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R Saffrich

Publications and source records attributed to R Saffrich.

28 records · Page 2Linked to original sources
PubMed1997

Cytoplasmic flows localize injected oskar RNA in Drosophila oocytes.

BACKGROUND: The oskar (osk) gene encodes a determinant of posterior identity in Drosophila, and the localization of osk RNA to the pole plasm at the posterior pole of the oocyte is essential for development of the embryo. The mechanisms by which osk RNA is localized are unknown. RESULTS: To study the mechanisms underlying localization of osk RNA, we have injected fluorescently labelled RNA into oocytes at stages 9, 10 and 11. Injected osk RNA localizes to the pole plasm, reproducing localization of the endogenous RNA. In oocytes at stages 10 and 11, the long-range movement of injected osk RNA is promoted by a vigorous, microtubule-dependent cytoplasmic flow, or ooplasmic streaming. Treatment with colchicine, a microtubule-destabilizing drug, inhibits ooplasmic streaming and prevents localization of the RNA from an injection site distal to the posterior pole. If the RNA is injected close to the posterior pole, however, it localizes even in the presence of colchicine. Similarly, in small oocytes, such as stage 9 oocytes, localization of injected osk RNA is insensitive to colchicine. CONCLUSIONS: These results reveal that microtubule-dependent cytoplasmic flows could contribute to the long-range transport of osk RNA, whereas microtubule-independent processes could mediate short-range transport. These results also highlight the role of the osk RNA anchor in the localization process.

Animals↗
PubMed1997

Cellular expression and proteolytic processing of presenilin proteins is developmentally regulated during neuronal differentiation.

We have determined the expression of the Alzheimer's disease-associated proteins presenilin-1 and presenilin-2 in primary cultures of rat hippocampal neurons. Neurons highly express presenilin-1 and presenilin-2, whereas both proteins were not detected in astrocytes. Further, we have analyzed the subcellular localization and expression in rat hippocampal neurons during development. Although presenilin proteins were localized predominantly to the endoplasmic reticulum in nonneuronal cells transfected with presenilin cDNAs, in neurons, presenilin proteins were also found in compartments not staining with antibodies to grp78(BiP). Presenilin-1 and presenilin-2 were predominantly detected in vesicular structures within the somatodendritic compartment with much less expression in axons. Polarized distribution of presenilin-1 and presenilin-2 differs slightly, with more presenilin-2 expressed in axons compared with presenilin-1. Presenilin expression was found to be developmentally regulated. Presenilin expression strongly increased during neuronal differentiation until full morphological polarization and then declined. No full-length presenilin-1 or presenilin-2 could be detected within cell lysates. At early developmental stages the expected approximately 34-kDa N-terminal proteolytic fragment of presenilin-1 and the approximately 38-kDa fragment of presenilin-2 were detected. Later during differentiation we predominantly detected a approximately 38-kDa fragment for presenilin-1 and a approximately 42-kDa fragment for presenilin-2. By epitope mapping, we show that these slower migrating peptides represent N-terminal proteolytic fragments, cleaved C-terminal to the conventional site of processing. It is noteworthy that both presenilin-1 and presenilin-2 undergo alternative proteolytic cleavage at the same stage of neuronal differentiation. Regulation of presenilin expression and proteolytic processing might have implications for the pathological as well as the biological function of presenilins during aging in the human brain.

Animals↗
PubMed1997

A heterotrimeric G protein-phospholipase A2 signaling cascade is involved in the regulation of peroxisomal motility in CHO cells.

Peroxisomal motility was studied in vivo in CHO cells following transfection with a green fluorescent protein construct containing the C-terminal peroxisomal targeting signal 1 (GFP-PTS1). Time-lapse imaging and evaluation of difference images revealed that peroxisomes attach to microtubules in a Ca2+ requiring step and are transported in an ATP-dependent manner. Following microinjection of guanosine-5'-O-(3-thiotri-phosphate) (GTP(gamma)S), peroxisomal movements were arrested, indicating regulation by GTP-binding proteins. The effect of GTP(gamma)S was mimicked by AlF4- and mastoparan, two drugs which are known to activate heterotrimeric G proteins. Pertussis toxin which prevents Gi/Go protein activation completely abolished the effect of GTP(gamma)S and mastoparan on peroxisomal motility suggesting that the G protein belongs to the Gi/Go class. At least one effector of the G protein is phospholipase A2 as demonstrated by the observation that the phospholipase A2 activating protein peptide efficiently blocks peroxisomal motility, and that the effect of mastoparan and AlF4- is largely abolished by various phospholipase A2 inhibitors. In summary, these data provide evidence for a new type of regulation of organelle motility mediated by a Gi/Go-phospholipase A2 signaling pathway. This type of regulation has not been observed so far with other cell organelles such as mitochondria, the endoplasmic reticulum or axonal vesicles. Thus, motility is regulated individually for each cell organelle by distinct mechanisms enabling the cell to fulfill its vital functions.

Animals↗
PubMed1996

Endosome dynamics regulated by a Rho protein.

Vesicular transport is a dynamic process that requires coordinated interactions between membrane and cytoskeleton. The mechanisms and molecules integrating these interactions are unclear. A Rho protein, RhoD, might provide a molecular link between membrane traffic and the cytoskeleton. Activated RhoD causes rearrangements of the actin cytoskeleton and cell surface, and governs early endosome motility and distribution.

Actins↗
PubMed1996

Activation of cyclin-dependent kinases by Myc mediates induction of cyclin A, but not apoptosis.

