centromeri

Centromeri, plural of centromere, is the region of a chromosome that forms the assembly site for the kinetochore and is essential for correct segregation during cell division. During mitosis and meiosis, spindle microtubules attach to kinetochores built on the centromeric chromatin to pull sister chromatids to opposite poles.

In most eukaryotes, centromeri are defined not by a unique DNA sequence but by specialized chromatin. The canonical histone H3 variant CENP-A replaces conventional H3 at centromeric nucleosomes, marking the site where the kinetochore assembles. The surrounding pericentromeric DNA often consists of long repetitive elements and is heterochromatic.

DNA composition of centromeri varies among species. In humans, centromeric DNA is dominated by long arrays of alpha-satellite repeats; in many other organisms, regional centromeri are defined by epigenetic specification rather than a strict sequence, whereas some yeasts possess small, sequence-defined point centromeri about 125 base pairs long.

The kinetochore is a multiprotein complex that forms on centromeric chromatin and mediates attachment to microtubules. Cohesin holds sister chromatids together until anaphase, enabling tension and proper segregation.

Centromeri function is robust but can fail, leading to aneuploidy and genomic instability observed in cancer and developmental disorders. Centromeri can also form at noncanonical sites (neocentromeres), illustrating that centromere identity is largely epigenetic.