scholarly journals Sensing a bud in the yeast morphogenesis checkpoint: a role for Elm1

2016 ◽  
Vol 27 (11) ◽  
pp. 1764-1775 ◽  
Author(s):  
Hui Kang ◽  
Denis Tsygankov ◽  
Daniel J. Lew
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Nuclear Division ◽  
Environmental Stresses ◽  
Bud Formation ◽  
Septin Ring ◽  
Bud Emergence ◽  
Bud Neck ◽  
Morphogenesis Checkpoint ◽  
Bud Site ◽  
Mitotic Inhibitor

Bud formation by Saccharomyces cerevisiae must be coordinated with the nuclear cycle to enable successful proliferation. Many environmental stresses temporarily disrupt bud formation, and in such circumstances, the morphogenesis checkpoint halts nuclear division until bud formation can resume. Bud emergence is essential for degradation of the mitotic inhibitor, Swe1. Swe1 is localized to the septin cytoskeleton at the bud neck by the Swe1-binding protein Hsl7. Neck localization of Swe1 is required for Swe1 degradation. Although septins form a ring at the presumptive bud site before bud emergence, Hsl7 is not recruited to the septins until after bud emergence, suggesting that septins and/or Hsl7 respond to a “bud sensor.” Here we show that recruitment of Hsl7 to the septin ring depends on a combination of two septin-binding kinases: Hsl1 and Elm1. We elucidate which domains of these kinases are needed and show that artificial targeting of those domains suffices to recruit Hsl7 to septin rings even in unbudded cells. Moreover, recruitment of Elm1 is responsive to bud emergence. Our findings suggest that Elm1 plays a key role in sensing bud emergence.

scholarly journals mRNAs Encoding Polarity and Exocytosis Factors Are Cotransported with the Cortical Endoplasmic Reticulum to the Incipient Bud in Saccharomyces cerevisiae

2007 ◽  
Vol 27 (9) ◽  
pp. 3441-3455 ◽  
Author(s):  
Stella Aronov ◽  
Rita Gelin-Licht ◽  
Gadi Zipor ◽  
Liora Haim ◽  
Einat Safran ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Nuclear Division ◽  
Mrna Localization ◽  
Dependent Manner ◽  
Protein Enrichment ◽  
Bud Emergence ◽  
Bud Site ◽  
Cortical Endoplasmic Reticulum ◽  
Asymmetrically Distributed

ABSTRACT Polarized growth in the budding yeast Saccharomyces cerevisiae depends upon the asymmetric localization and enrichment of polarity and secretion factors at the membrane prior to budding. We examined how these factors (i.e., Cdc42, Sec4, and Sro7) reach the bud site and found that their respective mRNAs localize to the tip of the incipient bud prior to nuclear division. Asymmetric mRNA localization depends upon factors that facilitate ASH1 mRNA localization (e.g., the 3′ untranslated region, She proteins 1 to 5, Puf6, actin cytoskeleton, and a physical association with She2). mRNA placement precedes protein enrichment and subsequent bud emergence, implying that mRNA localization contributes to polarization. Correspondingly, mRNAs encoding proteins which are not asymmetrically distributed (i.e., Snc1, Mso1, Tub1, Pex3, and Oxa1) are not polarized. Finally, mutations which affect cortical endoplasmic reticulum (ER) entry and anchoring in the bud (myo4Δ, sec3Δ, and srp101) also affect asymmetric mRNA localization. Bud-localized mRNAs, including ASH1, were found to cofractionate with ER microsomes in a She2- and Sec3-dependent manner; thus, asymmetric mRNA transport and cortical ER inheritance are connected processes in yeast.

scholarly journals Involvement of an Actomyosin Contractile Ring in Saccharomyces cerevisiae Cytokinesis

1998 ◽  
Vol 142 (5) ◽  
pp. 1301-1312 ◽  
Author(s):  
Erfei Bi ◽  
Paul Maddox ◽  
Daniel J. Lew ◽  
E.D. Salmon ◽  
John N. McMillan ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Separation ◽  
Cortical Actin ◽  
Primary Defect ◽  
Septum Formation ◽  
Bud Emergence ◽  
Bud Neck ◽  
Bud Site ◽  
Type Ii Myosin

