The Rim15-Endosulfine-PP2ACdc55 Signalling Module Regulates Entry into Gametogenesis and Quiescence via Distinct Mechanisms in Budding Yeast

Quiescence and gametogenesis represent two distinct survival strategies in response to nutrient starvation in budding yeast. Precisely how environmental signals are sensed by yeast cells to trigger quiescence and gametogenesis is not fully understood. A conserved signalling module consisting of Greatwall kinase, Endosulfine and Protein Phosphatase PP2A^Cdc55 proteins regulates entry into mitosis in Xenopus egg extracts and meiotic maturation in flies. We report here that an analogous signalling module consisting of the serine-threonine kinase Rim15, the Endosulfines Igo1 and Igo2 and the Protein Phosphatase PP2A^Cdc55, regulates entry into both quiescence and gametogenesis in budding yeast. PP2A^Cdc55 inhibits entry into gametogenesis and quiescence. Rim15 promotes entry into gametogenesis and quiescence by converting Igo1 into an inhibitor of PP2A^Cdc55 by phosphorylating at a conserved serine residue. Moreover, we show that the Rim15-Endosulfine-PP2A^Cdc55 pathway regulates entry into quiescence and gametogenesis by distinct mechanisms. In addition, we show that Igo1 and Igo2 are required for pre-meiotic autophagy but the lack of pre-meiotic autophagy is insufficient to explain the sporulation defect of igo1Δ igo2Δ cells. We propose that the Rim15-Endosulfine-PP2A^Cdc55 signalling module triggers entry into quiescence and gametogenesis by regulating dephosphorylation of distinct substrates.     

Cdc42 activity regulates hematopoietic stem cell aging and rejuvenation

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Highlights? Constitutively increasing Cdc42 activity causes aging of young HSCs ? Elevated Cdc42 activity correlates with a loss of cell polarity in aged HSCs ? Inhibition of Cdc42 activity rejuvenates aged LT-HSC function ? Cdc42 inhibition restores the level and spatial distribution of AcH4K16     

The structural basis for tight control of PP2A methylation and function by LCMT-1

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Highlights? LCMT-1 makes extensive contacts to PP2A active site for methylation of PP2A tail ? PP2A methylation is stimulated by phosphatase activation, hampered by inactivation ? LCMT-1 would facilitate efficient transition of activated PP2A to holoenzymes ? A high-affinity dnLCMT-1 mutant attenuates the cell cycle without causing cell death     

Inhibition of protein phosphatase 2A activity by PI3Kγ regulates β-adrenergic receptor function

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Highlights? PI3Kγ inhibits βAR resensitization by regulating PP2A activity ? PI3Kγ inhibits PP2A activity by phosphorylating I2PP2A on Serine 9 and 93 ? Phosphorylation of I2PP2A leads to its agonist-mediated interaction with PP2A ? siRNA-targeted depletion of I2PP2A results in βAR resensitization     

The PP2A Inhibitor I2PP2A Is Essential for Sister Chromatid Segregation in Oocyte Meiosis II

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Highlights? PP2A colocalizes with Rec8 in mouse oocyte meiosis II ? The PP2A inhibitor I2PP2A is expressed in ascidian and mouse oocyte meiosis ? I2PP2A colocalizes with PP2A in meiosis II, independently of bipolar attachment ? I2PP2A is required for sister separation in mouse oocyte meiosis II     

PP2A phosphatase acts upon SAS-5 to ensure centriole formation in C. elegans embryos

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Highlights? PP2A phosphatase is essential for centriole formation in C. elegans ? PP2A subunits genetically and physically interact with the SAS-5/SAS-6 complex ? PP2A-mediated dephosphorylation of SAS-5 is required for SAS-5/SAS-6 centriolar targeting ? Human PP2A is required for HsSAS-6 centriolar targeting and centriole formation     

The Molecular Basis for Substrate Specificity of the Nuclear NIPP1:PP1 Holoenzyme

