The role of the centrosome in genome integrity and epithelial cell polarity

Previous and current research
Asymmetric chromosome segregation is a hallmark of many human cancers. Gain or loss of chromosomes (also termed genomic instability) during mitosis or multipolar cell divisions leads to defective chromosome partitioning and hence aneuploidy. Multipolar mitotic spindles are generated by numerical, structural or functional abnormalities of the centrosome, the main microtubule organising centre in animal cells. Such aberrant spindle formations are particularly dangerous to cells as no surveillance mechanisms exist for their elimination. Centrosome anomalies are present in many aneuploid tumours including malignancies of breast, bladder and pancreas amongst others. Despite the apparent link between centrosome and cancer, we are at an early stage in understanding the normal function of the centrosome and we know even less about the mechanisms and consequences of its deregulation in disease. Our long term aim is to gain better understanding of the molecular basis of centrosome function in cell division, and tissue organisation.

Future projects
The TACC family of centrosomal proteins regulate the activity of ch-Tog, an essential microtubule-stabilising factor. Using RNA interference in human cells, I previously showed that reducing ch-Tog levels is sufficient to induce multipolar spindle formation, without the need for abnormal centrosome numbers. Cells with multipolar spindles often exit from mitosis, leading to aberrant interphase cells with multiple or satellite nuclei. We are now using a vertebrate reverse genetic system, DT40 cells, to create mutations in ch-Tog and the TACC proteins in order to quantify the rate of chromosome gain and loss over many cellular generations in the mutant backgrounds. We hope this approach will provide a molecular link between centrosome function and genomic instability. Disruption of tissue organisation and polarity is a common feature of many tumours. Polarisation in cells must be accompanied by changes in centrosome behaviour, however these changes are not well characterised. Cultured cells have serious limitations for modelling complex diseases such as cancer. Cells isolated from their normal microenvironment do not behave like their counterparts within an intact tissue. Therefore, in order to learn about centrosomal abnormalities in epithelial cancer, it is essential to use a model system that mimics tissue organisation. Currently, we are establishing three-dimensional cell culture models for the study of centrosome and microtubule function in polarised epithelial cells.