Abstract
The centromere is the DNA region of the eukaryotic chromosome that determines kinetochore formation and sister chromatid cohesion. Centromeres interact with spindle microtubules to ensure the segregation of chromatids during mitosis and of homologous chromosomes in meiosis. The origin of centromeres, therefore, is inseparable from the evolution of cytoskeletal components that distribute chromosomes to offspring cells. Although the origin of the nucleus has been debated, no explanation for the evolutionary appearance of centromeres is available. We propose an evolutionary scenario: The centromeres originated from telomeres. The breakage of the ancestral circular genophore activated the transposition of retroelements at DNA ends that allowed the formation of telomeres by a recombination-dependent replication mechanism. Afterward, the modification of the tubulin-based cytoskeleton that allowed specific subtelomeric repeats to be recognized as new cargo gave rise to the first centromere. This switch from actin-based genophore partition to a tubulin-based mechanism generated a transition period during which both types of cytoskeleton contributed to fidelity of chromosome segregation. During the transition, pseudodicentric chromosomes increased the tendency toward chromosomal breakage and instability. This instability generated multiple telocentric chromosomes that eventually evolved into metacentric or holocentric chromosomes.