Les tissus élaborateurs d'hormones stéroïdes chez les amphibiens urodèles

Résumé Les cellules du tissu glandulaire du testicule et de la glande interrénale de pleurodèle montrent les caractères généralement observés dans les cellules stéroïdogènes. Des différences existent entre les deux tissus. Le reticulum endoplasmique du tissu glandulaire est très développé et présent dans toutes les cellules qui sont d'aspect homogène. Au contraire, le tissu interrénal montre deux aspects cellulaires différents. Le premier se caractérise par un reticulum endoplasmique lisse relativement peu développé par rapport au tissu glandulaire, par des mitochondries petites et nombreuses, enfin par des liposomes denses et petits. Le deuxième aspect au contraire, se distingue par le petit nombre de mitochondries souvent géantes et à crêtes plus fréquemment organisées en faisceaux, par des liposomes nombreux de grandes dimensions et peu denses aux électrons.Le tissu glandulaire est très peu touché par l'hypophysectomie. Le reticulum persiste plusieurs mois comme d'ailleurs l'activité 5-3 -hydroxystéroïde deshydrogénase. Dans le tissu interrénal, la proportion des cellules d'aspects différents varie au profit des cellules à lipides abondants et à grandes mitochondries. L'activité 5-3 -hydroxystéroïde deshydrogénase est longtemps décelable.Le rôle du reticulum endoplasmique du tissu glandulaire est discuté en fonction des observations réalisées dans d'autres cellules stéroïdogènes à reticulum abondant. La signification des deux aspects cellulaires observés dans l'interrénale est discutée en relation avec les résultats expérimentaux obtenus en particulier chez le rat.Cette étude révèle que les critères d'activité d'une cellule stéroïdogène sont délicats à établir et doivent être différents d'un tissu à l'autre.

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Tissues secreting steroid hormones in urodele amphibians

Summary The fine structure of testis glandular tissue and interrenal gland cells of Pleurodeles shows the general features observed in other steroïdogenic cells. Certain differences exist between the two tissues. The agranular endoplasmic reticulum of the glandular tissue cells is well developed and present in all cells of similar appearance. On the contrary, the interrenal tissue cells show two different features. The first is characterised by a poorly developed smooth endoplasmic reticulum, compared with that of the glandular tissue, by small and numerous mitochondria, and finally by small electron dense lipid droplets. The second feature is the small number of mitochondria often giant and with fascicles of straight tubular cristae and numerous large lipid droplets of low electron density.The effect of hypophysectomy on the glandular tissue cells seem very slight. The endoplasmic reticulum and the 5-3 -hydroxysteroid dehydrogenase activity persists for several months. In the interrenal tissue, the proportions of the two different cellular features are modified. Cells rich in lipids and with large mitochondria are more abundant. It is possible to demonstrate a 5-3 -hydroxysteroid dehydrogenase activity for a long time after hypophysectomy. The functional significance of the agranular endoplasmic reticulum is discussed in relation to some other observations on different steroidogenic cells with a well developed agranular endoplasmic reticulum. The significance of the two cellular features observed in the interrenal gland is discussed in connection with experimental data obtained in the frog and the rat.This study shows that it is difficult to define criteria of cellular activity, which probably differ from one tissue to another.

Equipe de Recherche associée au C. N. R. S. Cytologie Ultrastructurale n 129.     

Bafoudiosbulbins F and G, further clerodane diterpenoids from Dioscorea bulbifera L. var sativa and revised structure of Bafoudiosbulbin B

From the bulbils of Dioscorea bulbifera L. var sativa, two clerodane diterpenoids, Bafoudiosbulbins F (1) and G (2), together with five known compounds: Bafoudiosbulbins A-C, 3,5,4'-trihydroxy-3'-methoxybibenzyl, and kaempferol were isolated. Their structures were established by spectroscopic techniques, including (1)H, (13)C NMR, NOESY, ROESY, COSY, TOCSY, HSQC, and HMBC. The relative stereochemistry of compounds 1 and 2 was assigned on the basis of X-ray crystallographic diffraction analysis. Furthermore, the structure of Bafoudiosbulbin B was revised using extensive 2D NMR techniques as well as chemical transformation.     

