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  • 1
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Les activités spécifiques totales de 5 hydrolases lysosomiques (phosphatase acide, N-acétyl-β-glucosaminidase,β-glucuronidase, aryl sulfatase et cathepsine) ontété dosées dans les intestins de larves de Discoglosse, avant et pendant leur métamorphose. Pour chacune des hydrolases, les activités présentent le même profil de variation, Elles s'accroissent significativement à la fin de la prométamorphose et au début du climax, cependant que lépithélium intestinal initial (ou primaire) dégénère. Les activités dosées décroissent à la fin du climax, au moment où un épithélium secondaire enzyme-négatif se met en place. L'activité spécifique libre de la phosphatase acide a été dosée dans ces mêmes intestins. Elle s'élève significativement à la fin de la prométamorphose et au début du climax, au moment de l'histolyse épithéliale. Cette composante libre croît plus vite que l'activité totale. Une augmentation parallèle est obtenue pour l'activité spécifique de la phosphatase acide liée (intralysosomique). L'élévation des activités enzymatiques totales peut impliquer une synthèse accélérée d'hydrolases lysosomiques par les épithéliocytes primaires, conditionnée par un accroissement simultané du taux plasmatique des hormones thyroïdiennes. L'activité libre de la phosphatase acide peut traduire aussi une perméabilité accrue ou une rupture de la paroi lysosomique, en présence de ces mêmes hormones.
    Notes: Summary The whole specific activities of 5 lysosomal enzymes (acid phosphatase, N-acetylβ-glucosaminidase,β-glucuronidase, cathepsin and aryl sulphatase) were measured in the guts of Discoglossus tadpoles, before and during metamorphosis. For each hydrolase, the activities show the same variation pattern. They significantly increase at the end of prometamorphosis and the beginning of the climax, while there is histolysis of the first (primary) epithelium of the gut. The measured activities decrease at the end of the climax, while a secondary, enzyme-negative epithelium is developing. The free specific activity of the acid phosphatase was measured in these same guts. It significantly increases at the end of prometamorphosis and the beginning of the climax, during the epithelial histolysis. The total activity increases more slowly than the free one. In the same way, an increase is obtained for the specific activity of the bound (intralysosomal) acid phosphatase. The changes in whole enzymatic activities may result from accelerated synthesis of lysosomal hydrolases due to the primary epitheliocytes, and induced by the simultaneous increase in the plasmatic level of the thyroid hormones. Furthermore the free activity of the acid phosphatase may produce an increased permeability or a breaking of the lysosomal membrane, by the same hormones.
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  • 2
    ISSN: 1040-452X
    Keywords: Differentiation ; Development ; RNA ; In situ ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The expression of the ras protooncogene was investigated in Xenopus laevis, throughout development, by in situ hybridization using a 35S-labelled antisense RNA probe. During oogenesis, the ras RNA was strongly expressed in the cytoplasm of previtellogenic oocytes and further diluted between yolk platelets; no specific localization of transcripts was observed. The signal density was particularly weak over embryo sections until the tailbud stage. On the other hand, a high level of ras RNA expression was detected on sections through the young tadpoles. An intense labelling was observed in several areas, including the branchial apparatus, gut, somites, nervous system, and lens. It is noteworthy that the heterogeneity of labelling increases as tadpoles grow older. Together, these results are discussed in relation to cellular events appearing throughout the early development.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Résumé Nous avons décrit l'ultrastructure de l'épithélium intestinal de la larve d'Alytes avant la régression de l'intestin. L'épithélium n'est pas villeux; il se compose principalement de cellules absorbantes dont la «bordure en brosse» diminue de hauteur au cours de l'ontogenèse. Le réticulum endoplasmique y est presqu'exclusivement de nature vésiculaire. Le cytoplasme supranucléaire contient de nombreuses mitochondries et, près du noyau, quelques cavités golgiennes; en outre, cette région renferme de nombreuses vacuoles autolytiques ainsi que de fréquents corps denses, lamellaires et myéliniques. Assez souvent, le cytoplasme infranucléaire ne contient que des vésicules du réticulum. Les cellules à sécrétion muqueuse sont plus rares; elles possèdent un appareil de Golgi bien développé dans la région supranucléaire. Près de la base de l'épithélium, on reconnaît les cellules souches; leur rapport nucléoplasmique est élevé et les ribosomes libres sont nombreux. Quelques cellules épithéliales dégénèrent: les mitochondries sont dilatéés et leur matrice devient claire, la «bordure en brosse» disparaît; d'autre part, des cellules arrondies renfermant de grands corps osmiophiles sont observées à divers niveaux de l'épithélium. La présence d'inclusions lytiques dans les cellules absorbantes, les altérations mitochondriales des cellules en dégénérescence, l'origine des cellules arrondies, en cours de lyse, ainsi que de leurs corps osmiophiles sont discutéés.
    Notes: Summary The fine structure of the intestinal epithelium of the larvalAlytes before the regressing changes of the intestine is described. The epithelium is not villous; it is mainly composed of absorbing cells the striated border of which decreases gradually in height during ontogenesis. Their endoplasmic reticulum is chiefly composed of vesicular components. The supranuclear cytoplasm contains numerous mitochondria and, near the nucleus, some Golgi complexes; moreover, this region abounds with autolytic vacuoles and dense, lamellar and myelin bodies. Not unfrequently, the infranuclear cytoplasm contains only vesicles of the reticulum. The mucous cells (goblet cells) are scanty; they own an important Golgi apparatus in the supranuclear region. The stem cells are located close to the basis of the epithelium; their nucleoplasmic ratio is high and free ribosomes are numerous. Some epithelial cells degenerate: the mitochondria are dilated and their matrix becomes clear, the striated border disappears. On the other hand, round cells containing large and osmiophilic bodies are observed at various levels of the epithelium. The presence of lytic inclusions in the absorbing cells, the mitochondrial alterations of degenerating cells, the origin of round and degenerating cells and of their osmiophilic bodies are discussed.
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  • 4
    ISSN: 1432-0878
    Keywords: X-rays ; Thyroxine ; Intestine ; Amphibian larvae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The conjoined effects of thyroxine and X-rays on the intestinal wall were studied using Alytes obstetricans tadpoles in premetamorphosis. Thyroxine alone induces degeneration of the larval epithelium (primary epithelium) and its replacement by a secondary epithelium. The latter is derived from stem cells via the development of islets. In animals submitted to irradiation only, many of these stem cells showed signs of necrosis. In irradiated larvae treated with thyroxine, the secondary epitheliocytes were rare and never formed islets. Radioautographic observations confirmed their very low proliferation rate. Contrary to what was observed in the hormone treated larvae, cell fragments of the primary epithelium were extruded in the connective tissue, and phagocytes appear to infiltrate the epithelium. In animals treated with thyroxine and later submitted to irradiation, islets of secondary epitheliocytes developed while some cells degenerated. There again, the phagocytes were noted in both the connective tissue and the epithelium.
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