Centromer

The centromere is the region of a chromosome that links sister chromatids and serves as the assembly site for the kinetochore during cell division. It is essential for correct chromosome segregation, providing the attachment point for spindle microtubules and helping to ensure accurate distribution of genetic material to daughter cells.

In most eukaryotes, centromere identity is defined more by epigenetic marks than by a specific DNA sequence. A specialized histone H3 variant called CENP-A marks centromeric chromatin and helps recruit kinetochore proteins. Centromeres can be regional, spanning large stretches of repetitive DNA, or, in some yeasts, point centromeres defined by particular sequences that specify kinetochore assembly.

The kinetochore is a multiprotein complex assembled on the centromere. The inner kinetochore contains components that connect to CENP-A–containing chromatin, while the outer kinetochore interfaces with spindle microtubules through networks such as the KMN core. This structure mediates the attachment and dynamics of microtubules during chromosome movement.

During mitosis and meiosis, sister chromatids stay together through cohesion until the onset of anaphase, when cohesin is cleaved and microtubules shorten to pull chromatids to opposite poles. Proper centromere function is therefore critical for maintaining genomic stability.

Centromere activity can be disrupted by structural rearrangements, leading to chromosome missegregation and aneuploidy. In some cases, neocentromeres can form at noncanonical loci, preserving chromosome segregation when a conventional centromere is absent. Across species, centromeric DNA sequences are highly variable, while the mechanism of kinetochore assembly and centromere identity remain conserved.