Selective inhibition of thymidine transport at low doses of the alkylating agents triethyleneiminobenzoquinone (Trenimon)

The alkylating antitumor agent triethyleneiminobenzoquinone (Trenimon) causes a rapid decrease in the incorporation of labeled thymidine into the DNA of Yoshida or Ehrlich ascites tumor cells. The effect is expressed 4 h after administration of 6 × 10⁻⁸ moles/kg of the drug to mice bearing Yoshida ascites tumors or of 6 × 10⁻⁷ moles/kg to Ehrlich ascites tumor-bearing animals, respectively. The reduced incorporation of labeled thymidine which is observed under these conditions is not due to an inhibition of DNA synthesis. DNA synthesis was measured by an isotope dilution assay after pulse-labeling with ³H-thymidine and by monitoring the increase in the total amount of DNA of the cell populations. The data demonstrate that DNA synthesis is not affected during the first 8 h after exposure to the drug. This conclusion is supported by cell kinetic measurements which indicate that the alkylating agent does not interfere with the progression of cells into the S phase, but exerts a block at the G 2 stage of the cell cycle. The reduced incorporation of thymidine into DNA is explained by a decreased transport of the nucleoside into the cells.     

A natural CD label to probe the structure of the purple membrane from Halobacterium halobium by means of exciton coupling effects.

The polyamine and ribosome contents during the logarithmic phase of growth were much higher than those in the late logarithmic or stationary phase of growth. On the other hand, the Mg²⁺ content did not vary markedly throughout the different growth phases. These data, together with the results of a previous communication (1), suggest that increased polyamines during the logarithmic phase of growth may play significant roles not only in the neutralization of the negative charges of increased ribosomes but also in the increase of the velocity of polypeptide chain elongation by binding to the ribosomes. The polyphenylalanine synthetic activity of ribosomes from the logarithmic phase of growth was higher than that of ribosomes obtained from the stationary phase of growth in the presence of optimal concentrations of spermidine.     

Biosynthesis of yeast mannan. Characterization of mannan-synthesizing enzyme systems from mutants defective in mannan structure

The yeastSaccharomyces cerevisiae X2180-1A (wild) and its mutants X2180-1A-4 (mnn 1) and X2180-1A-5 (mnn 2) defective in mannan biosynthesis were used as enzyme sources to catalyzein vitro mannosyl transfer from GDP-[¹⁴C-U]-mannose to endogenous glycoproteins as well as to exogenous, low-molecular weight acceptors. While the enzyme preparation from the wild strain exhibited all mannosyl transferase activities involved in mannan biosynthesis by catalyzing the synthesis of characteristic mannoprotein, the enzyme frommnn 1 mutant failed to catalyze the synthesis of α(1→3) mannoside linkages both with endogenous as well as with exogenous acceptors. The enzyme preparation from themnn 2 mutant catalyzed the formation of mannoprotein very similar to that obtained with the enzyme from the wild strain. The most important difference was the formation of a higher number of unsubstituted mannosyl units in the α(1→ 6) linked mannan backbone. The observed results support the hypothesis that in themnn 1 the mutation has altered the structural gene involved in biosynthesis of an α(1→3) mannosyl transferase catalyzing the addition of α(1→3) linked mannosyl units to α(1→2) linked mannotrioses in the polysaccharide side chains and in the oligosaccharides attached to serine and/or threonine in the protein part of mannan molecule. Themnn 2 mutant represents most probably a kind of regulatory mutation where the activity of an α(1→2) mannosyl transferase adding the mannosyl units directly to α(1→6) linked backbone in the outer region of polysacoharide part of yeast mannan is repressedin vivo but becomes significantin vitro.     

Effect of gibberellic Acid on crown gall tumor induction in aging primary pinto bean leaves

Gibberellic acid was tested for its effect on tumor induction by Agrobacterium tumefaciens in primary pinto bean (Phaseolus vulgaris) leaves in various stages of development. The hormone was found to promote tumor induction in partially aged leaves but did not effect tumor induction in very young leaves or in fully matured leaves. It is suggested that the natural loss of susceptibility to tumor induction in maturing pinto bean leaves is associated with a concomitant loss of endogenous gibberellins and/or a sensitivity to gibberellins.     

