aubergineencodes aDrosophilapolar granule component required for pole cell formation and related to eIF2C

Development ◽  
2001 ◽  
Vol 128 (14) ◽  
pp. 2823-2832 ◽  
Author(s):  
Adam N. Harris ◽  
Paul M. Macdonald
Keyword(s):  
Polar Granule ◽  
Cell Formation ◽  
Posterior Pole ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Dependent Manner ◽  
Eukaryotic Translation ◽  
Pole Cell ◽  
Body Patterning ◽  
Pole Plasm

In Drosophila oocytes, activation of Oskar translation from a transcript localized to the posterior pole is an essential step in the organization of the pole plasm, specialized cytoplasm that contains germline and abdominal body patterning determinants. Oskar is a component of polar granules, large particles associated with the pole plasm and the germline precursor pole cells of the embryo. aubergine mutants fail to translate oskar mRNA efficiently and are thus defective in posterior body patterning and pole cell formation. We have found that Aubergine protein is related to eukaryotic translation initiation factor 2C and suggest how it may activate translation. In addition, we found that Aubergine was recruited to the posterior pole in a vas-dependent manner and is itself a polar granule component. Consistent with its presence in these structures, Aubergine is required for pole cell formation independently of its initial role in oskar translation. Unlike two other known polar granule components, Vasa and Oskar, Aubergine remains cytoplasmic after pole cell formation, suggesting that the roles of these proteins diverge during embryogenesis.

Oskar anchoring restricts pole plasm formation to the posterior of the Drosophila oocyte

Development ◽  
2002 ◽  
Vol 129 (15) ◽  
pp. 3705-3714 ◽  
Author(s):  
Nathalie F. Vanzo ◽  
Anne Ephrussi
Keyword(s):  
Drosophila Melanogaster ◽  
Translational Control ◽  
Cell Formation ◽  
Positional Information ◽  
Mrna Localization ◽  
Posterior Pole ◽  
Tight Coupling ◽  
Anteroposterior Patterning ◽  
Pole Cell ◽  
Pole Plasm

Localization of the maternal determinant Oskar at the posterior pole of Drosophila melanogaster oocyte provides the positional information for pole plasm formation. Spatial control of Oskar expression is achieved through the tight coupling of mRNA localization to translational control, such that only posterior-localized oskar mRNA is translated, producing the two Oskar isoforms Long Osk and Short Osk. We present evidence that this coupling is not sufficient to restrict Oskar to the posterior pole of the oocyte. We show that Long Osk anchors both oskar mRNA and Short Osk, the isoform active in pole plasm assembly, at the posterior pole. In the absence of anchoring by Long Osk, Short Osk disperses into the bulk cytoplasm during late oogenesis, impairing pole cell formation in the embryo. In addition, the pool of untethered Short Osk causes anteroposterior patterning defects, owing to the dispersion of pole plasm and its abdomen-inducing activity throughout the oocyte. We show that the N-terminal extension of Long Osk is necessary but not sufficient for posterior anchoring, arguing for multiple docking elements in Oskar. This study reveals cortical anchoring of the posterior determinant Oskar as a crucial step in pole plasm assembly and restriction, required for proper development of Drosophila melanogaster.

scholarly journals IRE1α-Dependent Decay of CReP/Ppp1r15b mRNA Increases Eukaryotic Initiation Factor 2α Phosphorylation and Suppresses Protein Synthesis

2015 ◽  
Vol 35 (16) ◽  
pp. 2761-2770 ◽  
Author(s):  
Jae-Seon So ◽  
Sungyun Cho ◽  
Sang-Hyun Min ◽  
Scot R. Kimball ◽  
Ann-Hwee Lee
Keyword(s):  
Protein Synthesis ◽  
Er Stress ◽  
Translational Control ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Regulatory Subunit ◽  
Dependent Manner ◽  
Eukaryotic Translation ◽  
Eif2α Phosphorylation ◽  
The Unfolded Protein Response

