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  • 1
    ISSN: 1432-041X
    Keywords: Key words Drosophila ; Genital disc ; engrailed ; Compartment ; Homeotic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The genital disc of Drosophila, which gives rise to the genitalia and analia of adult flies, is formed by cells from different embryonic segments. To study the organization of this disc, the expressions of segment polarity and homeotic genes were investigated. The organization of the embryonic genital primordium and the requirement of the engrailed and invected genes in the adult terminalia were also analysed. The results show that the three primordia, the female and male genitalia plus the analia, are composed of an anterior and a posterior compartment. In some aspects, each of the three primordia resemble other discs: the expression of genes such as wingless and decapentaplegic in each anterior compartment is similar to that seen in leg discs, and the absence of engrailed and invected cause duplications of anterior regions, as occurs in wing discs. The absence of lineage restrictions in some regions of the terminalia and the expression of segment polarity genes in the embryonic genital disc suggest that this model of compartmental organization evolves, at least in part, as the disc grows. The expression of homeotic genes suggests a parasegmental organization of the genital disc, although these genes may also change their expression patterns during larval development.
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  • 2
    ISSN: 1432-072X
    Keywords: Yeasts ; Cell wall ; Mannoproteins ; Aculeacin A ; Glucan ; Protoplasts ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inhibition of the synthesis of alkali-insoluble glucan by aculeacin A in Saccharomyces cerevisiae cells caused a decrease in the incorporation of a high molecular weight heterogeneous mannoprotein material and of a 33000 mannoprotein into the wall network. This was concomitant with the excretion of the latter molecule into the growth medium. Regenerating yeast protoplasts liberated considerable amounts of the heterogeneous material to the medium independently of the presence of aculeacin. The protoplast walls did lack this component and contained only minor amounts of the 33000 molecule, which was also completely absent from walls of aculeacin-treated protoplasts. Considerable levels of the 33000 species were immunodetected in the supernatants from treated and untreated protoplasts. These results point to the existence of specific interactions between the glucan network of the yeast cell surface and some of the wall mannoproteins. On the other hand, the presence of a population of SDS-solubilizable mannoproteins in the wall was independent of glucan levels.
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  • 3
    ISSN: 1432-072X
    Keywords: Saccharomyces cerevisiae ; Mannoproteins ; Glucan ; Cell wall ; Population growth cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mannoproteins from cell walls of Saccharomyces cerevisiae synthesized at successive stages of the population growth cycle have been solubilized with Zymolyase and subsequently analyzed. The major change along the population cycle concerned a large size mannoprotein material; the size of the newly-synthesized molecules varied from 120,000–500,000 (mean of about 200,000) at early exponential phase to 250,000–350,000 (mean of about 300,000) at late exponential phase. These differences are due to modifications in the amount of N-glycosidically linked mannose residues, since the size of the peptide moiety was 90,000–100,000 at all growth stages and the level of O-glycosylation changed only slightly. After, incubation of the purified walls with concanavalin A-ferritin and subsequent analysis by electron microscopy, labelling was localized at the external and internal faces of the walls. The middle space of these was labelled after digestion of the glucan network with Zymolyase, which demonstrate the presence of mannoproteins in close contact with the structural glucan molecules throughout the wall.
