Dynamic chromosomal interactions and control of heterochromatin positioning by Ki67

Abstract Ki67 forms a protective layer around mitotic chromosomes and is involved in genome positioning around nucleoli during interphase. However, a lack of genomic interaction maps has hampered a detailed understanding of the role of Ki67 in chromatin organization. We used pA-DamID to map genome-Ki67 interactions in three human cell lines and throughout the cell cycle. In mitosis, Ki67 shows a surprising preference for the distal 15-30 Mb of each chromosome. Early in interphase, when Ki67 is present in pre-nucleolar bodies, this is replaced by a pattern of large domains that overlaps with late-replicating DNA, which gradually shifts towards small chromosomes. Nucleolar perturbations indicate that these cell cycle dynamics correspond to nucleolar maturation during interphase. Furthermore, Ki67 competes with the nuclear lamina for interaction with late-replicating DNA, and controls replication timing at (peri)centromeric regions. Together, these results reveal a highly dynamic choreography of genome interactions and roles for Ki67 in genome organization.