Messenger RNA levels and methylation patterns of GAPDH and beta-actin genes in rat liver, spleen and brain in relation to aging

Messenger RNA levels and methylation patterns of the glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) and beta-actin genes were studied in spleen, liver and brain of 6-, 24- and 36-month old female inbred rats. In the spleen, the mRNA levels of both housekeeping genes significantly increased between 24 and 36 months. No age-related alterations in the expression of GAPDH or beta-actin mRNA were observed in brain or liver. A considerable intertissue and interindividual variation was observed in the mRNA levels of these genes in all age-groups as compared to the level of 28 S rRNA, which was used as an internal control. In this respect the interindividual variation in the level of GAPDH mRNA paralleled the variation observed in the beta-actin mRNA level in the three tissues studied. The methylation pattern of beta-actin was found to be tissue-specific in contrast to that of GAPDH, which was identical in all three tissues. No significant age-related alterations were observed in the GAPDH methylation pattern, whereas beta-actin appeared to become slightly demethylated with age in the spleen at the CpG site for which tissue-specificity was observed.

Quantitative comparison of mRNA levels in mammalian tissues: 28S ribosomal RNA level as an accurate internal control

Images

The Caenorhabditis elegans genome contains monomorphic minisatellites and simple sequences

Many species have been shown to contain tandemly repeated short sequence DNA known as minisatellites and simple sequence motifs. Due to allelic variation in the copy number of the repeat unit these loci are usually highly polymorphic. Here we demonstrate the presence of sequences in the genome of the nematode Caenorhabditis elegans which are homologous to two sets of short sequence DNA. However, when two independent strains were compared no polymorphism for these sequences could be detected.

Two-dimensional DNA fingerprinting of human individuals

The limiting factor in the presently available techniques for the detection of DNA sequence variation in the human genome is the low resolution of Southern blot analysis. To increase the analytical power of this technique, we applied size fractionation of genomic DNA restriction fragments in conjunction with their sequence-dependent separation in denaturing gradient gels; the two-dimensional separation patterns obtained were subsequently transferred to nylon membranes. Hybridization analysis using minisatellite core sequences as probes resulted in two-dimensional genomic DNA fingerprints with a resolution of up to 625 separated spots per probe per human individual; by conventional Southern blot analysis, only 20-30 bands can be resolved. Using the two-dimensional DNA fingerprinting technique, we demonstrate in a small human pedigree the simultaneous transmission of 37 polymorphic fragments (out of 365 spots) for probe 33.15 and 105 polymorphic fragments (out of 625 spots) for probe 33.6. In addition, a mutation was detected in this pedigree by probe 33.6. We anticipate that this method will be of great use in studies aimed at (i) measuring human mutation frequencies, (ii) associating genetic variation with disease, (iii) analyzing genomic instability in relation to cancer and aging, and (iv) linkage analysis and mapping of disease genes.

Genetic instability and aging: theories, facts, and future perspectives

The fundamental mechanisms involved in the physiological deterioration observed with age in mammalian organisms have not yet been elucidated. It appears that random alterations in informational biomolecules and in their synthesis could be the basis of such physiological changes. There is, however, a lack of knowledge with respect to the frequency and characteristics of changes introduced in the cellular molecular machinery. Moreover, the driving force initiating the generation of such alterations and the order of events in which they occur are unknown at present. In this article, data concerning the hypothesis that the aging process is associated with widespread genetic instability are reviewed in the context of the complex interactions between the three major informational biomolecules, DNA, RNA, and protein. We conclude that the results obtained to date do not rule out the possibility that genetic instability in a wide sense is a major causal factor in a number of age-related phenomena. However, it appears that new strategies based on a new technology are ultimately necessary to elucidate the alterations in the intricately interwoven patterns of molecular control that could underlie the various aspects of the aging process. A first attempt is made to formulate the problems in this field and to provide some solutions.