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By means of a choroidal infarct located at the posterior pole current theories concerning the choroidal anatomy are demonstrated. The existence of watershed zones being adjacent in the macular area as postulated by S. S. Hayreh however cannot be confirmed.
The distance between the area pterionalis and the optic nerve, the depth of the recess of for the temporal pole and the form of the lateral part of the sphenoidal wing are described.
Report on a case of juvenile macular degeneration manifesting as dysplasia of the pigment layer of the posterior pole, accompanied by a hair abnormality, congenital total hypotrichosis.
It has been shown in an animal experiment that alterations of the renal vasculature and parenchyma after hemostasis performed by Infrared-Contact-Coagulation are best shown by intravital magnification angiography (magnification factor 2.22). Following pole resection and hemostasis the final morphologic state is reached 6 weeks postoperatively. The resulting scar penetrates into the parenchyma up to 1 cm. The loss of function corresponds to the parenchymal defect. There was no additional loss of renal function or damage to the parenchyma on nuclear medicine or histologic examinations.
It is known that one-dimensional potentials, V(R), with a local minimum and a finite barrier towards tunneling to a free particle continuum, can support a finite number of shape resonance states. Recently, we reported a formal derivation of the semiclassical Green's function, G(SC)(E), for such V(R), with one and two local minima, which was carried out in the framework of the theory of path integrals [Th. G. Douvropoulos and C. A. Nicolaides, J. Phys. B 35, 4453 (2002); J. Chem. Phys. 119, 8235 (2003)]. The complex poles of G(SC)(E) represent the energies and the tunneling rates of the unstable states of V(R). By analyzing the structure of G(SC)(E), here it is shown how one can compute the energy, E(nu), and the radiation-less width, gamma(nu), of each resonance state beyond the Wentzel-Kramers-Brillouin approximation. In addition, the energy shift, delta(nu), due to the interaction with the continuum, is given explicitly and computed numerically. The dependence of the accuracy of the semiclassical calculation of E(nu) and of gamma(nu) on the distance from the top of the barrier is demonstrated explicitly. As an application to a real system, we computed the vibrational energies, E(nu), and the lifetimes, tau(nu), of the 4He2++, nu = 0, 1, 2, 3, 4, and 4He3He++ nu = 0, 1, 2, 3, 1sigma(g)+ states, which autodissociate to the He(+)+He+ continuum. We employed the V(R) that was computed by Wolniewicz [J. Phys. B 32, 2257 (1999)], which was reported as being accurate, over a large range of values of R, to a fraction of cm(-1). For example, for J = 0, the results for the lowest and highest vibrational levels for the 4He2+ 1sigma(g)+ state are nu = 0 level, E0 = 10,309 cm(-1) below the barrier top, tau0 = 6400 s; nu = 4 level, E4 = 96.6 cm(-1) below the barrier top, tau4 = 31 x 10(-11) s. A brief presentation is also given of the quantal methods (and their results) that were applied previously for these shape resonances, such as the amplitude, the exterior complex scaling, and the lifetime matrix methods.
An ambiguous moving pattern which gives rise to the reverse of the barber-pole illusion is reported. When vertical sine-wave lines translate, vertically and endlessly, on a two-dimensional (2-D) plane, one can perceive rotating three-dimensional (3-D) helixes without the impression of translation. With a single sine-wave line, 3-D rotation was seen for about half the exposure period. With three sine-wave lines shifted in phase by 120 degrees, this illusion easily arose when one fixated a point near the endpoints of the lines, which moved horizontally and sinusoidally along the imaginary upper edge of the screen. When 3-D rotation was seen, the sine-wave lines which were intersecting on a 2-D display were perceptually decomposed into pairs of lines separated in depth. On fixating a point at the center of the figure, vertical translation was mainly seen. Foveal viewing of the horizontal sine movement of the endpoints of the lines produces the impression of 3-D rotation and the impression appears to provide some specific information towards solving the aperture problem and towards reconstructing the whole figure as such.
