Molecular Systems Biology 6 Article number: 376 doi:10.1038/msb.2010.34
Published online: 11 May 2010
Citation: Molecular Systems Biology 6:376
Nucleosome patterning evolution: steady aim despite moving targets
Chris Todd Hittinger1 & Jay R Hesselberth1
Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, CO, USA
Correspondence to: Chris Todd Hittinger1 Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, 12801 E. 17th Avenue, RC1 South, Room 10400B, PO Box 6511, Mail Stop 8101, Aurora, CO 80045-2530, USA. Tel.: +1 303 724 4596; Fax: +1 303 724 3215; Email: chris.hittinger@ucdenver.edu
Published online 11 May 2010
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Molecular systems are the scaffolding on which natural selection builds. Comparing the tendency of different molecular mechanisms to generate tolerable and useful raw genetic variation is a challenging interdisciplinary problem. Modulation of gene expression is thought to be an important source of interspecific phenotypic divergence, and as new mechanisms are revealed, their potential roles must be considered. In this issue of Molecular Systems Biology, Tirosh et al (2010) use an interspecies hybrid approach to examine the genetic basis of variation in nucleosome arrangement and its potential to explain differences in gene expression. They find that most nucleosome occupancy and position differences are explained by changes in nearby DNA, and these differences prove to be surprisingly poor predictors of gene expression differences between species.
If a gene differs in expression between two species, the causal genetic locus of variation could either be linked to the gene itself (cis) or located somewhere else (trans). With a few assumptions, whether the locus of change is in cis or transcan often be determined by examining gene expression in a hybrid of the two species (Wittkopp et al, 2004; Tirosh et al, 2009). In purely trans cases, the alleles of both species will be expressed identically in the hybrid, whereas alleles will retain the expression profile of their source species if all variation can be explained by cis changes. Although the proportion of trans variation is usually higher in crosses within a species (Brem et al, 2002), most gene expression differences between species are explained by variation that maps in cis (Wittkoppet al, 2004; Tirosh et al, 2009).
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