scholarly journals Microtubules Are Dispensable for the Initial Pathogenic Development but Required for Long-Distance Hyphal Growth in the Corn Smut FungusUstilago maydis

2005 ◽  
Vol 16 (6) ◽  
pp. 2746-2758 ◽  
Author(s):  
Uta Fuchs ◽  
Isabel Manns ◽  
Gero Steinberg
Keyword(s):  
Cell Fusion ◽  
Hyphal Growth ◽  
Nuclear Migration ◽  
Structural Basis ◽  
Polarized Growth ◽  
Long Distance ◽  
Cycle Arrest ◽  
Similar Phenotype ◽  
A Cell ◽  
Cell Cell

Fungal pathogenicity often involves a yeast-to-hypha transition, but the structural basis for this dimorphism is largely unknown. Here we analyze the role of the cytoskeleton in early steps of pathogenic development in the corn pathogen Ustilago maydis. On the plant yeast-like cells recognize each other, undergo a cell cycle arrest, and form long conjugation hyphae, which fuse and give rise to infectious filaments. F-actin is essential for polarized growth at all these stages and for cell-cell fusion. Furthermore, F-actin participates in pheromone secretion, but not perception. Although U. maydis contains prominent tubulin arrays, microtubules are neither required for cell-cell recognition, nor for cell-cell fusion, and have only minor roles in morphogenesis of yeast-like cells. Without microtubules hyphae are formed, albeit at 60% reduced elongation rates, but they reach only ∼50 μm in length and the nucleus fails to migrate into the hypha. A similar phenotype is found in dynein mutants that have a nuclear migration defect and stop hyphal elongation at ∼50 μm. These results demonstrate that microtubules are dispensable for polarized growth during morphological transition, but become essential in long-distance hyphal growth, which is probably due to their role in nuclear migration.

scholarly journals Mechanical stress impairs pheromone signaling via Pkc1-mediated regulation of the MAPK scaffold Ste5

2019 ◽  
Vol 218 (9) ◽  
pp. 3117-3133 ◽  
Author(s):  
Frank van Drogen ◽  
Ranjan Mishra ◽  
Fabian Rudolf ◽  
Michal J. Walczak ◽  
Sung Sik Lee ◽  
...  
Keyword(s):  
Mechanical Stress ◽  
Cell Fusion ◽  
Polarized Growth ◽  
Conserved Residues ◽  
Cellular Processes ◽  
Pheromone Signaling ◽  
Stress Signals ◽  
Cell Cell

Cells continuously adapt cellular processes by integrating external and internal signals. In yeast, multiple stress signals regulate pheromone signaling to prevent mating under unfavorable conditions. However, the underlying crosstalk mechanisms remain poorly understood. Here, we show that mechanical stress activates Pkc1, which prevents lysis of pheromone-treated cells by inhibiting polarized growth. In vitro Pkc1 phosphorylates conserved residues within the RING-H2 domains of the scaffold proteins Far1 and Ste5, which are also phosphorylated in vivo. Interestingly, Pkc1 triggers dispersal of Ste5 from mating projections upon mechanically induced stress and during cell–cell fusion, leading to inhibition of the MAPK Fus3. Indeed, RING phosphorylation interferes with Ste5 membrane association by preventing binding to the receptor-linked Gβγ protein. Cells expressing nonphosphorylatable Ste5 undergo increased lysis upon mechanical stress and exhibit defects in cell–cell fusion during mating, which is exacerbated by simultaneous expression of nonphosphorylatable Far1. These results uncover a mechanical stress–triggered crosstalk mechanism modulating pheromone signaling, polarized growth, and cell–cell fusion during mating.

scholarly journals TMEM16F phospholipid scramblase mediates trophoblast fusion and placental development

2019 ◽  
Author(s):  
Yang Zhang ◽  
Trieu Le ◽  
Ryan Grabau ◽  
Zahra Mohseni ◽  
Hoejeong Kim ◽  
...  
Keyword(s):  
Cell Surface ◽  
Cell Fusion ◽  
Placental Development ◽  
Cellular Mechanisms ◽  
Developmental Defects ◽  
Phospholipid Scramblase ◽  
A Cell ◽  
Fusion Signal ◽  
Multicellular Organisms ◽  
Cell Cell

AbstractCell-cell fusion or syncytialization is fundamental to the reproduction, development and homeostasis of multicellular organisms. In addition to various cell-type specific fusogenic proteins, cell surface externalization of phosphatidylserine (PS), a universal eat-me signal in apoptotic cells, has been observed in different cell-fusion events. Nevertheless, molecular underpinnings of PS externalization and cellular mechanisms of PS-facilitated cell-cell fusion are unclear. Here we report that TMEM16F, a Ca2+-activated phospholipid scramblase (CaPLSase), plays an indispensable role in placental trophoblast fusion by translocating PS to the cell surface independent of apoptosis. Consistent with its essential role in trophoblast fusion, the placentas from TMEM16F-deficient mice exhibit deficiency in syncytialization, placental developmental defects and perinatal lethality. Our findings thus identify a cell-cell fusion mechanism by which TMEM16F CaPLSase-dependent externalization of PS serves as a critical cell fusion signal to facilitate trophoblast syncytialization and placental development.

