Azione dei virus poliomielitico e Coxsackie sulle cellule renali di scimmia (Macaca mulatta shaw)

Summary The authors found several modifications, particularly in the nucleolus, in kidney epithelial cells ofMacaca mulatta, kept in culture for 6–8 days, after infection with polio and Coxsackie viruses. They observed, after infection with polio virus, some groups of virus-like bodies, which indicate the possibility that a provocation took place in it.     

Comportamento delle fosfatasi alcaline all'azione di alcuni veleni carioclasici

Summary The effect of an aqueous solution (6 · 10^–3 M) of mustard oil on phosphatases was tested in cymotoid oocytes by treatment either of fixed and sectioned ovaries or of fresh gonads. Nuclear and cytoplasmic mono- and diphosphatases are destroyed; nucleolar phosphatases on the contrary are unaltered or only slightly damaged.The authors put forward the hypothesis that nucleolar phosphatases have a different kind of enzymatic active groups which might have a low competition factor in regard to mustard oil. Possibly the caryoclasic action of this substance is due, at least in part, to the destruction of alkaline phosphatases which are necessary to mitotic processes.     

Modulation of SMN nuclear foci and cytoplasmic localization by its C-terminus

The survival of motor neuron ( SMN1) gene product, SMN, is detected both in the cytoplasm and in nuclear gems and cajal bodies. We show here that SMN exon 6 is essential both for formation of its nuclear foci and for its cytoplasmic localization. However, exon 7 inhibits the formation of SMN nuclear foci but promotes SMN cytoplasmic localization. More interestingly, we find that a random C-terminal tag of five or more amino acids downstream of exon 6 is sufficient to inhibit the occurrence of multiple nuclear foci and to promote cytoplasmic localization of SMNDelta7, the primary product of the SMN2 gene. Moreover, SMNDelta7 proteins that bear spinal muscular atrophy mutations in exon 6 either showed defects in nuclear foci formation or enhanced cytoplasmic localization. We conclude that exon 6 and exon 7 synergistically regulate SMN distribution that may require specific exon 6 motifs but is independent of specific sequences in exon 7.     

Passaggio di nucleoli attraverso la membrana nucleare negli ovociti in accrescimento diPatella coerulea L. (Moll. Gast. Pros.)

Summary The author has found in increasing ovocytes ofPatella coerulea, particularly in the nuclear membrane, a real passage of small nucleoli from the nucleus to the cytoplasm. Thus not all the nucleoli which appear little by little in the nucleus are amphinucleoli.     

Activation concomitante par l'hétéroauxine de la résorption du corps paranucléaire ribonucléique et de la germination des zygotes chezAllomyces

Summary Heteroauxin (optimal concentration 10^–5) activates the germination of the zygotes and the dissolution of their RNA nuclear cap inAllomyces javanicus.Alkaline phosphatase has been located cytochemically in the cytoplasm surrounding the RNA nuclear cap.These new observations lead the author to postulate a relationship between the stimulating action of heteroauxin, activation of the phosphatases and awakening of the RNA-protein synthesis dynamic system during the germination of the zygotes inAllomyces.     

Friedrich Miescher Prize awardee lecture review. A conserved family of nuclear export receptors mediates the exit of messenger RNA to the cytoplasm

The distinguishing feature of eukaryotic cells is the segregation of RNA biogenesis and DNA replication in the nucleus, separate from the cytoplasmic machinery for protein synthesis. As a consequence, messenger RNAs (mRNAs) and all cytoplasmic RNAs from nuclear origin need to be transported from their site of synthesis in the nucleus to their final cytoplasmic destination. Nuclear export occurs through nuclear pore complexes (NPCs) and is mediated by saturable transport receptors, which shuttle between the nucleus and cytoplasm. The past years have seen great progress in the characterization of the mRNA export pathway and the identification of proteins involved in this process. A novel family of nuclear export receptors (the NXF family), distinct from the well-characterized family of importin β-like proteins, has been implicated in the export of mRNA to the cytoplasm. Received 23 January 2001; received after revision 12 April 2001; accepted 12 April 2001     

Über die Ausschleusung nukleolärer Substanz im Milchdrüsenepithel der weissen Maus

Summary Mammary glands of the white mouse in different stages of lactation were fixed in Carnoy's fluid and the sections stained with Gallocyanin-chromalum für microscopic observation. After dislocation of the nucleolus to the nuclear membrane or the formation of a heterochromatic pathway between nucleolus and nuclear membrane the extrusion of nucleolar substance into the cytoplasm was observed.     