Many sensory systems involve multiple steps of signal amplification to produce a significant response. One such mechanism may be the clustering of transmembrane receptors. In bacterial chemotaxis, where a stoichiometric His-Asp phosphorelay from the kinase CheA to the response regulator CheY plays a central role, the chemoreceptors (methyl-accepting chemotaxis proteins) cluster together with CheA and the adaptor CheW, at a pole of a rod-shaped cell. This clustering led to a proposal that signal amplification occurs through an interaction between chemoreceptor homodimers. Here, by using in vivo disulfide crosslinking assays, we examined an interdimer interaction of the aspartate chemoreceptor (Tar). Two cysteine residues were introduced into Tar: one at the subunit interface and the other at the external surface of the dimer. Crosslinked dimers and higher oligomers (especially a deduced hexamer) were detected and their abundance depended on CheA and CheW. The ligand aspartate significantly reduced the amounts of higher oligomers but did not affect the polar localization of Tar-GFP. Thus, the binding of aspartate alters the rate of collisions between Tar dimers in assembled signaling complexes, most likely due to a change in the relative positions or trajectories of the dimers. These collisions could occur within a trimer-ofdimers predicted by crystallography, or between such trimers. These results are consistent with the proposal that the interaction of chemoreceptor dimers is involved in signal transduction.
The Lactococcus lactis Ll.LtrB group II intron encodes a reverse transcriptase (LtrA protein) that binds the intron RNA to promote RNA splicing and intron mobility. Here, we used LtrA-GFP fusions and immunofluorescence microscopy to show that LtrA localizes to cellular poles in Escherichia coli and Lactococcus lactis. This polar localization occurs with or without coexpression of Ll.LtrB intron RNA, is observed over a wide range of cellular growth rates and expression levels, and is independent of replication origin function. The same localization pattern was found for three nonoverlapping LtrA subsegments, possibly reflecting dependence on common redundant signals and/or protein physical properties. When coexpressed in E. coli, LtrA interferes with the polar localization of the Shigella IcsA protein, which mediates polarized actin tail assembly, suggesting competition for a common localization determinant. The polar localization of LtrA could account for the preferential insertion of the Ll.LtrB intron in the origin and terminus regions of the E. coli chromosome, may facilitate access to exposed DNA in these regions, and could potentially link group II intron mobility to the host DNA replication and/or cell division machinery.
Microtubules mediate mitochondrial distribution in the yeast Schizosaccharomyces pombe and many higher eukaryotic cells. In higher eukaryotes, kinesin motor proteins have been shown to transport mitochondria along microtubules, but the nature of the mitochondria-microtubule interactions in S. pombe has not been explored. By time lapse, total internal reflection fluorescence microscopy, or spinning-disk confocal microscopy, mitochondria appeared to be both tethered to ends and bound laterally along the sides of microtubules. Mitochondrial tubules extended and retracted when attached to the tips of elongating or shortening microtubules, respectively, but translocation along established microtubules was never observed. Mitochondria that were not associated with microtubules were largely immobile until they were "captured" by a growing microtubule. In mitotic cells, a portion of the mitochondria was tethered to the spindle-pole bodies and moved to the cellular ends during spindle elongation. This association may be important for organelle inheritance during cell division. Thus, in contrast to kinesin-mediated transport used by higher eukaryotes, mitochondrial motility and distribution in fission yeast are driven largely by microtubule polymerization and the elongation of the mitotic spindle.
We report on the preliminary result of a search for anisotropy in the cosmic background radiation (CBR). Our receiver operates with four equally spaced channels from 25 to 35 GHz with a beam size of approximately 1.5 degrees full width at half maximum. The system operated successfully for 500 hr at the South Pole during 1990-1991 austral summer. The data from one region, representing 25 hr after editing, are presented here. A strong signal is present in the lower-frequency channels with a spectrum unlike CBR fluctuations. The highest-frequency channel has the smallest contribution from this signal and has been used to set a 95% confidence level upper limit DeltaT/T </= 1.4 10-5.
Observations of the large-scale structure of the universe suggest inhomogeneities on scales between 100h-1 and 150h-1 Mpc (where h approximately 0.5-1 is the Hubble constant in units of 100 km.s-1.Mpc-1; 1 pc = 3.09 x 10(16) m). A deep redshift survey with a "pencil-beam" geometry of galaxies at the galactic poles indicated strong clustering, with a provocative regularity at 128h-1 Mpc [Broadhurst, T. J., Ellis, R. S., Koo, D. C. & Szalay, A. S. (1990) Nature (London) 343, 726-728]. Using newly acquired data, we demonstrate how multiple deep probes overcome most of the statistical problems associated with single pencil beams. Our results from cross correlations of multiple pencil beams, containing over 1200 galaxies, indicate that the strong peak in the power spectrum results from structures of large transverse size, in agreement with our original conjecture. We also discuss the sensitivity of pencil-beam surveys to the topology of large-scale structures and compare them with sparsely sampled wide-angle local surveys.
