The role of small GTPases in mammalian cytokinesis

Yu, Xinzi (2007) The role of small GTPases in mammalian cytokinesis. PhD thesis, University of Glasgow.

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Cytokinesis is the final physical separation of two daughter cells, which occurs at the end of mitosis. Emerging evidence has placed membrane trafficking at the heart of mammalian cytokinesis, as it is clear that the control of membrane traffic into the cleavage furrow created by the ingressed acto-myosin contractile ring is vital for the expansion of surface area and proper separation. These findings also indicated that both the secretory and endocytic recycling pathways could be the potential internal membrane stores contributing to this process. Small GTPases are known to play crucial roles in the regulation of intracellular membrane traffic. Recent studies from diverse model systems highlighted roles for two GTPases Rab11 and Arf6 in Drosophila cellularisation, Caenorabditis elegans and mammalian cytokinesis. These proteins are both involved in endosomal recycling, and disraption of them by expressing mutants and RNAi results in severe cytokinesis defects. In a previous study, our group have identified Ai-fophilin2/Rab11-FIP4 as a dual Rab11/Arf binding protein. Immunofluorescence data revealed that FIP4 strikingly localises to the cleavage furrow and the midbody in mammalian cells during cell division. With this information in mind, it is proposed that the interaction of Rab11/Arf6 with Rab11-FIP3/4 may serve to regulate delivery of recycling endosomes (RE) to the furrow/midbody during cytokinesis in mammalian cells. In this thesis, studies were earned out to investigate the function of Rab11 and Arf6 in mitosis. Firstly, the localisation of Rab11 and Arf6 throughout mitosis was examined. Both of the proteins were concentrated at the furrow/midbody region similar to Rab11-FIP4. Using GTP-deficient mutants and RNAi approaches, it was shown that Rab11 and Ajrf6 are both required for mammalian cytokinesis. Furthermore, time-lapse microscopy revealed that these two proteins both function in the late stage of cytokinesis, possibly midbody abscission but not furrow ingression. Many Rab proteins have overlapping endosomal distributions, and therefore the second part of this study examined whether other endosomal Rabs also localise to the dividing site and contribute to membrane delivery to the furrow/midbody. Although none of the Rabs investigated showed characteristic distribution at the cleavage site, interference with one of the Rab GTPases, Rab4, did result in a minor defect in cytokinesis, implicating a role in this process. Finally, preliminary study of regulation mechanism of FIP3 and FIP4 in mitosis was carried out. Bioinformatics and immunoflurorescence experiments implicated that the FIPs may be regulated by cell-cycle dependent kinases. Hence the possibility of FIP3 and FIP4 being phosphorylated by mitotic kinases, such as Aurora B and Polo-like kinase (Plk) was examined. This will provide more leads to elucidate FIP3 and FIP4's function in cell division and better our understanding of the membrane trafficking pathway during cytokinesis.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Developmental biology.
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Gould, Prof. Gwyn
Date of Award: 2007
Depositing User: Enlighten Team
Unique ID: glathesis:2007-71662
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 09:31
Last Modified: 01 Jun 2021 10:07
Thesis DOI: 10.5525/gla.thesis.71662
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