Effect of ethanol on structural transitions of DNA and polyphosphates under Ca2+ ions action in mixed solutions

In the present work using the IR spectroscopy method the effect of ethanol on structural transitions of DNA and polyphosphates under the action of Ca2+ ions in mixed solutions containing ethanol (0-25 vol.%) was studied. It was shown that, on its interaction with Ca2+ ions, in aqueous and mixed solutions DNA becomes transformed into compact form. With the increase of concentration of ethanol the degree of Ca2+-induced DNA compactisation rises. It was found that, in mixed solutions containing ethanol, Ca2+-induced DNA compactisation depends not only on the solution's dielectric permeability but also on the solution structure. On stabilisation of the water structure in the presence of low ethanol concentrations a stabilisation of the DNA macromolecule occurs that leads to the increase of the Ca2+ ion concentration necessary for DNA compactisation. Comparison of the effects of ethanol on Ca2+-induced structural transitions in DNA and polyphosphates in mixed solvents permits to suppose that at alcohol concentrations in solution resulting in disruption of the water spatial structure, some peculiarities are observed in the behavior of those molecules whose hydrophobic interactions are essential.     

Adult monozygotic twins discordant for intra-uterine growth have indistinguishable genome-wide DNA methylation profiles

Background

Low birth weight is associated with an increased adult metabolic disease risk. It is widely discussed that poor intra-uterine conditions could induce long-lasting epigenetic modifications, leading to systemic changes in regulation of metabolic genes. To address this, we acquire genome-wide DNA methylation profiles from saliva DNA in a unique cohort of 17 monozygotic monochorionic female twins very discordant for birth weight. We examine if adverse prenatal growth conditions experienced by the smaller co-twins lead to long-lasting DNA methylation changes.

Results

Overall, co-twins show very similar genome-wide DNA methylation profiles. Since observed differences are almost exclusively caused by variable cellular composition, an original marker-based adjustment strategy was developed to eliminate such variation at affected CpGs. Among adjusted and unchanged CpGs 3,153 are differentially methylated between the heavy and light co-twins at nominal significance, of which 45 show sensible absolute mean β-value differences. Deep bisulfite sequencing of eight such loci reveals that differences remain in the range of technical variation, arguing against a reproducible biological effect. Analysis of methylation in repetitive elements using methylation-dependent primer extension assays also indicates no significant intra-pair differences.

Conclusions

Severe intra-uterine growth differences observed within these monozygotic twins are not associated with long-lasting DNA methylation differences in cells composing saliva, detectable with up-to-date technologies. Additionally, our results indicate that uneven cell type composition can lead to spurious results and should be addressed in epigenomic studies.     

Studies of calcium ion binding to poly A

Ultraviolet differential spectra of poly A we studied in the presence of Ca2+ ions with 10(-3)M Na+ in the solution. At concentrations lower than 10(-3)M Ca2+, the ions bind to phosphate groups of the single helical polymer, thus increasing its degree of helicity. At higher concentrations, the ions start binding to the bases of poly A, producing aggregates whose effective radius, as found with an electric microscope, is not more than 10(2) A. These particles stack to form aggregates of an order-of-magnitude higher size. The mutual orientation of bases in the poly A aggregates is of a high degree of order. The calculation of concentration dependences of Ca2+-poly A binding constants shows that this process is cooperative.