In Saccharomyces cerevisiae, the mother cell and bud are connected by a narrow neck. The mechanism by which this neck is closed during cytokinesis has been unclear. Here we report on the role of a contractile actomyosin ring in this process. Myo1p (the only type II myosin in S. cerevisiae) forms a ring at the presumptive bud site shortly before bud emergence. Myo1p ring formation depends on the septins but not on F-actin, and preexisting Myo1p rings are stable when F-actin is depolymerized. The Myo1p ring remains in the mother–bud neck until the end of anaphase, when a ring of F-actin forms in association with it. The actomyosin ring then contracts to a point and disappears. In the absence of F-actin, the Myo1p ring does not contract. After ring contraction, cortical actin patches congregate at the mother–bud neck, and septum formation and cell separation rapidly ensue. Strains deleted for MYO1 are viable; they fail to form the actin ring but show apparently normal congregation of actin patches at the neck. Some myo1Δ strains divide nearly as efficiently as wild type; other myo1Δ strains divide less efficiently, but it is unclear whether the primary defect is in cytokinesis, septum formation, or cell separation. Even cells lacking F-actin can divide, although in this case division is considerably delayed. Thus, the contractile actomyosin ring is not essential for cytokinesis in S. cerevisiae. In its absence, cytokinesis can still be completed by a process (possibly localized cell–wall synthesis leading to septum formation) that appears to require septin function and to be facilitated by F-actin.

scholarly journals Dynamics of septin ring and collar formation in Saccharomyces cerevisiae

2011 ◽  
Vol 392 (8-9) ◽  
pp. 689-697 ◽  
Author(s):  
Hsin Chen ◽  
Audrey S. Howell ◽  
Alex Robeson ◽  
Daniel J. Lew
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Septin Ring ◽  
Ring Assembly ◽  
Bud Emergence ◽  
Steady Rate ◽  
Constant Rate ◽  
Bud Neck ◽  
Quantitative Analyses ◽  
Reduced Rate ◽  
Mother Cells

Abstract Although the septin ring and collar in budding yeast were described over 20 years ago, there is still controversy regarding the organization of septin filaments within these structures and about the way in which the ring first forms and about how it converts into a collar at the mother-bud neck. Here we present quantitative analyses of the recruitment of fluorescently-tagged septins to the ring and collar through the cell cycle. Septin ring assembly began several minutes after polarity establishment and this interval was longer in daughter than in mother cells, suggesting asymmetric inheritance of septin regulators. Septins formed an initial faint and irregular ring, which became more regular as septins were recruited at a constant rate. This steady rate of septin recruitment continued for several minutes after the ring converted to a collar at bud emergence. We did not detect a stepwise change in septin fluorescence during the ring-to-collar transition. After collar formation, septins continued to accumulate at the bud neck, though at a reduced rate, until the onset of cytokinesis when the amount of neck-localized septins rapidly decreased. Implications for the mechanism of septin ring assembly are discussed.

scholarly journals The Checkpoint Kinase Hsl1p Is Activated by Elm1p-dependent Phosphorylation

2008 ◽  
Vol 19 (11) ◽  
pp. 4675-4686 ◽  
Author(s):  
Lee Szkotnicki ◽  
John M. Crutchley ◽  
Trevin R. Zyla ◽  
Elaine S.G. Bardes ◽  
Daniel J. Lew
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Stress Responses ◽  
Outdoor Environment ◽  
Checkpoint Kinase ◽  
Autoinhibitory Domain ◽  
Bud Emergence ◽  
Bud Neck ◽  
Mitotic Delay ◽  
Mitotic Inhibitor ◽  
Previous Identification

