Genome-wide mapping of CTCF binding in asynchronous and mitotic cells

CCCTC-binding factor (CTCF), a conserved and essential regulator of genome architecture bearing a unique complement of 11 zinc fingers (ZFs), has been reported to remain associated with chromatin throughout mitosis and has thus been proposed to act as a bookmark to ensure rapid reestablishment of chromatin structure after cell division. However, little is known about how CTCF is regulated during mitosis. Using a phospho-specific antibody, we found that phosphorylation of CTCF threonine 431, contained within an atypical ZF linker unique to vertebrate CTCF, is highly enriched in mitotic cells and that this phosphorylated form of CTCF is preferentially localized to mitotic chromosomes. We show that T431 mutations abolish the association of CTCF with mitotic chromatin, arguing that T431 phosphorylation is necessary for CTCF mitotic retention. Furthermore, mutation of the CTCF paralog BORIS to accommodate phosphorylation at the residue corresponding to CTCF T431 induces mitotic retention of BORIS. Our data support previous work demonstrating mitotic retention of CTCF and provide new insight into how CTCF remains associated with chromatin during mitosis. Furthermore, our results indicate that phosphorylation of ZF linkers is not exclusively associated with dissociation of ZF-containing proteins from DNA during mitosis. Overall design: Examination of CTCF binding in asynchronous and mitotic cells