 80% or greater power of test (alpha = 0.05) to detect a frequency difference; e) pooling stages into 3-4 groups is recommended to improve the power of detecting a treatment difference.     

Estimation of the Power of the Kruskal-Wallis Test

Power calculations of a statistical test require that the underlying population distribution(s) be completely specified. Statisticians, in practice, may not have complete knowledge of the entire nature of the underlying distribution(s) and are at a loss for calculating the exact power of the test. In such cases, an estimate of the power would provide a suitable substitute. In this paper, we are interested in estimating the power of the Kruskal-Wallis one-way analysis of variance by ranks test for a location shift. We investigated an extension of a data-based power estimation method presented by Collings and Hamilton (1988), which requires no prior knowledge of the underlying population distributions other than necessary to perform the Kruskal-Wallis test for a location shift. This method utilizes bootstrapping techniques to produce a power estimate based on the empirical cumulative distribution functions of the sample data. We performed a simulation study of the extended power estimator under the conditions of k = 3 and k = 5 samples of equal sizes m = 10 and m = 20, with four underlying continuous distributions that possessed various location configurations. Our simulation study demonstates that the Extended Average × & Y power estimation method is a reliable estimator of the power of the Kruskal-Wallis test for k = 3 samples, and a more conservative to a mild overestimator of the true power for k = 5 samples.     

The Root of the Tree of Life in the Light of the Covarion Model

A few duplicated genes have been found useful to root the universal tree of life. Despite controversial results, the consensus led to locate the root in the eubacterial branch. However, we demonstrated (Philippe and Forterre 1999) that all these markers were in fact unsuitable for any firm conclusion, mainly because of their high level of mutational saturation, which masks a major part of the phylogenetic signal. But then, the very persistence of signal for events as early as the separation of the three domains becomes puzzling. This paradox was studied here for translation elongation factor proteins, EF-1α and EF-2, which appeared to be one of the least confusing markers. We showed that these proteins do not conform to a classical rate-across-sites pattern, as those modeled by a gamma law, but rather to a covarion-based model, because the evolutionary rate of a given position often changes between taxonomic groups. Conservation of the very ancient signal can thus be better explained by the covarion model: a substitution can occur in deep branches, and the position remains constant afterward, as ``fossilized' by a change of covation. As no reconstruction method has up to now taken into account this complex model, we devised a simple method for extracting the phylogenetic signal, by considering the variability of sequence positions within predefined phylogenetic groups. We showed that noise quantitatively prevailed upon signal. Parsimony will produce erroneous topologies, because it has to minimize primarily the number of steps of the noise. In contrast, our method effectively concentrated the signal and was more suitable for inferring ancient events. We consequently found the eubacterial rooting to be presumably due to a long branch attraction artifact, because of the higher evolutionary rate of Eubacteria for these proteins. Among the two other rooting possibilities, the eukaryotic rooting appeared to be more supported, although not enough to be conclusive.     

Optimization criteria of the mechanism governing the stability of the membrane potential

For small changes in ion concentration within the physiological range the membrane potential transients can be explained in terms of two linear models both for passive and active transport. Using frog sartorius muscle as a suitable model system the ion pump is considered to work within the steepest range of the flux-concentration characteristic. Further for the small perturbations the equations describing passive ion transport can be safely linearized. The conclusion appears inescapable that for the muscle membrane the intracellular ion concentration adjusts itself in some optimal manner to the level of the extracellular ions. The active ion transport represents a control parameter for the membrane potential. The model structure corresponds to a dynamic system, the control processes of which are optimized with respect to a quadratic integral-criterion function. Here, both the performance index of the control sequence in the membrane processes and the energy consumed by the ion fluxes have been considered for small perturbations of Na⁺, K⁺, and Cl^? in the neighbourhood of the physiological working point. As it is, the control system governing the active and passive ion transport processes is essentially optimized with respect to a minimal energy usage. The amount of energy consumed during the transients predicted by the model has been calculated.     

Measuring the Closeness of Relationships: A Comprehensive Evaluation of the 'Inclusion of the Other in the Self' Scale

Understanding the nature and influence of social relationships is of increasing interest to behavioral economists, and behavioral scientists more generally. In turn, this creates a need for tractable, and reliable, tools for measuring fundamental aspects of social relationships. We provide a comprehensive evaluation of the ''Inclusion of the Other in the Self'' (IOS) Scale, a handy pictorial tool for measuring the subjectively perceived closeness of a relationship. The tool is highly portable, very easy for subjects to understand and takes less than 1 minute to administer. Across our three online studies with a diverse adult population (n = 772) we show that six different scales designed to measure relationship closeness are all highly significantly positively correlated with the IOS Scale. We then conduct a Principal Component Analysis to construct an Index of Relationship Closeness and find that it correlates very strongly (ρ = 85) with the IOS Scale. We conclude that the IOS Scale is a psychologically meaningful and highly reliable measure of the subjective closeness of relationships.     

