Roles and regulation of the actin cytoskeleton

Prof K R Ayscough

Cells of all organisms receive many signals that must be interpreted in order to make appropriate responses. It is important for cells to be able to co-ordinate these different signalling pathways so they can perform their correct functions. Research in my laboratory is aimed at determining essential features of cells that allow them to integrate the many ongoing processes. We are particularly interested in the function of one protein called actin. Actin is part of a structure called the cytoskeleton (meaning cell skeleton) that helps give a cell its shape. Unlike a human skeleton however, actin is very dynamic and constantly rearranging. The ability of actin filaments to assembly and disassemble on a very short timescale is critical for many cell processes including polarity and motility. We also believe that this dynamic quality allows actin to act as a sensor of cell environment to assess energy levels and whether the cell is under stress. If the environment is good, then essential cell processes can go ahead. If actin cannot function properly due to low energy or because it is modified by oxidants it can cause cells to enter a process resulting in cell-death

We work on a number of proteins that interact with actin to regulate its organisation and dynamic properties during endocytosis and membrane trafficking in both healthy and stressed cells. While this is a fundamental cell biology problem, which we study mostly using the model organism Saccharomyces cerevisiae (budding yeast), knowing how cells integrate responses to these signals impacts on our understanding of disorders including neurodegeneration and cancer.

Within the lab we use a broad range of approaches to understand this fundamental cell protein including genetics, biochemistry, molecular and cell biology. PhD students who train in the lab usually learn a wide range of skills that can be applied to many different research fields.

Figure 1. Actin in yeast can be studied by staining the protein with a specific stain. This allows us to determine whether changes in the genetic make-up of the cell influence the behaviour and organisation of actin structures. The images show actin localisation in cells at different stages of the cell cycle. The small actin spots or ‘patches’ are sites of endocytosis while the longer cables are thought to represent tracks for movement of vesicles to sites of exocytosis.

Figure 2: Schematic illustrating the functions of actin-regulatory proteins in driving the endocytic process. Endocytosis is necessary to allow remodelling of plasma membrane protein and lipids and for downregulation of certain receptor proteins. This process can also be exploited by certain toxins and virus to facilitate their entry into the cell. Defects with the endocytic machinery can be observed in many neurodegenerative disorders including Huntingdon’s and Alzheimers

Selected Publications

Aghamohammadzadeh, S. and Ayscough K.R (2010). The Yeast Actin Cytoskeleton and its Function in Endocytosis. Fungal Biology Reviews. In Press.

Aghamohammadzadeh, S. and Ayscough K.R (2009) Differential Requirements for Actin during Yeast and Mammalian Endocytosis. Nature Cell Biol. 11. 1039-1042.

Du, W. and Ayscough KR. (2009) Methyl ¾-Cyclodextrin reduces accumulation of reactive oxygen species and cell death in yeast. Free Radic. Biol. Med. 46. 1478-1487.

Francois, I.E.J.A., A. Bink, J. Vandercappellen, K.R. Ayscough, A. Toulmay, R. Schneiter, E. van Gyseghem, G. Van den Mooter, M. Borgers, D. Vandenbosch, T. Coenye, B.P.A. Cammue, and K. Thevissen. Membrane rafts are involved in intracellular miconazole accumulation in yeast cells. (2009) J. Biol. Chem. 284. 32680-5

Robertson, A.S., Allwood, E.G., Smith, A.P., Gardiner, F.C., Costa, R., Winder, S.J. and Ayscough, K.R. (2009) The WASP homolog Las17 activates the novel actin-regulatory activity of Ysc84 to promote endocytosis in yeast. Mol. Biol. Cell. 20. 1618-1628

Robertson, A.S., Smythe, E. and Ayscough, K.R. (2009) The Functions of Actin in Endocytosis. Cell and Molecular Life Sciences 66. 2049-2065

Leadsham JE, Miller K, Ayscough KR, Colombo S, Martegani E, Sudbery P, Gourlay CW (2009) Whi2p links nutritional sensing to actin-dependent Ras-cAMP-PKA regulation and apoptosis in yeast. J Cell Sci. 122 706-715

D.M. Gheorghe, S. Aghamohammadzadeh, I. I. Smaczynska-de Rooij, E.G Allwood, S.J. Winder and K.R. Ayscough (2008) Interactions between the yeast Sm22 homologue Scp1 and actin demonstrate the importance of actin bundling in endocytosis. J. Biol. Chem. 283. 15037-46

Smaczynska-de Rooij, I.I., Costa, R., Ayscough, K.R. (2008) Yeast Arf3p modulates plasma membrane PtdIns(4,5)P2 levels to facilitate endocytosis. Traffic 9: 559-573

Gardiner, F.C, Costa, R. and Ayscough, K.R. (2007) Nucleocytoplasmic trafficking is required for functioning of the adaptor protein Sla1p in endocytosis. Traffic 8: 347-358.

Thevissen, K. Ayscough, K.R. Aerts, A.M., Du,W., De Brucker, K., Meert, E.M.K., Ausma, J., Borgers, M. Cammue, B., Francois, I.E.J.A. (2007) Miconazole induces changes in actin cytoskeleton prior to ROS induction in yeast. J.Biol. Chem. 282: 21592-21597.

Gourlay, C.W. and K.R. Ayscough, (2006) Apoptosis in Yeast - mechanisms and benefits to a unicellular organism. Molecular Microbiology. 62, 1515-1521.

Smythe, E. and Ayscough, K.R. (2006) Regulation of Actin in Endocytosis. Journal of Cell Science. 119, 4589-4587

Gourlay, C.W. and Ayscough, K.R.(2006) Actin induced hyperactivation of the Ras signaling pathway leads to apoptosis in S. cerevisiae. Mol. Cell Biol. 26; 6487-6501

Gourlay C.W. and Ayscough K.R. (2005) The actin cytoskeleton: a key regulator of apoptosis and ageing? Nature Reviews Molecular and Cell Biology. 6: 583-589

C.W. Gourlay, L..N. Carpp, P. Timpson, S.J. Winder, and K.R. Ayscough. (2004) A Role for the Actin Cytoskeleton in Cell Death and Ageing in Yeast J. Cell Biol. 164: 803-809