The unfolded protein response (UPR) regulates endoplasmic reticulum (ER) homeostasis and protects cells from ER stress. IRE1α is a central regulator of the UPR that activates the transcription factor XBP1s through an unconventional splicing mechanism using its endoribonuclease activity. IRE1α also cleaves certain mRNAs containing XBP1-like secondary structures to promote the degradation of these mRNAs, a process known as regulated IRE1α-dependent decay (RIDD). We show here that the mRNA of CReP/Ppp1r15b, a regulatory subunit of eukaryotic translation initiation factor 2α (eIF2α) phosphatase, is a RIDD substrate. eIF2α plays a central role in the integrated stress response by mediating the translational attenuation to decrease the stress level in the cell. CReP expression was markedly suppressed in XBP1-deficient mice livers due to hyperactivated IRE1α. Decreased CReP expression caused the induction of eIF2α phosphorylation and the attenuation of protein synthesis in XBP1-deficient livers. ER stress also suppressed CReP expression in an IRE1α-dependent manner, which increased eIF2α phosphorylation and consequently attenuated protein synthesis. Taken together, the results of our study reveal a novel function of IRE1α in the regulation of eIF2α phosphorylation and the translational control.

scholarly journals Light dependent activation of the GCN2 kinase under cold and salt stress is mediated by the photosynthetic status of the chloroplast

2019 ◽  
Author(s):  
Ansul Lokdarshi ◽  
Philip W. Morgan ◽  
Michelle Franks ◽  
Zoe Emert ◽  
Catherine Emanuel ◽  
...  
Keyword(s):  
Salt Stress ◽  
Reactive Oxygen ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Dependent Manner ◽  
Α Subunit ◽  
Eukaryotic Translation ◽  
The Status ◽  
Eukaryotic Translation Initiation

ABSTRACTRegulation of cytosolic mRNA translation is a key node for rapid adaptation to environmental stress conditions. In yeast and animals, phosphorylation of the α-subunit of eukaryotic translation initiation factor eIF2 is the most thoroughly characterized event in regulating global translation under stress. In plants, the GCN2 kinase (General Control Non-derepressible-2) is the only known kinase for eIF2α. GCN2 is activated under a variety of stresses including reactive oxygen species. Here we provide new evidence that the GCN2 kinase in Arabidopsis is also activated rapidly and in a light dependent manner by cold and salt treatments. These treatments alone did not repress global mRNA ribosome loading in a major way. The activation of GCN2 was attenuated by inhibitors of photosynthesis and antioxidants, suggesting that it is gated by the redox poise or the reactive oxygen status of the chloroplast. In keeping with these results, gcn2 mutant seedlings were more sensitive than wild type to both cold and salt in a root elongation assay. These data suggest that cold and salt stress may both affect the status of the cytosolic translation apparatus via the conserved GCN2-eIF2α module. The potential role of the GCN2 kinase pathway in the global repression of translation under abiotic stress will be discussed.

Drosophila virilis oskar transgenes direct body patterning but not pole cell formation or maintenance of mRNA localization in D. melanogaster

Development ◽  
1994 ◽  
Vol 120 (7) ◽  
pp. 2027-2037 ◽  
Author(s):  
P.J. Webster ◽  
J. Suen ◽  
P.M. Macdonald
Keyword(s):  
Drosophila Melanogaster ◽  
Germ Cell ◽  
Cell Formation ◽  
Mrna Localization ◽  
Early Embryo ◽  
Posterior Pole ◽  
Early Embryogenesis ◽  
Drosophila Virilis ◽  
Pole Cell ◽  
Body Patterning

The Drosophila melanogaster gene oskar is required for both posterior body patterning and germline formation in the early embryo; precisely how oskar functions is unknown. The oskar transcript is localized to the posterior pole of the developing oocyte, and oskar mRNA and protein are maintained at the pole through early embryogenesis. The posterior maintenance of oskar mRNA is dependent upon the presence of oskar protein. We have cloned and characterized the Drosophila virilis oskar homologue, virosk, and examined its activity as a transgene in Drosophila melanogaster flies. We find that the cis-acting mRNA localization signals are conserved, although the virosk transcript also transiently accumulates at novel intermediate sites. The virosk protein, however, shows substantial differences from oskar: while virosk is able to rescue body patterning in a D. melanogaster oskar- background, it is impaired in both mRNA maintenance and pole cell formation. Furthermore, virosk induces a dominant maternal-effect lethality when introduced into a wild-type background, and interferes with the posterior maintenance of the endogenous oskar transcript in early embryogenesis. Our data suggest that virosk protein is unable to anchor at the posterior pole of the early embryo; this defect could account for all of the characteristics of virosk mentioned above. Our observations support a model in which oskar protein functions both by nucleating the factors necessary for the activation of the posterior body patterning determinant and the germ cell determinant, and by anchoring these factors to the posterior pole of the embryo. While the posterior body patterning determinant need not be correctly localized to provide body patterning activity, the germ cell determinant may need to be highly concentrated adjacent to the cortex in order to direct pole cell formation.