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  • 4
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Poor mechanical properties of biological tissue are known to cause wear, leading to the failure of cardiac bioprostheses made of calf pericardium. Different chemical agents such as sodium dodecyl sulfate (SDS) are presently being tested as possible inhibitors of the calcification process. The objective of this report was to determine the mechanical behavior of calf pericardium treated with SDS for 24 h and the influence of the suture on the mechanical properties of the tissue. Forty-eight samples were tested: 24 subjected to a standard treatment with glutaraldehyde (12 sewn with 4/0 silk suture thread) and 24 incubated with SDS for 24 h (12 sewn with the same suture thread). Each sutured and nonsutured sample was cut into two strips to yield paired samples. All were subjected to tensile stress to breaking point. The mean stress at breaking point in the nonsutured series treated with glutaraldehyde alone was 16.42 and 13.85 MPa, depending on the region of the pericardium, while in the sutured samples subjected to glutaraldehyde the mean stress was 7.50 and 7.63 MPa, respectively, differences which were statistically significant (p=0.03 and p=0.003, respectively) when the means for nonsutured samples from equivalent regions treated with glutaraldehyde were compared. The stress at breaking point was lower in the SDS-treated series, ranging between 2.60 and 3.56 MPa. The mathematical functions that govern the stress/strain or deformation were obtained. In the series of pericardium treated with SDS, deformations of 10% were produced with stresses of under 0.4 MPa, an outcome that is intolerable from the constructive point of view. We established a regression model that enabled us to determine the mechanical behavior of a sutured sample by testing a contiguous piece of tissue, with a high correlation coefficient (r 〉 0.99). We consider this finding to be of interest in the selection of pericardium for use in the construction of leaflets for cardiac bioprostheses. ©2000 Kluwer Academic Publishers
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  • 5
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The biological heart prostheses present midterm and long term problems owing to the progressive deterioration and calcification of the tissue. In the attempt to study the latter problem, we have compared the effectiveness of anticalcification treatments in calf pericardium samples implanted into female Wistar rats after undergoing the following procedures: Group I, control, treatment with glutaraldehyde; group II, treated with 0.1m Al3+ for 24 h; and group III, subjected to lipid removal by chemical treatment with chloroform/methanol for 1 h. Positive results were obtained with both treatments, but the results after 60 days of implantation were more favourable with lipid removal than with Al3+ treatment.
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  • 6
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The objective of the study was to determine the shearing stress exerted by the suture thread under conditions of normal working stress. Thirty-six samples of calf pericardium, similar to that employed in the manufacture of bioprosthetic cardiac valve leaflets, were subjected to tensile testing. Prior to the trial, a continuous suture was sewn in the central zone of each sample, at a 45° angle to the longest axis of the sample, using commercially-available threads (silk, Gore-Tex, Surgilene and nylon). Application of the Mohr circle for combined wear revealed that the shearing stress ranged between 2.68-fold greater (for samples sewn with silk) and 5.48-fold greater (for samples sewn with nylon) than the working tensile stress in the region of the suture. It is concluded that the shearing stress is responsible for the limited durability of sutured samples of calf pericardium prepared to simulate bioprosthetic cardiac valve leaflets. © 1998 Chapman & Hall
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  • 7
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Poor mechanical properties of biological tissue are known to cause wear, leading to the failure of cardiac bioprostheses made of calf pericardium. Different chemical agents such as sodium dodecyl sulfate (SDS) are presently being tested as possible inhibitors of the calcification process. The objective of this report was to determine the mechanical behavior of calf pericardium treated with SDS for 24 h and the influence of the suture on the mechanical properties of the tissue. Forty-eight samples were tested: 24 subjected to a standard treatment with glutaraldehyde (12 sewn with 4/0 silk suture thread) and 24 incubated with SDS for 24 h (12 sewn with the same suture thread). Each sutured and non-sutured sample was cut into two strips to yield paired samples. All were subjected to tensile stress to breaking point. The mean stress at breaking point in the non-sutured series treated with glutaraldehyde alone was 16.42 and 13.85 MPa depending on the region of the pericardium, while in the sutured samples subjected to glutaraldehyde the mean stress was 7.50 and 7.63 MPa, respectively, differences which were statistically significant (p = 0.03 and p = 0.003, respectively) when the means for non-sutured samples from equivalent regions treated with glutaraldehyde were compared. The stress at breaking point was lower in the SDS-treated series, ranging between 2.60 and 3.56 MPa. The mathematical functions that govern the stress/strain or deformation were obtained. In the series of pericardium treated with SDS, deformations of 10% were produced with stresses of under 0.4 MPa, an outcome that is intolerable from the constructive point of view. We established a regression model that enabled us to determine the mechanical behavior of a sutured sample by testing a contiguous piece of tissue, with a high correlation coefficient (r 〉 0.99). We consider this finding to be of interest in the selection of pericardium for use in the construction of leaflets for cardiac bioprostheses.
