Constitutive centromere-associated network controls centromere drift in vertebrate cells

Centromeres are specified by sequence-independent epigenetic mechanisms, and the centromere position may drift at each cell cycle, but once this position is specified, it may not be frequently moved. Currently, it is unclear whether the centromere position is stable. To address this question, we systematically analyzed the position of nonrepetitive centromeres in 21 independent clones isolated from a laboratory stock of chicken DT40 cells using chromatin immunoprecipitation combined with massive parallel sequencing analysis with anti–CENP-A antibody. We demonstrated that the centromere position varies among the clones, suggesting that centromere drift occurs during cell proliferation. However, when we analyzed this position in the subclones obtained from one isolated clone, the position was found to be relatively stable. Interestingly, the centromere drift was shown to occur frequently in CENP-U– and CENP-S–deficient cells. Based on these results, we suggest that the centromere position can change after many cell divisions, but this drift is suppressed in short-term cultures, and the complete centromere structure contributes to the suppression of the centromere drift.

Cytological Investigation of Brazilian Nightshade (Solanum seaforthianam Andr.)

Solanum genus namely Solanum seaforthianum Andr. belongs to the Solanaceae family, and comprises only dioeciously species. These plants are distributed between 29º and 40º south. All species of this genus are diploid with chromosome numbers of 2n = 24, 28 and 30. According to literature, the basic chromosome number in this genus is x = 12, 14 and 15. Solanum genus with a chromosome complement of 2n = 30 has a symmetric karyotype with a median and sub median centromere position. Because ancestral species have a symmetric karyotype, it seems that x = 12 is the initial basic chromosome number in this genus and the x = 14 and x = 15 derived from x = 12. So it seems that diploid phenomena played an important role in evolution and speciation

Assembly in G1 phase and long-term stability are unique intrinsic features of CENP-A nucleosomes

Centromeres are the site of kinetochore formation during mitosis. Centromere protein A (CENP-A), the centromere-specific histone H3 variant, is essential for the epigenetic maintenance of centromere position. Previously we showed that newly synthesized CENP-A is targeted to centromeres exclusively during early G1 phase and is subsequently maintained across mitotic divisions. Using SNAP-based fluorescent pulse labeling, we now demonstrate that cell cycle–restricted chromatin assembly at centromeres is unique to CENP-A nucleosomes and does not involve assembly of other H3 variants. Strikingly, stable retention is restricted to the CENP-A/H4 core of the nucleosome, which we find to outlast general chromatin across several cell divisions. We further show that cell cycle timing of CENP-A assembly is independent of centromeric DNA sequences and instead is mediated by the CENP-A targeting domain. Unexpectedly, this domain also induces stable transmission of centromeric nucleosomes, independent of the CENP-A deposition factor HJURP. This demonstrates that intrinsic properties of the CENP-A protein direct its cell cycle–restricted assembly and induces quantitative mitotic transmission of the CENP-A/H4 nucleosome core, ensuring long-term stability and epigenetic maintenance of centromere position.