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Structural Transitions of Centromeric Chromatin Regulate Cell Cycle-dependent Recruitment of CENP-N

May 13, 2015     Email"> PrintText Size

The centromere is a specialized chromatin domain that provides a platform for kinetochore assembly and microtubule attachment and plays a crucial role in chromosome segregation during mitosis. Centromere-specific histone H3 variant, centromere protein A (CENP-A), functions as an epigenetic mark for the formation and maintenance of centromeres.

Centromere protein N (CENP-N) was identified as the first “reader” of epigenetic marks present in the CENP-A chromatin. Specific recognition of CENP-A chromatin by CENP-N is an essential process in the assembly of the kinetochore complex at centromeres prior to mammalian cell division. However, the mechanism of CENP-N recruitment to centromeres remains unknown.

Professor LI Guohong's group at the Institute of Biophysics (IBP) of Chinese Academy of Sciences revealed the dual function of CENP-A in the recruitment of CENP-N and the folding of centromeric chromatin. The group found that a CENP-A-specific RG loop (Arg80/Gly81) plays an essential role in the recruitment of CENP-N. CENP-A chromatin forms a featured “ladder-like” structure and the RG loop assists the formation of the “ladder-like” structure. CENP-N specifically binds to open CENP-A chromatin and compaction of CENP-A chromatin impairs the binding of CENP-N.

The researchers demonstrated that the higher-order organization of centromeric chromatin undergoes a structural transition from a compact state in Gap 1 (G1) phase to an open state in Synthesis (S) phase. They also verified that CENP-N is stably loaded in middle/late S phase. This structural transition of chromatin is consistent with the dynamic loading of CENP-N onto centromeres during the cell cycle. Thus they proposed that structural transitions of higher-order structure of centromeric chromatin orchestrate the temporal loading of CENP-N to centromeres via regulating the accessibility of the RG loop in CENP-A chromatin during the cell cycle.

This work provided critical insight to better understand the structure and function of centromeric chromatin and how the epigenetic information encoded in CENP-A-containing nucleosomes is read and transmitted.

The paper entitled “Structural transitions of centromeric chromatin regulate the cell cycle-dependent recruitment of CENP-N” was published in Genes & Development.

This study is supported by the Ministry of Science and Technology of China, the National Natural Science Foundation, and the Chinese Academy of Sciences.


Figure: Model for structural transitions of centromeric chromatinregulating the cell cycle-dependent recruitment of CENP-N (Image by IBP) 


(Editor: CHEN Na)


LI Guohong

National Laboratory of Biomacromolecule, Institute of Biophysics

E-mail: liguohong@sun5.ibp.ac.cn

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