Preventing chromosome segregation errors in anaphase

To sustain life, cells must be able to divide into two genetically identical daughters. During cell division, chromosomes must be precisely apportioned into the two daughter cells so that all the genetic information remains intact. Although surveillance mechanisms exist to ensure the accuracy of this process, errors can occur. These errors can lead to cells with the wrong numbers of chromosomes and to birth defects, miscarriage, cancer and ageing. One of the key proteins involved in error correction is an enzyme known as Aurora B, and work from many laboratories has shown that Aurora B acts early during cell division to minimise mistakes. However, it is clear that the error correction machinery is not foolproof, and certain types of error are not detected during the early stages of cell division. The aim of this project is to understand how cells deal with persistent errors and, in particular, to determine how Aurora B regulates chromosome sorting during the late stages of cell division to make sure that accurate inheritance of genetic material is maintained.

Proper chromosome segregation is essential for genome integrity. Errors lead to birth defects and may contribute to carcinogenesis and ageing. To prevent mis-segregation, sister chromatids must be properly attached to microtubules emanating from opposite spindle poles, and the separation of chromatids in anaphase must be repressed until all chromosomes are attached to the spindle in a bi-oriented state. Even in normal cells, numerous attachment errors occur before bi-orientation is established. These errors are generally detected during prometaphase by surveillance mechanisms that allow their release and correction by the centromeric kinase Aurora-B. In addition, the mitotic checkpoint prevents anaphase until all chromosomes are attached. However, certain errors (e.g. merotelic attachments) are inefficiently corrected and not detected by the mitotic checkpoint. This leads to chromosomes lagging near the midzone of the cell during anaphase, a source of aneuploidy, DNA damage and chromothrypsis (extensive chromosomal rearrangements found in cancer). Because Aurora-B is removed from
centromeres in anaphase, it is commonly assumed that its role in error correction ends, and it remains unclear how cells deal with lagging chromosomes in late mitosis. However, we have found that Aurora B substrates are phosphorylated at the kinetochores specifically of lagging chromosomes in anaphase. We will therefore determine how Aurora-B regulates chromosome attachments by phosphorylation of kinetochores on lagging chromosomes. The work may reveal a new error correction mechanism for chromosome segregation during anaphase.

The project proposed here will reveal a novel error correction mechanism for chromosome segregation during anaphase and lead to a clearer understanding of the function of intracellular gradients in biology. This will provide a high impact in the scientific research community in the short and long term. The most immediate impact will be in the cell division research community mainly through publication of new findings in high impact open access journals and talks at international conferences.

During the project, we will develop, modify and refine reagents and chemical- and opto-genetic tools to allow us to study Aurora B activity within specific time frames of mitosis. These cutting-edge research techniques to allow tight regulation of protein localization and activity in time and space within cells are based on tools developed by leaders in the field in the USA. These will be brought back to Newcastle where members of the Higgins group, the Bio-Imaging Unit, the wider university, and other UK collaborators will be able to adopt these generally applicable techniques. New reagents will be made available to the general academic community after publication. The RA working on the project will benefit from improved skills, knowledge and experience gained from the research, and also from associated training. This work will also more generally benefit other members of the Cell Division Biology Group, including PhD students, through exposure to new techniques and developing theories.

This project will have high impact in the cell division and aneuploidy research community, and, in the longer term, for oncology, ageing and fertility treatment. Understanding a new mechanism that monitors or controls chromosome segregation during late mitosis (and meiosis) would almost certainly provide new insight into the origin of these defects, facilitating diagnosis and screening during IVF treatments, for example. Moreover, understanding the biological function of the anaphase gradient will provide new insight into cell division mechanisms, and potentially could contribute to the development of novel preventative and therapeutic techniques for cancer. Members of the Cell Division Biology Research Group in Newcastle, including Profs Higgins, Endicott and Noble have direct experience in developing new small molecule inhibitors, and are involved in one of only four major small molecule cancer drug discovery programmes in the UK, based on the Northern Cancer Institute at Newcastle University.

Commercially exploitable intellectual property (IP) will be assessed prior to publication in partnership with Newcastle University's Commercial Development Team (CDT), which includes specialists in corporate finance, legal, management and marketing. The University provides funding to aid patent protection where necessary, and has a history of supporting spin-out companies for commercialisation of IP directly arising from its research activities. Therefore, there is a clear path to impact through the development of new tool or drug compounds.

The project will also provide opportunities to engage the general public. Both the PI and the named RA have a demonstrated interest in this, having already been involved in scientific outreach to schools and youth organisations, and helping with the successful "Soap Box Science" event in central Newcastle, and a "Meet the Scientist" day focusing on cell division at the International Centre for Life museum. These activities will encouraged and continued.