Conservation and chromosomal localization of DNA satellites in balenopterid whales

DNA satellites were isolated from three balenopterid species, viz. the minke, sei, and fin whales. In each of them at least two DNA satellites were recognizable with buoyant densities in neutral CsCl of =1.702/1.703 and =1.710/1.711, respectively. cRNAs from each satellite group were used for filter and in situ hybridisations. Homo- and heterologous DNA-cRNA hybrids within each satellite group yielded virtually identical melting curve profiles showing conservation of at least a considerable part of the DNA satellite sequences. There was no evident sequence homology between the =1.702/1.703 and the =1.710/1.711 satellites by filter hybridisation. — The in situ hybridisation showed that in each species the =1.702/1.703 satellite was located in centromeric-paracentromeric C-bands in a few pairs, whereas the =1.710/1.711 satellite was located in terminal C-bands throughout the karyotypes. — The data on the whale DNA satellites indicate that the quantitative evolution of the satellite DNA sequences preceded species divergence of the balenopterids and that the satellite sequences have remained relatively unaltered since the divergence took place. The function of satellite DNA is considered to imply the introduction of both chromosomal and genic polymorphisms and thus being of great importance in speciation. Based upon these concepts a model is postulated for the function of satellite DNA. According to this model at meiotic pairing euchromatin-heterochromatin overlapping between homologous chromosomes is considered to be of a general occurrence. This overlapping is presumed to be accentuated by the size heteromorphism frequently observed between homologous heterochromatic segments (C-bands). In the region of such euchromatin-heterochromatin overlapping, crossing-over would be excluded. The overlapping is suggested to be rectified progressively in the chromosome arms, leaving unaffected crossing-over distant to the euchromatin-heterochromatin junctions. The consequence of this will be that genes in the proximity of the junctions are collectively inherited and selected, whereas genes distant to the heterochromatin will be independently assorted and selected.     

Phenotypic conversion of cultured mouse embryo cells by aza pyrimidine nucleosides.

Cells of the $\text{C3H}\text{10}\text{T}\text{1}\text{2}\text{CL8}$ line, which are nonmyoblastic in nature, form functional myotubes when treated with low concentrations of 5-azacytidine. Further characterization of the myotubes revealed that they arise from the fusion of mononucleated precursors and not as a result of endoreplication. They accumulate histochemically detectable myosin ATPase activity as well as acetylcholine receptors capable of binding radioactively labeled α-bungarotoxin. The deoxy analog, 5-aza-2′-deoxycytidine, induced myogenic conversion at one-tenth of the maximally effective concentration of 5-azacytidine. The ability of both analogs to induce myotube formation and to cause cytotoxicity was strongly influenced by cotreatment with certain pyrimidine nucleosides. These effects were consistent with a requirement for metabolism of both aza compounds to phosphorylated derivatives and with a mechanism of action based on their incorporation into DNA. Concentrations of the analogs causing myogenic conversion did not substantially alter rates of DNA, RNA, or protein synthesis as measured by precursor incorporation into intact cells. The induction of myotubes by 5-azacytidine in cells synchronized by two different methods required that treatment with the analog was carried out at a critical phase early in S phase. Thus the mechanism of drug action appears to be linked to specific DNA synthesis.     

Development of wheat bulb fly (Della coarctata fall.) larvae and pupae at different temperatures

When eggs of wheat bulb fly were added to young winter wheat plants in pots and kept at 5°, 8°, 10°, 12°, 15° and 20°, only 14%–44% of the eggs added produced larvae that succeeded in invading plants, but when newly hatched larvae were added directly 54%–92% were successful. At temperatures from 5° to 25°, the number of days required for larvae to complete their development in well-grown plants ranged from 11–14 days at 25° to 55–80 days at 5°. This corresponds to an accumulated temperature of approximately 286 day degrees C above the developmental threshold of 0.5°.The daily rate of development of larvae was marginally most rapid between 12° and 18°. When larvae were feeding in small, poorly growing plants, development was delayed and more shoots were needed before pupation than for healthy plants.The pupal stage which develops in the field from the end of April to June needs approximately 400 and 420 day degrees for completion in males and females (threshold 5°). Total day degrees required for the hatching of the egg to adult are about 700 (males) and 720 (females).Records of maximum and minimum temperatures from a meteorological screen 1 m above the ground can be used to calculate the number of day degrees accumulated from 1 May to 12 June, from which the dates of peak emergence of wheat bulb fly can be predicted. If 350 day degrees or more accumulate during this period, the peak emergence occurs near 20 June and with 200 or fewer day degrees it occurs near 11 July.The amount of damage to wheat by wheat bulb fly larvae in 1953, 1954, 1965 and 1966 depended largely on the number of eggs laid, the date of sowing, and also on the rate at which temperature accumulated in the autumn and winter; in all years, late sown crops would have had little opportunity to grow beyond the susceptible stage by the time they were attacked.

