Temporal dynamics of morphogenesis and gene expression reveals distinctions between and filamentation.

is a common human fungal pathogen that is also a commensal of the oral cavity and gastrointestinal tract. pathogenesis is linked to its transition from budding yeast to filamentous morphologies including hyphae and pseudohyphae. The centrality of this virulence trait to pathobiology has resulted in extensive characterization of a wide range of factors associated with filamentation with a strong focus on transcriptional regulation. The vast majority of these experiments have used conditions to induce the yeast-to-filament transition. Taking advantage of approaches to quantitatively characterize both morphology and gene expression during filamentation during mammalian infection, we have investigated the dynamics of these two aspects of filamentation and compared them to filament induction with "host-like" tissue culture media supplemented with serum at mammalian body temperature. Although filamentation shares many common features in the two conditions, we have found two significant differences. First, alternative carbon metabolism genes are expressed early during filamentation and late , suggesting significant differences in glucose availability. Second, begins a hyphae-to-yeast transition after 4-h incubation while we find little evidence of hyphae-to-yeast transition up to 24 h post-infection. We show that the low rate of hyphae-to-yeast transition is likely due to the very low expression of , a key driver of lateral yeast and that heterologous expression of is sufficient to trigger lateral yeast formation .IMPORTANCE filamentation is correlated with virulence and is an intensively studied aspect of biology. The vast majority of studies on filamentation are based on induction of hyphae and pseudohyphae. Here we used an filamentation assay and expression profiling to compare the tempo of morphogenesis and gene expression between and filamentation. Although the hyphal gene expression profile is induced rapidly in both conditions, it remains stably expressed over a 12-h time course while it peaks after 4 h and is reduced. This reduced hyphal gene expression correlates with reduced hyphae and increased hyphae-to-yeast transition. By contrast, there is little evidence of hyphae-to-yeast transition .