Professor Tomo Tanaka
To maintain genetic integrity, eukaryotic cells must duplicate their chromosomes and then segregate them to their daughter cells with high fidelity during each cell division cycle. The unravelling of the mechanisms ensuring these processes should improve our understanding of various human diseases such as cancers and congenital disorders, which are characterized by chromosome instability and aneuploidy.
For our studies, we use mainly budding yeast because of the amenable genetics and detailed proteomic information available for this organism. Overwhelming evidence suggests that the basic mechanisms of chromosome regulation are well conserved from yeast to humans. Budding yeast is therefore an excellent model organism for the study of chromosome duplication and segregation. In particular, we focus on the following research topics:
1) Chromosome duplication in space and time
Chromosome duplication is a highly organized process both in space and time. Using time-lapse microscopy, we have developed a novel assay to analyse dynamics of DNA replication in live cells (Kitamura et al, 2006). We found that sister replication forks, generated from the same origin, are associated with each other during DNA replication (Kitamura et al, 2006). We also found that multiple pairs of sister forks stochastically associate to create replication factories where cells undergo de novo DNA replication (Saner et al 2013) (Figure 1). We investigate further how chromosome duplication is regulated spatially and temporally and how the dynamics of this vary from cell to cell.
2) Kinetochore-microtubule interaction in mitosis
Kinetochores are large protein complexes formed at the centromere region of chromosomes. For high-fidelity chromosome segregation, kinetochores must be properly caught on the mitotic spindle (reviewed in Tanaka TU 2010). We have found that kinetochores initially interact with the lateral surface of a single microtubule extending from a spindle pole (Tanaka K et al, 2005, Kitamura et al, 2007) (Figure 2, step 2); this process is often facilitated by microtubules generated at kinetochores (Kitamura et al, 2010) (Figure 2, step 1). Subsequently kinetochores are tethered at the microtubule plus ends (Tanaka K et al, 2007; Maure et al, 2011) (Figure 2, step 3; Figure 3). When this process encounters problems, a failsafe mechanism prevents kinetochore detachment from a microtubule (Gandhi et al, 2011), giving another chance of end-on kinetochore tethering (Figure 3). We are studying the mechanisms regulating these processes in further detail.
Following the initial interaction with microtubules, sister kinetochores must interact with microtubules extending from opposite spindle poles (sister kinetochore bi-orientation) before anaphase onset (Figure 2, step 6). If this interaction occurs with aberrant orientation (Figure 2, step 4), such errors must be corrected by turnover of the kinetochore-microtubule attachment (error correction) (Figure 2, step 5). We have found that Aurora B/Ipl1 kinase, Mps1 kinase and cohesins have crucial roles in this process (Dewar et al, 2004; Maure et al, 2007; Keating et al, 2009), and we are investigating relevant mechanisms in more detail.
3) Three wise kinetochore functions
The main function of kinetochores is to create microtubule attachment sites. However, kinetochores have at least two additional functions: first they promote robust sister chromatid cohesion at pericentromeres, and second they advance replication timing of centromeric regions. Both functions are important for high fidelity chromosome segregation in mitosis. We identified a common molecular mechanism promoting these functions (Natsume at al 2013) and we study how exactly this mechanism works.
4) Sister chromatid separation and segregation
Once all sister kinetochores have bi-oriented on the spindle, separation and segregation of sister chromatids are initiated by removal of sister chromatid cohesion. We have found that, to complete sister chromatid separation, condensins play crucial roles in recoiling stretched chromosomes, thus removing residual cohesion between sister chromatids along chromosome arm regions(Renshaw et al, 2010) (Figure 4). We are studying this mechanism further and extending our studies to vertebrate cells.
Lectures in Level 3 and Level 4 modules (BS31006 Gene Regulation and Expression; 4B11 cell cycle)
Supervisor of honours degree and PhD students
Major publications from the group
Saner N, Karschau J, Natsume T, Gierlinski M, Retkute R, Hawkins M, Nieduszynski CA, Blow JJ, de Moura APS, and Tanaka TU. Stochastic association of neighboring replicons creates replication factories in budding yeast. J Cell Biol, 202, 1001-12. (2013)
Natsume T, Müller CA, Katou Y, Retkute R, Araki H, Blow JJ, Shirahige, K, Nieduszynski CA, Tanaka TU. Kinetochores coordinate pericentromeric cohesion and early DNA replication by Cdc7-Dbf4 kinase recruitment. Mol Cell, 50, 661-74. (2013).
Gandhi S.R, Gierlinski M, Mino A, Tanaka K, Kitamura E, Clayton L & Tanaka T.U. (2011). Kinetochore-dependent microtubule rescue ensures their efficient and sustained interactions in early mitosis. Dev Cell, 21, 920-33. PMID: 22075150 View Paper
Maure J-F*, Komoto S*, Oku Y, Mino A, Pasqualato S, Natsume K, Clayton L, Musacchio A & Tanaka T.U. (2011).The Ndc80 loop region facilitates formation of kinetochore attachment to the dynamic microtubule plus end. Curr Biol, 21, 207-13. (* equal contribution) PMID: 21256019 View Paper
Tanaka T.U. (2010). Kinetochore-microtubule interactions: steps towards bi-orientation. Embo J, 29, 4070-82. PMID: 21102558 View Paper
Renshaw MJ, Ward JJ, Kanemaki M, Natsume K, Nedelec FJ & Tanaka T.U. (2010). Condensins promote chromosome recoiling during early anaphase to complete sister chromatid separation. Dev Cell, 19, 232-44. PMID: 20708586 View Paper
Kitamura E*, Tanaka K*, Komoto S*, Kitamura Y, Antony C & Tanaka T.U. (2010). Kinetochores generate microtubules with distal plus ends: their roles and limited lifetime in mitosis. Dev Cell, 18, 248-59. (* equal contribution) PMID: 20159595 View Paper
Maure J-F, Kitamura E & Tanaka T.U. (2007). Mps1 kinase promotes sister kinetochore bi-orientation by a tension-dependent mechanism. Curr Biol, 17, 2175-82. PMID: 18060784 View Paper
Kitamura E, Tanaka K, Kitamura Y & Tanaka T.U. (2007). Kinetochore-microtubule interaction during S phase in Saccharomyces cerevisiae. Genes Dev, 21, 3319-30. PMID: 18079178 View Paper
Tanaka K, Kitamura E, Kitamura Y & Tanaka T.U. (2007). Molecular mechanisms of microtubule-dependent kinetochore transport towards spindle poles. J Cell Biol, 178, 269-81. PMID: 17620411 View Paper
Kitamura E, Blow J.J & Tanaka T.U. (2006). Live-cell imaging reveals replication of individual replicons in eukaryotic replication factories. Cell, 125, 1297-308. PMID: 16814716 View Paper
Tanaka K, Mukae N, Dewar H, van Breugel M, James EK, Prescott AR, Antony C & Tanaka T.U. (2005). Molecular mechanisms of kinetochore capture by spindle microtubules. Nature 434, 987-94. PMID: 15846338 View Paper
Dewar H, Tanaka K, Nasmyth K & Tanaka T.U. (2004). Tension between two kinetochores suffices for their bi-orientation on the mitotic spindle. Nature 428, 93-97. PMID: 14961024 View Paper
Errors in chromosome duplication or segregation generate cells with missing or excessive chromosomes (aneuploidy). Aneuploidy could cause various human diseases such as cancers and congenital disorders. It is therefore crucial to understand the molecular mechanisms ensuring proper chromosome duplication and segregation.