Saccharomyces cerevisiae cells growing in the outdoor environment must adapt to sudden changes in temperature and other variables. Many such changes trigger stress responses that delay bud emergence until the cells can adapt. In such circumstances, the morphogenesis checkpoint delays mitosis until a bud has been formed. Mitotic delay is due to the Wee1 family mitotic inhibitor Swe1p, whose degradation is linked to bud emergence by the checkpoint kinase Hsl1p. Hsl1p is concentrated at the mother-bud neck through association with septin filaments, and it was reported that Hsl1p activation involved relief of autoinhibition in response to septin interaction. Here we challenge the previous identification of an autoinhibitory domain and show instead that Hsl1p activation involves the phosphorylation of threonine 273, promoted by the septin-associated kinase Elm1p. We identified elm1 mutants in a screen for defects in Swe1p degradation and show that a phosphomimic T273E mutation in HSL1 bypasses the need for Elm1p in this pathway.

scholarly journals Roles of Hsl1p and Hsl7p in Swe1p Degradation: beyond Septin Tethering

2012 ◽  
Vol 11 (12) ◽  
pp. 1496-1502 ◽  
Author(s):  
Kindra King ◽  
Michelle Jin ◽  
Daniel Lew
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Cell Division ◽  
Nuclear Division ◽  
Cell Division Cycle ◽  
Cyclin Dependent Kinase ◽  
Bud Formation ◽  
Content Type ◽  
Cell Cycle Delay ◽  
Bud Neck

ABSTRACT The morphogenesis checkpoint in Saccharomyces cerevisiae couples bud formation to the cell division cycle by delaying nuclear division until cells have successfully constructed a bud. The cell cycle delay is due to the mitosis-inhibitory kinase Swe1p, which phosphorylates the cyclin-dependent kinase Cdc28p. In unperturbed cells, Swe1p is degraded via a mechanism thought to involve its tethering to a cortical scaffold of septin proteins at the mother-bud neck. In cells that experience stresses that delay bud formation, Swe1p is stabilized, accumulates, and promotes a G 2 delay. The tethering of Swe1p to the neck requires two regulators, called Hsl1p and Hsl7p. Hsl1p interacts with septins, and Hsl7p interacts with Swe1p; tethering occurs when Hsl1p interacts with Hsl7p. Here we created a version of Swe1p that is artificially tethered to the neck by fusion to a septin so that Swe1p no longer requires Hsl1p or Hsl7p for its localization to the neck. We show that the interaction between Hsl1p and Hsl7p, required for normal Swe1p degradation, is no longer needed for septin-Swe1p degradation, supporting the idea that the Hsl1p-Hsl7p interaction serves mainly to tether Swe1p to the neck. However, both Hsl1p and Hsl7p are still required for Swe1p degradation, implying that these proteins play additional roles beyond localizing Swe1p to the neck.

scholarly journals Determinants of Swe1p Degradation in Saccharomyces cerevisiae

2002 ◽  
Vol 13 (10) ◽  
pp. 3560-3575 ◽  
Author(s):  
John N. McMillan ◽  
Chandra L. Theesfeld ◽  
Jacob C. Harrison ◽  
Elaine S. G. Bardes ◽  
Daniel J. Lew
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Ubiquitin Ligase ◽  
Degradation Pathway ◽  
Interacting Protein ◽  
Bud Formation ◽  
Cycle Arrest ◽  
Bud Neck ◽  
Ubiquitin Conjugating Enzyme ◽  
Morphogenesis Checkpoint

