scholarly journals Fine-tuning the orientation of the polarity axis by Rga1, a Cdc42 GTPase-activating protein

2017 ◽  
Vol 28 (26) ◽  
pp. 3773-3788 ◽  
Author(s):  
Kristi E. Miller ◽  
Wing-Cheong Lo ◽  
Mid Eum Lee ◽  
Pil Jung Kang ◽  
Hay-Oak Park
Keyword(s):  
Cell Polarization ◽  
Fine Tuning ◽  
Gtpase Activating Protein ◽  
Animal Cells ◽  
Daughter Cells ◽  
Division Site ◽  
Lim Domains ◽  
Mother Cells ◽  
Bud Site ◽  
Selection Of

In yeast and animal cells, signaling pathways involving small guanosine triphosphatases (GTPases) regulate cell polarization. In budding yeast, selection of a bud site directs polarity establishment and subsequently determines the plane of cell division. Rga1, a Cdc42 GTPase-activating protein, prevents budding within the division site by inhibiting Cdc42 repolarization. A protein complex including Nba1 and Nis1 is involved in preventing rebudding at old division sites, yet how these proteins and Rga1 might function in negative polarity signaling has been elusive. Here we show that Rga1 transiently localizes to the immediately preceding and older division sites by interacting with Nba1 and Nis1. The LIM domains of Rga1 are necessary for its interaction with Nba1, and loss of this interaction results in premature delocalization of Rga1 from the immediately preceding division site and, consequently, abnormal bud-site selection in daughter cells. However, such defects are minor in mother cells of these mutants, likely because the G1 phase is shorter and a new bud site is established prior to delocalization of Rga1. Indeed, our biphasic mathematical model of Cdc42 polarization predicts that premature delocalization of Rga1 leads to more frequent Cdc42 repolarization within the division site when the first temporal step in G1 is assumed to last longer. Spatial distribution of a Cdc42 GAP in coordination with G1 progression may thus be critical for fine-tuning the orientation of the polarity axis in yeast.

scholarly journals Interactions among Rax1p, Rax2p, Bud8p, and Bud9p in Marking Cortical Sites for Bipolar Bud-site Selection in Yeast

2004 ◽  
Vol 15 (11) ◽  
pp. 5145-5157 ◽  
Author(s):  
Pil Jung Kang ◽  
Elizabeth Angerman ◽  
Kenichi Nakashima ◽  
John R. Pringle ◽  
Hay-Oak Park
Keyword(s):  
Cell Cortex ◽  
Type I ◽  
Yeast Saccharomyces Cerevisiae ◽  
Daughter Cells ◽  
Division Site ◽  
Distal Pole ◽  
Mother And Daughter ◽  
Mother Cells ◽  
Diploid Cells ◽  
Bud Site

In the budding yeast Saccharomyces cerevisiae, selection of the bud site determines the axis of polarized cell growth and eventual oriented cell division. Bud sites are selected in specific patterns depending on cell type. These patterns appear to depend on distinct types of marker proteins in the cell cortex; in particular, the bipolar budding of diploid cells depends on persistent landmarks at the birth-scar-distal and -proximal poles that involve the proteins Bud8p and Bud9p, respectively. Rax1p and Rax2p also appear to function specifically in bipolar budding, and we report here a further characterization of these proteins and of their interactions with Bud8p and Bud9p. Rax1p and Rax2p both appear to be integral membrane proteins. Although commonly used programs predict different topologies for Rax2p, glycosylation studies indicate that it has a type I orientation, with its long N-terminal domain in the extracytoplasmic space. Analysis of rax1 and rax2 mutant budding patterns indicates that both proteins are involved in selecting bud sites at both the distal and proximal poles of daughter cells as well as near previously used division sites on mother cells. Consistent with this, GFP-tagged Rax1p and Rax2p were both observed at the distal pole as well as at the division site on both mother and daughter cells; localization to the division sites was persistent through multiple cell cycles. Localization of Rax1p and Rax2p was interdependent, and biochemical studies showed that these proteins could be copurified from yeast. Bud8p and Bud9p could also be copurified with Rax1p, and localization studies provided further evidence of interactions. Localization of Rax1p and Rax2p to the bud tip and distal pole depended on Bud8p, and normal localization of Bud8p was partially dependent on Rax1p and Rax2p. Although localization of Rax1p and Rax2p to the division site did not appear to depend on Bud9p, normal localization of Bud9p appeared largely or entirely dependent on Rax1p and Rax2p. Taken together, the results indicate that Rax1p and Rax2p interact closely with each other and with Bud8p and Bud9p in the establishment and/or maintenance of the cortical landmarks for bipolar budding.