Measurement of Outflow Facility Using iPerfusion

Elevated intraocular pressure (IOP) is the predominant risk factor for glaucoma, and reducing IOP is the only successful strategy to prevent further glaucomatous vision loss. IOP is determined by the balance between the rates of aqueous humour secretion and outflow, and a pathological reduction in the hydraulic conductance of outflow, known as outflow facility, is responsible for IOP elevation in glaucoma. Mouse models are often used to investigate the mechanisms controlling outflow facility, but the diminutive size of the mouse eye makes measurement of outflow technically challenging. In this study, we present a new approach to measure and analyse outflow facility using iPerfusion^™, which incorporates an actuated pressure reservoir, thermal flow sensor, differential pressure measurement and an automated computerised interface. In enucleated eyes from C57BL/6J mice, the flow-pressure relationship is highly non-linear and is well represented by an empirical power law model that describes the pressure dependence of outflow facility. At zero pressure, the measured flow is indistinguishable from zero, confirming the absence of any significant pressure independent flow in enucleated eyes. Comparison with the commonly used 2-parameter linear outflow model reveals that inappropriate application of a linear fit to a non-linear flow-pressure relationship introduces considerable errors in the estimation of outflow facility and leads to the false impression of pressure-independent outflow. Data from a population of enucleated eyes from C57BL/6J mice show that outflow facility is best described by a lognormal distribution, with 6-fold variability between individuals, but with relatively tight correlation of facility between fellow eyes. iPerfusion represents a platform technology to accurately and robustly characterise the flow-pressure relationship in enucleated mouse eyes for the purpose of glaucoma research and with minor modifications, may be applied in vivo to mice, as well as to eyes from other species or different biofluidic systems.     

Aminopyrazine CB1 receptor inverse agonists

A series of 5,6-diaryl-2-amino-pyrazines were prepared and found to have antagonist-like properties at the CB1 receptor. Subsequent SAR studies optimized both receptor potency and drug-like properties including solubility and Cytochrome-P450 inhibition potential. Optimized compounds were demonstrated to be inverse agonists and compared in vivo with rimonabant for their ability to inhibit food intake, to occupy central CB1 receptors and to influence hormonal markers associated with obesity.     

Genome-wide analysis of heteroduplex DNA in mismatch repair-deficient yeast cells reveals novel properties of meiotic recombination pathways

Meiotic DNA double-strand breaks (DSBs) initiate crossover (CO) recombination, which is necessary for accurate chromosome segregation, but DSBs may also repair as non-crossovers (NCOs). Multiple recombination pathways with specific intermediates are expected to lead to COs and NCOs. We revisited the mechanisms of meiotic DSB repair and the regulation of CO formation, by conducting a genome-wide analysis of strand-transfer intermediates associated with recombination events. We performed this analysis in a SK1 × S288C Saccharomyces cerevisiae hybrid lacking the mismatch repair (MMR) protein Msh2, to allow efficient detection of heteroduplex DNAs (hDNAs). First, we observed that the anti-recombinogenic activity of MMR is responsible for a 20% drop in CO number, suggesting that in MMR-proficient cells some DSBs are repaired using the sister chromatid as a template when polymorphisms are present. Second, we observed that a large fraction of NCOs were associated with trans-hDNA tracts constrained to a single chromatid. This unexpected finding is compatible with dissolution of double Holliday junctions (dHJs) during repair, and it suggests the existence of a novel control point for CO formation at the level of the dHJ intermediate, in addition to the previously described control point before the dHJ formation step. Finally, we observed that COs are associated with complex hDNA patterns, confirming that the canonical double-strand break repair model is not sufficient to explain the formation of most COs. We propose that multiple factors contribute to the complexity of recombination intermediates. These factors include repair of nicks and double-stranded gaps, template switches between non-sister and sister chromatids, and HJ branch migration. Finally, the good correlation between the strand transfer properties observed in the absence of and in the presence of Msh2 suggests that the intermediates detected in the absence of Msh2 reflect normal intermediates.     

Extracellular enzyme activities during humic acid degradation by the white rot fungi Phanerochaete chrysosporium and Trametes versicolor

Abstract The relationship between humic acid biodegradation and extracellular lignin peroxidase and Mn-dependent peroxidase activities of two white rot fungi, Phanerochaete chrysosporium and Tranetes versicolor , reported to be lignin degraders, was examined. In experimental conditions promoting culture aeration, particularly with T. versicolor no extracellular peroxidase activity could be detected unless humic acids were included in the culture medium. In the presence of humic acids, appreciable enzymatic activities were determined in the culture filtrate of the two fungi. However, T. versicolor was a more effective degrader than P. chrysosporium , and mineralization assays on synthetic humic acids with culture filtrates showed the important role played by Mn²⁺. The surfactant properties of humic acids are suggested to be responsible for the increase of enzymatic activities.