Receptor and nonreceptor protein tyrosine phosphatases in the nervous system

Protein tyrosine phosphatases (PTPs) have emerged as a new class of signaling molecules that play important roles in the development and function of the central nervous system. They include both tyrosine-specific and dual-specific phosphatases. Based on their cellular localization they are also classified as receptor-like or intracellular PTP. However, the intracellular mechanisms by which these PTPs regulate cellular signaling pathways are not well understood. Evidence gathered to date provides some insight into the physiological function of these PTPs in the nervous system. In this review, we outline what is currently known about the functional role of PTPs expressed in the brain.Received 31 March 2003; received after revision 7 May 2003; accepted 22 May 2003     

Pyk2 cytonuclear localization: mechanisms and regulation by serine dephosphorylation

Cytonuclear signaling is essential for long-term alterations of cellular properties. Several pathways involving regulated nuclear accumulation of Ser/Thr kinases have been described but little is known about cytonuclear trafficking of tyrosine kinases. Proline-rich tyrosine kinase 2 (Pyk2) is a cytoplasmic non-receptor tyrosine kinase enriched in neurons and involved in functions ranging from synaptic plasticity to bone resorption, as well as in cancer. We previously showed the Ca²⁺-induced, calcineurin-dependent, nuclear localization of Pyk2. Here, we characterize the molecular mechanisms of Pyk2 cytonuclear localization in transfected PC12 cells. The 700–841 linker region of Pyk2 recapitulates its depolarization-induced nuclear accumulation. This region includes a nuclear export motif regulated by phosphorylation at residue S778, a substrate of cAMP-dependent protein kinase and calcineurin. Nuclear import is controlled by a previously identified sequence in the N-terminal domain and by a novel nuclear targeting signal in the linker region. Regulation of cytonuclear trafficking is independent of Pyk2 activity. The region regulating nuclear localization is absent from the non-neuronal shorter splice isoform of Pyk2. Our results elucidate the mechanisms of Ca²⁺-induced nuclear accumulation of Pyk2. They also suggest that Pyk2 nuclear accumulation is a novel type of signaling response that may contribute to specific long-term adaptations in neurons.     

Über die Wirkung von Cobalt-II-nitrat auf Kern und Cytoplasma vonAcetabularia mediterranea

Summary The effect of Cobalt-II-nitrate was tested on the marine green algaAcetabularia. Application of Co immediately stopped regeneration as well as synthesis of cytoplasmic proteins. Later on a decrease of the protein contents was observed. Without affecting the size of the nucleus, Co caused a reduction of the nucleolar size and shape within 4 days. By histochemical methods, Co was found to be stored in the nucleus and nucleolus. However, it is not clear whether the Co was already boundin vivo. Size and distribution of the polyphosphate bodies were not changed within 6 days. No storage of Coin vivo could be observed within the polyphosphates.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Détection cytochimique de l'acide ribonucléique dans les chromosphères pré- et post-méiotiques des sporanges de résistance d'Allomyces

Summary Premeiotic chromospheres in the immature resistant sporangia (RS) ofAllomyces lose their basophily after treatment with trichloracetic acid, perchloric acid or ribonuclease. Postmeiotic chromospheres in the mature RS, becoming the nuclear caps of the ‘reduced’ zoospores, do not stain with toluidine blue or pyronine after ribonuclease digestion. It is concluded that, as gametic and zoosporic nuclear caps, pre- and postmeiotic chromospheres are transitory cytoplasmic organites rich in RNA.      

Change in compatibility after microinjection of cytoplasm in amoebae

Summary A cytoplasmic fraction from D32, a clone of amoebae derived fromAmoeba proteus injected with cytoplasm fromA. discoides, inhibited cell division inA. proteus but not inA. discoides indicating a permanent change with respect to compatibility.     

