Septins and Generation of Asymmetries in Fungal Cells

Abstract

Polarized growth is critical for the development and maintenance of diverse organisms and tissues, but particularly central to fungi where nutrient uptake, communication, and reproduction all rely on cell asymmetries. To achieve polarized growth, fungi spatially organize both their cytosol and cortical membranes. The septins, a family of GTP-binding proteins, have emerged as key regulators of spatial compartmentalization in fungi and other eukaryotes. By forming higher-order structures on fungal plasma membranes, septins are thought to contribute to the generation of cell asymmetries by acting as molecular scaffolds and forming diffusional barriers. Here we discuss the links between septins and polarized growth and consider molecular models for how septins contribute to cellular asymmetry in fungi.

Forging the ring: from fungal septins' divergent roles in morphology, septation and virulence to factors contributing to their assembly into higher order structures

“…Participation of septins in different cellular processes is due to their ability to act as scaffolds, recruiting other proteins to specific cellular regions and acting as diffusion barriers (Khan et al, 2015). In Sac.…”

“…cerevisiae, septins at the bud neck recruit a variety of proteins, including kinases and protein phosphatase 2A (PP2A) regulatory subunits, that have cell cycle regulatory roles (Gladfelter et al, 2001;McMurray & Thorner, 2009;Renz et al, 2016). These regulatory proteins associate with the septin complex at different stages of the cell cycle, suggesting that a yet-unknown mechanism can regulate septin-protein interaction (Bertin et al, 2008;Khan et al, 2015;Renz et al, 2016). For example, septins recruit the kinase Gin4, which negatively regulates the flippase Fpk1 (Roelants et al, 2015).…”

“…cerevisiae septin mutant cdc12-6 is grown at restrictive temperature, Its2 and the polarisome complex are no longer restricted to the bud cells (Takizawa et al, 2000). Recent studies implicate the possibility of septins acting as endoplasmic reticulum (ER) diffusion barriers (Khan et al, 2015) for several possible reasons. First, Its2 primarily resides in the ER membranes (Wolf et al, 2012).…”

“…Lastly, Epo1 and Scs2 (ER-associated proteins) interact with septin Shs, and this interaction is integral for the compartmentalization of the ER membranes (Chao et al, 2014). Nonetheless, the ER and plasma membrane diffusion barrier functions of septins are not necessarily mutually exclusive and more detailed investigation into these two possible roles is required (Khan et al, 2015).…”

“…One possible mechanism proposed is by the generation of asymmetries in fungal cells (Khan et al, 2015). In order to generate asymmetries, septins assemble into higher order structures.…”