scholarly journals hnRNP K Binds a Core Polypyrimidine Element in the Eukaryotic Translation Initiation Factor 4E (eIF4E) Promoter, and Its Regulation of eIF4E Contributes to Neoplastic Transformation

2005 ◽  
Vol 25 (15) ◽  
pp. 6436-6453 ◽  
Author(s):  
Mary Lynch ◽  
Li Chen ◽  
Michael J. Ravitz ◽  
Sapna Mehtani ◽  
Kevin Korenblat ◽  
...  
Keyword(s):  
Translation Initiation ◽  
Binding Protein ◽  
Neoplastic Transformation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Dependent Manner ◽  
Eukaryotic Translation Initiation Factor ◽  
Hnrnp K ◽  
Eukaryotic Translation ◽  
Eukaryotic Translation Initiation

ABSTRACT Translation initiation factor eukaryotic translation initiation factor 4E (eIF4E) plays a key role in regulation of cellular proliferation. Its effects on the m7GpppN mRNA cap are critical because overexpression of eIF4E transforms cells, and eIF4E function is rate-limiting for G1 passage. Although we identified eIF4E as a c-Myc target, little else is known about its transcriptional regulation. Previously, we described an element at position −25 (TTACCCCCCCTT) that was critical for eIF4E promoter function. Here we report that this sequence (named 4EBE, for eIF4E basal element) functions as a basal promoter element that binds hnRNP K. The 4EBE is sufficient to replace TATA sequences in a heterologous reporter construct. Interactions between 4EBE and upstream activator sites are position, distance, and sequence dependent. Using DNA affinity chromatography, we identified hnRNP K as a 4EBE-binding protein. Chromatin immunoprecipitation, siRNA interference, and hnRNP K overexpression demonstrate that hnRNP K can regulate eIF4E mRNA. Moreover, hnRNP K increased translation initiation, increased cell division, and promoted neoplastic transformation in an eIF4E-dependent manner. hnRNP K binds the TATA-binding protein, explaining how the 4EBE might replace TATA in the eIF4E promoter. hnRNP K is an unusually diverse regulator of multiple steps in growth regulation because it also directly regulates c-myc transcription, mRNA export, splicing, and translation initiation.

scholarly journals Structural basis for eIF2B inhibition in integrated stress response

Science ◽  
2019 ◽  
Vol 364 (6439) ◽  
pp. 495-499 ◽  
Author(s):  
Kazuhiro Kashiwagi ◽  
Takeshi Yokoyama ◽  
Madoka Nishimoto ◽  
Mari Takahashi ◽  
Ayako Sakamoto ◽  
...  
Keyword(s):  
Stress Response ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Structural Basis ◽  
Dependent Manner ◽  
Integrated Stress Response ◽  
Nucleotide Exchange ◽  
Electron Microscopic ◽  
Eukaryotic Translation ◽  
Initiation Factor 2

A core event in the integrated stress response, an adaptive pathway common to all eukaryotic cells in response to various stress stimuli, is the phosphorylation of eukaryotic translation initiation factor 2 (eIF2). Normally, unphosphorylated eIF2 transfers the methionylated initiator tRNA to the ribosome in a guanosine 5′-triphosphate–dependent manner. By contrast, phosphorylated eIF2 inhibits its specific guanine nucleotide exchange factor, eIF2B. To elucidate how the eIF2 phosphorylation status regulates the eIF2B activity, we determined cryo–electron microscopic and crystallographic structures of eIF2B in complex with unphosphorylated or phosphorylated eIF2. The unphosphorylated and phosphorylated forms of eIF2 bind to eIF2B in completely different manners: the nucleotide exchange-active and -inactive modes, respectively. These structures explain how phosphorylated eIF2 dominantly inhibits the nucleotide exchange activity of eIF2B.