Zum Proliferations-Stoffwechsel der Rattenleber nach Teilhepatektomie. Autoradiographische Untersuchungen mit3H-Cytidin,-Phenylalanin und -Thymidin

Summary During the first wave of parenchymal liver regeneration in adult rats after partial hepatectomy, the cellular synthesis and migration of RNA and the metabolism of protein were studied by autoradiography following an injection of³H-cytidine or³H-l-phenylalanine and double injections of 1 of these precursors +³H-thymidine. The following results were obtained: the synthesis and migration of RNA and the metabolism of protein are enhanced under these conditions of proliferation. In spite of this, the relation of metabolic activity in nucleolus, karyoplasm and cytoplasm remains constant. By double injection techniques it is proved that no differences exist in migration of RNA into the cytoplasm and cytoplasmic protein synthesis between cells with or without DNA synthesizing nuclei.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Biogenesis of prokaryotic pores.

The prokaryotic pore-forming proteins are synthesized in the cytoplasm, and are assembled in their functional form in the outer membrane. They begin to traverse the cytoplasmic membrane via the SecY/SecA export pathway, which is shared also by periplasmic proteins. The sorting signals that direct these proteins to the outer membrane could be present in the three-dimensional conformations of the proteins, but some results suggest that they may be present in short, contiguous sequences. Outer membrane proteins share a rather hydrophilic amino acid composition, and appear to be rich in beta-sheets (with the exception of lipoproteins). This observation as well as the demonstration of periplasmic export intermediates favor the secretion pathway through the periplasm, as opposed to export through fusion sites between the inner and the outer membrane, but such intermediates have not yet been observed with the wild type proteins under physiological conditions.     

Functions of nuclear bodies as revealed by ultrastructural autoradiography and cytochemistry

Summary The simple nuclear body containing a few RNA particles appears through the nuclear pores in the cytoplasm, originating from the nucleolus. The complex nuclear body consisting mainly of RNA components is highly active in the incorporation of RNA precursors. Accordingly, the appearance of nuclear bodies may be related either to transport to the cytoplasm of nucleolar components or to the enhancement of rRNA synthesis.     

The vault complex

Vaults are large ribonucleoprotein particles found in eukaryotic cells. They are composed of multiple copies of a M _r 100,000 major vault protein and two minor vault proteins of M _r 193,000 and 240,000, as well as small untranslated RNAs of 86–141 bases. The vault components are arranged into a highly characteristic hollow barrel-like structure of 35 × 65 nm in size. Vaults are predominantly localized in the cytoplasm where they may associate with cytoskeletal elements. A small fraction of vaults are found to be associated with the nucleus. As of yet, the precise cellular function of the vault complex is unknown. However, their distinct morphology and intracellular distribution suggest a role in intracellular transport processes. Here we review the current knowledge on the vault complex, its structure, components and possible functions.Received 23 January 2003; received after revision 13 March 2003; accepted 26 March 2003     

Signal regulation by family conspiracy

The signal regulating proteins (SIRPs) are a family of ubiquitously expressed transmembrane glycoproteins composed of two subgroups: SIRPα and SIRPβ, containing more than ten members. SIRPα has been shown to inhibit signalling through a variety of receptors including receptor tyrosine kinases and cytokine receptors. This function involves protein tyrosine kinases and is dependent on immunoreceptor tyrosine-based inhibition motifs which recruit key protein tyrosine phosphatases to the membrane. Negative regulation by SIRPα may also involve its ligand, CD47, in a bi-directional signalling mechanism. The SIRPβ subtype has no cytoplasmic domain but instead associates with at least one other transmembrane protein (DAP-12, or KARAP). DAP-12 possesses immunoreceptor tyrosine-based activation motifs within its cytoplasmic domain that are thought to link SIRPβ to activating machinery. SIRPα and SIRPβ thus have complementary roles in signal regulation and may conspire to tune the response to a stimulus. Received 6 July 2000; revised 2 August 2000; accepted 5 August 2000