1,720,976 research outputs found
Unique characteristics of Ca2+ homeostasis of the trans-Golgi compartment.
No full textTaking advantage of a fluorescent Ca(2+) indicator selectively targeted to the trans-Golgi lumen, we here demonstrate that its Ca(2+) homeostatic mechanisms are distinct from those of the other Golgi subcompartments: (i) Ca(2+) uptake depends exclusively on the activity of the secretory pathway Ca(2+) ATPase1 (SPCA1), whereas the sarco-endoplasmic reticulum Ca(2+) ATPase (SERCA) is excluded; (ii) IP(3) generated by receptor stimulation causes Ca(2+) uptake rather than release; (iii) Ca(2+) release can be triggered by activation of ryanodine receptors in cells endowed with robust expression of the latter channels (e.g., in neonatal cardiac myocyte). Finally, we show that, knocking down the SPCA1, and thus altering the trans-Golgi Ca(2+) content, specific functions associated with this subcompartment, such as sorting of proteins to the plasma membrane through the secretory pathway, and the structure of the entire Golgi apparatus are dramatically altered
Ca2+ signalling in the Golgi apparatus
No full textThe Golgi apparatus plays a central role in lipid and protein post-translational modification and sorting. Morphologically the organelle is heterogeneous and it is possible to distinguish stacks of flat cysternae (cis- and medial Golgi), tubular-reticular networks and vesicles (trans-Golgi). These morphological differences parallel a distinct functionality with a selective distribution and complementary roles of the enzymes found in the different compartments. The Golgi apparatus has been also shown to be involved in Ca(2+) signalling: it is indeed endowed with Ca(2+) pumps, Ca(2+) release channels and Ca(2+) binding proteins and is thought to participate in determining the spatio-temporal complexity of the Ca(2+) signal within the cell, though this role is still poorly understood. Recently, it has been demonstrated that the organelle is heterogeneous in terms of Ca(2+) handling and selective reduction of Ca(2+) concentration, both in vitro and in a genetic human disease, within one of its sub-compartment results in alterations of protein trafficking within the secretory pathway and of the entire Golgi morphology. In this paper we review the available information on the Ca(2+) toolkit within the Golgi, its heterogeneous distribution in the organelle sub-compartments and discuss the implications of these characteristics for the physiopathology of the Golgi apparatus
The trans-Golgi compartment. A new distinct intracellular Ca2+ store.
No full textThe Golgi apparatus (GA) is an intracellular organelle that plays a central role in lipid and protein posttranslational modification and sorting. In addition, the GA has been also shown to be involved in Ca(2+) signalling, as: (i) it accumulates Ca(2+) within its lumen in an ATP-dependent process catalyzed by two enzymes, the sarco-endoplasmic reticulum Ca(2+) ATPase (SERCA) and the secretory pathway Ca(2+) ATPase1 (SPCA1), and (ii) it releases Ca(2+) during cell stimulation in response to inositol 1,4,5-trisphosphate (IP(3)) receptor activation. Therefore, on this aspect, the GA appears to behave similarly to the major intracellular Ca(2+) store, the endoplasmic reticulum (ER). By using a new FRET-based Ca(2+) probe, specifically targeted to the trans-compartment of the GA, we demonstrate that the organelle is heterogeneous in terms of Ca(2+) handling, the trans-Golgi being insensitive to IP(3) and capable of accumulating Ca(2+) solely through the activity of SPCA1. The SERCA and the IP(3) receptor appear to be restricted to the cis- and intermediate GA compartments. Moreover, selective reduction of Ca(2+) concentration within the trans-Golgi, obtained by reducing the level of SPCA1 by RNAi, results in major alterations of protein trafficking within the secretory pathway and induces the collapse of the entire GA morphology
Organelle-targeted Ca2+ probes help to visualize store Ca2+ handling by wild-type and mutant presenilin-2.
No full textBackground. Our previously data suggest that FAD-linked PS2 mutants (M239I, T122R and N141I) cause a different type of Ca2+ dysregulation compared to the majority of FAD-linked PS1 mutants. In fact, at the store level, “Ca2+ reduction” instead of “Ca2+ overload” was invariably reported with these mutants, when studied in different experimental systems ranging from endogenous expression in fibroblasts from FAD patients to both stable and transient expression in cell lines and primary rat neuronal cultures (1-3).
Methods. By employing recombinant aequorins or cameleons, specifically targeted to the ER and the Golgi apparatus, we here monitor the Ca2+ concentration inside their lumen in different cell types including SH-SY5Y, MEFs - either wt or devoid of endogenous PSs (DKO MEFs) – and primary neurons and investigate the mechanisms by which PS2 variants alter store calcium handling.
Results. We provide evidence that: i) not only over-expression of wt and mutant PS2 but also the endogenous level of PS2 reduces the store calcium content mainly by reducing the ER calcium uptake due to SERCA pumps (4); ii) the full-length (FL) form of the protein is required to interfere with store calcium handling (4); iii) at variance with the ER, the trans-Golgi compartment is not as much as affected by PS2, indicating that the secretory pathway Ca2+/Mn2+ ATPase type (SPCA) is likely not a target of PS2; iv) mitochondria Ca2+ uptake is also affected by mutant PS2; whether this is a direct effect or it is mediated by the ER-mitochondria cross-talk is now under investigation. Conclusions. At variance with the majority of PS1 mutants that leave unchanged or even overloaded the intracellular calcium stores, making the cells more susceptible to toxic stimuli, PS2 mutants, by depressing the store Ca2+ content and altering the ER-mitochondria cross-talk might play a completely different role on cellular Ca2+ homeostasis that needs a careful reconsideration.
1. Zatti et al., Neurobiology of Disease 15, 269-278, 2004.
2.Giacomello et al., Neurobiology of Disease 18, 638-648, 2005.
3. Zatti et al., Cell Calcium 39, 539-550, 2006
4. Brunello et al., 2009 (submitted
Compartmentalized phosphodiesterase-2 activity blunts beta-adrenergic cardiac inotropy via an NO/cGMP-dependent pathway
No full textbeta-Adrenergic signaling via cAMP generation and PKA activation mediates the positive inotropic effect of catecholamines on heart cells. Given the large diversity of protein kinase A targets within cardiac cells, a precisely regulated and confined activity of such signaling pathway is essential for specificity of response. Phosphodiesterases (PDEs) are the only route for degrading cAMP and are thus poised to regulate intracellular cAMP gradients. Their spatial confinement to discrete compartments and functional coupling to individual receptors provides an efficient way to control local [cAMP]i in a stimulus-specific manner. By performing real-time imaging of cyclic nucleotides in living ventriculocytes we identify a prominent role of PDE2 in selectively shaping the cAMP response to catecholamines via a pathway involving beta3-adrenergic receptors, NO generation and cGMP production. In cardiac myocytes, PDE2, being tightly coupled to the pool of adenylyl cyclases activated by beta-adrenergic receptor stimulation, coordinates cGMP and cAMP signaling in a novel feedback control loop of the beta-adrenergic pathway. In this, activation of beta3-adrenergic receptors counteracts cAMP generation obtained via stimulation of beta1/beta2-adrenoceptors. Our study illustrates the key role of compartmentalized PDE2 in the control of catecholamine-generated cAMP and furthers our understanding of localized cAMP signaling
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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