Telomere Disruption Results in Non-Random Formation of De Novo Dicentric Chromosomes Involving Acrocentric Human Chromosomes

Abstract

Genome rearrangement often produces chromosomes with two centromeres (dicentrics) that are inherently unstable because of bridge formation and breakage during cell division. However, mammalian dicentrics, and particularly those in humans, can be quite stable, usually because one centromere is functionally silenced. Molecular mechanisms of centromere inactivation are poorly understood since there are few systems to experimentally create dicentric human chromosomes. Here, we describe a human cell culture model that enriches for de novo dicentrics. We demonstrate that transient disruption of human telomere structure non-randomly produces dicentric fusions involving acrocentric chromosomes. The induced dicentrics vary in structure near fusion breakpoints and like naturally-occurring dicentrics, exhibit various inter-centromeric distances. Many functional dicentrics persist for months after formation. Even those with distantly spaced centromeres remain functionally dicentric for 20 cell generations. Other dicentrics within the population reflect centromere inactivation. In some cases, centromere inactivation occurs by an apparently epigenetic mechanism. In other dicentrics, the size of the α-satellite DNA array associated with CENP-A is reduced compared to the same array before dicentric formation. Extra-chromosomal fragments that contained CENP-A often appear in the same cells as dicentrics. Some of these fragments are derived from the same α-satellite DNA array as inactivated centromeres. Our results indicate that dicentric human chromosomes undergo alternative fates after formation. Many retain two active centromeres and are stable through multiple cell divisions. Others undergo centromere inactivation. This event occurs within a broad temporal window and can involve deletion of chromatin that marks the locus as a site for CENP-A maintenance/replenishment.

Keep moving and stay in a good shape to find your homologous recombination partner

“…This would be particularly relevant at centromeric-repeated sequences in mammalian cells which deletion can lead to centromere inactivation (Stimpson et al 2010). However, both Drosophila and mammalian centromeric heterochromatin seem permissive to resection.…”

The Dicentric Chromosome dic(20;22) Is a Recurrent Abnormality in Myelodysplastic Syndromes and Is a Product of Telomere Fusion

“…However, most studies of telomere fusion use artificially generated or in vitro models [Rudolph et al, 2001;Vukovic et al, 2007;Stimpson et al, 2010;Gascoigne and Cheeseman 2013;Maciejowski et al, 2015], and there is little direct evidence for this mechanism occurring in vivo. The evidence that telomere erosion/telomere fusion causes genome instability in cancer is generally indirect, such as shortened telomeres or the presence of anaphase bridges [Rudolph et al, 2001;Gordon et al, 2003;Letsolo et al, 2010;Jones et al, 2012].…”

“…Robertsonian translocations, which are the result of translocation between the short arms of the acrocentric chromosomes, are the most common dicentric chromosomes in constitutional karyotypes and also in induced telomere fusions [Stimpson et al, 2010]. These translocations occur distal to the NOR material on the acrocentric short arms [Stimpson et al, 2010].…”

“…These translocations occur distal to the NOR material on the acrocentric short arms [Stimpson et al, 2010]. These dicentric chromosomes have short intercentromeric distances and are stable [Page and Shaffer, 1998].…”

Functional epialleles at an endogenous human centromere

“…On dicentric chromosomes that contain two regions of centromeric DNA, one centromere often is inactivated, suggesting that DNA sequence alone is insufficient for centromere function. An important epigenetic determinant of centromere identity is the centromeric histone, centromeric protein A (CENP-A)/centromeric histone 3 (CENH3), a histone H3 variant that is enriched within centromeric nucleosomes at endogenous centromeres (1)(2)(3) but is absent from inactive centromeres of dicentric chromosomes (4,5). CENP-A/CENH3 distinguishes the centromere from the rest of the genome by contributing to uniquely organized chromatin that exists as alternating domains of CENP-A/CENH3 and H3-containing nucleosomes (6,7).…”