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Highlights? The first structure of a nuclear PP1 holoenzyme, NIPP1:PP1 ? The NIPP1 helix defines a unique interaction site on PP1 ? Identification of a common PP1-binding pocket, the ΦΦ motif-binding pocket ? Explains the mechanism of nuclear substrate selection by PP1     

Protein Phosphatase 2A Catalytic Subunit α Plays a MyD88-Dependent,Central Role in the Gene-Specific Regulation of Endotoxin Tolerance

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Highlights? PP2Ac is constitutively activated and targets MyD88 in LPS-tolerized macrophages ? Constitutively active PP2Ac shifts a proinflammatory MyD88 to its prosurvival mode ? Constitutively active PP2Ac reprograms gene-specific chromatin modification landscape ? Constitutively active PP2Ac broadly defines ET at both signaling and epigenetic levels     

Ultrasensitivity in the Regulation of Cdc25C by Cdk1

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Highlights? The response of Cdc25C to Cdk1 in Xenopus egg extracts is ultrasensitive ? The Hill coefficient for the response is astronomical (～11–32) ? Multisite phosphorylation accounts for some of the ultrasensitivity ? The Cdc25C and Wee1A responses account for the bistability of the mitotic trigger     

Cdc6-induced conformational changes in ORC bound to origin DNA revealed by cryo-electron microscopy

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Highlights? We have determined the cryo-EM structures of ORC, ORC-DNA, and ORC-Cdc6-DNA ? We show that ORC is arranged as Orc1:Orc4:Orc5:Orc2:Orc3, with Orc6 binding to Orc2 ? DNA and Cdc6 binding causes large conformational changes in ORC ? Origin DNA is proposed to bind to the interior surface of the crescent-shaped ORC     

Budding Yeast Greatwall and Endosulfines Control Activity and Spatial Regulation of PP2ACdc55 for Timely Mitotic Progression

Entry into mitosis is triggered by cyclinB/Cdk1, whose activity is abruptly raised by a positive feedback loop. The Greatwall kinase phosphorylates proteins of the endosulfine family and allows them to bind and inhibit the main Cdk1-counteracting PP2A-B55 phosphatase, thereby promoting mitotic entry. In contrast to most eukaryotic systems, Cdc14 is the main Cdk1-antagonizing phosphatase in budding yeast, while the PP2A^Cdc55 phosphatase promotes, instead of preventing, mitotic entry by participating to the positive feedback loop of Cdk1 activation. Here we show that budding yeast endosulfines (Igo1 and Igo2) bind to PP2A^Cdc55 in a cell cycle-regulated manner upon Greatwall (Rim15)-dependent phosphorylation. Phosphorylated Igo1 inhibits PP2A^Cdc55 activity in vitro and induces mitotic entry in Xenopus egg extracts, indicating that it bears a conserved PP2A-binding and -inhibitory activity. Surprisingly, deletion of IGO1 and IGO2 in yeast cells leads to a decrease in PP2A phosphatase activity, suggesting that endosulfines act also as positive regulators of PP2A in yeast. Consistently, RIM15 and IGO1/2 promote, like PP2A^Cdc55, timely entry into mitosis under temperature-stress, owing to the accumulation of Tyr-phosphorylated Cdk1. In addition, they contribute to the nuclear export of PP2A^Cdc55, which has recently been proposed to promote mitotic entry. Altogether, our data indicate that Igo proteins participate in the positive feedback loop for Cdk1 activation. We conclude that Greatwall, endosulfines, and PP2A are part of a regulatory module that has been conserved during evolution irrespective of PP2A function in the control of mitosis. However, this conserved module is adapted to account for differences in the regulation of mitotic entry in different organisms.     

