Glucose monitoring in fission yeast via the Gpa2 galpha, the git5 Gbeta and the git3 putative glucose receptor

The git5 Gbeta and git11 Ggamma form an atypical Gbetagamma dimer acting in the fission yeast glucose/cAMP pathway

Fission yeast adenylate cyclase, like mammalian adenylate cyclases, is regulated by a heterotrimeric G protein. The gpa2 Galpha and git5 Gbeta are both required for glucose-triggered cAMP signaling. The git5 Gbeta is a unique member of the Gbeta family in that it lacks an amino-terminal coiled-coil domain shown to be essential for mammalian Gbeta folding and interaction with Ggamma subunits. Using a git5 bait in a two-hybrid screen, we identified the git11 Ggamma gene. Co-immunoprecipitation studies confirm the composition of this Gbetagamma dimer. Cells deleted for git11 are defective in glucose repression of both fbp1 transcription and sexual development, resembling cells lacking either the gpa2 Galpha or the git5 Gbeta. Overexpression of the gpa2 Galpha partially suppresses loss of either the git5 Gbeta or the git11 Ggamma, while mutational activation of the Galpha fully suppresses loss of either Gbeta or Ggamma. Deletion of gpa2 (Galpha), git5 (Gbeta), or git11 (Ggamma) confer quantitatively distinct effects on fbp1 repression, indicating that the gpa2 Galpha subunit remains partially active in the absence of the Gbetagamma dimer and that the git5 Gbeta subunit remains partially active in the absence of the git11 Ggamma subunit. The addition of the CAAX box from the git11 Ggamma to the carboxy-terminus of the git5 Gbeta partially suppresses the loss of the Ggamma. Thus the Ggamma in this system is presumably required for localization of the Gbetagamma dimer but not for folding of the Gbeta subunit. In mammalian cells, the essential roles of the Gbeta amino-terminal coiled-coil domains and Ggamma partners in Gbeta folding may therefore reflect a mechanism used by cells that express multiple forms of both Gbeta and Ggamma subunits to regulate the composition and activity of its G proteins.

Signal transduction cascades regulating fungal development and virulence

Cellular differentiation, mating, and filamentous growth are regulated in many fungi by environmental and nutritional signals. For example, in response to nitrogen limitation, diploid cells of the yeast Saccharomyces cerevisiae undergo a dimorphic transition to filamentous growth referred to as pseudohyphal differentiation. Yeast filamentous growth is regulated, in part, by two conserved signal transduction cascades: a mitogen-activated protein kinase cascade and a G-protein regulated cyclic AMP signaling pathway. Related signaling cascades play an analogous role in regulating mating and virulence in the plant fungal pathogen Ustilago maydis and the human fungal pathogens Cryptococcus neoformans and Candida albicans. We review here studies on the signaling cascades that regulate development of these and other fungi. This analysis illustrates both how the model yeast S. cerevisiae can serve as a paradigm for signaling in other organisms and also how studies in other fungi provide insights into conserved signaling pathways that operate in many divergent organisms.

Signal transduction cascades regulating fungal development and virulence

Cellular differentiation, mating, and filamentous growth are regulated in many fungi by environmental and nutritional signals. For example, in response to nitrogen limitation, diploid cells of the yeast Saccharomyces cerevisiae undergo a dimorphic transition to filamentous growth referred to as pseudohyphal differentiation. Yeast filamentous growth is regulated, in part, by two conserved signal transduction cascades: a mitogen-activated protein kinase cascade and a G-protein regulated cyclic AMP signaling pathway. Related signaling cascades play an analogous role in regulating mating and virulence in the plant fungal pathogen Ustilago maydis and the human fungal pathogens Cryptococcus neoformans and Candida albicans. We review here studies on the signaling cascades that regulate development of these and other fungi. This analysis illustrates both how the model yeast S. cerevisiae can serve as a paradigm for signaling in other organisms and also how studies in other fungi provide insights into conserved signaling pathways that operate in many divergent organisms.