Pitcher geometry facilitates extrinsically powered ‘springboard trapping' in carnivorous Nepenthes gracilis pitcher plants

Carnivorous pitcher plants capture insects in cup-shaped leaves that function as motionless pitfall traps. Nepenthes gracilis evolved a unique ‘springboard'' trapping mechanism that exploits the impact energy of falling raindrops to actuate a fast pivoting motion of the canopy-like pitcher lid. We superimposed multiple computed micro-tomography images of the same pitcher to reveal distinct deformation patterns in lid-trapping N. gracilis and closely related pitfall-trapping N. rafflesiana. We found prominent differences between downward and upward lid displacement in N. gracilis only. Downward displacement was characterized by bending in two distinct deformation zones whist upward displacement was accomplished by evenly distributed straightening of the entire upper rear section of the pitcher. This suggests an anisotropic impact response, which may help to maximize initial jerk forces for prey capture, as well as the subsequent damping of the oscillation. Our results point to a key role of pitcher geometry for effective ‘springboard'' trapping in N. gracilis.     

Controlled X‐chromosome dynamics defines meiotic potential of female mouse in vitro germ cells

The mammalian germline is characterized by extensive epigenetic reprogramming during its development into functional eggs and sperm. Specifically, the epigenome requires resetting before parental marks can be established and transmitted to the next generation. In the female germline, X‐chromosome inactivation and reactivation are among the most prominent epigenetic reprogramming events, yet very little is known about their kinetics and biological function. Here, we investigate X‐inactivation and reactivation dynamics using a tailor‐made in vitro system of primordial germ cell‐like cell (PGCLC) differentiation from mouse embryonic stem cells. We find that X‐inactivation in PGCLCs in vitro and in germ cell‐competent epiblast cells in vivo is moderate compared to somatic cells, and frequently characterized by escaping genes. X‐inactivation is followed by step‐wise X‐reactivation, which is mostly completed during meiotic prophase I. Furthermore, we find that PGCLCs which fail to undergo X‐inactivation or reactivate too rapidly display impaired meiotic potential. Thus, our data reveal fine‐tuned X‐chromosome remodelling as a critical feature of female germ cell development towards meiosis and oogenesis.     

Gap junction remodeling and altered connexin43 expression in the failing human heart

Gap junctions (GJ) are important determinants of cardiac conduction and the evidence has recently emerged that altered distribution of these junctions and changes in the expression of their constituent connexins (Cx) may lead to abnormal coupling between cardiomyocytes and likely contribute to arrhythmogenesis. However, it is largely unknown whether changes in the expression and distribution of the major cardiac GJ protein, Cx43, is a general feature of diverse chronic myocardial diseases or is confined to some particular pathophysiological settings. In the present study, we therefore set out to investigate qualitatively and quantitatively the distribution and expression of Cx43 in normal human myocardium and in patients with dilated (DCM), ischemic (ICM), and inflammatory cardiomyopathies (MYO). Left ventricular tissue samples were obtained at the time of cardiac transplantation and investigated with immunoconfocal and electron microscopy. As compared with the control group, Cx43 labeling in myocytes bordering regions of healed myocardial infarction (ICM), small areas of replacement fibrosis (DCM) and myocardial inflammation (MYO) was found to be highly disrupted instead of being confined to the intercalated discs. In all groups, myocardium distant from these regions showed an apparently normal Cx43 distribution at the intercalated discs. Quantitative immunoconfocal analyis of Cx43 in the latter myocytes revealed that the Cx43 area per myocyte area or per myocyte volume is significantly decreased by respectively 30 and 55% in DCM, 23 and 48% in ICM, and by 21 and 40% in MYO as compared with normal human myocardium. In conclusion, focal disorganization of GJ distribution and down-regulation of Cx43 are typical features of myocardial remodeling that may play an important role in the development of an arrhythmogenic substrate in human cardiomyopathies.     

Stress Responses of Male Guinea Pigs Predict Female Preference

Mate choice is a critical part of sexual selection. One constituent of mate choice is attractiveness, which serves as a projection surface for traits signalling quality and condition to prospective reproductive partners. In guinea pigs, females generally decide whom they will select as partner and when to switch to a new one. The aim of this study was to investigate for universality in male traits possibly associated with female preference. Characteristics of stress response were chosen, as they are relatively stable in their behavioural and physiological expression. Two consecutive experiments were done on isosexually kept males. In the first experiment, behavioural performance in a forced swim-test was noted, after basal endocrine status had been documented with three samples per individual. In a second experiment, the same males were presented to females in a round-robin choice paradigm. A discriminant analysis confirmed a categorization of males into groups that were preferred by different females either two times [more preferred (MP), n = 6] or less than that [less preferred (LP), n = 12]. Mean basal cortisol levels were comparable, but mean basal testosterone (T) was significantly higher in LP. This points at a scenario where higher T might be advantageous in male–male competition but perhaps less important for the formation of male–female bonds. Behaviourally, MP completed the swim-test significantly faster than LP, which may indicate greater goal directedness and motivation. We conclude that traits associated with stress responses may be components of male attractiveness, their stability perhaps reflecting adaptive qualities.