Biomedical subjects

Hans K Stenøien

Publications and source records attributed to Hans K Stenøien.

4 recordsLinked to original sources

PubMed2005

Global mRNA stability is not associated with levels of gene expression in Drosophila melanogaster but shows a negative correlation with codon bias.

A multitude of factors contribute to the regulation of gene expression in living cells. The relationship between codon usage bias and gene expression has been extensively studied, and it has been shown that codon bias may have adaptive significance in many unicellular and multicellular organisms. Given the central role of mRNA in post-transcriptional regulation, we hypothesize that mRNA stability is another important factor associated either with positive or negative regulation of gene expression. We have conducted genome-wide studies of the association between gene expression (measured as transcript abundance in public EST databases), mRNA stability, codon bias, GC content, and gene length in Drosophila melanogaster. To remove potential bias of gene length inherently present in EST libraries, gene expression is measured as normalized transcript abundance. It is demonstrated that codon bias and GC content in second codon position are positively associated with transcript abundance. Gene length is negatively associated with transcript abundance. The stability of thermodynamically predicted mRNA secondary structures is not associated with transcript abundance, but there is a negative correlation between mRNA stability and codon bias. This finding does not support the hypothesis that codon bias has evolved as an indirect consequence of selection favoring thermodynamically stable mRNA molecules.

Animals↗

PubMed2005

Genetic variability in natural populations of Arabidopsis thaliana in northern Europe.

Ten populations of the model plant Arabidopsis thaliana were collected along a north-south gradient in Norway and screened for microsatellite polymorphisms in 25 loci and variability in quantitative traits. Overall, the average levels of genetic diversity were found to be relatively high in these populations, compared to previously published surveys of within population variability. Six of the populations were polymorphic at microsatellite loci, resulting in an overall proportion of polymorphic loci of 18%, and a relatively high gene diversity for a selfing species (HE = 0.06). Of the overall variability, 12% was found within populations. Two of six polymorphic populations contained heterozygous individuals. Both FST and phylogenetic analyses showed no correlation between geographical and genetic distances. Haplotypic diversity patterns suggested postglacial colonization of Scandinavia from a number of different sources. Heritable variation was observed for many of the studied quantitative traits, with all populations showing variability in at least some traits, even populations with no microsatellite variability. There was a positive association between variability in quantitative traits and microsatellites within populations. Several quantitative traits exhibited QST values significantly less than FST, suggesting that selection may be acting to retard differentiation for these traits.

Arabidopsis↗

PubMed2004

Mutation and epimutation load in haploid and diploid life forms.

Epigenetic differentiation is the potentially heritable changes in levels of gene expression not caused by DNA sequence changes. Here, a classification scheme of mutations and epimutations is introduced, enabling a simple analysis of mutation and epimutation load in haploid and diploid organisms. It is found that the deleterious effect of epimutations is mainly determined by epimutation rate and degree of reversibility. Inherited epimutations have the same fitness consequences as inherited mutations. With complete reversibility and no inheritance, then epimutations have the same fitness consequences as somatic mutations. It is argued that organisms with somatic inheritance may experience more genetic load than organisms without somatic inheritance due to inherited epimutations in the former. This may partly explain the maintenance of soma/germ differentiation in many life forms. It is also argued that masking of deleterious somatic mutations may not necessarily explain the evolution of diploidy in life forms with inherited epimutations.

Animals↗

PubMed2004

Quantitative trait locus analyses and the study of evolutionary process.

The past decade has seen a proliferation of studies that employ quantitative trait locus (QTL) approaches to diagnose the genetic basis of trait evolution. Advances in molecular techniques and analytical methods have suggested that an exact genetic description of the number and distribution of genes affecting a trait can be obtained. Although this possibility has met with some success in model systems such as Drosophila and Arabidopsis, the pursuit of an exact description of QTL effects, i.e. individual gene effect, in most cases has proven problematic. We discuss why QTL methods will have difficulty in identifying individual genes contributing to trait variation, and distinguish between the identification of QTL (or marker intervals) and the identification of individual genes or nucleotide differences within genes (QTN). This review focuses on what ecologists and evolutionary biologists working with natural populations can realistically expect to learn from QTL studies. We highlight representative issues in ecology and evolutionary biology and discuss the range of questions that can be addressed satisfactorily using QTL approaches. We specifically address developing approaches to QTL analysis in outbred populations, and discuss practical considerations of experimental (cross) design and application of different marker types. Throughout this review we attempt to provide a balanced description of the benefits of QTL methodology to studies in ecology and evolution as well as the inherent assumptions and limitations that may constrain its application.

Adaptation, Biological↗