Alpha satellite DNA-repeat OwlAlp1 forms centromeres in Azara's owl monkey.

Centromeres play crucial roles in faithful chromosome segregation and genome integrity. In simian primates, centromeres possess tandem array of alpha satellite DNA (also referred to as alphoid DNA). Average sizes of alpha satellite repeat units vary between species, for example, 171 bp in human and 343-344 bp in many platyrrhini species (New World monkeys). Interestingly, Azara's owl monkey (Aotus azarae), a platyrrhini species, possesses alpha satellite DNA of two distinct unit sizes, OwlAlp1 (185 bp) and OwlAlp2 (344 bp), both of which present as megasatellite DNAs in the genome. It is, however, unknown which repeat sequence is responsible for functional centromere formation. To investigate the localization of centromeres in vivo, we carried out chromatin immunoprecipitation (ChIP) assay using Azara's owl monkey cells. We found that CENP-A, a histone H3 variant essential for centromere formation, was enriched at OwlAlp1, but not at OwlAlp2. Moreover, CENP-A was detected only at constricted regions of chromosomes by immunofluorescent microscopy. In contrast, trimethylation of histone H3-K9 (H3K9me3), a marker of heterochromatin, was enriched at both OwlAlp1 and OwlAlp2. Our results show that the shorter alpha satellite repeat, OwlAlp1, is selectively used for centromere formation in this monkey.