Modifications des propriétés cytophotométriques des ADN et des histones nucléaires au cours de la sénescence des tritons (Triturus vulgaris et Triturus cristatus)

DNA and histones were studied by cytophotometry, in cartilaginous cells from urodele amphibians (Triturus vulgaris and Triturus cristatus) during ageing. With the Feulgen reaction, the DNA colorability decreased and their acid hydrolysis was more difficult. The coloration of the histones linked to DNA in chromatin was also changed. The results are discussed in relation to numerous works on deoxyribonucleoprotein modifications during cell ageing.ADN et histones ont été étudiés par cytophotométrie dans les cellules cartilagineuses d'Amphibiens Urodèles (Triturus vulgaris et Triturus cristatus) au cours du viellissement. Nous avons observé une baisse des affinités tinctoriales des ADN et une augmentation de leur résistance á l'hydrolyse acide pratiquée dans le cadre de la réaction de Feulgen. La colorabilité des histones associées aux ADN dans la chromatine est aussi modifiée. Tous ces résultats sont discutés en liaison avec les nombreux travaux effectués sur les modifications des désoxyribonucléoprotéines au cours du viellissement cellulaire.     

Adénylate-cyclase/Lipase: Induction des récepteurs hormonaux

An adenylate cyclase activity (AC) was found in guinea pig brown adipose tissue (BAT), since the tissue's apparition. This enzymatic activity increased during the development and showed high values at the end of gestation. An increase of AC units per cell was observed, in addition to the cell multiplication. A norepinephrine stimulation of AC activity was observed at the end of gestation: this regulating action disappeared in the first days of extrauterine life. Neither glucagon nor ACTH had any regulating role upon AC activity during fetal and newborn life. The basal lipolytic activity which was observed in BAT of fetuses (61rst day) and neonate dramatically decreased around the 15th day. A potent lipolysis activation by norepinephrine was observed, but only after birth. The correlation observed between these enzymatic activities in presence of norepinephrine seems to indicate that the AC/lipase system was involved in the neonatal thermogenesis of guinea pigs.     

Influence des caractéristiques des glumelles sur la résistance variétale du riz aux insectes des stocks

Des relations sont recherchées entre les caractéristiques des grains de 58 variétés de riz paddy et leur sensibilité aux quatre principaux ravageurs primaires des stocks: Sitophilus oryzae, Sitophilus zeamais, Rhyzoperta dominica et Sitotroga cerealella. L'étude confirme la prépondérance de l'herméticité des glumelles comme facteur de résistance, et établit que les cassures mécaniques des enveloppes sont des voies de pénétration plus régulières que le défaut de coaptation entre lemma et palea. L'égrenage se révèle être un facteur de sensibilité à S. cerealella aussi déterminant que le défaut de fermeture des glumelles, car lié d'une part à la dureté du pédoncule par lequel les larves de cet insecte peuvent pénétrer, d'autre part au taux de casse des enveloppes provoqué par le battage plus ou moins intense qu'il nécéssite. S'agissant de riz non décortiqué, les caractéristiques des enveloppes expliquent pour une très large part la variabilité de la résistance aux insectes étudiés, dont le développement n'est que faiblement influencé par les caractéristiques propres du grain, tels le format ou la teneur en eau.     

Étude du mécanisme d'établissement des liaisons glutaraldéhyde-protéines

Commercial aqueous 25 per cent glutaraldehyde solutions contain no stable derivative of this aldehyde, but compounds of variable molecular weight which easily revert to glutaraldehyde. The effect of pH on the reaction of glutaraldehyde with amino acids and on the stability of the products under acid conditions, shows the importance of the structure modification of the dialdehyde which occurs when pH increases, and even leads to precipitation in highly alkaline solutions. This precipitate results from aldol condensation of glutaraldehyde molecules. It contains aldehyd groups conjugated with ethylenic double bonds. Such a structure reacts with amino groups to give an imino bond, stabilized by resonance with the ethylenic bond, and does not undergo Michael-type addition reactions.Therefore, glutaraldehyde does not react with proteins under its free form, but as an unsaturated polymer, which gives imino bonds stabilized by conjugation.     

