Cells that grow by apical extension, such as neurons, pollen tubes, root hairs and fungal hyphae, orient their growth in response to tip contact with physical cues in the environment (thigmotropism). I use Candida albicans, an opportunistic human fungal pathogen, as a model to assess tip re-orientation growth responses after contact. Thigmotropism is associated with virulence (Brand et al., 2008), therefore this thesis aims to characterise the responses that C. albicans displays after contact events in an enclosed chamber featuring various obstacles and shapes. It was found that hyphae grow along surfaces in a nose-down manner, presumably to identify and exploit gaps in the substrate. Further, hyphae preferentially grow nose-down on softer surfaces when given the option of two contrasting surfaces, implying novel substrate sensing mechanisms. Contact-dependent hyphal responses are outlined, where perpendicular contact with an obstacle induced various growth responses after re-orientation. Further, important cytoskeletal regulators of thigmotropism were identified, which subsequently regulate substrate indentations. The applied force generated by hyphal tips was quantified, which was enough to penetrate mammalian membranes without the need of hydrolytic enzymes, and this was modulated by a change in environmental carbon source. This thesis describes several new exploratory behaviours in C. albicans, which may apply to hyphae in general, since behaviours described here have also been observed in other filamentous fungi. Further, the role of septins as regulators of directional growth is discussed. The first chapter describes contact-dependent behaviours that support the ability of hyphae to be opportunistic and exploit their topographical environment to invade surfaces. The second chapter presents a detailed description of how the fungus responds to perpendicular contact events. Finally, the third chapter identifies cytoskeletal regulators important for thigmotropism. Together, this thesis brings together multiple aspects of cell biology and biophysics that apply during polarised tip growth, which adds knowledge to the narrative of why hyphae are such successful space invaders.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:600114 |
| Date | January 2014 |
| Creators | Thomson, Darren David |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=206607 |
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