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Modeling Meiotic Chromosomes Indicates a Size Dependent Contribution of Telomere Clustering and Chromosome Rigidity to Homologue Juxtaposition
PLoS Computational Biology, 8(5):0-0, 2012.
Abstract
Meiosis is the cell division that halves the genetic component of diploid
cells to form gametes or spores. To achieve this, meiotic cells undergo a radical
spatial reorganisation of chromosomes. This reorganisation is a prerequisite for
the pairing of parental homologous chromosomes and the reductional division, which
halves the number of chromosomes in daughter cells. Of particular note is the change
from a centromere clustered layout (Rabl configuration) to a telomere clustered
conformation (bouquet stage). The contribution of the bouquet structure to homologous
chromosome pairing is uncertain. We have developed a new in silico model to represent
the chromosomes of Saccharomyces cerevisiae in space, based on a worm-like chain
model constrained by attachment to the nuclear envelope and clustering forces. We
have asked how these constraints could influence chromosome layout, with particular
regard to the juxtaposition of homologous chromosomes and potential nonallelic,
ectopic, interactions. The data support the view that the bouquet may be sufficient
to bring short chromosomes together, but the contribution to long chromosomes is
less. We also find that persistence length is critical to how much influence the
bouquet structure could have, both on pairing of homologues and avoiding contacts
with heterologues. This work represents an important development in computer modeling
of chromosomes, and suggests new explanations for why elucidating the functional
significance of the bouquet by genetics has been so difficult.