Characterizing the link between small-scale chromatin structure and large-scale chromosome conformation is a prerequisite for understanding transcription. Yet, it remains poorly characterized. We present a simple biophysical model , where chromosomes are described in terms of folding of a chromatin sequence with alternating blocks of fibers with different thickness. We demonstrate that chromosomes undergo prominent conformational changes when the two fibers form separate domains. Conversely, when small stretches of the thinner fiber are randomly distributed, they act as impurities and conformational changes can be observed only at small length and time scales. Our results bring a limit to the possibility of detecting variations in the behavior of chromosomes due to chromatin modifications, and suggest that the debate whether chromosomes expand upon transcription, which is fueled by conflicting experimental observations, can be reconciled by examining how transcribed loci are distributed. Finally, to validate our conclusions, we compare our results to experimental FISH data .
Characterizing the link between small-scale chromatin structure and large-scale chromosome folding during interphase is a prerequisite for understanding transcription. Yet, this link remains poorly investigated. Here, we introduce a simple biophysical model where interphase chromosomes are described in terms of the folding of chromatin sequences composed of alternating blocks of fibers with different thicknesses and flexibilities, and we use it to study the influence of sequence disorder on chromosome behaviors in space and time. By employing extensive computer simulations,we thus demonstrate that chromosomes undergo noticeable conformational changes only on length-scales smaller than 10^5 basepairs and time-scales shorter than a few seconds, and we suggest there might exist effective upper bounds to the detection of chromosome URLanization in eukaryotes. We prove the relevance of our framework by modeling recent experimental FISH data on murine chromosomes .
R
conformation
folding during interphase
R
it remains poorly characterized. We present
this link remains poorly investigated. Here, we introduce
R
, where
where interphase
R
folding of a chromatin sequence with
the folding of chromatin sequences composed of
R
thickness. We
thicknesses and flexibilities, and we use it to study the influence of sequence disorder on chromosome behaviors in space and time. By employing extensive computer simulations,we thus
R
prominent conformational changes when the two fibers form separate domains. Conversely, when small stretches of the thinner fiber are randomly distributed, they act as impurities and conformational changes can be observed only at small length and time scales. Our results bring a limit to the possibility of detecting variations in the behavior of chromosomes due to chromatin modifications, and suggest that the debate whether chromosomes expand upon transcription, which is fueled by conflicting experimental observations, can be reconciled by examining how transcribed loci are distributed. Finally, to validate our conclusions, we compare our results to experimental FISH data
noticeable conformational changes only on length-scales smaller than 10^5 basepairs and time-scales shorter than a few seconds, and we suggest there might exist effective upper bounds to the detection of chromosome URLanization in eukaryotes. We prove the relevance of our framework by modeling recent experimental FISH data on murine chromosomes