Swe1p, the sole Wee1-family kinase in Saccharomyces cerevisiae, is synthesized during late G1 and is then degraded as cells proceed through the cell cycle. However, Swe1p degradation is halted by the morphogenesis checkpoint, which responds to insults that perturb bud formation. The Swe1p stabilization promotes cell cycle arrest through Swe1p-mediated inhibitory phosphorylation of Cdc28p until the cells can recover from the perturbation and resume bud formation. Swe1p degradation involves the relocalization of Swe1p from the nucleus to the mother-bud neck, and neck targeting requires the Swe1p-interacting protein Hsl7p. In addition, Swe1p degradation is stimulated by its substrate, cyclin/Cdc28p, and Swe1p is thought to be a target of the ubiquitin ligase SCFMet30 acting with the ubiquitin-conjugating enzyme Cdc34p. The basis for regulation of Swe1p degradation by the morphogenesis checkpoint remains unclear, and in order to elucidate that regulation we have dissected the Swe1p degradation pathway in more detail, yielding several novel findings. First, we show here that Met30p (and by implication SCFMet30) is not, in fact, required for Swe1p degradation. Second, cyclin/Cdc28p does not influence Swe1p neck targeting, but can directly phosphorylate Swe1p, suggesting that it acts downstream of neck targeting in the Swe1p degradation pathway. Third, a screen for functional but nondegradable mutants of SWE1 identified two small regions of Swe1p that are key to its degradation. One of these regions mediates interaction of Swe1p with Hsl7p, showing that the Swe1p-Hsl7p interaction is critical for Swe1p neck targeting and degradation. The other region did not appear to affect interactions with known Swe1p regulators, suggesting that other as-yet-unknown regulators exist.

scholarly journals Haspin Modulates the G2/M Transition Delay in Response to Polarization Failures in Budding Yeast

2021 ◽  
Vol 8 ◽  
Author(s):  
Martina Galli ◽  
Laura Diani ◽  
Roberto Quadri ◽  
Alessandro Nespoli ◽  
Elena Galati ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Cell Cycle Progression ◽  
M Cell ◽  
Checkpoint Activation ◽  
Bud Emergence ◽  
Morphogenesis Checkpoint ◽  
Transition Delay ◽  
Bud Site ◽  
Surveillance Mechanism

Symmetry breaking by cellular polarization is an exquisite requirement for the cell-cycle of Saccharomyces cerevisiae cells, as it allows bud emergence and growth. This process is based on the formation of polarity clusters at the incipient bud site, first, and the bud tip later in the cell-cycle, that overall promote bud emission and growth. Given the extreme relevance of this process, a surveillance mechanism, known as the morphogenesis checkpoint, has evolved to coordinate the formation of the bud and cell cycle progression, delaying mitosis in the presence of morphogenetic problems. The atypical protein kinase haspin is responsible for histone H3-T3 phosphorylation and, in yeast, for resolution of polarity clusters in mitosis. Here, we report a novel role for haspin in the regulation of the morphogenesis checkpoint in response to polarity insults. Particularly, we show that cells lacking the haspin ortholog Alk1 fail to achieve sustained checkpoint activation and enter mitosis even in the absence of a bud. In alk1Δ cells, we report a reduced phosphorylation of Cdc28-Y19, which stems from a premature activation of the Mih1 phosphatase. Overall, the data presented in this work define yeast haspin as a novel regulator of the morphogenesis checkpoint in Saccharomyces cerevisiae, where it monitors polarity establishment and it couples bud emergence to the G2/M cell cycle transition.

scholarly journals A Monitor for Bud Emergence in the Yeast Morphogenesis Checkpoint

2003 ◽  
Vol 14 (8) ◽  
pp. 3280-3291 ◽  
Author(s):  
Chandra L. Theesfeld ◽  
Trevin R. Zyla ◽  
Elaine G.S. Bardes ◽  
Daniel J. Lew
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Actin Cytoskeleton ◽  
Budding Yeast ◽  
Bud Formation ◽  
Bud Emergence ◽  
Checkpoint Pathway ◽  
Morphogenesis Checkpoint ◽  
External Signals ◽  
Biochemical Signals

Cell cycle transitions are subject to regulation by both external signals and internal checkpoints that monitor satisfactory progression of key cell cycle events. In budding yeast, the morphogenesis checkpoint arrests the cell cycle in response to perturbations that affect the actin cytoskeleton and bud formation. Herein, we identify a step in this checkpoint pathway that seems to be directly responsive to bud emergence. Activation of the kinase Hsl1p is dependent upon its recruitment to a cortical domain organized by the septins, a family of conserved filament-forming proteins. Under conditions that delayed or blocked bud emergence, Hsl1p recruitment to the septin cortex still took place, but hyperphosphorylation of Hsl1p and recruitment of the Hsl1p-binding protein Hsl7p to the septin cortex only occurred after bud emergence. At this time, the septin cortex spread to form a collar between mother and bud, and Hsl1p and Hsl7p were restricted to the bud side of the septin collar. We discuss models for translating cellular geometry (in this case, the emergence of a bud) into biochemical signals regulating cell proliferation.

