The aim of this study was to investigate the role of Ca<sup>2+</sup> signalling pathways in the growth, morphogenesis and hyphal reorientation responses of <i>C. albicans</i>. The genes <i>CCH1</i> and <i>MID1</i> were identified in <i>S. cerevisiae</i> as encoding putative Ca<sup>2+</sup> channels. These genes have since been shown to compose a Ca<sup>2+</sup> channel complex. Homologues of these genes were identified and cloned from <i>C. albicans</i>. <i>CaMID1</i> was disrupted by the Ura-blaster method, and the resulting mutant characterised. The <i>C. albicans</i> <i>mid1</i> mutant strain was sensitive to the depletion of Ca<sup>2+</sup> the presence of cell wall perturbing compounds such as SDS and Calcofluor. It formed hyphae more rapidly in the presence of serum, and had a propensity to grow as elongated cells or pseudohyphae in Ca<sup>2+</sup>-depleted medium, on SD, or on medium containing cell wall perturbing compounds. This suggests that depletion of Ca<sup>2+</sup>-uptake perturbs yeast-hypha morphogenesis, perhaps by inducing a nutrient starvation stress response. The <i>mid1</i> mutant and a number of other <i>C. albicans</i> Ca<sup>2+</sup> signalling mutants were defective in chlamydospore formation, suggesting a role for Ca<sup>2+</sup> in two morphogenetic genesises: the hyphae and of chlamydospores. The role of Mid1p in the thigmotropic reorientation responses of <i>C. albicans</i> hyphae was investigated. The <i>mid1</i> mutant strain displayed reduced ability to reorientate growth upon contact with ridges on an etched quartz slide. Suggesting that Mid1p may function as stretch-activated Ca<sup>2+</sup> channel in <i>C. albicans</i>. The ability of <i>C. albicans</i> <i>mid1</i> mutants to respond to an electric field was also attenuated, suggesting that Mid1p may form part of a voltage-sensitive Ca<sup>2+</sup> channel in <i>C. albicans</i> that plays a central role in the steering mechanism of <i>C. albicans</i> hyphae. The <i>C. albicans </i>kinase Cst20p may function downstream of Mid1p in growth reorientation responses.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:252135 |
| Date | January 2002 |
| Creators | Shanks, Scott G. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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