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An analysis of the role of the RasS protein in Dictyostelium cell movement and endocytosis.

Chubb, Jonathan Robert; (2000) An analysis of the role of the RasS protein in Dictyostelium cell movement and endocytosis. Doctoral thesis (Ph.D.), University College London. Green open access

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Abstract

Endocytosis and cell migration are cellular processes requiring transient localised remodelling of the cell cortex. Several lines of evidence suggest a key regulatory role in these activities for members of the Ras family of small GTPases. I have generated Dictyostelium cells lacking one member of this family, RasS, and the mutant cells are perturbed in both endocytosis and cell migration. Mutant amoebae are impaired in phagocytosis and strongly impaired in fluid-phase endocytosis. Conversely, the rasS- cells show an enhanced rate of migration, moving 3 times faster than wild-type controls. The mutant cells have abnormal morphology; they are highly polarised, carry many elongated microspikes and show a concomitant decrease in formation of pinocytotic crowns on the cell surface. 3D analysis of the movement of the mutant cells indicates their rapid movement is due to differences in pseudopodium behaviour. There are fewer pseudopodia per cell, but they have an increased volume and turn over more rapidly. The rasS- phenotype correlates with significant changes in the expression and organisation of components of the actin cytoskeleton. Under specific conditions, the mutant cells show a significant elevation in the expression levels of the actin-binding proteins, talin and coronin. The mutant cells also have abnormal levels of the polymerised form of actin. The polymerisation of actin which occurs in response to chemoattractant stimulation is also distinct in the mutant cells, which show a stronger response than parental cells. The level of the PI 3-kinase product, PI(3,4)P2, is normal in the mutants. The rasS- cells have a lowered cellular level of an unidentified lipid. The axenic mutations, which are known to impinge upon cell motility and endocytosis, can act as genetic modifiers of the rasS- phenotype.

Type: Thesis (Doctoral)
Qualification: Ph.D.
Title: An analysis of the role of the RasS protein in Dictyostelium cell movement and endocytosis.
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by Proquest
URI: https://discovery.ucl.ac.uk/id/eprint/10108291
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