Examining the role of RFG1 in Candida albicans filamentation and virulence

The major human fungal pathogen Candida albicans can switch its morphology between yeast and filamentous forms and it is this process that is thought to be pivotal to its ability to cause disease. Genetic analysis had revealed that this developmental process is both positively and negatively regulated by the interplay of a complex network of proteins. To this end, the transcription factors Efg1p, Cph1p and Czf1p function as positive regulators (required for filamentation) whereas Tup1p, Nrg1p and Rfg1p proteins operate as negative regulators. Previous studies from our lab focused on Nrg1p and its role in the control of C. albicans filamentation and virulence. This was achieved through the construction of a strain in which NRG1 gene expression could be manipulated both in-vitro and in-vivo. Experiments performed with this strain have provided the most compelling evidence to date linking filamentation to the ability of C. albicans to cause hematogenously disseminated candidiasis.;In an attempt to reinforce this connection, we have employed a similar strategy to analyze the role of the Rfg1p protein which has also been reported to function as a repressor of filamentation. Here we present details on the construction and characterization of an engineered strain in which we can control the expression of RFG1. Our results indicate that over expression of RFG1 does not inhibit filamentation in hypha inducing conditions in-vitro nor attenuate the virulence of the fungus in-vivo. Intriguingly, however overexpression of RFG1 drives the unexpected phenotype of pseudohyphal formation in conditions which normally support yeast form growth.