scholarly journals Patterns of bud-site selection in the yeast Saccharomyces cerevisiae.

1995 ◽  
Vol 129 (3) ◽  
pp. 751-765 ◽  
Author(s):  
J Chant ◽  
J R Pringle
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Time Lapse ◽  
Growth Conditions ◽  
Alpha Cells ◽  
Yeast Saccharomyces Cerevisiae ◽  
Cell Cycles ◽  
Daughter Cells ◽  
Division Site ◽  
Mother Cells ◽  
Bud Site

Cells of the yeast Saccharomyces cerevisiae select bud sites in either of two distinct spatial patterns, known as axial (expressed by a and alpha cells) and bipolar (expressed by a/alpha cells). Fluorescence, time-lapse, and scanning electron microscopy have been used to obtain more precise descriptions of these patterns. From these descriptions, we conclude that in the axial pattern, the new bud forms directly adjacent to the division site in daughter cells and directly adjacent to the immediately preceding division site (bud site) in mother cells, with little influence from earlier sites. Thus, the division site appears to be marked by a spatial signal(s) that specifies the location of the new bud site and is transient in that it only lasts from one budding event to the next. Consistent with this conclusion, starvation and refeeding of axially budding cells results in the formation of new buds at nonaxial sites. In contrast, in bipolar budding cells, both poles are specified persistently as potential bud sites, as shown by the observations that a pole remains competent for budding even after several generations of nonuse and that the poles continue to be used for budding after starvation and refeeding. It appears that the specification of the two poles as potential bud sites occurs before a daughter cell forms its first bud, as a daughter can form this bud near either pole. However, there is a bias towards use of the pole distal to the division site. The strength of this bias varies from strain to strain, is affected by growth conditions, and diminishes in successive cell cycles. The first bud that forms near the distal pole appears to form at the very tip of the cell, whereas the first bud that forms near the pole proximal to the original division site (as marked by the birth scar) is generally somewhat offset from the tip and adjacent to (or overlapping) the birth scar. Subsequent buds can form near either pole and appear almost always to be adjacent either to the birth scar or to a previous bud site. These observations suggest that the distal tip of the cell and each division site carry persistent signals that can direct the selection of a bud site in any subsequent cell cycle.

scholarly journals The Rsr1/Bud1 GTPase Interacts with Itself and the Cdc42 GTPase during Bud-Site Selection and Polarity Establishment in Budding Yeast

2010 ◽  
Vol 21 (17) ◽  
pp. 3007-3016 ◽  
Author(s):  
Pil Jung Kang ◽  
Laure Béven ◽  
Seethalakshmi Hariharan ◽  
Hay-Oak Park
Keyword(s):  
Budding Yeast ◽  
Cell Polarization ◽  
Spatial Cues ◽  
Division Site ◽  
Heterotypic Interactions ◽  
Polarity Establishment ◽  
Set Up ◽  
Bud Site

Cell polarization occurs along a single axis that is generally determined in response to spatial cues. In budding yeast, the Rsr1 GTPase and its regulators direct the establishment of cell polarity at the proper cortical location in response to cell type–specific cues. Here we use a combination of in vivo and in vitro approaches to understand how Rsr1 polarization is established. We find that Rsr1 associates with itself in a spatially and temporally controlled manner. The homotypic interaction and localization of Rsr1 to the mother-bud neck and to the subsequent division site are dependent on its GDP-GTP exchange factor Bud5. Analyses of rsr1 mutants suggest that Bud5 recruits Rsr1 to these sites and promotes the homodimer formation. Rsr1 also exhibits heterotypic interaction with the Cdc42 GTPase in vivo. We show that the polybasic region of Rsr1 is necessary for the efficient homotypic and heterotypic interactions, selection of a proper growth site, and polarity establishment. Our findings thus suggest that dimerization of GTPases may be an efficient mechanism to set up cellular asymmetry.

