Growth forms of the <i>age3</i>Δ/Δ strain after hyphal induction in YPD +10% bovine serum (A and B) or in GlcNAc medium (C).

(A) The strains SN87 (AGE3+/+), UZ22 (AGE3+/Δ), UZ45 (age3Δ/Δ) and UZ55 (age3Δ/Δ::AGE3) were induced for hyphal growth in YPD +10% bovine serum at 37°C. After five hours of growth, samples were inspected under the microscope (most pictures in phase contrast and some in Nomarsky optics). Note that the homozygous age3 mutant strain forms several distinct forms of filaments. Some of them are not true hyphal filaments. Most strikingly, a fraction of germ tubes and filaments show an untypically curved or spiral shape (images e, g, h and i). Some other filaments show constrictions between cells which are typical for pseudohyphae (i). There are also cell clusters seen which are composed of yeast-form cells (c) and others which show only poor polarized growth (d, f and b arrow head). (B) Each one true hyphal filament of the wild-type and the age3 mutant strains grown under the same conditions as in (A) were stained with Calcofluor white and DAPI to visualize septa (arrow heads) and nuclei, respectively. Compared to wild-type filaments, age3 mutant filaments are composed of shorter hyphal cells (except for the first cell following the blastospore in many cases). (C) The strains SN87 (AGE3+/+), UZ45 (age3Δ/Δ) and UZ55 (age3Δ/Δ::AGE3) were induced for hyphal growth in GlcNAc-containing medium. After three hours of growth at 37°C for each clone about 200 cells and filaments were classified as wild-type-like germ tubes and hyphae, yeast cells and aberrant forms of single cells, germ tubes or filaments (curved shape, short pseudohyphal elements, cells with thick germ tubes; as shown in (A)). The experiment was done in triplicate. The mean percentage of these morphologies and standard deviation are shown.