William C. Earnshaw博士 （University of Edinburgh）によるセミナーを開催します。 Earnshaw博士は、細胞分裂期染色体の構造とダイナミクスの細胞生物学者です。遺伝情報を均等に次世代へ引き継ぐ染色体安定性の分子メカニズムを解明し、近年は数理モデルと組み合わせて先端研究を展開されています。英国王立協会、米国National Academy of Sciencesのメンバーでおられます。本セミナーでは最新研究に加え、サイエンスへの情熱を聞けると思います。皆様のご来聴を心よりお待ちします。

 https://www.bioreg.kyushu-u.ac.jp/mib/topics/seminar/r20261106_j.html

第860回　生医研セミナー/ The 860th MIB Seminar

日時: 2026年11月6日（金）15:00〜16:00 / 15:00〜16:00 , Friday, November 6, 2026

場所：病院馬出キャンパス　総合研究棟　104セミナー室

      　Seminar Room 104, 1F, Biomedical Research Station, Hospital Campus

演者：Dr. William C. Earnshaw

所属：University of Edinburgh

タイトル: Approaching Mitotic Chromosome Formation from All Directions

要旨：Attempts to understand how the DNA is packaged in mitotic chromosomes are confounded by the huge size of the DNA, the incredible chromatin density in mitotic chromosomes and the complexity of the machinery that does the DNA packaging. We study this problem by combining chemical genetics, Hi-C genomic analysis, polymer modelling, light and electron microscopy and proteomics. In our system, an entire cell population of chicken DT40 lymphocytes enters mitosis with near perfect synchrony within 2 to 3 minutes of release of a G2 phase arrest. This allows us to “kinetically section” the process and perform biochemical and structural analyses with minute-by-minute resolution. The cells can be engineered so that chromosome formation is directed by single SMC complexes: cohesin, condensin I or condensin II. Our latest models suggest that chromosomes are a disorderly helix of loops created by the SMC complexes. Condensin II drives the formation of cylindrical chromosomes but is restrained from achieving its ideal state by residual cohesive cohesin. Our electron microscopy analysis in human cells reveals that nucleosomes achieve a near millimolar concentration in mitotic chromosomes. The data from our electron microscopy and modelling are most consistent with chromosome formation involving a combination of looping by SMC complexes and chromatin phase separation. However, the chromatin concentration in chromosomes is higher than the concentration of nucleosomes in phase-separated droplets in vitro. The mechanism responsible for this compaction of the chromatin is unknown and we have recently obtained evidence inconsistent with all previous models for how the compaction is achieved. Preliminary evidence suggests that a preference of condensin I for G:C_rich DNA may drive a radial organisation where A:T-rich DNA is preferentially located towards the chromosome periphery. Despite over 140 years of study, the essential mysteries of mitotic chromosome formation remain elusive.

参考文献：

Gibcus, J.H.*, K. Samejima*, A. Goloborodko*, I. Samejima, N. Naumova, J. Nuebler, M. Kanemaki, L. Xie, J.R. Paulson, W.C. Earnshaw†, L.A. Mirny†, J. Dekker†. (2018). A pathway for mitotic chromosome formation. SCIENCE 359: eaao6135. 

 Cisneros-Soberanis, F.†, E. Simpson†, A.J. Beckett, N, Pucekova, S. Corless, N.Y. Kochanova, I.A. Prior, D.G. Booth*, W.C. Earnshaw*. (2024). Near Millimolar Concentration of Nucleosomes in Mitotic Chromosomes from Late Prometaphase into Anaphase, J. CELL BIOL. 223: e202403165 

 K. Samejima†, J.H. Gibcus†, S. Abraham‡, F. Cisneros-Soberanis‡, I. Samejima‡, A.J. Beckett, N. Pučeková, M. Alba Abad, C. Spanos, B. Medina-Pritchard, J.R. Paulson, L. Xie, A.A. Jeyaprakash, I.A. Prior, L.A. Mirny*, J. Dekker*, A. Goloborodko* & W.C. Earnshaw*. (2025). Rules of engagement for condensins and cohesins guide mitotic chromosome formation. Science 388, eadq1709. 

 N.Y. Kochanova†, M. Deb†, M. Borsò†, S. Webb, I. Ustun, K. Samejima, I.i Forne, I. Samejima, C. Reid, L. Xie, J.R. Paulson., A. Imhof* & W.C. Earnshaw*. (2026).  A time-resolved atlas of histone modifications during mitotic entry MOL. CELL 86:1653-1672.e9. 

 世話人：生体防御医学研究所 がんゲノム制御学分野 斉藤典子

Noriko Saitoh, Division of Cancer Genome Biology, Medical Institute of Bioregulation

E-mail: saitoh.noriko.885@m.kyushu-u.ac.jp,

Phone: 092-642-4233