Polarization of plasma membrane lipids contributes to hyphal morphogenesis in Candida albicans.
Stephen Martin, Javier Alvarez, James Konopka
Molecular Genetics & Microbiol, SUNY Stony Brook, Life Sciences Bldg., Stony Brook, NY, 11794-5222, USA
Polarization of sterol- and sphingolipid-enriched domains (lipid rafts) has been linked to morphogenesis and cell movement in diverse cell types. In the yeast S. cerevisiae, dramatic polarization of strerol-rich domains to the shmoo tip was observed in pheromone-induced cells . We therefore examined whether plasma membrane lipid polarization contributes to the ability of the fungal pathogen C. albicans to grow in a highly polarized manner to form hyphae. Interestingly, staining with filipin revealed that membrane sterols were highly polarized to the leading edge of growth during all stages of hypha growth. Budding and pseudohyphal cells did not display polarized staining. Ergosterol polarization is apparently due to clustering of lipid rafts at the hyphal tip, since detergent resistant membranes, a hallmark of lipid rafts, were found in both budding and hyphal cells. Filipin staining was also enriched at septation sites in hyphae, where colocalization with septin proteins was observed, suggesting a role for the septins in forming a boundary domain. Furthermore, blocking either sphingolipid biosynthesis with myriocin, or sterol biosynthesis with ketoconazole, resulted in loss of ergosterol polarization and caused abnormal hyphal morphogenesis, suggesting lipid rafts are involved. Since hyphal growth is required for full virulence of C. albicans, these results suggest that membrane lipid polarization contributes to the pathogenesis of this organism.
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