The deletion of CaVPS34 in the human pathogenic yeast Candida albicans causes defects in vesicle-mediated protein sorting and nuclear segregation

A Candida albicans null mutant of the phosphatidylinositol (PI) 3-kinase ge ne (Ca VPS34) involved in virulence was examined by different microscopical techniques. We observed that vacuoles of the Cavps34 null mutant mere cons iderably enlarged and electron-transparent. An interesting result obtained by transmission electron microscopy analysis of Cavps34 mutant cells was th e aberrant patch-like accumulation of vesicles, which were localized in the periplasm close to the plasma membrane, We assume that the vesicles result from missorted prevacuolar compartments, In contrast to the accumulations of the specific endocytic dye FM4-64 in the vacuole membrane in C. albicans wild-type strains (ring staining pattern), the Cavps34 mutant strain showe d a staining of punctuate structures, possibly multivesicular bodies (MVB), that are scattered all over the cell. This defect indicates a late block i n endocytic vesicle transport. Measurement of the total activity of carboxy peptidase Y revealed significantly lower activity in Cavps34 mutant cells. This may indicate that carboxypeptidase Y is not properly activated as a re sult of mislocalization due to the lack of Vps34p, The deletion of the CaVP S34 gene caused disturbance of normal nuclear migration, which suggests tha t in the Cavps34 mutant the cell-size mediated control process of cell divi sion is affected. Copyright (C) 2001 John Wiley & Sons, Ltd.