Analysis of a cell cycle model based on unequal division of metabolic constituents to daughter cells during cytokinesis

We demonstrate that the unequal division of RNA during cytokinesis explains the dispersion of cell generation times in CHO cell cultures. Experimental cytometric results reported previously serve as a basis for a probabilistic model of cytokinesis. Unequal RNA division to daughter cells, together with two simple laws of RNA production, are used as a source of randomness within the cell cycle. The model reproduces the experimental growth of the CHO cell population, including the observed variability in RNA content. The model has stabilizing properties which explain why a cell population with increased RNA content characteristics, a few cell cycles, to the original pattern. Other cell cycle characteristics, like sister-to-sister and mother-to-daughter generation time correlations implied by the model, are close to their experimental analogs. The conceptual basis of the model is general enough to include unequal division of factors other than RNA (cell mass, cell proteins, etc.) as sources of generation time variability. It seems that the observed dispersion of cell generation times, explained previously in the terms of random transitions in some part of the cell cycle (the Smith & Martin A and B state hypothesis), can be reduced to the single random event of unequal division. This supplies a new convenient tool in the investigation of cell cycle kinetics.     

Removal of239Pu from mice with 3,4,3 LICAM(C) or N,N′, N″, N‴-tetra-(2,3-dihydroxybenzoyl)-spermine

Summary Male mice SAS/4 were injected i.v. with²³⁹Pu citr(IV) 0.27 µCikg^–1–9.99 kBqkg^–1. After 1 h 30 µmol kg^–1 of 3,4,3 LICAM(C), N, N, N, N-tetra-(2,3-dihydroxybenzoyl)-spermine or Na₃CaDTPA as a reference compound was given intraperitoneally. After 4 days the animals were sacrified and the Pu content in livers, kidneys, femurs and carcasses was determined by the liquid scintillation method. It was found that, as compared with the control, 3,4,3 LICAM(C) removed 83% of the Pu activity deposited in the liver, 71% of that in the femur and 79% of the Pu in the whole body. The Pu content in the kidneys exceeded the control value by about 50%. Na₃CaDTPA removed 96, 86, 40 and 72% of plutonium from the liver, kidneys, femurs and carcasses respectively.Tetra-DHB-spermine caused the excretion of 50, 57 and 39% of Pu from liver, bone and whole body respectively. The retention of Pu in the kidneys was increased to 400% of the control value.     

Effect of Protease Inhibitors on Early Events of Apoptosis

Proteolysis is an early event of apoptosis which appears to be associated with activation of the endonuclease which is responsible for internucleosomal DNA cleavage. The present study was designed to reveal the possible role of proteolysis in other early events, such as chromatin condensation, nuclear breakdown, and destabilization ofin situDNA double-stranded structure. Apoptosis of human leukemic HL-60 cells and rat thymocytes was induced by different agents, including DNA topoisomerase inhibitors, an RNA antimetabolite, and the glucocorticosteroid, prednisolone. DNA degradation was evaluated by pulsed field and conventional gel electrophoresis and by the presence ofin situDNA strand breaks. DNA stability was estimated by the measure of its sensitivityin situto denaturation. Chromatin condensation, nuclear breakdown, and other morphological changes were monitored by interference contrast and UV microscopy following cell staining with the DNA-specific fluorochrome 4′,6-diamidino-2-phenylindole. Several irreversible or reversible serine protease inhibitors prevented internucleosomal DNA degradation, nuclear breakdown, and destabilization of DNA double-stranded structure. The effective inhibitors, however, did not prevent the onset of chromatin condensation, nor the loss of the fine structural framework, nor the initial step of DNA cleavage generating DNA fragments of ≥50 kb in size. The data indicate that in both cell systems the activity of proteases sensitive to the inhibitors tested is needed for internucleosomal DNA cleavage to occur. The data also suggest that these proteases may be involved in dissolution of the nuclear envelope. Because nuclear matrix proteins and histones stabilize DNAin situ,and the decrease in DNA stability which occurs during apoptosis is precluded by the inhibitors, it is likely that serine proteases may degrade DNA stabilizing proteins. The activity of these proteases, however, appears needed neither for DNA cleavage to ≥50-kb fragments nor for the onset of chromatin condensation which is associated with dissolution of the structural framework of the nucleus.     

