Ocular disease-associated mutations diminish the mitotic chromosome retention ability of PAX6

Transcription factors play a key role in maintaining cell identity. One mechanism of such cell memory after multiple rounds of cell division cycles is through persistent mitotic chromosome binding, although how individual transcription factors achieve mitotic chromosome retention is not completely understood. Here we show that PAX6, a lineage-determining transcription factor, coats mitotic chromosomes. Using deletion and point mutants associated with human ocular diseases in live-cell imaging analysis, we identified two regions, MCR-D1 and MCR-D2, that were responsible for mitotic chromosome retention of PAX6. We also identified three nuclear localization signals (NLSs) that contributed to mitotic chromosome retention independent of their nuclear import functions. Full mitotic chromosome retention required the presence of DNA-binding domains as well as NLSs within MCR-Ds. Furthermore, disease-associated mutations and NLS mutations changed the distribution of intrinsically disordered regions (IDRs) in PAX6. Our findings not only identify PAX6 as a novel mitotic chromosome retention factor but also demonstrate that the mechanism of mitotic chromosome retention involves sequence-specific DNA binding, NLSs, and molecular conformation determined by IDRs. These findings link mitotic chromosome retention with PAX6-related pathogenesis and imply similar mechanisms for other lineage-determining factors in the PAX family.