scholarly journals Cleavage of Epstein–Barr virus glycoprotein B is required for full function in cell–cell fusion with both epithelial and B cells

2009 ◽  
Vol 90 (3) ◽  
pp. 591-595 ◽  
Author(s):  
Jessica Sorem ◽  
Richard Longnecker
Keyword(s):  
B Cells ◽  
Cell Fusion ◽  
Epstein Barr Virus ◽  
Glycoprotein B ◽  
Barr Virus ◽  
High Sequence Conservation ◽  
A Cell ◽  
Epstein Barr ◽  
Cleavage Motif ◽  
Cell Cell

Glycoprotein B (gB) homologues within the herpesvirus family display high sequence conservation, and a number of gB homologues contain a cleavage motif R-X-K/R-R recognized by the cellular protease furin. Epstein–Barr virus (EBV) gB contains this motif and cleaved gB is found in EBV virions. To determine the functional significance of this cleavage motif in EBV gB, a deletion mutant (gB Δfurin) was created lacking the motif. This cleavage mutant was expressed well in cell culture but was not cleaved. Experiments examining gB Δfurin in a cell-fusion assay revealed that fusion was reduced by 52 % in epithelial and 28 % in B cells when compared with wild-type EBV gB. This decrease in cell–cell fusion is similar to that observed with multiple alphaherpesvirus gB cleavage mutants and supports a conserved function for cleaved gB.

Inductive regulation of cell fusion in leech

Development ◽  
1999 ◽  
Vol 126 (15) ◽  
pp. 3381-3390 ◽  
Author(s):  
D.E. Isaksen ◽  
N.J. Liu ◽  
D.A. Weisblat
Keyword(s):  
Cell Fusion ◽  
Critical Period ◽  
Ribonuclease A ◽  
Fusion Event ◽  
Ricin A Chain ◽  
Helobdella Robusta ◽  
A Cell ◽  
A Chain ◽  
Ricin A ◽  
Cell Cell

Cell-cell fusion is a component of many different developmental processes, but little is known about how cell-cell fusion is regulated. Here we investigate the regulation of a stereotyped cell-cell fusion event that occurs among the endodermal precursor cells of the glossiphoniid leech Helobdella robusta. We find that this fusion event is regulated inductively by a cell that does not itself fuse. We also show that biochemical arrest (by microinjection with ricin A chain or ribonuclease A) of the inducer or either of the fusion partners prevents fusion, but only if the arrest is initiated during a critical period long before the time at which fusion normally occurs. If the arrest occurs after this critical period, fusion occurs on schedule. These results suggest that both fusion partners play active roles in the process and that neither the induction nor the fusion itself requires concomitant protein synthesis.

scholarly journals A Cell Fusion-Based Screening Method Identifies Glycosylphosphatidylinositol-Anchored Protein Ly6e as the Receptor for Mouse Endogenous Retroviral Envelope Syncytin-A

2017 ◽  
Vol 91 (18) ◽  
Author(s):  
Agathe Bacquin ◽  
Caroline Bireau ◽  
Maxime Tanguy ◽  
Charlotte Romanet ◽  
Cécile Vernochet ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Cell Fusion ◽  
Screening Method ◽  
Endogenous Retroviruses ◽  
Lymphocyte Antigen ◽  
Mouse Placenta ◽  
Mouse Tissues ◽  
A Cell ◽  
Mediate Cell ◽  
Cell Cell

