Quantitative Proteomics of the Mitotic Chromosome Scaffold Reveals the Association of BAZ1B with Chromosomal Axes[S]

• Published in: Molecular & cellular proteomics 2019-02, Vol.18 (2), p.169-181
• Main Authors: Ohta, Shinya, Taniguchi, Takako, Sato, Nobuko, Hamada, Mayako, Taniguchi, Hisaaki, Rappsilber, Juri
• Format: Article
• Language: English
• Subjects: Animals; Cell Biology; Cell Cycle; Cell Division; Cell Line; Chromatin Function or Biology; Chromosome; Chromosomes - metabolism; Gene Knockout Techniques; HeLa Cells; Humans; Mitosis; Proteomics - methods; SILAC; Transcription Factors - genetics; Transcription Factors - metabolism
• ISSN: 1535-9476; 1535-9484
• DOI: 10.1074/mcp.RA118.000923

Our quantitative proteomics study determined the protein composition of the mitotic chromosome scaffold. MS results revealed a novel component of the chromosome scaffold, BAZ1B, which was localized to the mitotic chromosome axis. Our results using BAZ1A/B double-KO cells suggest that BAZ1 proteins are essential for timely chromosome condensation at mitosis entry. [Display omitted] Highlights •Quantitative proteomics of mitotic chromosome scaffold isolated from chicken DT40 cells.•BAZ1B identified in the isolated mitotic chromosome scaffold localizes to mitotic chromosome axes.•BAZ1B knockout caused prophase delay because of altered chromosome condensation timing and impaired mitosis progression.•BAZ1B knockout did not affect prometaphase chromosome structure. In mitosis, chromosomes achieve their characteristic shape through condensation, an essential process for proper segregation of the genome during cell division. A classical model for mitotic chromosome condensation proposes that non-histone proteins act as a structural framework called the chromosome scaffold. The components of the chromosome scaffold, such as DNA topoisomerase IIα (TOP2A) and structural maintenance of chromosomes protein 2 (SMC2), are necessary to generate stable mitotic chromosomes; however, the existence of this scaffold remains controversial. The aim of this study was to determine the protein composition of the chromosome scaffold. We used the DT40 chicken cell line to isolate mitotic chromosomes and extract the associated protein fraction, which could contain the chromosome scaffold. MS revealed a novel component of the chromosome scaffold, bromodomain adjacent to zinc finger 1B (BAZ1B), which was localized to the mitotic chromosome axis. Knocking out BAZ1B caused prophase delay because of altered chromosome condensation timing and mitosis progression errors, and the effect was aggravated if BAZ1A, a BAZ1B homolog, was simultaneously knocked out; however, protein composition of prometaphase chromosomes was normal. Our results suggest that BAZ1 proteins are essential for timely chromosome condensation at mitosis entry. Further characterization of the functional role of BAZ1 proteins would provide new insights into the timing of chromosome condensation.