Determination of the structure of the MinD-ATP complex reveals the orientation of MinD on the membrane and the relative location of the binding sites for MinE and MinC

The three Min proteins spatially regulate Z ring positioning in Escherichia coli and are dynamically associated with the membrane. MinD binds to vesicles in the presence of ATP and can recruit MinC or MinE. Biochemical and genetic evidence indicate the binding sites for these two proteins on MinD overlap. Here we solved the structure of a hydrolytic-deficient mutant of MinD truncated for the C-terminal amphipathic helix involved in binding to the membrane. The structure solved in the presence of ATP is a dimer and reveals the face of MinD abutting the membrane. Using a combination of random and extensive site-directed mutagenesis additional residues important for MinE and MinC binding were identified. The location of these residues on the MinD structure confirms that the binding sites overlap and reveals that the binding sites are at the dimer interface and exposed to the cytosol. The location of the binding sites at the dimer interface offers a simple explanation for the ATP dependence of MinC and MinE binding to MinD.     

Some aspects of the fine structure of the statocysts of the molluscsPecten andPterotrachea

Summary The statocyst ofPecten is composed of hair cells and supporting cells. The hair cells bear kinocilia and microvilli at their distal ends and the supporting cells bear microvilli. The cilia have a 9+2 internal filament content, and arise from basal bodies that have roots, basal feet and microtubular connections. Two different ciliary arrangements are described, one with a small number of cilia arranged in a ring, and another with many more cilia arranged in rows. Below the hair cells are probable synapses. A ciliated duct connects to the lumen of the static sac and passes through the centre of the static nerve. The hair cells in the statocyst ofPterotrachea bear kinocilia and microvilli. The possible importance of cilia and microvilli in the transduction process is discussed.We would like to thank ProfessorJ. Z. Young for bringing specimens ofPterotrachea from Naples and also the staff of the Stazione Zoologica for the provision of specimens, Dr.M. Land for providing specimens ofPecten, the Science Research Council (U.K.) for providing the electron microscope used in much of the study and also for a grant to one of us (V.C.B.), and Mrs.J. Parkers and Mr.R. Moss and Mrs.J. Hamilton for much photographic and technical assistance.     

The dependence of the salt appetite of the rat on the hormonal consequences of sodium deficiency

Richter's discovery of the salt appetite that follows adrenalectomy (1936) raised the question: how does the brain appreciate the need for sodium so that it can mobilize the search for and ingestion of salty substances? It remains unanswered. Recent work suggests that the answer may come from an understanding of the behavioral effects of the hormones of sodium conservation. Fluharty and I have found (Behavioral Neuroscience, 1983) that treatment of salt replete rats with low doses of both angiotensin (Ang II) and a mineralocorticoid (DOCA) evokes a rapid, reliable, and specific appetite for sodium solutions, and we have proposed that the hormones of renal sodium conservation are also the hormones for the behavioral defense against sodium deficiency. We can now report: That the same combined endocrine treatment will compel rats that do not need salt to search for it in a runway. That is, sodium replete rats that have been primed for 3 days with DOCA (500 micrograms/day), which does not produce an appetite for salt, and are then given a pulse intracerebroventricular (ICV) injection of Ang II (60 ng), which by itself does not produce an appetite for salt, will run in an alleyway in order to ingest small drops of 3% NaCl. The hormones act together to make the rat avid for salt and their action is sufficient to drive it to seek salt at a distance and to ingest it at a concentration that untreated rats avoid.(ABSTRACT TRUNCATED AT 250 WORDS)     

三角梅属植物的生物学研究进展

三角梅属(Bougainvil lea)属于紫茉莉科(Nyctaginaceae), 有14个种。该文综述了三角梅属植物的生物学特性, 展望了该属植物在增进人类健康、丰富精神生活以及保护环境等方面的应用前景。三角梅属植物因其苞片的形态色彩以及植株形态的变化而具有独特的观赏价值。三角梅属植物不仅作为花卉备受关注, 近年来, 有关三角梅其它应用价值的研究使人们对其有了新的认识。从三角梅叶片中分离得到具有类胰岛素功能的松醇(D-pini tol )对替代胰岛素治疗糖尿病以及减轻胰岛素疗法带来的副作用具有重要意义。研究还表明, 三角梅叶片和根中至少含有2种抗病毒蛋白——BAPI和 Bouganin, 它们对于多种植物病毒具有不同程度的抑制作用。这些研究结果对于开发低毒高效的生物农药具有十分积极的意义。三角梅还是研究甜菜色素代谢的重要模式植物之一, 其甜菜色素的种类和含量之丰富为开发安全的天然食用色素开辟了广阔的前景。这些相关研究展示了三角梅作为资源植物的多元价值, 为进一步开发三角梅的观赏、医药、生物农药价值和作为天然食用色素以及发挥环境修复作用提供了充分的科学依据。     

Effect of zinc on the toxicity of the mycotoxin sporidesmin to the rat

The toxicity of sporidesmin to rats fed diets containing either 4 ppm or 200 ppm Zn was determined. The high zinc diet doubled the LD₅₀ level for sporidesmin given as a single dose, but the LD₅₀ dose for rats on a zinc deficient diet was not significantly different from that for rats on a diet containing zinc at levels sufficient for normal growth. Subsequent trials demonstrated that large doses of ZnSO₄ given orally protected rats from sporidesmin poisoning. The protection was short lived as zinc needed to be given at or soon after sporidesmin challenge.     

Representing the object of controversy: the case of the molecular clock

Through a case study of the controversies surrounding the molecular clock, this paper examines the role of visual representation in the dynamics of scientific controversies. Representations of the molecular clock themselves became objects of controversy and so were not a means for closure. Instead visual representations of the molecular clock became tools for the further articulation of an ongoing controversy.