Étude expérimentale de l'auto-association des molécules modèles dipeptidiques. II. Association stéréosélective des molécules énantiomères

Modes of aggregation fo alanine-, norvaline- and valine-contaiing dpepetides with the general formula R₁? C₁O₁? N₂H₂? CHR₂? C₂O₂? N₃H₃? R₃ have been studied in CCl₄ solution by using infrared and nuclear magnetic resonance spectroscopies. Solutions of the pure L isomer and of the racemic mixture do not give identical data. At a given concentration, the racemic mixtrue is more aggregated than the pure enantiomer, and the difference, negligible in the case of alanine derivative, increases wiht the bulkiness of the side cahin R₂. The results show that a selective interaction takes place between enantiomeric molecules, resulting ina dimer associating tow inverse configurated C₅ conformers. The stabilizaion of this dimer proceeds from two symmetrical and intermolecular H₃ … O₁ hydrogen bondings.     

Analyse des pedigrees et calcul des coefficients d'identité par les arbres géniques

Two genes in a pedigree are identical by descent if they are two copies of a common ancestor gene. To obtain an unambiguous definition of the set of genes, at some autosomal locus, any gene is defined as an ordered pair of zygotes: the zygote who carries the gene, and the parent who transmitted it. The natural ordered structure on the set of zygotes yields an ordered structure upon the set of genes. Any event of the mendelian segregation splits down the set of genes into non-overlaping classes of identical genes: when considered as an ordered sub-set of genes, each class is shown to have the algebraic properties of a tree. Given a sub-set ?? of genes, a family of exclusive events ensuring identity between all genes of ?? is identified as a family of genic trees with some property. This relationship between segregational events and genic trees is extended to the case where two sub-sets ?? and ??′ of genes are considered together. As a consequence, a general method is obtained to compute either identity coefficients involving any number of genes splitted into one or two identity classes, or the fifteen coefficients defined among four genes, whichever the relationships between zygotes and genes might be. Using this approach to deal with the allelic structure in a set of genes carried by related zygotes is suggested.     

Polymorphisme et caractère glycoprotéique des lectines de Ricinus communis purifiées par chromatographie d'affinité

Two lectin fractions (S^o_{20 w} = 6,8 and 4,9 S) were purified from Ricinus communis seeds. The purification was carried out in four steps : ammonium sulfate fractionation, affinity chromatography on Sepharose 4 B, gel filtration on Sephadex G 150 and chromatography on CM cellulose. The purified lectins were glycoproteins whose chemical composition was determined. Amino terminal analysis of the two fractions revealed glycine and serine. Polyacrylamide gel electrophoresis of the higher molecular weight fraction allowed the separation of several components with different affinity for PAS staining.     

Différenciation des mécanismes induisant la segmentation et l'asymétrie des chromatides, après traitement par le 5-bromodéoxyuridine

5-Bromodeoxyuridine (BUdR)-induced segmentation and BUdR-induced asymmetry of the chromatids probably reflect a two-stage mechanism. The first stage consists of a BUdR substitution of the thymidine in the DNA during S period. The second stage, less obviously demonstrated, involves either alteration of chromosomal proteins or an imperfect association between substituted DNA and normal or abnormal proteins. This second stage takes place at different times, according to the type of chromatid modification: during S or G 2 period in the case of segmentation, and during G 1 in the case of asymmetry. One important implication of our experimental results is that the appearance of metaphasic chromatids is at least partly determined by the time of the G 1 period.L'induction d'une asymétrie, ou d'une segmentation des chromatides par un traitement au BUdR, résulte probablement d'un mécanisme à deux étapes distinctes. La première consiste en une substitution de la thymidine par le BUdR survenant lors de la replication de l'ADN. La seconde, plus difficile à mettre en évidence, consiste en une modification des protéines chromosomiques, ou en une mauvaise association entre les protéines, modifiées ou non, et l'ADN ayant incorporé le BUdR. Cette seconde étape est nécessairement différente selon la modification chromatidienne induite: elle se déroule en phase S ou G 2, en cas de segmentation, et en phase G 1 surtout, en cas d'asymétrie. Dans l'un et l'autre cas, la modification de l'association ADN-protéines pourrait être en rapport avec la régulation chromosomique. Une déduction importante de nos résultats expérimentaux est que l'aspect des deux chromatides métaphasiques dépend, au moins en partie, de la constitution de l'ADN dès la phase G 1.