ABSTRACT Syncytin genes are envelope genes of retroviral origin that have been exapted for a role in placentation. They are involved in the formation of a syncytial structure (the syncytiotrophoblast) at the fetomaternal interface via their fusogenic activity. The mouse placenta is unique among placental mammals since the fetomaternal interface comprises two syncytiotrophoblast layers (ST-I and ST-II) instead of one, as observed in humans and all other hemochorial placentae. Each layer specifically expresses a distinct mouse syncytin, namely, syncytin-A (SynA) for ST-I and syncytin-B (SynB) for ST-II, which have been shown to be essential to placentogenesis and embryo survival. Their cognate cellular receptors, which are necessary to mediate cell-cell fusion and syncytiotrophoblast formation, are still unknown. By devising a sensitive method that combines a cell-cell fusion assay with the screening of a mouse cDNA library, we succeeded in identifying the glycosylphosphatidylinositol (GPI)-anchored membrane protein lymphocyte antigen 6E (Ly6e) as a candidate receptor for SynA. Transfection of cells with the cloned receptor led to their fusion to cells expressing SynA, with no cross-reactive fusion activity with SynB. Knocking down Ly6e greatly reduced SynA-induced cell fusion, thus suggesting that Ly6e is the sole receptor for SynA in vivo. Interaction of SynA with Ly6e was further demonstrated by a competition assay using the soluble ectodomain of Ly6e. Finally, reverse transcription-quantitative PCR (RT-qPCR) analysis of Ly6e expression on a representative panel of mouse tissues shows that it is significantly expressed in the mouse placenta together with SynA. IMPORTANCE Syncytin genes are envelope genes of endogenous retroviruses, co-opted for a physiological function in placentation. Syncytins are fusogenic proteins that mediate cell-cell fusion by interacting with receptors present on the partner cells. Here, by devising a sensitive in vitro fusion assay that enables the high-throughput screening of normalized cDNA libraries, we identified the long-sought receptor for syncytin-A (SynA), a mouse syncytin responsible for syncytiotrophoblast formation at the maternofetal interface of the mouse placenta. This protein, Ly6e (lymphocyte antigen 6E), is a GPI-anchored membrane protein, and small interfering RNA (siRNA) experiments targeting its deletion as well as a decoy assay using a recombinant soluble receptor show that Ly6e is the necessary and sufficient partner of SynA. Its profile of expression is consistent with a role in both ancestral endogenization of a SynA founder retrovirus and present-day placenta formation. This study provides a powerful general method to identify genes involved in cell-cell fusion processes.

scholarly journals The Combination of gQ1 and gQ2 in Human Herpesvirus 6A and 6B Regulates the Viral Tetramer Function for Their Receptor Recognition

2020 ◽  
Author(s):  
Aika Wakata ◽  
Lidya Handayani Tjan ◽  
Mitsuhiro Nishimura ◽  
Akiko Kawabata ◽  
Anna Lystia Poetranto ◽  
...  
Keyword(s):  
Cell Fusion ◽  
Essential Gene ◽  
Critical Role ◽  
Specific Interaction ◽  
Human Herpesvirus ◽  
Assay System ◽  
Virus Propagation ◽  
Receptor Recognition ◽  
A Cell ◽  
Cell Cell

Human herpesvirus 6A (HHV-6A) and HHV-6B use different cellular receptors, human CD46 and CD134, respectively and have different cell tropisms although they have 90% similarity at the nucleotide level. An important feature that characterizes HHV-6A/6B is the glycoprotein H (gH)/gL/gQ1/gQ2 complex (a tetramer) that each virus has specifically on its envelope. Here, to determine which molecules in the tetramer contribute to the specificity for each receptor, we developed a cell-cell fusion assay system for HHV-6A and HHV-6B that uses the cells expressing CD46 or CD134. With this system, when we replaced the gQ1 or gQ2 of HHV-6A with that of HHV-6B in the tetramer, the cell fusion activity mediated by glycoproteins via CD46 was lower than that done with the original-type tetramer. When we replaced the gQ1 or the gQ2 of HHV-6A with that of HHV-6B in the tetramer, the cell fusion mediated by glycoproteins via CD134 was not seen. In addition, we generated two types of C-terminal truncation mutants of HHV-6A gQ2 (AgQ2) to examine the interaction domains of HHV-6A gQ1 (AgQ1) and AgQ2. We found that amino acid residues 163 to 185 in AgQ2 are important for interaction of AgQ1 and AgQ2. Finally, to investigate whether HHV-6B gQ2 (BgQ2) can complement AgQ2, an HHV-6A genome harboring BgQ2 was constructed. The mutant could not produce an infectious virus, indicating that BgQ2 cannot work for the propagation of HHV-6A. These results suggest that gQ2 supports the tetramer's function, and the combination of gQ1 and gQ2 is critical for virus propagation. IMPORTANCE Glycoprotein Q2 (gQ2), an essential gene for virus propagation, forms a heterodimer with gQ1. The gQ1/gQ2 complex has a critical role in receptor recognition in the gH/gL/gQ1/gQ2 complex (a tetramer). We investigated whether gQ2 regulates the specific interaction between the HHV-6A or -6B tetramer and CD46 or CD134. We established a cell-cell fusion assay system for HHV-6A/6B and switched the gQ1 or gQ2 of HHV-6A with that of HHV-6B in the tetramer. Although cell fusion was induced via CD46 when gQ1 or gQ2 was switched between HHV-6A and -6B, the activity was lower than that of the original combination. When gQ1 or gQ2 was switched in HHV-6A and -6B, no cell fusion was observed via CD134. HHV-6B gQ2 could not complement the function of HHV-6A's gQ2 in HHV-6A propagation, suggesting that the combination of gQ1 and gQ2 is critical to regulate the specificity of the tetramer's function for virus entry.

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