scholarly journals The ER Stress Inducer l-Azetidine-2-Carboxylic Acid Elevates the Levels of Phospho-eIF2α and of LC3-II in a Ca2+-Dependent Manner

Cells ◽  
2018 ◽  
Vol 7 (12) ◽  
pp. 239 ◽  
Author(s):  
Gemma Roest ◽  
Evelien Hesemans ◽  
Kirsten Welkenhuyzen ◽  
Tomas Luyten ◽  
Nikolai Engedal ◽  
...  
Keyword(s):  
Carboxylic Acid ◽  
Er Stress ◽  
Adenosine Diphosphate ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Parp Cleavage ◽  
Dependent Manner ◽  
Atpase Inhibitor ◽  
Eukaryotic Translation ◽  
The Unfolded Protein Response

Accumulation of misfolded proteins in the endoplasmic reticulum (ER) activates the unfolded protein response (UPR) to reduce protein load and restore homeostasis, including via induction of autophagy. We used the proline analogue l-azetidine-2-carboxylic acid (AZC) to induce ER stress, and assessed its effect on autophagy and Ca2+ homeostasis. Treatment with 5 mM AZC did not induce poly adenosine diphosphate ribose polymerase (PARP) cleavage while levels of binding immunoglobulin protein (BiP) and phosphorylated eukaryotic translation initiation factor 2α (eIF2α) increased and those of activating transcription factor 6 (ATF6) decreased, indicating activation of the protein kinase RNA-like ER kinase (PERK) and the ATF6 arms of the UPR but not of apoptosis. AZC treatment in combination with bafilomycin A1 (Baf A1) led to elevated levels of the lipidated form of the autophagy marker microtubule-associated protein light chain 3 (LC3), pointing to activation of autophagy. Using the specific PERK inhibitor AMG PERK 44, we could deduce that activation of the PERK branch is required for the AZC-induced lipidation of LC3. Moreover, both the levels of phospho-eIF2α and of lipidated LC3 were strongly reduced when cells were co-treated with the intracellular Ca2+ chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N′,N′-tetraaceticacid tetra(acetoxy-methyl) ester (BAPTA-AM) but not when co-treated with the Na+/K+ ATPase inhibitor ouabain, suggesting an essential role of Ca2+ in AZC-induced activation of the PERK arm of the UPR and LC3 lipidation. Finally, AZC did not trigger Ca2+ release from the ER though appeared to decrease the cytosolic Ca2+ rise induced by thapsigargin while also decreasing the time constant for Ca2+ clearance. The ER Ca2+ store content and mitochondrial Ca2+ uptake however remained unaffected.

scholarly journals Effect of Orexin-A on Cortisol Secretion in H295R Cells via p70S6K/4EBP1 Signaling Pathway

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Xiaocen Chang ◽  
Yuyan Zhao ◽  
Lei Guo
Keyword(s):  
Signaling Pathway ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Dependent Manner ◽  
Cortisol Secretion ◽  
Adrenocortical Cells ◽  
Orexin A ◽  
Eukaryotic Translation ◽  
Mitogen Activated Protein ◽  
H295r Cells

Orexin-A is a neuropeptide that orchestrates diverse central and peripheral processes. It is now clear that orexin system plays a central role in the regulation of endocrine, paracrine, and neurocrine. It is involved in the regulation of growth hormone, adrenocorticotropic hormone, thyroid, mineralocorticoid, and cortisol secretion. These hormones may also serve as a kind of signal linking energy balance regulation, reproduction, stress response, and cardiovascular regulation. Many studies have demonstrated the ability of orexin-A to regulate adrenocortical cells through the MAPK (mitogen-activated protein kinases) pathway. The aim of our study is to investigate the effect of orexin-A on cortisol secretion via the protein 70 ribosomal protein S6 kinase-1 (p70S6K) and eukaryotic translation initiation factor 4E binding proteins (4EBP1) signaling pathway in adrenocortical cells. We reported the first evidence that orexin-A stimulated p70S6K and 4EBP1 in human H295R adrenocortical cells in a concentration and time-dependent manner. 10−6 M orexin-A treatment for 1 hour was the most potent. Our results also indicated that p70S6K and 4EBP1 kinases participated in controlling cortisol secretion via OX1receptor in H295R cells, which implied important role of p70S6K and 4EBP1 kinases in regulating adrenal function induced by orexin-A.

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