Multiplicity of beta lactamases: a problem of isoenzymes]

Analytical isoelectric focusing of beta lactamases is a very sensitive and powerful technique which generally shows a number of satellites near the main enzymatic spike. By this technique we studied two bacterial groups known to produce different beta lactamases, but only one by germ. Analytical isoelectric focusing showed that all bacteria from the same group produce the same satellite system which differs only in relative activity.     

GNSS接收机伪距测量对定位的影响

伪距测量是全球卫星导航系统（GNSS）与其它无线通信系统一大显著区别之一。在卫星导航定位系统中,必须通过PRN码测出用户接收机到各颗卫星的距离,才能定位。卫星钟差、用户钟差、多普勒效应、电离层延迟、对流层延迟等,都使测距产生一定的误差,所以称为伪距。伪距测量的精度,直接影响到定位的精度。为定量分析伪距测量对定位结果的影响,本文给出选择不同星的伪距和同一伪距不同误差情况下对最终定位结果的影响,为接收机的研发提供重要的参考。     

Functional characterization of CP148, a novel key component for centrosome integrity in Dictyostelium

The Dictyostelium centrosome consists of a layered core structure surrounded by a microtubule-nucleating corona. A tight linkage through the nuclear envelope connects the cytosolic centrosome with the clustered centromeres within the nuclear matrix. At G2/M the corona dissociates, and the core structure duplicates, yielding two spindle poles. CP148 is a novel coiled coil protein of the centrosomal corona. GFP-CP148 exhibited cell cycle-dependent presence and absence at the centrosome, which correlates with dissociation of the corona in prophase and its reformation in late telophase. During telophase, GFP-CP148 formed cytosolic foci, which coalesced and joined the centrosome. This explains the hypertrophic appearance of the corona upon strong overexpression of GFP-CP148. Depletion of CP148 by RNAi caused virtual loss of the corona and disorganization of interphase microtubules. Surprisingly, formation of the mitotic spindle and astral microtubules was unaffected. Thus, microtubule nucleation complexes associate with centrosomal core components through different means during interphase and mitosis. Furthermore, CP148 RNAi caused dispersal of centromeres and altered Sun1 distribution at the nuclear envelope, suggesting a role of CP148 in the linkage between centrosomes and centromeres. Taken together, CP148 is an essential factor for the formation of the centrosomal corona, which in turn is required for centrosome/centromere linkage.     

中巴地球资源卫星的应用现状分析

通过对中巴地球资源卫星的介绍以及与其它外国遥感卫星参数的比较,说明中巴地球资源卫星的特性,进一步阐述现在中巴地球资源卫星在农业、林业、水资源、国土资源、生态环境和区域规划等方面的应用现状,同时针对在应用中出现的“瓶颈”,提出对中巴地球资源卫星数据进行处理的方法,加强与相关学科的结合,进一步挖掘中巴地球资源卫星的应用潜力和前景。     

Show me your license, please: deregulation of centriole duplication mechanisms that promote amplification

Centrosomes are organelles involved in generating and organizing the interphase microtubule cytoskeleton, mitotic spindles and cilia. At the centrosome core are a pair of centrioles, structures that act as the duplicating elements of this organelle. Centrioles function to recruit and organize pericentriolar material which nucleates microtubules. While centrioles are relatively simple in construction, the mechanics of centriole biogenesis remain an important yet poorly understood process. More mysterious still are the regulatory mechanisms that oversee centriole assembly. The fidelity of centriole duplication is critical as defects in either the assembly or number of centrioles promote aneuploidy, primary microcephaly, birth defects, ciliopathies and tumorigenesis. In addition, some pathogens employ mechanisms to promote centriole overduplication to the detriment of the host cell. This review summarizes our current understanding of this important topic, highlighting the need for further study if new therapeutics are to be developed to treat diseases arising from defects of centrosome duplication.     

A kinesin-mediated mechanism that couples centrosomes to nuclei

The M-type kinesin isoform, Kif9, has recently been implicated in maintaining a physical connection between the centrosome and nucleus in Dictyostelium discoideum. However, the mechanism by which Kif9 functions to link these two organelles remains obscure. Here we demonstrate that the Kif9 protein is localized to the nuclear envelope and is concentrated in the region underlying the centrosome point of attachment. Nuclear anchorage appears mediated through a specialized transmembrane domain located in the carboxyl terminus. Kif9 interacts with microtubules in in vitro binding assays and effects an endwise depolymerization of the polymer. These results suggest a model whereby Kif9 is anchored to the nucleus and generates a pulling force that reels the centrosome up against the nucleus. This is a novel activity for a kinesin motor, one important for progression of cells into mitosis and to ensure centrosome-nuclear parity in a multinuclear environment.     