scholarly journals O-Glycosylation of Axl2/Bud10p by Pmt4p Is Required for Its Stability, Localization, and Function in Daughter Cells

1999 ◽  
Vol 145 (6) ◽  
pp. 1177-1188 ◽  
Author(s):  
Sylvia L. Sanders ◽  
Martina Gentzsch ◽  
Widmar Tanner ◽  
Ira Herskowitz
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Site Selection ◽  
Surface Proteins ◽  
Cell Type ◽  
Yeast Saccharomyces Cerevisiae ◽  
Cell Surface Proteins ◽  
Daughter Cells ◽  
Mother Cells ◽  
And Function ◽  
Bud Site

Cells of the yeast Saccharomyces cerevisiae choose bud sites in a manner that is dependent upon cell type: a and α cells select axial sites; a/α cells utilize bipolar sites. Mutants specifically defective in axial budding were isolated from an α strain using pseudohyphal growth as an assay. We found that a and α mutants defective in the previously identified PMT4 gene exhibit unipolar, rather than axial budding: mother cells choose axial bud sites, but daughter cells do not. PMT4 encodes a protein mannosyl transferase (pmt) required for O-linked glycosylation of some secretory and cell surface proteins (Immervoll, T., M. Gentzsch, and W. Tanner. 1995. Yeast. 11:1345–1351). We demonstrate that Axl2/Bud10p, which is required for the axial budding pattern, is an O-linked glycoprotein and is incompletely glycosylated, unstable, and mislocalized in cells lacking PMT4. Overexpression of AXL2 can partially restore proper bud-site selection to pmt4 mutants. These data indicate that Axl2/Bud10p is glycosylated by Pmt4p and that O-linked glycosylation increases Axl2/ Bud10p activity in daughter cells, apparently by enhancing its stability and promoting its localization to the plasma membrane.

Budding of melanized Cryptococcus neoformans in the presence or absence of l-dopa

Microbiology ◽  
2003 ◽  
Vol 149 (7) ◽  
pp. 1945-1951 ◽  
Author(s):  
Joshua D. Nosanchuk ◽  
Arturo Casadevall
Keyword(s):  
Cell Wall ◽  
Cryptococcus Neoformans ◽  
De Novo ◽  
Pathogenic Fungus ◽  
Parent Cell ◽  
Daughter Cells ◽  
Substantial Progress ◽  
Mother Cells ◽  
Bud Site ◽  
Dopa Melanin

Cryptococcus neoformans is a pathogenic fungus that produces melanin when incubated in the presence of certain phenolic substrates such as l-3,4-dihydroxyphenylalanine (l-dopa). Melanin is an enigmatic polymer that is deposited in the cell wall and contributes to virulence. Substantial progress has been made in understanding the synthesis of melanin and the mechanisms by which it contributes to virulence, but relatively little is known about how melanin is rearranged during growth and budding. In this study we used transmission and scanning electron microscopy and immunofluorescence of melanized cells and melanin ‘ghosts' to study the process of melanization during replication. Budding in melanized C. neoformans results in focal disruption of cell-wall melanin at the bud site. In the presence of l-dopa, bud-related melanin defects are repaired and daughter cells are melanized. However, in the absence of substrate, mother cells cannot repair their melanin defects and daughter cells are non-melanized. Hence, melanin in the parent cell is not carried to the daughter cells, but rather is synthesized de novo in buds. These results imply that melanin remodelling occurs during cell growth in a process that involves degradation and synthesis at sites of budding.

scholarly journals The LIM domain-containing Dbm1 GTPase-activating protein is required for normal cellular morphogenesis in Saccharomyces cerevisiae.

