Septins: cytoskeletal polymers or signalling GTPases?

Field, Christine M.; Kellogg, Douglas R.

doi:10.1016/s0962-8924(99)01632-3

Cited by 252 publications

(219 citation statements)

References 48 publications

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“…First, the filaments formed by septin complexes serve as a scaffold that recruits other proteins and, perhaps, activates them [26]. In S. cerevisiae, the localization of at least 21 proteins at the bud neck requires proper assembly of septin filaments.…”

Section: Septin Functionsmentioning

confidence: 99%

Some assembly required: yeast septins provide the instruction manual

Versele

Thorner

2005

Trends in Cell Biology

201

199

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Septins are a family of conserved proteins that form hetero-oligomeric complexes that assemble into filaments. The filaments can be organized into linear arrays, coils, rings and gauzes. They serve as membrane-associated scaffolds and as barriers to demarcate local compartments, especially for the establishment of the septation site for cytokinesis. Studies in budding and fission yeast have revealed many of the protein-protein interactions that govern the formation of multi-septin complexes. GTP binding and phosphorylation direct the polymerization of filaments that is required for septin-collar assembly in budding yeast, whereas a homolog of anillin instructs timely formation of the ring of septin filaments at the medial cortex in fission yeast. These insights should aid understanding of the organization and function of the diverse septin structures in animal cells.

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Section: Septin Functionsmentioning

confidence: 99%

Some assembly required: yeast septins provide the instruction manual

Versele

Thorner

2005

Trends in Cell Biology

201

199

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“…A ring of proteins called septins, encoded by the genes CDC3, CDC10, CDC11, CDC12, and SHS1, is a prominent landmark of the neck. Septins are recruited to the nascent bud site in a Cdc42p-dependent manner, and then remain at that location as a ring around the neck of the emerging and growing bud, and finally divide into two rings at cell separation ( Figure S2A and B; for review, see Field and Kellogg, 1999;Gladfelter et al, 2001;Faty et al, 2002;Longtine and Bi, 2003). However, the septins play a variety of roles, promoting the proper activation of the B-cyclins for cell cycle progression (Barral et al, 1999;McMillan et al, 1999;Shulewitz et al, 1999;Longtine et al, 2000;Hanrahan and Snyder, 2003), maintaining a diffusion barrier between the bud and mother cortices , and recruiting cytokinetic (Bi et al, 1998;Lippincott and Li, 1998) and cell wall-synthesizing machinery (DeMarini et al, 1997) to the bud neck.…”

Section: Actin Assembly At the Bud Neck Requires The Septinsmentioning

confidence: 99%

Stable and Dynamic Axes of Polarity Use Distinct Formin Isoforms in Budding Yeast

Pruyne

Gao

et al. 2004

MBoC

151

208

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Bud growth in yeast is guided by myosin-driven delivery of secretory vesicles from the mother cell to the bud. We find transport occurs along two sets of actin cables assembled by two formin isoforms. The Bnr1p formin assembles cables that radiate from the bud neck into the mother, providing a stable mother-bud axis. These cables also depend on septins at the neck and are required for efficient transport from the mother to the bud. The Bni1p formin assembles cables that line the bud cortex and target vesicles to varying locations in the bud. Loss of these cables results in morphological defects as vesicles accumulate at the neck. Assembly of these cables depends on continued polarized secretion, suggesting vesicular transport provides a positive feedback signal for Bni1p activation, possibly by rho-proteins. By coupling different formin isoforms to unique cortical landmarks, yeast uses common cytoskeletal elements to maintain stable and dynamic axes in the same cell. INTRODUCTIONProper cell polarization requires a balance between dynamism and stability. Persistent systems, such as the apical and basolateral domains of epithelial cells, show a higher stability than flexible systems, such as cells undergoing chemotaxis. However, both types can use similar cytoskeletal components, so an important task in understanding the control of polarity is to identify features that influence persistence, and how those features integrate with the core cytoskeletal machinery providing the physical expression of polarity.The process of bud growth of the yeast Saccharomyces cerevisiae provides a model for examining the control of polarity (for reviews, see Bretscher, 2003;Chang and Peter, 2003). Secretory organelles, such as the Golgi and endoplasmic reticulum, are distributed throughout the bud and mother cell, whereas post-Golgi secretory vesicles concentrate at discrete growth sites at the cell cortex. These vesicles are guided to these sites along what are essentially two axes of polarity: a stable axis directing traffic from the mother into the bud, and a dynamic axis that fine-tunes delivery from the bud neck to specific regions in the bud, sending vesicles first to the small bud tip, then to the entire bud surface, and finally back toward the neck during mother/daughter separation. On delivery to these locations, post-Golgi vesicles fuse with the cell surface to promote localized cell expansion.Two class-V myosins, with heavy chains encoded by MYO2 (Johnston et al., 1991) and MYO4 (Haarer et al., 1994), propel cellular components, including vesicles, organelles, mRNAs, and microtubules, from the mother into the bud during growth and organelle segregation. The myosins move along cables of actin filaments that radiate throughout the cell in arrays oriented toward growth sites (Adams and Pringle, 1984;Kilmartin and Adams, 1984).Assembly of these cables depends on two formin homologues, Bni1p and Bnr1p (Evangelista et al., 2002;Sagot et al., 2002a), members of a family of cytoskeletal regulatory proteins defined by conserved fo...

