Abstract
The septin family of proteins can assemble into filaments that further organize into different higher order structures to perform a variety of different functions in different cell types and organisms. In the budding yeast Saccharomyces cerevisiae, the septins localize to the presumptive bud site as a cortical ring prior to bud emergence, expand into an hourglass at the bud neck (cell division site) during bud growth, and finally “split” into a double ring sandwiching the cell division machinery during cytokinesis. While much work has been done to understand the functions and molecular makeups of these structures, the mechanisms underlying the transitions from one structure to another have largely remained elusive. Recent studies involving advanced imaging and in vitro reconstitution have begun to reveal the vast complexity involved in the regulation of these structural transitions, which defines the focus of discussion in this mini-review.
Highlights
We recently provided the first evidence of such regulation using genetic perturbations and platinum-replica electron microscopy (PREM) analyses of the septin hourglass in vivo (Marquardt et al, 2020)
We discovered that the septin hourglass was selectively destabilized with mostly the daughter half of the hourglass mislocalized to the growing bud cortex in elm1Δ mutants in both a kinase-dependent and -independent manner (Figure 1D, left and center panels) and that these phenotypes are at least partially mediated through Bni5 (Marquardt et al, 2020)
By utilizing genetic perturbations and following septin kinetics via confocal microscopy and septin filament architecture via PREM, these studies have begun to elucidate the mechanisms of septin organization in vivo at an unprecedented resolution
Summary
Septins are GTP-binding proteins that assemble into heteropolymers that can organize into various filament-containing structures such as rings, hourglasses, and gauzes in different cell types (Byers and Goetsch, 1976a; Kim et al, 1991; Frazier et al, 1998; Lippincott et al, 2001; Ihara et al, 2005; Kissel et al, 2005; Rodal et al, 2005; John et al, 2007; Sirajuddin et al, 2007; Tada et al, 2007; Xie et al, 2007; Bertin et al, 2008; Ong et al, 2014; Renshaw et al, 2014; Karasmanis et al, 2019; Wang et al, 2019).
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