Such small hands: the roles of centrins/caltractins in the centriole and in genome maintenance

Centrins are small, highly conserved members of the EF-hand superfamily of calcium-binding proteins that are found throughout eukaryotes. They play a major role in ensuring the duplication and appropriate functioning of the ciliary basal bodies in ciliated cells. They have also been localised to the centrosome, which is the major microtubule organising centre in animal somatic cells. We describe the identification, cloning and characterisation of centrins in multiple eukaryotic species. Although centrins have been implicated in centriole biogenesis, recent results have indicated that centrosome duplication can, in fact, occur in the absence of centrins. We discuss these data and the non-centrosomal functions that are emerging for the centrins. In particular, we discuss the involvement of centrins in nucleotide excision repair, a process that repairs the DNA lesions that are induced primarily by ultraviolet irradiation. We discuss how centrin may be involved in these diverse processes and contribute to nuclear and cytoplasmic events.     

Biophysical properties of porin pores from mitochondrial outer membrane of eukaryotic cells

Summary The matrix space of mitochondria is surrounded by two membranes. The mitochondrial inner membrane contains the respiration chain and a large number of highly specific carriers for the mostly anionic substrates of mitochondrial metabolism. In contrast to this the permeability properties of the mitochondrial outer membrane are by far less specific. It acts as a molecular sieve for hydrophilic molecules with a defined exclusion limit around 3000 Da. Responsible for the extremely high permeability of the mitochondrial outer membrane is the presence of a pore-forming protein termed mitochondrial porin. Mitochondrial porins have been isolated from a variety of eukaryotic cells. They are basic proteins with molecular masses between 30 and 35 kDa. Reconstitution experiments define their function as pore-forming components with a single-channel conductance of about 0.40 nS (nano Siemens) in 0.1 M KCl at low voltages. In the open state mitochondrial porin behaves as a general diffusion pore with an effective diameter of 1.7 nm. Eukaryotic porins are slightly anion-selective in the open state but become cation-selective after voltage-dependent closure.     

Biophysical properties of porin pores from mitochondrial outer membrane of eukaryotic cells.

The matrix space of mitochondria is surrounded by two membranes. The mitochondrial inner membrane contains the respiration chain and a large number of highly specific carriers for the mostly anionic substrates of mitochondrial metabolism. In contrast to this the permeability properties of the mitochondrial outer membrane are by far less specific. It acts as a molecular sieve for hydrophilic molecules with a defined exclusion limit around 3000 Da. Responsible for the extremely high permeability of the mitochondrial outer membrane is the presence of a pore-forming protein termed mitochondrial porin. Mitochondrial porins have been isolated from a variety of eukaryotic cells. They are basic proteins with molecular masses between 30 and 35 kDa. Reconstitution experiments define their function as pore-forming components with a single-channel conductance of about 0.40 nS (nano Siemens) in 0.1 M KCl at low voltages. In the open state mitochondrial porin behaves as a general diffusion pore with an effective diameter of 1.7 nm. Eukaryotic porins are slightly anion-selective in the open state but become cation-selective after voltage-dependent closure.     

Molecular mechanisms of centrosome and cytoskeleton anchorage at the nuclear envelope

Cell polarization is a fundamental process underpinning organismal development, and tissue homeostasis, which requires an orchestrated interplay of nuclear, cytoskeletal, and centrosomal structures. The underlying molecular mechanisms, however, still remain elusive. Here we report that kinesin-1/nesprin-2/SUN-domain macromolecular assemblies, spanning the entire nuclear envelope (NE), function in cell polarization by anchoring cytoskeletal structures to the nuclear lamina. Nesprin-2 forms complexes with the kinesin-1 motor protein apparatus by associating with and recruiting kinesin light chain1 (KLC1) to the outer nuclear membrane. Similar to nesprin-2, KLC1 requires lamin A/C for proper NE localization. The depletion of nesprin-2 or KLC1, or the uncoupling of nesprin-2/SUN-domain protein associations impairs cell polarization during wounding and dislodges the centrosome from the NE. In addition nesprin-2 loss has profound effects on KLC1 levels, the cytoskeleton, and Golgi apparatus organization. Collectively these data show that NE-associated proteins are pivotal determinants of cell architecture and polarization.     

