PAX3 loads onto pericentromeric heterochromatin during S phase through PARP1.

Background: Proper re-establishment of heterochromatin after each round of DNA replication is critical to the preservation of cell identity. Paired box 3 (PAX3), a transcription factor important in embryonic development, was found to mediate the formation of pericentromeric heterochromatin. However, how PAX3 recognizes the heterochromatic environment and re-establishes it after DNA replication remains unclear. Materials and Methods: Cell-cycle synchronization, fluorescence microscopic analyses, and co-immunoprecipitation were used to analyze the heterochromatic localization of PAX3 in HEK 293 cells and NIH 3T3 cells. Results: We found that PAX3 binds pericentromeric heterochromatin during middle-to-late S phase. Loading of PAX3 onto pericentromeric heterochromatin requires poly(ADP-ribose) polymerase 1 (PARP1). Furthermore, loss of PAX3 or PARP1 delays cell-cycle progression through the S phase. Conclusion: Our results reveal how PAX3 recognizes and maintains pericentromeric heterochromatin at the S phase of the cell cycle.