A Molecular Motor,KIF13A,Controls Anxiety by Transporting the Serotonin Type 1A Receptor

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Highlights? Kif13a^?/? mice show elevated-anxiety-like behavioral defects ? 5HT_1A receptors are not properly transported in Kif13a^?/? neurons ? The forkhead-associated domain of KIF13A associates directly with 5HT_1A receptors ? KIF13A can translocate 5HT_1A receptors in vivo and in vitro     

STIM1 Juxtaposes ER to Phagosomes,Generating Ca2+ Hotspots that Boost Phagocytosis

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Highlights? STIM1 drives store-operated recruitment of ER cisternae to phagosomes ? STIM1 is required for Ca²⁺-dependent, high-efficiency phagocytosis ? STIM1 gates phagosomal Ca²⁺ channels, generating periphagosomal Ca²⁺ microdomains     

Characterization and In Vivo Pharmacological Rescue of a Wnt2-Gata6 Pathway Required for Cardiac Inflow Tract Development

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Highlights? Wnt2 is required for atrial and inflow tract morphogenesis ? Wnt2 regulates expansion of secondary heart field progenitors ? Defects in Wnt2^?/? mutants can be rescued using Wnt signaling agonists ? Wnt2 cooperates with Gata6 to regulate cardiac inflow tract development     

ADF/cofilin regulates secretory cargo sorting at the TGN via the Ca2+ ATPase SPCA1

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Highlights? ADF/cofilin localizes to the TGN and binds SPCA1 in an actin-dependent manner ? Dynamic actin regulates the activity of the Ca²⁺ pump SPCA1 ? ADF/cofilin facilitates secretory cargo sorting in a Ca²⁺-dependent manner     

Cdc42 Explores the Cell Periphery for Mate Selection in Fission Yeast

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Highlights? Active Cdc42 forms dynamic zones at the periphery of mating S. pombe cells ? This defines a novel exploratory phase, without cell wall synthase exocytosis or growth ? Zone dynamics occur upon exposure to low- but not high-level pheromone ? Mating partner choice is compromised in absence of low-level pheromone signaling     

A master switch couples Mg²⁺-assisted catalysis to domain motion in B. stearothermophilus tryptophanyl-tRNA Synthetase

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Highlights? Combinatorial mutagenesis at four remote sites shifts reaction coordinate stabilities ? Cooperative action of all four sites accounts for the entire catalytic role of Mg2⁺ ? Catalysis of ATP utilization by Mg2⁺ occurs if, and only if, the conformation changes ? This type of allosteric effect may explain vectorial coupling in transducing NTPases     

Comparative genetic analysis of PP2A-Cdc55 regulators in budding yeast

Cdc55, a regulatory B subunit of the protein phosphatase 2A (PP2A) complex, plays various functions during mitosis. Sequestration of Cdc55 from the nucleus by Zds1 and Zds2 is important for robust activation of mitotic Cdk1 and mitotic progression in budding yeast. However, Zds1-family proteins are found only in fungi but not in higher eukaryotes. In animal cells, highly conserved ENSA/ARPP-19 family proteins bind and inhibit PP2A–B55 activity for mitotic entry.

In this study, we compared the relative contribution of Zds1/Zds2 and ENSA-family proteins Igo1/Igo2 on Cdc55 functions in budding yeast mitosis. We confirmed that Igo1/Igo2 can inhibit Cdc55 in early mitosis, but their contribution to Cdc55 regulation is relatively minor compared with the role of Zds1/Zds2. In contrast to Zds1, which primarily localized to the sites of cell polarity and in the cytoplasm, Igo1 is localized in the nucleus, suggesting that Igo1/Igo2 inhibit Cdc55 in a manner distinct from Zds1/Zds2.

Our analysis confirmed an evolutionarily conserved function of ENSA-family proteins in inhibiting PP2A-Cdc55, and we propose that Zds1-dependent sequestration of PP2A-Cdc55 from the nucleus is uniquely evolved to facilitate closed mitosis in fungal species.     

Tmem64 Modulates Calcium Signaling during RANKL-Mediated Osteoclast Differentiation

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Highlights? Tmem64-deficient mice show increased bone volume ? Tmem64 deficiency reduces [Ca²⁺]_i oscillation in response to RANKL stimulation ? Tmem64 interacts with SERCA2 ? Tmem64 positively regulates osteoclast formation via SERCA2/Ca²⁺ signaling