Yeast RHO3 and RHO4 ras superfamily genes are necessary for bud growth, and their defect is suppressed by a high dose of bud formation genes CDC42 and BEM1

1992 ◽  
Vol 12 (12) ◽  
pp. 5690-5699 ◽  
Author(s):  
Y Matsui ◽  
A Toh-E
Keyword(s):  
Cell Polarity ◽  
Inhibitory Effect ◽  
High Dose ◽  
Yeast Saccharomyces Cerevisiae ◽  
Bud Formation ◽  
Stabilizing Agents ◽  
Daughter Cells ◽  
Bud Emergence ◽  
Ras Superfamily ◽  
Bud Site

RHO3 and RHO4 are members of the ras superfamily genes of the yeast Saccharomyces cerevisiae and are related functionally to each other. Experiments using a conditionally expressed allele of RHO4 revealed that depletion of both the RHO3 and RHO4 gene products resulted in lysis of cells with a small bud, which could be prevented by the presence of osmotic stabilizing agents in the medium. rho3 rho4 cells incubated in medium containing an osmotic stabilizing agent were rounded and enlarged and displayed delocalized deposition of chitin and delocalization of actin patches, indicating that these cells lost cell polarity. Nine genes whose overexpression could suppress the defect of the RHO3 function were isolated (SRO genes). Two of them were identical with CDC42 and BEM1, bud site assembly genes involved in the process of bud emergence. A high dose of CDC42 complemented the rho3 defect, whereas overexpression of RHO3 had an inhibitory effect on the growth of mutants defective in the CDC24-CDC42 pathway. These results, along with comparison of cell morphology between rho3 rho4 cells and cdc24 (or cdc42) mutant cells kept under the restrictive conditions, strongly suggest that the functions of RHO3 and RHO4 are required after initiation of bud formation to maintain cell polarity during maturation of daughter cells.

scholarly journals Genetic Interactions among Regulators of Septin Organization

2004 ◽  
Vol 3 (4) ◽  
pp. 847-854 ◽  
Author(s):  
Amy S. Gladfelter ◽  
Trevin R. Zyla ◽  
Daniel J. Lew
Keyword(s):  
Genetic Interactions ◽  
Septin Ring ◽  
Clear Cut ◽  
Cell Functions ◽  
Bud Emergence ◽  
Mutant Strains ◽  
Signaling Center ◽  
Bud Site ◽  
Isogenic Strains ◽  
Initial Assembly

ABSTRACT Septins form a cortical scaffold at the yeast mother-bud neck that restricts the diffusion of cortical proteins between the mother and bud and serves as a signaling center that is important for governing various cell functions. After cell cycle commitment in late G1, septins are assembled into a narrow ring at the future bud site, which spreads to form a mature septin hourglass immediately after bud emergence. Although several septin regulators have been identified, it is unclear how they cooperate to assemble the septin scaffold. We have examined septin localization in isogenic strains containing single or multiple mutations in eight septin organization genes (CDC42, RGA1, RGA2, BEM3, CLA4, GIN4, NAP1, and ELM1). Our results suggest that these regulators act largely in parallel to promote either the initial assembly of the septin ring (CDC42, RGA1, RGA2, BEM3, and CLA4) or the conversion of the ring to a stable hourglass structure at the neck (GIN4, NAP1, and ELM1). Aberrant septin localization patterns in mutant strains could be divided into apparently discrete categories, but individual strains displayed heterogeneous defects, and there was no clear-cut correspondence between the specific mutations and specific categories of defect. These findings suggest that when they are deprived of their normal regulators, septin scaffolds collapse into a limited repertoire of aberrant states in which the nature of the mutant regulators influences the probability of a given aberrant state.

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