Functional Genomics of Adhesion, Invasion, and Mycelial Formation in Schizosaccharomyces pombe

Abstract

Investigation into the switch between single-celled and filamentous forms of fungi may provide insights into cell polarity, differentiation, and fungal pathogenicity. At the molecular level, much of this investigation has fallen on two closely related budding yeasts, Candida albicans and Saccharomyces cerevisiae. Recently, the much more distant fission yeast Schizosaccharomyces pombe was shown to form invasive filaments after nitrogen limitation (E. Amoah-Buahin, N. Bone, and J. Armstrong, Eukaryot. Cell 4:1287-1297, 2005) and this genetically tractable organism provides an alternative system for the study of dimorphic growth. Here we describe a second mode of mycelial formation of S. pombe, on rich media. Screening of an S. pombe haploid deletion library identified 12 genes required for mycelial development which encode potential transcription factors, orthologues of S. cerevisiae Sec14p and Tlg2p, and the formin For3, among others. These were further grouped into two phenotypic classes representing different stages of the process. We show that galactose-dependent cell adhesion and actin assembly are both required for mycelial formation and mutants lacking a range of genes controlling cell polarity all produce mycelia but with radically altered morphology.Many fungi are capable of growth either as single-celled yeasts or in a variety of multicellular and invasive forms. The ability to switch between these forms may be related to the ability to undertake different phases of infection (28). Thus, the study of this switching process may provide not only an understanding of a basic process of eukaryotic differentiation but also an insight into mechanisms of pathogenicity.The fission yeast Schizosaccharomyces pombe is well established as a model eukaryote to study the cell cycle and control of polarized growth. It had widely been considered to exist only in a single-celled form. However, we discovered that under conditions of nitrogen limitation, S. pombe can form elaborate branched multicellular structures which deeply invade the growth medium, for which the cyclic AMP (cAMP) signaling pathway is required (2). Subsequently, it was shown that, as in Saccharomyces cerevisiae, a putative ammonium transporter is also required, presumably to sense the nitrogen concentration (18). In contrast to budding yeasts (25), invasion appeared to occur only within a very narrow range of conditions (2).Here we describe a second form of invasive growth by S. pombe which occurs on rich media. This allowed us to devise a simple screening of a collection of approximately 2,600 haploid deletion mutants for strains unable to invade the medium. This identified 12 genes associated with a range of functions, including transcriptional regulation, membrane trafficking, and control of actin assembly. Their roles in the invasion process could be further ordered into phases of adhesion to the surface and subsequent invasion of the medium. We investigated the role of specific sugars in this adhesion process and of the actin cytoskeleton in the fo...

Asp1, a Conserved 1/3 Inositol Polyphosphate Kinase, Regulates the Dimorphic Switch inSchizosaccharomyces pombe

“…The tea2⌬ strain did not show invasive growth after 20 days of incubation; however, a tea2⌬ strain can grow invasively after prolonged incubation (Fig. 6C) (19) . Double mutants carrying mal3⌬, tea1⌬, tea2⌬, peg1-1 H397A mutant strain ( Fig.…”

“…Filamentous invasive growth has been described for S. pombe (1,19,61), but we have analyzed for the first time the growth pattern of such cells. Invasive growth of wild-type and asp1 H397A cells is a variation on the same theme that is a combination of different properties, such as cell-cell and cell-substrate adhesion, defects in cell separation, the ability to alter cell shape in response to environmental constraints, and an alteration of the normal growth pattern.…”

“…S. pombe multicellular invasive growth has been observed for specific strains under specific conditions, such as nitrogen and ammonium limitation and the presence of excess iron (1,19,50,61).…”

MADS Box Transcription Factor Mbx2/Pvg4 Regulates Invasive Growth and Flocculation by Inducing gsf2 + Expression in Fission Yeast

“…We recently reported that gsf2 ϩ , encoding a flocculin that binds to galactose residues located on cell surface glycoconjugates, is essential not only for nonsexual flocculation but also for filamentous invasive growth in S. pombe (7,20). Cell surface glycoproteins play a key role in flocculation and filamentous invasive growth in yeasts.…”

Reorganization of the Growth Pattern of Schizosaccharomyces pombe in Invasive Filament Formation

“…However, we found that it could be induced to invade the medium, forming elaborate elongated and branching structures very different from the well-known growth pattern (1). Invasion requires high cell density and can be encouraged by a combination of low nitrogen levels and abundant carbon (1,5). We identified several genes necessary for different stages of the process (5), while the nutritional effect requires the cyclic AMP signaling pathway (1).…”