Circular proteoglycans from sponges: first members of the spongican family

Species-specific cell adhesion in marine sponges is mediated by a new family of modular proteoglycans whose general supramolecular structure resembles that of hyalectans. However, neither their protein nor their glycan moieties have significant sequence homology to other proteoglycans, despite having protein subunits equivalent to link proteins and to proteoglycan monomer core proteins, and glycan subunits equivalent to hyaluronan and to the glycosaminoglycans of hyalectans. In some species, these molecular components are assembled into a structure with a circular core formed by the link protein- and hyaluronan-like subunits. Besides their involvement in cell adhesion, these sponge proteoglycans, for which we propose the term spongicans, participate in signal transduction processes and are suspected to play a role in sponge self-nonself recognition. Their in vivo roles and the mild methods used to purify large amounts of functionally active spongicans make them ideal models to study the functions and possible new applications of proteoglycans in biomedical research. Received 21 May 2002; received after revision 5 July 2002; accepted 10 July 2002 RID="*" ID="*"Corresponding author.     

Synapse elimination in the developing cerebellum

Neural circuits in neonatal animals contain numerous redundant synapses that are functionally immature. During the postnatal period, unnecessary synapses are eliminated while functionally important synapses become stronger and mature. The climbing fiber (CF) to the Purkinje cell (PC) synapse is a representative model for the analysis of postnatal refinement of neuronal circuits in the central nervous system. PCs are initially innervated by multiple CFs with similar strengths around postnatal day 3 (P3). Only a single CF is selectively strengthened during P3–P7 (functional differentiation), and the strengthened CF undergoes translocation from soma to dendrites of PCs from P9 on (dendritic translocation). Following the functional differentiation, supernumerary CF synapses on the soma are eliminated, which proceeds in two distinct phases: the early phase from P7 to around P11 and the late phase from around P12 to P17. Here, we review our current understanding of cellular and molecular mechanisms of CF synapse elimination in the developing cerebellum.     

Specific localization of the catalytic subunits of protein kinase CK2 at the centrosomes

The protein kinase CK2 holoenzyme is composed of two regulatory β subunits and two catalytic α or α' subunits. Although experimental evidence for involvement of the enzyme in the regulation of cell proliferation is accumulating, the exact mechanism of its action is still unclear. The subcellular localization of the enzyme may be a key to its function. We have recently shown that the CK2 holoenzyme is tightly associated with the Golgi complex and the endoplasmic reticulum. Centrosomes, which organize spindle formation during the cell cycle and microtubule cytoskeleton formation and, thereby, the location and orientation of different organelles in the cell, are in close vicinity to the Golgi complex. Because several kinases and phosphatases have been described to regulate the functions of the centrosome, we analysed the association of CK2 with these organelles. Using biochemical cell fractionation and coimmunoprecipitation, we never found the holoenzyme but only the catalytic asubunits associated with the centrosome. These data were confirmed by immunoelectron microscopy. Thus, the present data point to a particular role of the catalytic α and α' subunit of protein kinase CK2, which may be different from their roles in the holoenzyme. Received 2 August 2002; received after revision 2 October 2002; accepted 22 October 2002 RID="*" ID="*"Corresponding author.     

DNA methylation in dedifferentiating plant pith tissue

Summary A dedifferentiating system in plant tissue (Nicotiana glauca pith tissue grown in vitro) is described, where DNA amplification was demonstrated both cytologically and biochemically. In this system a DNA statellite is synthesized and reaches its maximum around 48 h of culture. This satellite is highly methylated and there are 2 methylation and there are 2 methylation peaks around 24 and 72 h of culture. The results are discussed in relation to recent evidence of the involvement of methylation in differentiation processes.     

Satellite RNA (RNA3) of tomato black ring virus is found with one of the 2 major RNAs (RNA2) in a new capsid nucleoprotein]

Tomato Black Ring Virus (TBRV) like other NEPOviruses posseses two nucleoproteins M and B and two major RNAs, RNA1 and RNA2 respectively distributed in B and M. A new nucleoprotein has just been discovered and comprises one molecule of RNA2 associated with one molecule of RNA3. RNA3 is a small RNA of molecular weight 500,000 d considered to be a satellite RNA. Its level appears to depend on the infection stage, local or systemic. RNA3 is able to modify the relative proportions of nucleoproteins M and B and their respective RNAs. The satellite RNA, might be part of the genome and represent a monocistronic mRNA for protein capsid synthesis. However it seems perhaps more tempting to correlate TBRV-RNA3 with satellite RNA5 of certain strains of Cucumber mosaic virus.     