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  • 8
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Comparisons were made of the tissue response to the implantation of two different polytetrafluoroethylene prostheses: Soft Tissue Patch (STP) and Mycro Mesh (MM). A 7 × 5 cm prosthesis of STP (n=12) or MM (n=12) was implanted into a defect of the same size (involving all layers except skin) created in the anterior abdominal wall in 24 New Zealand rabbits. The prostheses were anchored to the recipient tissue, in direct contact with the intestinal loops and connective tissue. After 14, 30, 60 and 90 days, groups of six implants were studied macroscopically and samples were taken to be processed by light microscopy, scanning electron microscopy (SEM), immunohistochemical studies and tensiometry. All animals were valid for the study. In three cases STP implants presented very loose adhesions in the peripheral zones corresponding to the sutures. They were also observed on three MM implants, in the area of the perforations. Light and scanning microscopy revealed the formation of a capsule of scar tissue surrounding both types of prosthesis. At day 90, bridges of connective tissue had formed in the perforated areas of MM. Good vascularization was established in the areas of recipient tissue corresponding to both implants. The macrophage reaction to both biomaterials was maximal at 14 days, after which it progressively decreased until day 90. Tensile testing revealed no significant differences between the two biomaterials. It is concluded that (a) behaviour in the peritoneal interface is similar in the two prostheses, (b) both biomaterials become encapsulated rather than integrated into the recipient tissue, (c) the foreign body reaction does not determine the success or failure of the implants, (d) The perforations of the MM prosthesis do not increase its resistance to stress, or at least not after 90 days of implantation into rabbit abdominal wall.
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  • 9
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: The use of biomaterials for reconstruction of the ossicular chain in middle ear involves a different approach from that associated with other regions of the organism. The features of the implantation site and the composition of the prosthesis are responsible for functional failures that result from deterioration or extrusion of the implant. Since the fifties, different types of materials, both biological and synthetic, have been employed in the attempt to achieve the ideal middle ear prosthesis. We present a reprospective study of 166 patients who underwent ossicular chain reconstruction involving autografts and homografts of cartilage or auditory ossicle (n=104) or synthetic prostheses (n=62). We compare prostheses of different compositions on the basis of the cases of extrusion and the histological deterioration encountered with each. In our experience, polymers are associated with frequent extrusion and deterioration of the biomaterial, while the results are better with biological implants and those made of hydroxyapatite.
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  • 10
    ISSN: 1573-5052
    Keywords: Air temperature ; Edaphic moisture ; Fagus sylvatica ; Forest micrometeorology ; Meteorological station ; P.A.R. ; Photoperiodicity ; Quercus pyrenaica ; Relative humidity ; Tree foliation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We compared the flowering and fruiting phenology of Symphytum tuberosum L. (Boraginaceae), Hyacinthoides non-scripta (L.) Chouard (Liliaceae) and Melittis melissophyllum L. (Labiatae) in a beech wood and an oak wood situated in the same valley, taking into account their different microclimatic and edaphic characteristics and carrying out correlation and simple regression analyses. Differences observed in the phenological cycles of the species studied included earlier flowering and longer cycles in the oak wood, except for H. non-scripta. The most important climatic factors were soil moisture and the relative humidity, followed by temperature and the number of daylight hours and photosynthetically active radiation (P.A.R.). The M. melissophyllum cycle depended mainly on water availability, H. non-scripta on solar radiation, soil moisture and a temperature threshold value, while no specific climatic parameter was found to affect S. tuberosum. Temperature was found to be less important than previously believed as it seems only to correlate with S. tuberosum flowering. The strong correlation observed in the fruiting of the three species indicated clear synchronization.
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