Holokinetic chromosomes beat selfish centromeres

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In eukaryotic lineages with monocentric chromosomes, centromeres and centromeric histone H3 (CENH3) undergo a recurrent evolutionary conflict, whereby selfish centromeres subvert female meiosis, and CENH3 evolves adaptively to counterbalance the deleterious consequences of centromere drive. Positively selected CENH3 can therefore provide an indication as to whether this evolutionary arms race has occurred in a given lineage.

The model of centromere drive in monocentric chromosomes and its suppression by chromosomal holokinetism.
The model of centromere drive in monocentric chromosomes and its suppression by chromosomal holokinetism. In the first stage, an expansion of centromeric satellite repeats (grey rectangles) at one of the monocentric homologues leads to an expansion of CenH3 nucleosomes (circles) and thus to a larger kinetochore providing a transmission advantage in asymmetric meiosis. Then there are two possibilities: either (1) an adaptive CenH3 mutation changes its binding affinity for centromeric satellites thereby restoring meiotic parity and suppressing centromere drive until a new selfish satellite arises and the cycle begins again, or (2) the evolution of holokinetic chromosomes ends the arms race permanently by means of the extended kinetochore.

Zedek and Bureš analysed selective pressures acting on CENH3 in Luzula (Juncaceae), a genus with holokinetic chromosomes. They found an absence of positive selection, concluding that holokinetic chromosomes could have evolved as a defence against centromere drive.

Reference

Zedek, F., & Bureš, P. (2016). Absence of positive selection on CenH3 in Luzula suggests that holokinetic chromosomes may suppress centromere drive. Annals of Botany, 118(7), 1347–1352. https://doi.org/10.1093/aob/mcw186


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