The activation of conditional alleles of Myc induces both cell proliferation and apoptosis in serum-deprived RAT1 fibroblasts. Entry into S phase and apoptosis are both preceded by increased levels of cyclin E- and cyclin D1-dependent kinase activities. To assess which, if any, cellular responses to Myc depend on active cyclin-dependent kinases (cdks), we have microinjected expression plasmids encoding the cdk inhibitors p16, p21 or p27, and have used a specific inhibitor of cdk2, roscovitine. Expression of cyclin A, which starts late in G1 phase, served as a marker for cell cycle progression. Our data show that active G1 cyclin/cdk complexes are both necessary and sufficient for induction of cyclin A by Myc. In contrast, neither microinjection of cdk inhibitors nor chemical inhibition of cdk2 affected the ability of Myc to induce apoptosis in serum-starved cells. Further, in isoleucine-deprived cells, Myc induces apoptosis without altering cdk activity. We conclude that Myc acts upstream of cdks in stimulating cell proliferation and also that activation of cdks and induction of apoptosis are largely independent events that occur in response to induction of Myc.

3T3 Cells↗
PubMed1996

Microtubule-based peroxisome movement.

The association of peroxisomes with cytoskeletal structures was investigated both by electron microscopy and by kinetic analysis of peroxisome movement. The morphological studies indicated distinct interactions of peroxisomes with microtubules and frequently revealed multiple contact sites. The kinetic approach utilised microinjection and import of fluorescein-labeled luciferase in order to mark and track peroxisomes in vivo. Peroxisomal motility was analysed by time-lapse imaging and fluorescence microscopy. According to their movement peroxisomes were classified into two groups. Group 1 peroxisomes comprising the majority of organelles at 37 degrees C moved slowly with an average velocity of 0.024 +/- 0.012 micron/second whereas the movement of group 2 peroxisomes, 10-15% of the total population, was saltatory exhibiting an average velocity of 0.26 +/- 0.17 micron/second with maximal values of more than 2 microns/second. Saltations were completely abolished by the microtubule-depolymerising drug nocodazole and were slightly reduced by about 25% by cytochalasin D which disrupts the actin microfilament system. Double fluorescence labeling of both peroxisomes and microtubules revealed peroxisome saltations linked to distinct microtubule tracks. Cellular depletion of endogenous levels of NTPs as well as the use of 5'-adenylylimidodiphosphate, a nonhydrolysable ATP analog, applied to a permeabilised cell preparation both completely blocked peroxisomal movement. These data suggest an ATPase dependent, microtubule-based mechanism of peroxisome movement. Both the intact and the permeabilised cell system presented in this paper for the first time allow kinetic measurements on peroxisomal motility and thus will be extremely helpful in the biochemical characterisation of the motor proteins involved.

Actins↗
PubMed1994

Regulation of G1 progression by E2A and Id helix-loop-helix proteins.

In NIH3T3 fibroblasts, the ubiquitous helix-loop-helix (HLH) protein E2A (E12/E47) and the myogenic HLH proteins MyoD, MRF4 and myogenin are growth-inhibitory, while two ubiquitous Id proteins lacking the basic region are not. The dimerization domain mediates inhibition. However, in addition to the HLH region, E2A contains two inhibitory regions over-lapping with the main transcriptional activation domains. The growth-suppressive activity of the intact E47 as well as MyoD was counteracted by the Id proteins. When E47 lacking the HLH domain was overexpressed, Id could no longer reverse growth inhibition. By increasing the amount of E47 with an inducible system or neutralizing the endogenous Id with microinjected anti-Id antibodies, withdrawal from the cell cycle occurred within hours before the G1-S transition point. The combined results suggest that the Id proteins are required for G1 progression. The antagonism between the E2A and Id proteins further suggests that both are involved in regulatory events prior to or near the restriction point in the G1 phase of the cell cycle.

3T3 Cells↗
PubMed1993

Assessing the quality of solution nuclear magnetic resonance structures by complete cross-validation.

Structure determination of macromolecules in solution by nuclear magnetic resonance (NMR) spectroscopy involves the fitting of atomic models to the observed nuclear Overhauser effect (NOE) data. Complete cross-validation has been used to define reliable and unbiased criteria for the quality of solution NMR structures. The method is based on the partitioning of NOE data into test sets and the cross-validation of statistical quantities for each of the test sets. A high correlation between cross-validated measures of fit, such as distance bound violations and NMR R values, and the quality of solution NMR structures was observed. Less complete data resulted in poorer satisfaction of the cross-validated measures of fit. Optimization of cross-validated measures of fit will likely produce solution NMR structures with maximal information content.

Bacterial Proteins↗
PubMed1989

1H-nuclear magnetic resonance studies of the neuropeptide head activator.

The 1H-NMR spectrum of the neuropeptide head activator in aqueous solution has been completely assigned by two-dimensional NMR spectroscopy and selective deuteration. The apparent pseudo-first-order exchange rate, kex, of the backbone amide protons and the correspondent activation enthalpies, delta H not equal to, were determined. The exchange rates decrease and the activation enthalpies increase from the N-terminal to the C-terminal part of the peptide. The exchange rates vary from 21 to 0.3 s-1 at 274 K, the activation enthalpies from 60 to 75 kJ.mol-1. The pK values of the terminal carboxyl group and of the lysine amino group have been estimated as 3.3 and 10.3, respectively. The NMR results are in line with a dimeric structure in an antisymmetric arrangement of the subunits, forming an antiparallel beta-pleated sheet between C-terminal segments. The peptide bonds between pGlu-1, Pro-2 and Pro-3 are predominantly in trans-configuration, in fact no cis-isomers can be observed spectroscopically. The structure appears to be very stable; in the temperature and pH range studied, i.e., from 274 to 338 K and from pH 0.8 to pH 11.6, there are no spectroscopic indications for a global structural change.

Hot Temperature↗