Raimondi, E. | Search bioRxiv

bioRxiv2024

CENP-A/CENP-B uncoupling in the evolutionary reshuffling of centromeres

BackgroundWhile CENP-A is the epigenetic determinant of the centromeric function, the role of CENP-B, the sole centromeric protein binding a specific DNA sequence (CENP-B-box), remains elusive. In the few mammalian species analyzed so far, the CENP-B box is contained in the major satellite repeat that is present at all centromeres. We previously demonstrated that, in the genus Equus, some centromeres lack any satellite repeat. ResultsHere, we show that, in four Equus species, CENP-B is expressed but does not bind the numerous satellite-free and the majority of satellite-based centromeres while it is localized at several ancestral now inactive centromeres. The absence of CENP-B is related to the lack of CENP-B boxes rather than to peculiar features of the protein itself. CENP-B boxes are comprised in a previously undescribed repeat which is not the major satellite bound by CENP-A. Comparative sequence analysis suggests that this satellite was centromeric in the equid ancestor, lost centromeric function during evolution and gave rise to a short CENP-A bound repeat not containing the CENP-B box but being enriched in dyad symmetries. Centromeres lacking CENP-B are functional and recruit normal amounts of the centromeric proteins CENP-A and CENP-C. ConclusionsWe propose that the uncoupling between CENP-B and CENP-A may have played a role in the evolutionary reshuffling of equid centromeres. This study provides new insights into the complexity of centromere organization in a largely biodiverse world where the majority of mammalian species still have to be studied.

genomics↗

bioRxiv2022

Neocentromere formation through Robertsonian fusion and centromere repositioning during the evolution of zebras

Centromeres are epigenetically specified by the histone H3 variant CENP-A and typically associated to highly repetitive satellite DNA. We previously discovered natural satellite-free neocentromeres in Equus caballus and E. asinus. Here, through ChIP-seq with an anti-CENP-A antibody, we found an extraordinarily high number of centromeres lacking satellite DNA in the zebras E. burchelli (15 of 22) and E. grevyi (13 of 23), demonstrating that the absence of satellite DNA at the majority of centromeres is compatible with genome stability and species survival and challenging the role of satellite DNA in centromere function. Nine neocenstromeres are shared between the two species in agreement with their recent separation. We de novo assembled all neocentromeric regions and improved the reference genome of E. burchelli. Sequence analysis of the CENP-A binding domains revealed that they are LINE-1 and AT-rich with four of them showing DNA amplification. In the two zebras, satellite-free centromeres emerged from centromere repositioning or following Robertsonian fusion. In five chromosomes, the centromeric function arose near the fusion points, which are located within regions marked by traces of ancestral pericentromeric sequences. Therefore, besides centromere repositioning, Robertsonian fusions are an important source of satellite-free centromeres during evolution. Finally, in one case, a neocentromere was seeded on an inversion breakpoint. At eleven chromosomes, whose primary constrictions seemed to be associated to satellite repeats by cytogenetic analysis, neocentromeres were instead located near the ancestral inactivated satellite-based centromeres, therefore, the centromeric function has shifted away from a satellite repeat containing locus to a satellite-free new position.

genomics↗