Septins enforce morphogenetic events during sexual reproduction and contribute to virulence of Cryptococcus neoformans

Abstract

Summary Septins are conserved, cytoskeletal GTPases that contribute to cytokinesis, exocytosis, cell surface organization, and vesicle fusion by mechanisms that are poorly understood. Roles of septins in morphogenesis and virulence of a human pathogen and basidiomycetous yeast Cryptococcus neoformans were investigated. In contrast to a well established paradigm in S. cerevisiae, Cdc3, and Cdc12 septin homologs are dispensable for growth in C. neoformans yeast cells at 24°C but are essential at 37°C. In a bilateral cross between septin mutants, cells fuse but the resulting hyphae exhibit morphological abnormalities including lack of properly fused specialized clamp cells and failure to produce spores. Interestingly, post-mating hyphae of the septin mutants have a defect in nuclear distribution. Thus, septins are essential for the development of spores, clamp cell fusion and also play a specific role in nuclear dynamics in hyphae. In the post-mating hyphae the septins localize to discrete sites in clamp connections, to the septa, and the bases of the initial emerging spores. Strains lacking CDC3 or CDC12 exhibit significantly reduced virulence in a Galleria mellonella model of infection. Thus, C. neoformans septins are vital to morphology of the hyphae and contribute to virulence.

The Septin AspB in Aspergillus nidulans Forms Bars and Filaments and Plays Roles in Growth Emergence and Conidiation

“…Finally, there have been recent reports of similar septin bar and filament structures in other filamentous fungi. In C. albicans Cdc10 septin filaments were observed during the final stage of chlamydospore morphogenesis (42), and Cdc3 and Cdc10 filaments were observed in a small percentage of C. neoformans dikaryotic hyphae (36). In A. gossypii, a series of short bars has been observed to form the mature septin ring (15).…”

“…In the filamentous fungus Ashbya gossypii septins appear to promote mitosis near new branches and septins form rings made of discrete thick septin bars in hyphae and thin filaments at hyphal tips. In the basidiomycete Cryptococcus neoformans, septins are involved in morphology, sporulation, clamp cell fusion, and nuclear dynamics and septins localize to emerging spores, septa, and clamp connections (36). In addition, Cdc10 and Cdc3 were occasionally observed to form filaments in hyphae.…”

Analysis ofCryptococcus neoformansSexual Development Reveals Rewiring of the Pheromone-Response Network by a Change in Transcription Factor Identity

“…These known "mating genes" included those encoding mating pheromone (MFa1, MFa2, MFa3), the pheromone receptor (STE3a), and other mate recognition and signaling components (CPK1, GPA2, GPA3, RAC1, RAS1, RAS2, STE6, STE7, STE14, and STE12a) (Alspaugh et al 2000;Chang et al 2000;Davidson et al 2003;Hsueh and Shen 2005;Vallim et al 2005;Hsueh et al 2007). Structural components known as septins are critical during conjugation tube formation preceding cellular fusion (Kozubowski and Heitman 2010). Known septins CDC3, CDC10, CDC11, and CDC12 and the uncharacterized predicted septin CNB04900 are all members of cluster 1 (average fivefold induction during the 0.5-to 6-hr interval).…”

Cryptococcus neoformans Phosphoinositide-Dependent Kinase 1 (PDK1) Ortholog Is Required for Stress Tolerance and Survival in Murine Phagocytes

“…Because our studies as well as those reported by Lee et al (32) and Liu et al (31) indicated that loss of PKH2-02 affects a number of important cellular processes that could also influence pathogenesis, we hypothesized that pkh2-02⌬ mutants might display virulence defects independent of high-temperature growth. To test this hypothesis, we took advantage of the ability of C. neoformans to cause disease in Galleria mellonella at temperatures below mammalian body temperature (37°C) as a means to further dissect the role of PKH2-02 in C. neoformans pathogenesis (48). As shown in Fig.…”