Regulation of X. laevis M18BP1 centromeric localization and CENP-A assembly

Area of Science:

• Cell Biology
• Epigenetics
• Molecular Biology

Background:

• Eukaryotic chromosome segregation relies on kinetochore-microtubule attachments for proper cell division.
• Kinetochores assemble on centromeres, epigenetically marked by CENP-A, a histone H3 variant.
• CENP-A is duplicated during DNA replication and reassembled in G1, but the regulation of this timing is key.

Purpose of the Study:

• To investigate the cell cycle-dependent regulation of CENP-A nucleosome assembly.
• To identify the role of the Mis18 complex, specifically M18BP1, in timing CENP-A deposition.
• To elucidate a novel phosphoregulatory mechanism controlling M18BP1 binding to CENP-A.

Main Methods:

• Studied cell cycle-dependent phosphorylation of *Xenopus laevis* M18BP1.
• Assessed the impact of phosphorylation on M18BP1 binding to CENP-A nucleosomes across different cell cycle phases.
• Investigated the functional consequences of this phosphorylation switch on CENP-A nucleosome assembly.

Main Results:

• Identified cell cycle-dependent phosphorylation of M18BP1 between metaphase and interphase.
• Demonstrated that phosphorylation disrupts M18BP1 binding to CENP-A in metaphase.
• Showed that dephosphorylation in interphase enables M18BP1 binding and regulates CENP-A assembly.

Conclusions:

• A novel phosphoregulatory switch in M18BP1 controls its interaction with CENP-A nucleosomes.
• This mechanism restricts the timing of new CENP-A assembly to the appropriate cell cycle phase.
• This regulation is critical for the epigenetic maintenance of centromeres and kinetochores.