Maintenance of Mating Cell Integrity Requires the Adhesin Fig2p

Abstract

Fungal adhesins represent a large family of serine/threonine-rich secreted glycoproteins. Adhesins have been shown to play roles in heterotypic and homotypic cell-cell adhesion processes, morphogenetic pathways and invasive/pseudohyphal growth, frequently in response to differentiation cues. Here we address the role of the Saccharomyces cerevisiae mating-specific adhesin Fig2p. Cells lacking FIG2 possess a variety of mating defects that relate to processes involving the cell wall, including morphogenetic defects, cell fusion defects, and alterations in agglutination activities. We found that mating-specific morphogenetic defects caused by the absence of FIG2 are suppressible by increased external osmolarity and that, during mating, fig2⌬ cells display reduced viability relative to wild-type cells. These defects result from alterations in signaling activated by the mating and cell integrity pathways. Finally, we show that fig2⌬ zygotes also have defects in zygotic spindle positioning that are osmoremedial, whereas the requirements for FIG2 in normal cell-cell agglutination and cell fusion during mating are insensitive to changes in the extracellular osmotic environment. We conclude that FIG2 performs distinct functions in the mating cell wall that are separable with respect to their ability to be suppressed by changes in external osmolarity and that a fundamental role of FIG2 in mating cells is the maintenance of cell integrity.

Role of the Cell Wall Integrity and Filamentous Growth Mitogen-Activated Protein Kinase Pathways in Cell Wall Remodeling during Filamentous Growth

“…These mucin-like proteins might themselves play a role in cell wall integrity. For example, the adhesin glycoprotein Fig2p promotes cell wall integrity during mating (171). We show that retention/shedding of Msb2p is influenced by the ß-glucan layer of the cell wall.…”

Posttranslational Modifications Required for Cell Surface Localization and Function of the Fungal Adhesin Aga1p

“…Agglutination assays. Agglutination assays of mating yeast cells were performed as described by Zhang et al (76). Agglutination activities were expressed as an agglutination index, AI, where AI ϭ 1 Ϫ (2 ϫ A aϩϰ )/(A a ϩ A ϰ ) (66,76).…”

“…The expression patterns of many of the genes encoding adhesins are regulated in response to developmental or environmental cues (19,26,55,57,59,65). In S. cerevisiae, activation of the mating pathway induces the expression of the agglutinin genes AGA1, AGA2, and SAG1/AG␣1 and the morphogenesis and agglutination-modifying gene FIG2 (19,36,40,58,76). Pseudohyphal, invasive growth differentiation and nutritional signals also serve to modulate the expression of the flocculin genes FLO1, FLO5, FLO9, FLO10, and FLO11, which is also required for biofilm formation of yeast cells (26,42,50,52,63,73).…”

A Biochemical Guide to Yeast Adhesins: Glycoproteins for Social and Antisocial Occasions

“…Aga1p or the similar protein Fig2p is essential for completion of mating and for matingdependent invasion of agar (41). Little is known about whether these proteins act directly as adhesins, but Fig2p has a role in signal transduction to the wall stress pathway and therefore has a role in maintenance of cell wall integrity during mating (59,138). It is pheromone induced and has an indirect role in attenuating sexual agglutination in mating type ␣ cells (59,138).…”