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

Abstract

The ability to undergo dramatic morphological changes in response to extrinsic cues is conserved in fungi. We have used the model yeast Schizosaccharomyces pombe to determine which intracellular signal regulates the dimorphic switch from the single-cell yeast form to the filamentous invasive growth form. The S. pombe Asp1 protein, a member of the conserved Vip1 1/3 inositol polyphosphate kinase family, is a key regulator of the morphological switch via the cAMP protein kinase A (PKA) pathway. Lack of a functional Asp1 kinase domain abolishes invasive growth which is monopolar, while an increase in Asp1-generated inositol pyrophosphates (PP) increases the cellular response. Remarkably, the Asp1 kinase activity encoded by the N-terminal part of the protein is regulated negatively by the C-terminal domain of Asp1, which has homology to acid histidine phosphatases. Thus, the fine tuning of the cellular response to environmental cues is modulated by the same protein. As the Saccharomyces cerevisiae Asp1 ortholog is also required for the dimorphic switch in this yeast, we propose that Vip1 family members have a general role in regulating fungal dimorphism.

Cell Signalling by Inositol Pyrophosphates

“…Little is known about the Vip1/PP-IP5K acid phosphatise domain. However, recent evidence indicates that the phosphatase domain of Schizosaccharomyces pombe Asp1 protein (Vip1 homologous) negatively regulates the N-terminal kinase domain in controlling the dimorphic switch (Pohlmann and Fleig 2010). Mammalian organisms possess two PP-IP 5 Ka, b proteins, while yeast possess only one Vip1 enzyme.…”

Fungal Morphogenesis, from the Polarized Growth of Hyphae to Complex Reproduction and Infection Structures

“…The absence of Vip1-generated IPPs resulted in an inability to activate the second growth zone in growing cells and abolished correct growth zone definition after reentry into the cell cycle (196). Furthermore, the morphological transition from the yeast cell form to the pseudohyphal invasive growth form, which represents a foraging response, depends on Vip1-made IPPs (200) (Fig. 6).…”

Sos7, an Essential Component of the Conserved Schizosaccharomyces pombe Ndc80-MIND-Spc7 Complex, Identifies a New Family of Fungal Kinetochore Proteins

“…For Western blots, we used the following first antibodies: anti-HA antibody (monoclonal mouse; Roche Diagnostics, Alameda, CA), anti-cMyc antibody (monoclonal mouse; Roche Diagnostics), anti-GFP antibody (polyclonal rabbit; Invitrogen), ␥-tubulin antibody (monoclonal mouse GTU-88; Sigma-Aldrich, St. Louis, MO), and our anti-Sos7 antibody and anti-Spc7 antibody. The secondary antibodies used were anti-rabbit IgI (Fc)-alkaline phosphatase conjugate (Promega, Madison, WI) or anti-mouse IgG(HϩL)-alkaline phosphatase conjugate (Promega), which were detected as described previously (53). Sos7-GFP bands on Western blots were quantified using ImageJ 1.44 (National Institutes of Health) and normalization to the ␥-tubulin loading control.…”