Abstract
The centromere is a specific chromosomal region where the kinetochore assembles to ensure the faithful segregation of sister chromatids during mitosis and meiosis. Centromeres are defined by a local enrichment of the specific histone variant CenH3 mostly at repetitive satellite sequences. A larger pericentromeric region containing repetitive sequences and transposable elements surrounds the centromere that adopts a particular chromatin state characterized by specific histone variants and post-translational modifications and forms a transcriptionally repressive chromosomal environment. In the model organism Arabidopsis thaliana centromeric and pericentromeric domains form conspicuous heterochromatin clusters called chromocenters in interphase. Here we discuss, using Arabidopsis as example, recent insight into mechanisms involved in maintenance and establishment of centromeric and pericentromeric chromatin signatures as well as in chromocenter formation.
Highlights
The centromere is a specific chromosomal region where the kinetochore assembles to ensure the faithful segregation of sister chromatids during mitosis and meiosis
A larger pericentromeric region containing repetitive sequences and transposable elements surrounds the centromere that adopts a particular chromatin state characterized by specific histone variants and post-translational modifications and forms a transcriptionally repressive chromosomal environment
The centromeric and the surrounding pericentromeric chromosomal regions form heterochromatin domains that remain condensed during interphase (Heitz, 1928) and in some species like Arabidopsis thaliana these are clustered into chromocenter structures (Figure 1; Fransz et al, 2002)
Summary
Centromeric sequences consist in most organisms of short repetitive DNA sequences arranged in tandem and/or transposable elements (Plohl et al, 2014). An additional domain involved in adaptive evolution is the histone fold domain including the loop 1 region that makes multiple contacts with DNA (Cooper and Henikoff, 2004) This histone fold domain has been found sufficient for CenH3 loading at centromeric sequences (Lermontova et al, 2006) and a single point mutation close to the loop region reduces CenH3 loading substantially (Karimi-Ashtiyani et al, 2015). Loss of KNL2 negatively impacts CenH3 expression and deposition (Lermontova et al, 2013), and reduces DNA methylation and affects histone methyltransferase expression, suggesting that the chromatin context of centromeric or pericentromeric sequences repeats may play a role in CenH3 loading. CenH3 is sumoylated and removed by the AAA-ATPase molecular chaperone CDC48A to be targeted for proteolysis (Mérai et al, 2014)
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