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Résumé Quand des jeunes plants de blé d'hiver en pots sont contaminés avec des oeufs de Delia coarctata et maintenus à des températures respectives de 5°, 8°, 10°, 12°, 15° et 20° C, seulement 14% à 44% de ces oeufs donnent des larves qui parviennent á attaquer les plants, alors que si on utilise directement des larves nouveau-nées on obtient 54 à 92% d'attaques réussies. Aux températures de 5° à 25° le temps nécessaire aux larves pour achever leur développement dans les plants bien développés avant de gagner le sol pour la pupaison, est de 11 à 14 jours à 25° contre 55 à 80 jours à 5°.Une courbe de la vitesse de développement établie à partir de la durée du stade larvaire de l'éclosion à la pupaison aux differentes températures montre que le développement est le plus rapide entre 12° et 18° et que le zéro de développement est aux alentours de 0,5°. Le nombre de degrésjours accumulés par la larve de l'éclosion à la pupaison est d'environ 286. Quand les larves se nourrissent aux dépens de plants petits à croissance faible, leur développement est retardé et exige plus de temps et plus de plantes avant la pupaison que lorsqu'elles se nourrissent sur des plants vigoureux.Le stade pupal qui intervient dans la nature de fin avril à juin, nécessite approximativement 400 à 420 degrés-jours pour le développement du mâle et de la femelle au-dessus d'une supposée température de base de 5°. Le nombre total de degrés-jours de l'oeuf à l'adulte est respectivement de 686 et 706 pour le mâle et la femelle.Les enregistrements des températures maxima et minima dans un abri météorologique à 1 m audessus du sol peuvent être utilisés pour établir le nombre de degrés-jours accumulés du 1 er'mai au 12 juin; à partir de ces données les pics d'émergence de D. coarctata peuvent être prédits. Si 350 degrésjours ou plus sont accumulés durant cette période, le pic d'émergence apparaît vers le 20 juin, mais si 200 degres-jours au moins sont notés le pic sera proche du 11 juillet.L'importance des dégâts occasionnés au bleî d'hiver en Angleterre par les larves de D. coarctata en 1953, 1954, 1965 et 1966 dépend largement du nombre d'oeufs pondus, de la date du semis et de la température accumulée en automne et en hiver; au cours de chacune de ces années les cultures à semis tardif auraient eu peu de possibilité de dépasser le stade sensible avant le moment où elles ont été attaquées.

     

Protein metabolism. 6. Trichostrongylus colubriformis: skeletal protein catabolism in primary and secondary infections of the guinea pig

The urinary excretion of 3-methylhistidine (3-MH) was used as an index of muscle protein catabolism in primary and secondary infections of the guinea pig with Trichostrongylus colubriformis and in uninfected animals fed quantitatively reduced rations. Catabolism, which was depressed in all three groups, was directly related to a fall in food consumption. Possible explanations for the greater depression of catabolism in the primary infection than in the uninfected guinea pigs and its fall in the secondary infection in spite of little change in consumption are briefly discussed. It was concluded that the faster rate of whole-body protein turnover reported earlier in this series on protein metabolism in intestinal nematode infection was not partly due to a faster rate of muscle protein catabolism. It was shown that the urinary excretion of 3-MH could be validly expressed in terms of unit creatinine.     

The condensed tannins of pasture legume species

Condensed tannins have been isolated from legume pasture species and purified by gel chromatography on Sephadex G-50 and LH-20 media. Molecular size di     

Studies on the Secretion of Maize Root Cap Slime: IV. Evidence for the Involvement of Dictyosomes

