A kymograph, displaying the passage of time on the x axis, shows how chromosome separation is regulated in cell division, or more specifically, mitotic anaphase. From the lab of Hélder Maiato at the University of Porto, Portugal, multiple kinetochore pairs (CID-mCherry, red) and spindle microtubules (GFP–α-tubulin, blue above/green below) are visible as a cell progresses through mitosis.
The lab uses RNAi to knock out specific gene expression, along with laser microsurgery and fluorescent-speckle microscopy to study kinetochore function in living animal cells.
Our present research interests are focused in understanding how mitotic fidelity is regulated in space and time, paying particular attention to how the spindle matrix confines SAC signaling and how error-correction mechanisms at the kinetochore-microtubule interface are regulated throughout mitosis.
Maiato began studying +TIPs as a graduate student, focusing his early efforts on the importance of a protein family called CLASPs in mitosis. He has shown that CLASPs shape the mitotic spindle by working both at kinetochores and centrosomes.
“Not satisfied with narrowly studying one protein,” he has since broadened his inquiries into other +TIPs and into mitosis more generally.
Recently, Maiato curated an issue of Chromosome Research on the topic of biased chromosome segregation, an area of study based on an idea from 1975 that non-random chromosome segregation is one way in which stem cells retain their pluripotency, through passing on the newly synthesised (i.e. more probably mutated) strand to the differentiating somatic cell. This came to be known as the immortal DNA strand hypothesis, and seems to still be much under dispute.
In the base of this controversy over the years lie a number of experimental limitations, such as the difficulty of unequivocally distinguishing and selecting stem cells, of correlating these cells with selective labeling of older or newer DNA strands, and of labeling DNA in a nontoxic manner. The debate is also motivated by the near absence of a clear working model for how the mitotic apparatus distinguishes and segregates sister chromatids, such as to separate them according to the age of their respective DNA strands.
Finally, discussions have also concerned what the function of biased chromosome segregation might be, questioning its role in conserving sequence information but suggesting that it could play an important role in the segregation of epigenetic states. In any case, these discussions made clear that here, as in many other fields of cell biology, the demonstration of the molecular mechanisms underlying a given process is paramount to establishing its true nature and allowing discussions about its possible meaning
The issue contains a particularly interesting proposal from Arnold Bendich, that uniparental inheritance of organelle DNA may be seen as “a mechanism of DNA abandonment in organelles that have been exposed to extensive DNA damaging agents,” e.g. reactive oxygen species.
This week's Journal of Cell Biology features an interview with Maiato, providing a glimpse into his life both in and out of the lab. Read it here.
► Chromosome Research, May 2013: Biased Chromosome Segregation
► Maiato lab research page
► Matos et al (2009) Synchronizing chromosome segregation by flux-dependent force equalization at kinetochores. Journal of Cell Biology 186(1): 11–26
► Cairns (1975) Mutation selection and the natural history of cancer. Nature 255:197–200
► Salmon et al (2002) Dual-wavelength fluorescent speckle microscopy reveals coupling of microtubule and actin movements in migrating cells. Journal of Cell Biology, 158(1):31–37
► Magidson et al (2007) Laser microsurgery in the GFP era: a cell biologist's perspective. Methods in Cell Biology 82: 239-66
► Lara-Gonzalez et al (2012) The Spindle Assembly Checkpoint. Current Biology 22, R966–R980
