Centromere sliding on a mammalian chromosome

Area of Science:

• Epigenetics
• Chromatin Biology
• Molecular Genetics

Background:

• The centromere is crucial for chromosome segregation during cell division.
• Centromere identity is epigenetically regulated by centromere protein A (CENP-A) nucleosomes.
• Mammalian centromeres are typically associated with repetitive satellite DNA, hindering molecular analysis.

Purpose of the Study:

• To investigate the molecular architecture of a unique satellite DNA-free centromere on horse chromosome 11.
• To determine the precise localization and organization of CENP-A binding domains.
• To understand the dynamics and sequence-independence of centromeric epigenetic domains.

Main Methods:

• Utilized a satellite DNA-free horse chromosome 11 centromere as a model system.
• Employed chromatin immunoprecipitation followed by high-resolution array hybridization (ChIP-on-chip) to map CENP-A binding domains.
• Analyzed domain organization using single nucleotide polymorphism (SNP)-based approaches and single-molecule chromatin fiber analysis.

Main Results:

• Discovered distinct and variable arrangements of CENP-A binding domains across five individuals.
• Identified seven distinct 'positional alleles' of CENP-A binding domains within a 500 kb region.
• Demonstrated that CENP-A domains are sequence-autonomous and exhibit positional instability, suggesting a sliding mechanism.

Conclusions:

• CENP-A binding domains are dynamic and positionally unstable, independent of the underlying DNA sequence.
• This positional instability may represent a common mechanism in mammalian centromeres.
• The findings suggest a novel model for the establishment of epigenetic alleles at centromeres.