Architecture, remodeling, and functions of the septin cytoskeleton

Abstract

The septin family of proteins has fascinated cell biologists for decades due to the elaborate architecture they adopt in different eukaryotic cells. Whether they exist as rings, collars, or gauzes in different cell types and at different times in the cell cycle illustrates a complex series of regulation in structure. While the organization of different septin structures at the cortex of different cell types during the cell cycle has been described to various degrees, the exact structure and regulation at the filament level are still largely unknown. Recent advances in fluorescent and electron microscopy, as well as work in septin biochemistry, have allowed new insights into the aspects of septin architecture, remodeling, and function in many cell types. This mini-review highlights many of the recent findings with an emphasis on the budding yeast model.

A Septin Cytoskeleton-Targeting Small Molecule, Forchlorfenuron, Inhibits Epithelial Migration via Septin-Independent Perturbation of Cellular Signaling

“…The septin cytoskeleton, which is the fourth cytoskeletal element of eukaryotic cells, has a number of homeostatic and specialized functions in different tissues [1,[24][25][26]. In contrast to the extensive toolbox for probing the structure and dynamics of either actin cytoskeleton or microtubules, experimental tools to probe septin functions are limited.…”

Molecular form and function of the cytokinetic ring

“…However, how these are organized into the CR as a whole is unclear. Other than septins, which form filaments on the plasma membrane and bind components of the CR (Marquardt et al, 2018), most other CR components have not been detected by EM. Super-resolution microscopy can probe their organization at the nanoscale level and two such studies have been performed in S. pombe (Laplante et al, 2016;McDonald et al, 2017).…”

Cdc24, the source of active Cdc42, transiently interacts with septins to create a positive feedback between septin assembly and bud site formation in yeast cells

“…A critical step in the PBS assembly involves the recruitment of the septins. The four septin-units Cdc11, Cdc12, Cdc3 and Cdc10 form octameric rods that polymerize at the bud neck into filaments and higher-order structures like rings and collars (Bertin et al, 2008;Marquardt et al, 2019). Cdc11 is the subunit that caps the rod at its both ends and thus plays a critical role in filament formation (Garcia et al, 2011;Brausemann et al, 2016).…”

“…Cdc11 is the subunit that caps the rod at its both ends and thus plays a critical role in filament formation (Garcia et al, 2011;Brausemann et al, 2016). During mitosis the septins split into two rings and enclose the space where cytokinesis and abscission occurs (Marquardt et al, 2019). After abscission septins are disassembled from the site of cytokinesis and transferred in a Cdc42 GTP -dependent manner to the new PBS (Gladfelter et al, 2002;Caviston et al, 2003).…”

“…The ring remains at the base of the bud during further membrane and cell wall growth and restricts the free movement of the plasma membrane between mother and daughter cell (Barral et al, 2000). The mechanisms of septin recruitment and assembly are not fully understood (Marquardt et al, 2019). A central role is played by the PAK Cla4 and the paralogous proteins Gic1 and Gic2 (Kadota et al, 2004).…”