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Investigating the role of IPIP27 in cell division.
[Thesis]. Manchester, UK: The University of Manchester; 2017.
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Abstract
Cytokinesis is the physical process of cell division. It is a fundamental process drivenby the dynamic remodelling of an actomyosin contractile ring coupled to thecoordinated reorganisation of the plasma membrane. The dynamic rearrangement ofthe actin cytoskeleton for the successful completion of cytokinesis relies upon theprecise spatio-temporal coordination of several pathways. OCRL1, thephosphatidylinositol-4,5-bisphosphate 5-phosphatase that is mutated in LoweSyndrome, is involved in mediating successful cytokinesis by remodelling the actincytoskeleton through the hydrolysis of its substrate, PtdIns(4,5)P2 in order to regulatethe progression of cytokinesis. However, the mode of action and the interactionsinvolved in OCRL1 function in cytokinesis remain to be determined. IPIP is a bindingpartner of OCRL1 that also interacts with actin-associated proteins. In this study, therole of IPIP in cell division was investigated as well as its potential assistance toOCRL1 function in cytokinesis.Investigations were carried out in two cell-based systems; mammalian cells andDrosophila S2 cells using an RNAi approach. Live imaging revealed actin-dependentcortical instability during cell division in the absence of IPIP in both systems. Inaddition, the loss of IPIP increased the frequency of cytokinesis failure with anaccumulation of actin- and PtdIns(4,5)P2-rich intracellular vacuoles in Drosophila cells,thereby phenocopying the loss of OCRL1 in these cells. Similar investigations into theactin-associated interaction partners of IPIP showed that the depletion of F-BARdomain protein pacsin2 also resulted in cortical instabilities comparable to the depletionof IPIP. Moreover, rescue experiments suggest that the interaction of IPIP with pacsin2, or another SH3 domain protein, is required for its function in successful cytokinesis.Based on the data, two non-mutually exclusive models for IPIP function in cell divisionare proposed. In the first model, IPIP helps to stabilise OCRL1 recruitment toendosomes and enhances its catalytic activity through binding to pacsin2, in order tomodulate endosomal PtdIns(4,5)P2 homeostasis that in turn is essential for corticalactin stability and assembly of the cytokinetic ring. In the second model, IPIP directlypromotes cortical actin stability through an interaction with pacsin2 at the plasmamembrane, helping to stabilise its association with actin, the plasma membrane andother cortical components. Together, the data reveal that IPIP is a novel player in celldivision, and suggest that it functions to regulate actin dynamics during this keyprocess.
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an accompanying CD with the movies of the stills shown in figures in the thesis written on it.