1996 ◽  
Vol 16 (4) ◽  
pp. 1376-1390 ◽  
Author(s):  
G C Chen ◽  
L Zheng ◽  
C S Chan
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Site Selection ◽  
Yeast Cells ◽  
Gtpase Activating Protein ◽  
Lim Domain ◽  
Yeast Saccharomyces Cerevisiae ◽  
Lim Domains ◽  
Bud Site

Normal cell growth in the yeast Saccharomyces cerevisiae involves the selection of genetically determined bud sites where most growth is localized. Previous studies have shown that BEM2, which encodes a GTPase-activating protein (GAP) that is specific for the Rho-type GTPase Rho1p in vitro, is required for proper bud site selection and bud emergence. We show here that DBM1, which encodes another putative Rho-type GAP with two tandemly arranged cysteine-rich LIM domains, also is needed for proper bud site selection, as haploid cells lacking Dbm1p bud predominantly in a bipolar, rather than the normal axial, manner. Furthermore, yeast cells lacking both Bem2p and Dbm1p are inviable. The nonaxial budding defect of dbm1 mutants can be rescued partially by overproduction of Bem3p and is exacerbated by its absence. Since Bem3p has previously been shown to function as a GAP for Cdc42p, and also less efficiently for Rho1p, our results suggest that Dbm1p, like Bem2p and Bem3p, may function in vivo as a GAP for Cdc42p and/or Rho1p. Both LIM domains of Dbm1p are essential for its normal function. Point mutations that alter single conserved cysteine residues within either LIM domain result in mutant forms of Dbm1p that can no longer function in bud site selection but instead are capable of rescuing the inviability of bem2 mutants at 35 degrees C.

scholarly journals Evaluation of Optimal Vibrotactile Feedback for Force-Controlled Upper Limb Myoelectric Prostheses

Sensors ◽  
2019 ◽  
Vol 19 (23) ◽  
pp. 5209 ◽  
Author(s):  
Andrea Gonzalez-Rodriguez ◽  
Jose L. Ramon ◽  
Vicente Morell ◽  
Gabriel J. Garcia ◽  
Jorge Pomares ◽  
...  
Keyword(s):  
Real Time ◽  
Upper Limb ◽  
Closed Loop ◽  
Fine Tuning ◽  
Vibrotactile Feedback ◽  
Loop Control ◽  
Myoelectric Prostheses ◽  
Amplitude Level ◽  
Real Time Application ◽  
Selection Of

The main goal of this study is to evaluate how to optimally select the best vibrotactile pattern to be used in a closed loop control of upper limb myoelectric prostheses as a feedback of the exerted force. To that end, we assessed both the selection of actuation patterns and the effects of the selection of frequency and amplitude parameters to discriminate between different feedback levels. A single vibrotactile actuator has been used to deliver the vibrations to subjects participating in the experiments. The results show no difference between pattern shapes in terms of feedback perception. Similarly, changes in amplitude level do not reflect significant improvement compared to changes in frequency. However, decreasing the number of feedback levels increases the accuracy of feedback perception and subject-specific variations are high for particular participants, showing that a fine-tuning of the parameters is necessary in a real-time application to upper limb prosthetics. In future works, the effects of training, location, and number of actuators will be assessed. This optimized selection will be tested in a real-time proportional myocontrol of a prosthetic hand.

Cybersecurity Standards in the Context of Operating System

2021 ◽  
Vol 54 (3) ◽  
pp. 1-36
Author(s):  
Syed Wasif Abbas Hamdani ◽  
Haider Abbas ◽  
Abdul Rehman Janjua ◽  
Waleed Bin Shahid ◽  
Muhammad Faisal Amjad ◽  
...  
Keyword(s):  
Organizational Context ◽  
Cyber Attacks ◽  
Fine Tuning ◽  
Security Vulnerabilities ◽  
Compliance Testing ◽  
Depth Analysis ◽  
Minimum Requirements ◽  
Security Standards ◽  
High Degree ◽  
Selection Of