Effect of linolenic acid on release of the 43 kDa polypeptide and manganese from photosystem II membranes depleted of the 33 kDa extrinsic polypeptide

The effect of linolenic acid (18:3) on release of the 43 kDa polypeptide and manganese from photosystem II ( PS II ) membranes depleted of extrinsic polypeptides was studied. In both control and NaCl-washed particles which were depleted of the extrinsic 23 and 16 kDa polypeptides, the 18:3 treatment caused a 20% release of the 33 and 43 kDa polypeptides. In CaCl₂, (or urea + NaCl)-washed particles, which were depleted of the 33 kDa polypeptide in addition to the 23 and 16 kDa polypeptides, the release of the 43 kDa polypeptide increased to 70%, whereas only 25% of the 47 kDa polypeptide was removed. These findings suggest (i) that the 33 and the 43 kDa polypeptides are neighbows in the photosynthetic membrane and (ii) that the 33 kDa polypeptide shields the 43 kDa polypeptide against the action of 18:3. Incubation of CaCl₂, or (urea + NaCI)-treated PSII particles in the presence or absence of 18:3 resulted in the loss of only 2 of the 4 Mn atoms present per reaction center. this indicates that the 2 Mn atoms more firmly associated with PSII are not affected by the removal of the extrinsic 16, 23 and 33 kDa polypeptides, and the intrinsic 43 kDa polypeptide. nor by the treatment with linolenic acid.     

Correlates of stability and diversity in weevil communities

Summary Among the parameters describing weevil communities two groups of parameters, which are positively correlated among themselves, were found. The first group includes: relative abundance, number of species, and participation of habitat generalists, the second: stability, mean body size, and participation of habitat specialists. The parameters belonging to opposite groups were negatively correlated.Among the parameters describing host plants of the weevils, no correlation was found between species number and relative abundance, while a negative correlation was found between total mass of host plants and their relative abundance.Weevil species diversity and the group of its correlates were positively correlated with analogical parameters of their host plants while weevil stability showed positive correlation with the total mass of host plants and the proportion of these plants in the total mass of vegetation.The reasons for negative correlation between stability and diversity of weevils and relations of these two parameters to selection strategy of these beetles are discussed.     

The role of the IGF1 receptor in the regulation of cdc2 mRNA levels in fibroblasts

The levels of cdc2 mRNA increase when quiescent cells are stimulated by growth factors. In BALB/c 3T3, both platelet-derived growth factor and insulin-like growth factor 1 (IGF-1) are required to increase cdc2 mRNA levels. In p6 cells, which constitutively overexpress the IGF-1 receptor, IGF-1 is sufficient. The importance of the IGF-1/IGF-1 receptor interaction in regulating the levels of cdc2 mRNA was further confirmed by showing that an antisense oligodeoxynucleotide to the IGF-1 receptor RNA inhibited the IGF-1-mediated increase.     

Localization of mucidin-resistant locus muc3 on mitochondrial DNA with respect to ubiquinol-cytochrome c reductase deficient box loci. Locus muc3 is allelic to box2

Summary Genetic relations between mitochondrial mucidin-resistant locus muc3 and ubiquinol-cytochrome c reductase-deficient box loci have been studied by recombination and petite deletion analysis. It was found that the locus muc3 maps in the segment of mitochondrial DNA corresponding to the locus box2. The results suggest the participation of box2/muc3 locus in the sequences of the structural gene for cytochrome b.     

Functional characteristics of green alga Scenedesmus obliquus (Chlorophyceae): 276–6 wild type and its two photosystems deficient mutants cultured under photoautotrophic,mixotrophic and heterotrophic conditions

Functional features of Scenedesmus obliquus: wild type 276–6 strain (WT) and its two mutants reported as photosystem I‐deficient (mutant 56.80) and photosystem II‐deficient (mutant 57.80) were characterized. Algae were cultured aseptically under continuous light or in darkness on mineral bold basal medium (BBM), yeast extract‐enriched BBM and yeast extract to evaluate the physiology of algal cells under photoautotrophic, mixotrophic and heterotrophic conditions. Growth, superoxide dismutase activity and photosynthetic parameters, including polyphasic fluorescence rise during the first seconds of chlorophyll a illumination (OJIP), were analyzed to find relationships between the photosynthetic/respiratory activity of the cells, occurrence of oxidative stress and trophic conditions applied to PSs‐deficient algae. Despite the highest superoxide dismutase activity, indicating the presence of oxidative stress, mixotrophic conditions appeared to be optimal for S. obliquus WT and mutant strains kept in non‐aerated cultures. OJIP analysis indicated that in mutant 56.80 part of photosystem (PS) I was functional and in mutant 57.80 residual PS II activity was found.