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“…One major role for the septins in various organisms is in cytokinesis (Hartwell, 1971;Neufeld and Rubin, 1994;Kinoshita et al, 1997;Bi et al, 1998;Lippincott and Li, 1998). Consistent with this, the septins typically localize to the division site (cleavage furrow) at least during the cytokinesis phase of the cell cycle (Longtine et al, 1996;Field and Kellogg, 1999;Trimble, 1999;Nguyen et al, 2000;Westfall and Momany, 2002). However, the precise molecular role(s) of the septins in cytokinesis have not yet been elucidated in any cell type.…”

mentioning

confidence: 94%

“…The septin family of proteins was first recognized in yeast and now appears to be ubiquitous in fungi and animals, although not in plants (Longtine et al, 1996;Field and Kellogg, 1999;Trimble, 1999;Nguyen et al, 2000;Momany et al, 2001;Macara et al, 2002). Typical septins have a variable N-terminal region, a conserved core that includes the elements of a GTP-binding site, and a variable C-terminal region that (in all but a few cases) includes a predicted coiled-coil domain.…”

Section: Introductionmentioning

confidence: 99%

“…Proteins involved both in cytokinesis and in these other diverse processes are targeted to the mother-bud neck in a septin-dependent manner with a variety of temporal and spatial patterns (Gladfelter et al, 2001b). Thus, the septins have been proposed to function as a scaffold at the neck for protein anchoring and organization (Longtine et al, 1996(Longtine et al, , 1998aField and Kellogg, 1999;Gladfelter et al, 2001b). In addition, the septins appear to provide a diffusion barrier at the neck that prevents membrane-associated proteins from moving freely between the mother and bud compartments Takizawa et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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The Role of Cdc42p GTPase-activating Proteins in Assembly of the Septin Ring in Yeast

Caviston

Longtine

Pringle

et al. 2003

MBoC

228

281

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The septins are a conserved family of GTP-binding, filament-forming proteins. In the yeast Saccharomyces cerevisiae, the septins form a ring at the mother-bud neck that appears to function primarily by serving as a scaffold for the recruitment of other proteins to the neck, where they participate in cytokinesis and a variety of other processes. Formation of the septin ring depends on the Rho-type GTPase Cdc42p but appears to be independent of the actin cytoskeleton. In this study, we investigated further the mechanisms of septin-ring formation. Fluorescence-recovery-after-photobleaching (FRAP) experiments indicated that the initial septin structure at the presumptive bud site is labile (exchanges subunits freely) but that it is converted into a stable ring as the bud emerges. Mutants carrying the cdc42 V36G allele or lacking two or all three of the known Cdc42p GTPase-activating proteins (GAPs: Bem3p, Rga1p, and Rga2p) could recruit the septins to the cell cortex but were blocked or delayed in forming a normal septin ring and had accompanying morphogenetic defects. These phenotypes were dramatically enhanced in mutants that were also defective in Cla4p or Gin4p, two protein kinases previously shown to be important for normal septin-ring formation. The Cdc42p GAPs colocalized with the septins both early and late in the cell cycle, and overexpression of the GAPs could suppress the septin-organization and morphogenetic defects of temperature-sensitive septin mutants. Taken together, the data suggest that formation of the mature septin ring is a process that consists of at least two distinguishable steps, recruitment of the septin proteins to the presumptive bud site and their assembly into the stable septin ring. Both steps appear to depend on Cdc42p, whereas the Cdc42p GAPs and the other proteins known to promote normal septin-ring formation appear to function in a partially redundant manner in the assembly step. In addition, because the eventual formation of a normal septin ring in a cdc42 V36G or GAP mutant was invariably accompanied by a switch from an abnormally elongated to a more normal bud morphology distal to the ring, it appears that the septin ring plays a direct role in determining the pattern of bud growth. INTRODUCTIONThe septin family of proteins was first recognized in yeast and now appears to be ubiquitous in fungi and animals, although not in plants (Longtine et al., 1996;Field and Kellogg, 1999;Trimble, 1999;Nguyen et al., 2000;Momany et al., 2001;Macara et al., 2002). Typical septins have a variable N-terminal region, a conserved core that includes the elements of a GTP-binding site, and a variable C-terminal region that (in all but a few cases) includes a predicted coiled-coil domain. In each species examined to date, there are two or more septins that form heterooligomeric complexes to perform their specific functions. Purified septins from yeast, Drosophila, Xenopus, and mammalian cells form filaments of 7-9 nm diameter and of variable length (Field et al., 1996;Frazier et al., 1998;Hsu et al...

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Septins: cytoskeletal polymers or signalling GTPases?

Cited by 252 publications

References 48 publications

Some assembly required: yeast septins provide the instruction manual

Some assembly required: yeast septins provide the instruction manual

Stable and Dynamic Axes of Polarity Use Distinct Formin Isoforms in Budding Yeast

The Role of Cdc42p GTPase-activating Proteins in Assembly of the Septin Ring in Yeast

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