Cyber threats have been growing tremendously in recent years. There are significant advancements in the threat space that have led towards an essential need for the strengthening of digital infrastructure security. Better security can be achieved by fine-tuning system parameters to the best and optimized security levels. For the protection of infrastructure and information systems, several guidelines have been provided by well-known organizations in the form of cybersecurity standards. Since security vulnerabilities incur a very high degree of financial, reputational, informational, and organizational security compromise, it is imperative that a baseline for standard compliance be established. The selection of security standards and extracting requirements from those standards in an organizational context is a tedious task. This article presents a detailed literature review, a comprehensive analysis of various cybersecurity standards, and statistics of cyber-attacks related to operating systems (OS). In addition to that, an explicit comparison between the frameworks, tools, and software available for OS compliance testing is provided. An in-depth analysis of the most common software solutions ensuring compliance with certain cybersecurity standards is also presented. Finally, based on the cybersecurity standards under consideration, a comprehensive set of minimum requirements is proposed for OS hardening and a few open research challenges are discussed.

scholarly journals Activation of Cdc42 GTPase upon CRY2-Induced Cortical Recruitment Is Antagonized by GAPs in Fission Yeast

Cells ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 2089 ◽  
Author(s):  
Iker Lamas ◽  
Nathalie Weber ◽  
Sophie G. Martin
Keyword(s):  
Fission Yeast ◽  
Positive Feedback ◽  
Antagonistic Activity ◽  
Cell Polarization ◽  
Small Gtpase ◽  
Nucleotide Exchange ◽  
Gtpase Activating Protein ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Cell Architecture

The small GTPase Cdc42 is critical for cell polarization in eukaryotic cells. In rod-shaped fission yeast Schizosaccharomyces pombe cells, active GTP-bound Cdc42 promotes polarized growth at cell poles, while inactive Cdc42-GDP localizes ubiquitously also along cell sides. Zones of Cdc42 activity are maintained by positive feedback amplification involving the formation of a complex between Cdc42-GTP, the scaffold Scd2, and the guanine nucleotide exchange factor (GEF) Scd1, which promotes the activation of more Cdc42. Here, we use the CRY2-CIB1 optogenetic system to recruit and cluster a cytosolic Cdc42 variant at the plasma membrane and show that this leads to its moderate activation also on cell sides. Surprisingly, Scd2, which binds Cdc42-GTP, is still recruited to CRY2-Cdc42 clusters at cell sides in individual deletion of the GEFs Scd1 or Gef1. We show that activated Cdc42 clusters at cell sides are able to recruit Scd1, dependent on the scaffold Scd2. However, Cdc42 activity is not amplified by positive feedback and does not lead to morphogenetic changes, due to antagonistic activity of the GTPase activating protein Rga4. Thus, the cell architecture is robust to moderate activation of Cdc42 at cell sides.

scholarly journals Examining and Fine-tuning the Selection of Glycan Compositions with GlyConnect Compozitor

2020 ◽  
Vol 19 (10) ◽  
pp. 1602-1618 ◽  
Author(s):  
Thibault Robin ◽  
Julien Mariethoz ◽  
Frédérique Lisacek
Keyword(s):  
Search Engine ◽  
Posttranslational Modifications ◽  
Search Engines ◽  
Web Application ◽  
Contextual Information ◽  
Fine Tuning ◽  
Data Sources ◽  
Web Interface ◽  
Definition Of ◽  
Selection Of

A key point in achieving accurate intact glycopeptide identification is the definition of the glycan composition file that is used to match experimental with theoretical masses by a glycoproteomics search engine. At present, these files are mainly built from searching the literature and/or querying data sources focused on posttranslational modifications. Most glycoproteomics search engines include a default composition file that is readily used when processing MS data. We introduce here a glycan composition visualizing and comparative tool associated with the GlyConnect database and called GlyConnect Compozitor. It offers a web interface through which the database can be queried to bring out contextual information relative to a set of glycan compositions. The tool takes advantage of compositions being related to one another through shared monosaccharide counts and outputs interactive graphs summarizing information searched in the database. These results provide a guide for selecting or deselecting compositions in a file in order to reflect the context of a study as closely as possible. They also confirm the consistency of a set of compositions based on the content of the GlyConnect database. As part of the tool collection of the Glycomics@ExPASy initiative, Compozitor is hosted at https://glyconnect.expasy.org/compozitor/ where it can be run as a web application. It is also directly accessible from the GlyConnect database.

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