Description of neurons immunoreactive to anti-beta-endorphin immune serum present in the infundibular nucleus in man]

Neurons containing peptide (s) immunologically related to beta-endorphin have been detected by immunochemistry in human adult and fetal hypothalami. Their perikarya are located in the infundibular nucleus. Some fibres terminate close to vessels in the median eminence, others form pericellular baskets around perikarya of non-immunoreactive neurons of the infundibular nucleus. These results suggest that the central nervous system elaborates beta-endorphin or immunologically related peptides.     

Pleiotropic effects of sonic hedgehog on muscle satellite cells

Muscle satellite cells are believed to form a stable, self-renewing pool of stem cells in adult muscle where they function in tissue growth and repair. A regulatory disruption of growth and differentiation of these cells is assumed to result in tumor formation. Here we provide for the first time evidence that sonic hedgehog (Shh) regulates the cell fate of adult muscle satellite cells in mammals. Shh promotes cell division of satellite cells (and of the related model C2C12 cells) and prevents their differentiation into multinucleated myotubes. In addition, Shh inhibits caspase-3 activation and apoptosis induced by serum deprivation. These effects of Shh are reversed by simultaneous administration of cyclopamine, a specific inhibitor of the Shh pathway. Taken together, Shh acts as a proliferation and survival factor of satellite cells in the adult muscle. Our results support the hypothesis of the rhabdomyosarcoma origin from satellite cells and suggest a role for Shh in this process.Received 23 February 2005; received after revision 2 May 2005; accepted 9 June 2005     

Routes and machinery of primary cilium biogenesis

Primary cilia are solitary, microtubule-based protrusions of the cell surface that play fundamental roles as photosensors, mechanosensors and biochemical sensors. Primary cilia dysfunction results in a long list of developmental and degenerative disorders that combine to give rise to a large spectrum of human diseases affecting almost any major body organ. Depending on the cell type, primary ciliogenesis is initiated intracellularly, as in fibroblasts, or at the cell surface, as in renal polarized epithelial cells. In this review, we have focused on the routes of primary ciliogenesis placing particular emphasis on the recently described pathway in renal polarized epithelial cells by which the midbody remnant resulting from a previous cell division event enables the centrosome for initiation of primary cilium assembly. The protein machinery implicated in primary cilium formation in epithelial cells, including the machinery best known for its involvement in establishing cell polarity and polarized membrane trafficking, is also discussed.     

Objective probability and the mind-body relation

Objectiveprobability in quantum mechanics is often thought to involve a stochastic process whereby an actual future is selected from a range of possibilities. Everett's seminal idea is that all possible definite futures on the pointer basis exist as components of a macroscopic linear superposition. I demonstrate that these two conceptions of what is involved in quantum processes are linked via two alternative interpretations of the mind-body relation. This leads to a fission, rather than divergence, interpretation of Everettian theory and to a novel explanation of why a principle of indifference does not apply to self-location uncertainty for a post-measurement, pre-observation subject, just as Sebens and Carroll claim. Their Epistemic Separability Principle is shown to arise out of this explanation and the derivation of the Born rule for Everettian theory is thereby put on a firmer footing.     

Myelin sheaths: glycoproteins involved in their formation,maintenance and degeneration

Myelin sheaths are formed around axons by extending, biochemically modifying and spiraling plasma membranes of Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS). Because glycoproteins are prominent components of plasma membranes, it is not surprising that they have important roles in the formation, maintenance and degeneration of myelin sheaths. The emphasis in this review is on four integral membrane glycoproteins. Two of them, protein zero (P0) and peripheral myelin protein-22 (PMP-22), are components of compact PNS myelin. The other two are preferentially localized in membranes of sheaths that are distinct from compact myelin. One is the myelin-associated glycoprotein, which is localized at the inside of sheaths where it functions in glia-axon interactions in both the PNS and CNS. The other is the myelin-oligodendrocyte glycoprotein, which is preferentially localized on the outside of CNS myelin sheaths and appears to be an important target antigen in autoimmune demyelinating diseases such as multiple sclerosis. Received 8 April 2002; received after revision 13 May 2002; accepted 22 May 2002