PT  - JOURNAL ARTICLE
AU  - Shujun Cai
AU  - Chen Chen
AU  - Zhi Yang Tan
AU  - Yinyi Huang
AU  - Jian Shi
AU  - Lu Gan
TI  - Cryo-ET reveals nucleosome reorganisation in condensed mitotic chromosomes <em>in vivo</em>
AID  - 10.1101/178996
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 178996
4099  - http://biorxiv.org/content/early/2017/11/24/178996.short
4100  - http://biorxiv.org/content/early/2017/11/24/178996.full
AB  - Chromosomes condense during mitosis in most eukaryotes. This transformation involves rearrangements at the nucleosome level and has consequences for transcription, but the details remain unclear. Here, we use cryo-electron tomography to determine the 3-D arrangement of nucleosomes and other large nuclear features in frozen-hydrated fission-yeast cells. Nucleosomes can form irregular clusters in both interphase and mitotic cells, but they are smaller than expected for Hi-C domains. The nucleosomes are co-mingled with two features: nucleosome-free pockets and megadalton-sized “megacomplexes”. Compared to interphase, the nucleosomes in mitotic chromosomes pack into slightly larger clusters. However, nearest-neighbor distance analysis reveals that mitotic nucleosome clusters have the same internal packing density as in interphase. Furthermore, mitotic chromosomes contain fewer megacomplexes. This uneven chromosome condensation helps explain a longstanding enigma of mitosis: most genes are repressed but a subset is upregulated.