Molecular mechanisms of mitotic progression and completion
The major focus of my laboratory is to precisely define the mechanisms regulating a mitotic cell division. Cell division (mitosis) results in the generation of two independent daughter cells. It is the final phase of the cell cycle and consists of six distinct stages – prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis. Progression through these phases is highly regulated and is thought to involve membrane trafficking proteins, such as those required for endocytosis. However, their role is poorly understood and it is not known if these proteins function in an endocytic-dependent or –independent manner. We and others have reported on the mitotic roles of the endocytic proteins, dynamin II (dynII) and clathrin, and both participate in this process independent of each other and in a non-endocytic-dependent manner. In addition to dynII and clathrin, we have since discovered 12 other endocytic proteins, e.g. sorting nexin 9 (SNX9) that are also required for mitotic progression and completion. These proteins appear to function during cytokinesis in an endocytic-dependent manner but during earlier stages of mitosis in an endocytic-independent manner. This represents a significantly new and broad concept in mitosis that endocytic proteins are intimately linked with mitosis. Many of these endocytic proteins, e.g. dynII, SNX9, intersectin 2, are phosphorylated during mitosis. Given phosphorylation regulates their endocytic function, we hypothesise that their mitotic function is also regulated by phosphorylation. We have generated tagged-expression constructs and siRNA molecules targeting each endocytic protein. Thus, we are now in a unique position and research projects in this area aim to ascribe new roles to this subset of endocytic proteins. The outcomes of the research will be an improved understanding of the molecular mechanisms of mitosis and insight into the pathways that regulate this process. The results will directly contribute to improved understanding of cancer progression as cancer cells frequently harbor an altered mitotic program as well as the identification of druggable targets to treat this disease.
Projects currently in the lab are:
1) SNX9 has two mitotic roles: i) in stabilising the mitotic spindle poles for chromosome alignment and segregation during metaphase; and ii) in regulating vesicular trafficking during cytokinesis to generate two independent daughter cells. We have also identified 7 phosphorylation sites on SNX9. This project aims to understand the molecular mechanisms of action of SNX9 during mitosis and how these are regulated by each of the distinct phosphorylation sites.
2) Using large-scale proteomics and super-resolution microscopy (SRM) we show that clathrin has two mitotic roles: i) during prophase in spindle assembly; and ii) during metaphase in spindle stabilisation for chromosome alignment and segregation. Using SRM we have shown that this second role involves clathrin localising to the mitotic spindle in a highly ordered manner. This project aims to understand the underlying reason for this localisation and to determine the proteins that it forms a complex with at the mitotic spindle.
3) During cytokinesis, vesicles traffic towards the abscission site to generate two independent cells. We discovered that a calcium influx activates the phosphatase, calcineurin, to dephosphorylate dynII immediated prior to membrane abscission and completion of cytokinesis. This project aims to understand the temporal and spatial deliver of calcium and thus calcineurin activation and how this relates to vesicle trafficking.
The Children’s Medical Research Institute (CMRI) is an award-winning state-of-the-art medical research facility, with over 100 full-time scientists dedicated to researching the genes and proteins important for health and human development. The CMRI is supported in part by its key fundraiser Jeans for Genes®. Our scientists are internationally recognised research leaders and foster excellence in postgraduate training. CMRI graduates are highly sought after nationally and internationally. CMRI is located at Westmead, a major hub for research and medicine in NSW, and is affiliated with the University of Sydney. Easy to access by public transport. Projects are multi-disciplinary with training in molecular and cellular biology techniques, with some involving mass spectrometry, proteomics, protein-protein interactions, transgenic animals or live cell imaging. We are looking for top quality students who can prove a dedicated interest and enthusiasm for scientific research.
Candidates may apply for a CMRI PhD scholarship, which exceeds the Australian Postgraduate Awards and NHMRC scholarships in value; visit the CMRI http://www.cmri.org.au/Research/For-Students for details.
Projects in the Cell Cycle Unit involve cell biology, molecular biology and biochemistry techniques such as cell culture, immunofluorescence and time-lapse live cell microscopy as well as cutting-edge high-speed and super-resolution microscopy, protein-protein interaction assays and detection and functional analysis of post-translational modifications as well as anti-cancer drug analysis in cells and in vivo.Eligibility: PhD entry: Hons I classification, lab-based research experience is preferable.
Want to find out more?
mitosis, cytokinesis failure, aneuploidy, protein phosphorylation, endocytic proteins, dynamin, mitotic inhibitory drugs, cell cycle, Cancer, the final stage of mitosis, cytokinesis, cell signaling, clathrin, SNX9, intersectin 2, metaphase, mitotic spindle assembly checkpoint
The opportunity ID for this research opportunity is: 1013
Other opportunities with Dr Megan Chircop (nee Fabbro)