Directional fixation of mutations in vertebrate evolution

Summary We have made pairwise comparisons between the coding sequences of 21 genes from coldblooded vertebrates and 41 homologous sequences from warm-blooded vertebrates. In the case of 12 genes, GC levels were higher, especially in third codon positions, in warm-blooded vertebrates compared to cold-blooded vertebrates. Six genes showed no remarkable difference in GC level and three showed a lower level. In the first case, higher GC levels appear to be due to a directional fixation of mutations, presumably under the influence of body temperature (see Bernardi and Bernardi 1986b). These GC-richer genes of warm-blooded vertebrates were located, in all cases studied, in isochores higher in GC than those comprising the homologous genes of cold-blooded vertebrates. In the third case, increases appear to be due to a limited formation of GC-rich isochores which took place in some cold-blooded vertebrates after the divergence of warm-blooded vertebrates. The directional changes in the GC content of coding sequences and the evolutionary conservation of both increased and unchanged GC levels are in keeping with the existence of compositional constraints on the genome.     

Lymphocyte clones from old subjects: growing rate and functional activity

Old subjects exhibit a decline in circulating T cells and an impaired proliferative response to mitogens, plus a relative increase in cells with NK phenotype not associated with a concomitant increase in their cytolitic activity.In the present study a limiting dilution assay was used to evaluate the phenotype, the functional activity and the proliferative capacity of clones obtained from peripheral blood lymphocytes of old and young subjects. CD5+ CD8+ clones from old people showed a significant impairment in their proliferative capacity and a decreased lytic activity against K562 and P815-IgG cell lines.     

Hidden smectic properties of a chiral side-chain co-oligomer

We recently showed that a side-chain industrial co-oligosiloxane presents a quenchable enlarged blue phase behaviour at the cholesteric-isotropic phase transition. In this paper, we present the results of a structural study based on X-ray diffraction, differential scanning calorimetry and optical measurements. In particular, the smectic A organisation is demonstrated in the lower temperature domain, which was hitherto understood as a cholesteric phase. A structural model for this phase is proposed on the basis of the analysis of the anisotropic scattering of stretched fibers. Our results also suggest that the observed glass transition is indeed a rather complex phenomenon, which seems to involve not only the freezing of the main chains, but also smectic correlations at the side-chain level. Moreover, the calorimetric study indicates that, notwithstanding the conservation of the processed film's optical properties, low kinetic reorganisations occur at room temperature.     

Existence of very weak level of residual multiple innervation of Purkinje cells through climbing fibers in the cerebellum of the normal adult rat

Extra- or intracellular unit responses of Purkinje cells to the activation of climbing fibres were recorded in the cerebellum of adult rats. Out of 1.719 cels studied, only 4 were found to be innervated by more than one climbing fibre. This very small rate of residual multiple innervation in the normal adult illustrates the accuracy of the synaptic elimination process which leads to the innervation of each Purkinje cell through only one climbing fibre during normal development in the rat.     

Analysis of protein distribution in budding yeast

Flow cytometry is a fast and sensitive method that allows monitoring of different cellular parameters on large samples of a population. Protein distributons give relevant information on growth dynamics, since they are related to the age distribution and depend on the law of growth of the population and the law of protein accumulation during the cell cycle. We analyzed protein distributions to evaluate alternative growth models for the budding yeast Saccharomyces cerevisiae and to monitor the changes in population dynamics that result from environmental modifications; such an analysis could potentially give parameters useful in the control of biotechnological processes. Theoretical protein distributions (taking into account the unequal division of yeast cells and the exponential law of protein accumulation during a cell cycle) quantitatively fit experimental distributions, once appropriate variability sources are introduced. Best fits are obtained when the protein threshold required for bud emergence increases at each new generation of parent cells.     

Lack of genotoxic properties of the hair-dye component N-methyl-amino-2-nitro-4-N',N'-bis-(2-hydroxyethyl)-aminobenzene, in mammalian cells in vitro, and in yeasts

N-Methyl-amino-2-nitro-4-N',N'-bis-(2-hydroxyethyl)-aminobenzene is a hair-dye ingredient. Its potential ability to induce gene mutations, in the yeast S. pombe and in cultured mammalian CH-V79 cells, mitotic gene conversion in the yeast S. cerevisiae, and unscheduled DNA synthesis in cultured human HeLa cells was evaluated. The chemical proved unable to induce detectable genotoxic effects according to these tests. The present data, together with others that show that the chemical is not mutagenic in Salmonella typhimurium or Drosophila, and is not clastogenic in mammalian cytogenetic assays (in vitro or in vivo), strongly support the non-genotoxicity of the chemical.