Molecular Dissection Of SUV39H1-Histone 3-HP1α Axis Underlying Chromosome Dynamics In Mitosis

The mainly function of mitosis is to segregate the duplicated sister chromatids into two daughter cells and maintain the correct genetics. The protein post-translational modification determines the lifespan of proteins, the interaction between proteins, proteins positional distribution and some biochemical function. Some common protein modifications include phosphorylation, acetylation, methylation and ubiquitination. Histone H3K9 trimethylation, as one important epigenetics marker distributed to the transcriptional repression gene, is catalyzed by SUV39H1, a methykransferase specific responsible for H3K9 trimethylation. It has been demonstrated SUV39H1 localizes to centromere in mitosis, and plays an important role in mitotic progression. However, the regulatary mechanism of centromeric H3K9me3 in chromosomes segregation is still not well-known, therefore it is essential to delineate how centromeric H3K9me3 gradient is orchestrated during chromosome segregation and how it achieve chromosome segregation regulation during mitosis.We have exmamined the temporal dynamics of protein methylation in the centromere by SUV39H1, using fluorescence resonance energy transfer-based sensors in HeLa cells and immunofluorescence of native SUV39H1 substrates. A quantitative analysis of methylation dynamics, using centromere-targeted sensors, reveals a temporal change during chromosome alignment and segregation. These dynamics result in an accurate chromosome congression to and alignment at the equator as an inhibition of methylation dynamics using SUV39H1 inhibitor perturbs chromosome congression in living HeLa cells. Surprisingly, this inhibition of methylation results in a brief increase in Aurora B activity and an enrichment of microtubule depolymerase MCAK in the centromere with a concomitant kinetochore-microtubule destabilization and a reduced tension across the sister kinetochores with ultimate chromosome misalignments. We reason that SUV39H1 generates a gradient of methylation marks at the kinetochore that provides spatiotemporal information essential for accurate chromosome segregation in mitosis.Heterochromatin protein 1 alpha (HP1α)is involved in many biology events such as heterochromatin formation, transcription and DNA damage repair through its N terminal chromodomain recognizing H3K9me2/3, and C terminal interacting with a diverse set of proteins. It is known HP1α localizes to centromeric from interphase to mitosis, dissociates from chromosome structure at early mitosis. However, the centromeric HP la localization mechanism during interphase and mitosis and physiological role of HP1α dissociation from chromsome at onset of mitosis are still not well-known. By expressing HP1α mutants (V22M, I165E and W174A) in HeLa cells and SUV39H1 inhibitor treatment assay, we have found interphase centromeric HP1α localization is depended on SUV39H1 activity while early mitotic centromeric localization is relied on some proteins containing PxVxL motif. We also have found HP1α dissociation from chromosome at early mitosis is essential for accurate kinetochore localization of CPC complex, Sgol, Mis14 and MCAK by expressing H2B-HP1α in HeLa cells. A quantitative analysis of sister chromatids separation phenotype, using HP1α rescue assay and chromosome spread analysis, reveals HP1α recuits Sgol to interphase chromatin and mitotic chromosome to protect sister chromatids cohesion. Aurora B antagonizes this HP1-Sgol protection mechanism by promoting HPla dissociation from chromosomes. Our results also suggest persistent chromosome localized HP1α results in the increase of spindle length, the abnormality of chromosomes alignment and segregation by expressing H2B-HPla in HeLa cells, suggesting HP1α dissociation fom chromosome is essential for accurate spindle plasticity and sister chromatids segregation. All of these imply that HP1α dynamics guarrantees the faithful mitotic progression.In sum, our study showed the activity of SUV39H1 is spatio-temporal dynaic during mitosis, and the this dynamics is essential for accurate chromosome alignment. The SUV39H1 interaction protein HP1α localization is also dynamic, we have demonstrated its different localization mechanism from interphase to mitosis and the physiological role of its dissociation from chromosome. In addition, we found Aurora B involved in sister chromatids cohesion deprotection by antagonizing HP1-Sgol pathway. All of these find provides new clue for the mitotic chromosome segregation study.