Myosin I Is Required for Hypha Formation in Candida albicans

Abstract

The pathogenic yeast Candida albicans can undergo a dramatic change in morphology from round yeast cells to long filamentous cells called hyphae. We have cloned the CaMYO5 gene encoding the only myosin I in C. albicans. A strain with a deletion of both copies of CaMYO5 is viable but cannot form hyphae under all hypha-inducing conditions tested. This mutant exhibits a higher frequency of random budding and a depolarized distribution of cortical actin patches relative to the wild-type strain. We found that polar budding, polarized localization of cortical actin patches, and hypha formation are dependent on a specific phosphorylation site on myosin I, called the "TEDS-rule" site. Mutation of this serine 366 to alanine gives rise to the null mutant phenotype, while a S366D mutation, the product of which mimics a phosphorylated serine, allows hypha formation. However, the S366D mutation still causes a depolarized distribution of cortical actin patches in budding cells, similar to that in the null mutant. The localization of CaMyo5-GFP together with cortical actin patches at the bud and hyphal tips is also dependent on serine 366. Intriguingly, the cortical actin patches in the majority of the hyphae of the mutant expressing Camyo5 S366D were depolarized, suggesting that although their distribution is dependent on myosin I localization, polarized cortical actin patches may not be required for hypha formation.

Transcript Profiles of Candida albicans Cortical Actin Patch Mutants Reflect Their Cellular Defects: Contribution of the Hog1p and Mkc1p Signaling Pathways

“…In C. albicans, perturbations in the actin cytoskeleton are coupled to defects in hyphal development. For example, myosin I function is important for proper cortical actin patch distribution and for endocytosis and is critical for the formation of true hyphae (41,42). The sla2⌬ mutant also exhibits defects in both hyphal formation and the organization of cortical actin patches (5) (see Fig.…”

“…Cultures of the various strains grown overnight in YPD were diluted 1:20 in YPD supplemented with 10% fetal bovine serum and grown for 1 to 2 h at 37°C. Rhodamine-phalloidin (Molecular Probes, Eugene, Oregon) and calcofluor white (Sigma) staining was done as described by Oberholzer et al (41). Cytochalasin A was added where indicated to a final concentration of 5 M. Staining of lipid rafts with filipin III (Sigma) was done as described previously (36), as was the procedure for visualizing FM4-64 uptake (54).…”

“…The actin cytoskeleton of the fungal pathogen C. albicans plays a key role in morphogenesis and hyphal formation (1,4,5,32,41,55,58). In yeasts, this cytoskeleton is comprised of cortical actin patches found at sites of polarized growth and actin cables that serve as tracks for secretion of vesicles to sites of polarized growth (11,45,46).…”

“…S. cerevisiae myosin I (Myo3/5p) and Sla2p have been shown to play important roles in organizing the actin cytoskeleton and mediating endocytosis by the cortical actin patches (18,28,33,34). In addition, C. albicans SLA2 and MYO5 are required for hyphal formation, MYO5 being the unique gene encoding myosin I, hereby designated Myo5p (5,41).…”

A Class-V Myosin Required for Mating, Hyphal Growth, and Pathogenicity in the Dimorphic Plant PathogenUstilago maydis [W]

“…The best-characterized myosin is MyoA, a class-I myosin from Aspergillus nidulans (McGoldrick et al, 1995), which is involved in endocytosis and hyphal morphogenesis (Osherov et al, 1998;Yamashita and May, 1998). Such a role of class-I myosins in the formation of hyphae was confirmed recently in Candida albicans (Oberholzer et al, 2002). However, studies with Saccharomyces cerevisiae and Schizosaccaromyces pombe demonstrate that class-V myosins are major organelle transporters that mediate secretory vesicle delivery and morphogenesis (Govindan et al, 1995;Karpova et al, 2000;Motegi et al, 2001;Win et al, 2001).…”