Takashi Toda

Mitotic spindle microtubules and genome stability control

It has become clear that the understanding of genome stability is a key for the biology of cancer cells and pharmaceutics for cancer therapy. Using fission yeast as a model system, our laboratory has been attempting to elucidate the molecular bases underlying genome stability.

Not surprisingly a number of factors, extracellular and intracellular cues, result in genome instability, and the cell has developed various strategies in order to tackle these adverse conditions. At the heart of genome stability is the mechanism that ensures the accurate partition of genetic materials, DNA packed as chromosomes. In eukaryotic cells, spindles, which are mitotic-specific structures of polarised microtubules, play an essential role in capturing, pulling and segregating sister chromatids. Central for spindle function in chromosome segregation is its bipolarity.

Multiple structural and regulatory networks underlie spindle bipolarity. Firstly, the centrosomes are to duplicate and separate, thereby acting as the MTOC (MicroTubule Organising Centre), which is required for the formation of two half spindles emanating from the two opposite poles. Second, the plus ends of spindles are to capture the kinetochores in a bivalent fashion, namely the spindles attach each pair of sister chromatids at the kinetochore. Thirdly, the kinetochore of each sister chromatid is to be bi-oriented so that bivalent attachment of the kinetochores to the spindles is secured. One of the key questions in establishment of this bivalent attachment is how a physical interaction between the mitotic spindles and the kinetochore is achieved.

Our laboratory isolated a number of temperature-sensitive mutants that are defective in chromosome segregation and spindle structures ^1-4. The graduate student will work on these mutants in order to understand the molecular function of these gene products. Techniques involved are yeast genetics, molecular biology, biochemistry and cell biology. In particular we will focus our efforts on cell biology. This includes live cell analysis using GFP-tagged proteins and immunofluorescence microscopy.

Cancer Research UK has an excellent microscopy unit, which helps our work. If proteins of our interest are evolutionarily conserved, characterisation of human homologues using tissue culture cells will be pursued.

References

1. Sato M and Toda T. Alp7/TACC is a crucial target in Ran-GTPase-dependent spindle formation in fission yeast. Nature 2007; 447: 334-337.
2. Toya M, Sato M, Haselmann U, Asakawa K, Brunner D, Antony C, Toda T. Gamma-tubulin complex-mediated anchoring of spindle microtubules to spindle-pole bodies requires Msd1 in fission yeast. Nat Cell Biol 2007; 9: 646-653.
3. Asakawa K, Toya M, Sato M, Kanai M, Kume K, Goshima T, Garcia MA, Hirata D, Toda T. Mal3, the fission yeast EB1 homologue, cooperates with Bub1 spindle checkpoint to prevent monopolar attachment. EMBO Rep 2005; 6: 1194-1120.
4. Harrison C, Katayama S, Dhut S, Chen D, Jones N, Bähler J, Toda T. SCF(Pof1)-ubiquitin and its target Zip1 transcription factor mediate cadmium response in fission yeast. EMBO J 2005; 24: 599-610.