The involvement of dictyosomes and their vesicles in secretion of slime by maize root cap cells is demonstrated by kinetic and organelle fractionation experiments using l-fucose as a specific marker for the secreted slime. Pulse-chase experiments show that l-[1-(3)H]fucose is incorporated into two distinct fractions of root cap cells. Incorporation into a water-soluble, ethyl alcohol-insoluble fraction of the homogenate has a peak at 20 minutes of chasing followed by rapid loss of label. Seventy per cent of the radioactivity in this fraction is secreted from the tissue during a 2-hour chase period. Incorporation of label from [(3)H]fucose into a water-insoluble fraction is kinetically different suggesting that in situ incorporation of label is occurring into the cell wall. Labeling of the water-soluble, ethyl alcohol-insoluble fraction with an (14)C-amino acid mixture differs from that of [(3)H]fucose. Thus, while release of the [(3)H]fucose-containing polymer begins after 10 to 15 minutes of chasing, the release of the (14)C-amino acid polymer is delayed an additional 5 to 10 minutes and occurs at a lower rate. Cesium chloride density gradient centrifugation of secreted material labeled with radioactivity from [(3)H]fucose indicates the presence of only one major component having a buoyant density similar to that of purified root cap slime (1.63 g cm(-3)). Sucrose density gradient centrifugation of homogenates of [(3)H]fucose-labeled root cap tissue shows that radioactivity in nondialyzable material occurs as a broad band between densities 1.12 and 1.18 g cm(-3) with a peak at density 1.15 g cm(-3), the same density at which dictyosomes were localized by electron microscopy. Autoradiography of organelle fractions shows that radioactivity was associated almost exclusively with dictyosomes.     

Nitrate reductase activity and growth in Paul's Scarlet rose suspension cultures in relation to nitrogen source and molybdenum

Growth and nitrate reductase activity were measured in Paul's Scarlet rose cell suspensions, cultured in media purified from molybdenum and containing nitrate or urea as sole nitrogen source with or without added Mo. Urea could replace nitrate to yield 80% of the fresh weight in nitrate medium. Nitrate reductase activities were compared by in vivo and in vitro assays. The latter varied due to inactivation during extraction. Compared with activities in cells in complete NO₃ ^- medium, activity in NO₃ ^--Mo cells was reduced to 30% and, in urea-grown cells, to trace amounts. Increases in nitrate reductase activity were found when NO₃ ^- alone was added to NO₃ ^- or urea+Mo cultures. In NO₃ ^--Mo cultures, Mo alone or with NO₃ ^- caused a similar increase in activity, whereas urea-Mo cultures required both NO₃ ^- and Mo for enzyme induction.Abbreviations FAD flavin adenine dinucleotide - Mo molybdenum - NADH reduced nicotinamide adenine dinucleotide - NO₃ ^-+Mo standard MX₁ culture medium - NO₃ ^--Mo MX₁ medium purified of Mo and used for continuous subculture with nitrate - NR nitrate reductase - PSR Paul's Scarlet rose - PVP polyvinylpyrrolidone - U urea - U+Mo MX₁ medium containing urea instead of nitrate - U-Mo MX₁ medium containing urea instead of nitrate and also purified of Mo     

The electrophoretic properties and aggregation of mouse lymphoma cells, chinese-hamster fibroblasts and a somatic-cell hybrid.

1. The electrophoretic mobilities of a mouse lymphoma cell, a Chinese-hamster fibroblast and a somatic-cell hybrid (also fibroblastic), produced by fusion of the hamster cell and a mouse lymphoma cell, were measured at 25 degrees C over a range of pH, concentration of Ca2+ ions and concentration of La3+ ions. 2. All the cells have pI at pH3.5. 3. Ca2+ ions decrease the mobilities and zeta potentials of the cells to zero in the range 1-100mM. 4. La3+ ions lower the mobilities and zeta potentials in the range 10 muM-1 mM, and the cells become positively charged above 1 mM. 5. The data are consistent with specific adsorption of La3+ ions on approx. 2 X 10(14) sites/m2 of cell surface with a free energy of approx. -37kJ/mol. 6. The effects of Ca2+, La3+ and ionic strength on the extent of aggregation of the cells and of neuraminidase-treated cells were studied. 7. Ca2+ ions do not markedly increase aggregation, whereas La3+ ions gave rise to extensive aggregation in the range 10 muM-1 mM, corresponding to the region of La3+ adsorption. 8. Both fibroblastic cell lines are aggregated at high ionic strength. 9. The fibroblastic cells have larger amounts of trypsin-sensitive carbohydrate than does the lymphoma cell; the possible role of this material in cellular aggregation is discussed.     

Down syndrome in British Columbia, 1952-73: incidence and mean maternal age.

Records of children with Down syndrome (DS) at the BC Health Surveillance Registry were linked to their Birth Registrations to derive maternal ages. Incidence and maternal-age specific rates were calculated for 1952-73. Mean maternal age has declined both for normal and DS children, the latter to a marked degree, so that in 1972-73 80% were born to women under 35 years. Using maternal age of 40 and over as an indication for amniocentesis would only detect 10% of DS children. The crude incidence rate (mean 1.28/1000 livebirths) has not changed appreciably over the study period except for 1969 in which a statistically significant peak occurred. The standarized rate showed an increasing trend but it is not clear whether this was a true biological increase or resulted from better ascertainment.