Octameric CENP-A Nucleosomes Are Present at Human Centromeres throughout the Cell Cycle

Abstract

The presence of a single centromere on each chromosome that signals formation of a mitotic kinetochore is central to accurate chromosome segregation. The histone H3 variant centromere protein-A (CENP-A) is critical for centromere identity and function; CENP-A chromatin acts as an epigenetic mark to direct both centromere and kinetochore assembly. Interpreting the centromere epigenetic mark ensures propagation of a single centromere per chromosome to maintain ploidy. Thus, understanding the nature of CENP-A chromatin is crucial for all cell divisions. However, there are ongoing debates over the fundamental composition of centromeric chromatin. Here we show that natively assembled human CENP-A nucleosomes are octameric throughout the cell cycle. Using total internal reflection fluorescence (TIRF)-coupled photobleaching-assisted copy-number counting of single nucleosomes obtained from cultured cells, we find that the majority of CENP-A nucleosomes contain CENP-A dimers. In addition, we detect the presence of H2B and H4 in these nucleosomes. Surprisingly, CENP-A associated with the chaperone HJURP can exist as either monomer or dimer, indicating possible assembly intermediates. Thus, our findings indicate that octameric CENP-A nucleosomes mark the centromeric region to ensure proper epigenetic inheritance and kinetochore assembly.

Structural transitions of centromeric chromatin regulate the cell cycle-dependent recruitment of CENP-N

“…A recent study showed that CENP-A nucleosomes undergo transitions in nucleosome composition during the cell cycle (Bui et al 2012). However, other studies support the notion that CENP-A nucleosomes are octameric throughout the cell cycle (Hasson et al 2013;Padeganeh et al 2013).…”

“…Based on several earlier studies, a number of contradictory models have been proposed for the composition and stoichiometry of CENP-A nucleosomes (Furuyama and Henikoff 2009;Black and Cleveland 2011;Bui et al 2012;Miell et al 2013Miell et al , 2014Padeganeh et al 2013;Codomo et al 2014;Walkiewicz et al 2014). However, several more recent reports supported the idea that, throughout the entire cell cycle, CENP-A chromatin mainly consists of octameric nucleosomes rather than nonoctameric forms (for example, tetrasomes, hemisomes, and hexasomes) (Hasson et al 2013;Padeganeh et al 2013).…”

Distinct modes of centromere protein dynamics during cell cycle progression in Drosophila S2R+ cells

“…In human cells, however, octasomes were proposed to be present in S phase and not during mitosis. Although in human cells many of these observations have also been questioned (Miell et al, 2013;Hasson et al, 2013;Padeganeh et al, 2013b), the possibility that different nucleosome structures could contribute to the different centromeric Cid states during the S2R+ cell cycle might deserve consideration.…”

The increase in medial prefrontal glutamate/glutamine concentration during memory encoding is associated with better memory performance and stronger functional connectivity in the human medial prefrontal–thalamus–hippocampus network

“…The literature on the medial prefrontal cortex (mPFC) is dominated by studies regarding its role in decision making (Euston, Gruber, & McNaughton, 2012), but recent evidence suggests that the mPFC may also play a role in memory (Szczepanski and Knight, 2014; Preston and Eichenbaum, 2013; van Kesteren, Rijpkema, Ruiter, & Fernández, 2013; Euston et al, 2012; van Kesteren, Ruiter, Fernandez, & Henson, 2012; Takashima et al, 2006; Bontempi, Laurent‐Demir, Destrade, & Jaffard, 1999). The mPFC appears to serve as a critical hub obtaining, integrating and applying knowledge for long‐term use (Fernández, 2017).…”