Project Summary: Candida albicans is an opportunistic fungal pathogen capable of causing mucosal and
systemic disease. Oropharyngeal candidiasis (OPC) is a frequent fungal disease in humans, and can potentially
spread to other locations in the body causing systemic infections. Even with clinical intervention, systemic
candidiasis has a mortality rate of ~40%. OPC involves the formation of biofilms in the oral mucosa that contain
multiple C. albicans morphotypes, including both yeast and hyphal cells. The ability of C. albicans to form
different cell types is crucial for virulence and contributes to its capacity to colonize different host tissues.
The transition between yeast and hyphal cells is regulated by a network of transcription factors (TFs) that
include the co-repressor Ssn6. Deletion of Ssn6 blocks formation of hyphal cells and attenuates C. albicans
virulence. Ssn6 is also integral to a second TF network that regulates transitions between ‘white’ and ‘opaque’
states that exhibit different tissue tropisms in the host. Importantly, the Bennett lab has uncovered that multiple
TFs (including Ssn6) in both networks contain prion-like domains (PrLDs) and that these can promote phase
separation of the corresponding proteins. Phase separation refers to the process of liquid demixing that can
generate protein condensates with liquid-like properties. This phenomenon is now implicated in the formation of
many cellular structures including nucleoli, Cajal bodies, stress granules, and transcriptional complexes. While
a number of studies on TF phase separation have been conducted, these studies primarily focus on
transcriptional activators and not on transcriptional co-repressors such as Ssn6.
Previous work in our lab has shown that C. albicans TFs containing PrLDs readily form phase-separated
condensates when purified or when expressed in mammalian cells. Moreover, deletion or mutation of PrLDs can
eliminate the ability of these TFs to function in C. albicans cells. My preliminary data shows Ssn6 is also able to
form condensates, both individually and with other fungal TFs. I hypothesize that phase separation plays a key
role in the ability of Ssn6 to act as a co-repressor in regulating cell morphology, and that it will contribute to
virulence during OPC. In Aim 1, I will examine the biochemical properties of Ssn6 condensates. In Aim 2, I will
address how changes to Ssn6 properties impact C. albicans morphotypes in vitro as well as virulence using a
mouse model of OPC.
Additionally, the goals of this fellowship include developing skill sets in order to lead a successful research
career. Attending conferences, presenting to the department and graduate program, and regular meetings with
the sponsor are planned to this end. The training plan will be carried out in an environment that benefits from the
Molecular Biology, Cell Biology, and Biochemistry Graduate Program. Completion of the proposed goals will
advance both the field of Candida biology and the ability of the recipient to become an effective independent
scientific researcher.
