NudCL2 is required for cytokinesis by stabilizing RCC2 with Hsp90 at the midbody

Cytokinesis is required for faithful division of cytoplasmic components and duplicated nuclei into two daughter cells.Midbody,a protein-dense organelle that forms at the intercellular bridge,is indispensable for success-ful cytokinesis.However,the regulatory mechanism of cytokinesis at the midbody still remains elusive.Here,we unveil a critical role for NudC-like protein 2(NudCL2),a co-chaperone of heat shock protein 90(Hsp90),in cytokinesis regulation by stabilizing regulator of chromosome condensation 2(RCC2)at the midbody in mam-malian cells.NudCL2 localizes at the midbody,and its downregulation results in cytokinesis failure,multinu-cleation,and midbody disorganization.Using iTRAQ-based quantitative proteomic analysis,we find that RCC2 levels are decreased in NudCL2 knockout(KO)cells.Moreover,Hsp90 forms a complex with NudCL2 to stabilize RCC2,which is essential for cytokinesis.RCC2 depletion mirrors phenotypes observed in NudCL2-downregulated cells.Importantly,ectopic expression of RCC2 rescues the cytokinesis defects induced by NudCL2 deletion,but not vice versa.Together,our data reveal the significance of the NudCL2/Hsp90/RCC2 pathway in cytokinesis at the midbody.

Dynamic distribution of Ser-10 phosphorylated histone H3 in cytoplasm of MCF-7 and CHO cells during mitosis

The dynamic distribution of phosphorylated Histone H3 on Ser10 (phospho-H3) in cells was investigated to determineits function during mitosis. Human breast adenocarcinoma cells MCF-7, and Chinese hamster cells CHO were analyzedby indirect immunofluorescence staining with an antibody against phospho-H3. We found that the phosphorylationbegins at early prophase, and spreads throughout the chromosomes at late prophase. At metaphase, most of the phospho-H3 aggregates at the end of the condensed entity of chromosomes at equatorial plate. During anaphase and telophase,the fluorescent signal of phospho-H3 is detached from chromosomes into cytoplasm. At early anaphase, phospho-H3shows ladder bands between two sets of separated chromosome, and forms “sandwich-like structure” when the chro-mosomes condensed. With the cleavage progressing, the “ladders” of the histone contract into a bigger bright dot. Thenthe histone aggregates and some of compacted microtubules in the midbody region are composed into a “bar-like”complex to separate daughter cells. The daughter cells seal their plasma membrane along with the ends of the “bar”,inside which locates microtubules and modified histones, to finish the cytokinesis and keep the “bar complex” out of thecells. The specific distribution and kinetics of phospho-H3 in cytoplasm suggest that the modified histones may takepart in the formation of midbody and play a crucial role in cytokinesis.