In the budding yeast Saccharomyces cerevisiae, the spindle pole body (SPB) serves as the microtubule-organizing center and is the functional analog of the centrosome of higher organisms. By expressing a fusion of a yeast SPB-associated protein to the Aequorea victoria green fluorescent protein, the movement of the SPBs in living yeast cells undergoing mitosis was observed by fluorescence microscopy. The ability to visualize SPBs in vivo has revealed previously unidentified mitotic events. During anaphase, the mitotic spindle has four sequential activities: alignment at the mother-daughter junction, fast elongation, translocation into the bud, and slow elongation. These results indicate that distinct forces act upon the spindle at different times during anaphase.
The subcellular localization of the SopB protein, which is encoded by the Escherichia coli F plasmid and is involved in the partition of the single-copy plasmid, was directly visualized through the expression of the protein fused to the jellyfish green fluorescent protein (GFP). The fusion protein, but not GFP itself, was found to localize to positions close but not at the poles of exponentially growing cells. Neither the presence of other F-encoded proteins nor the binding of SopB to its recognition sites within the sopC locus of F is required for this localization. Examination of derivatives of the fusion protein lacking various regions of SopB suggests that the signal for the cellular localization of SopB resides in a region close to its N terminus. It is plausible that the near polar localization of SopB may serve the function of keeping a segregated pair of F plasmids apart while the cell septum is being formed. The plausible relation between the specific location of SopB and its suppression of sopC-linked genes when overexpressed is also discussed.
In yeast, microtubules are organized by the spindle pole body (SPB). The SPB is a disk-like multilayered structure that is embedded in the nuclear envelope via its central plaque, whereas the outer and inner plaques are exposed to the cytoplasm and nucleoplasm, respectively. How the SPB assembles is poorly understood. We show that the inner/central plaque is composed of a stable SPB subcomplex, containing the gamma-tubulin complex-binding protein Spc110p, calmodulin, Spc42p, and Spc29p. Spc29p acts as a linker between the central plaque component Spc42p and the inner plaque protein Spc110p. Evidence is provided that the calmodulin-binding site of Spc110p influences the binding of Spc29p to Spc110p. Spc42p also was identified as a component of a cytoplasmic SPB subcomplex containing Spc94p/Nud1p, Cnm67p, and Spc42p. Spc29p and Spc42p may be part of a critical interface of nucleoplasmic and cytoplasmic assembled SPB subcomplexes that form during SPB duplication. In agreement with this, overexpressed Spc29p was found to be a nuclear protein, whereas Spc42p is cytoplasmic. In addition, an essential function of SPC29 during SPB assembly is indicated by the SPB duplication defect of conditional lethal spc29(ts) cells and by the genetic interaction of SPC29 with CDC31 and KAR1, two genes that are involved in SPB duplication.
A mutation in the Schizosaccharomyces pombe sid4(+) (septation initiation defective) gene was isolated in a screen for mutants defective in cytokinesis. We have cloned sid4(+) and have found that sid4(+) encodes a previously unknown 76.4-kDa protein that localizes to the spindle pole body (SPB) throughout the cell cycle. Sid4p is required for SPB localization of key regulators of septation initiation, including the GTPase Spg1p, the protein kinase Cdc7p, and the GTPase-activating protein Byr4p. An N-terminally truncated Sid4p mutant does not localize to SPBs and when overproduced acts as a dominant-negative mutant by titrating endogenous Sid4p and Spg1p from the SPB. Conversely, the Sid4p N-terminal 153 amino acids are sufficient for SPB localization. Biochemical studies demonstrate that Sid4p interacts with itself, and yeast two-hybrid analysis shows that its self-interaction domain lies within the C-terminal half of the protein. Our data indicate that Sid4p SPB localization is a prerequisite for the execution of the Spg1p signaling cascade.
Mutations in Aurora of Drosophila and related Saccharomyces cerevisiae Ipl1 kinase are known to cause abnormal chromosome segregation. We have isolated a cDNA encoding a novel human protein kinase of 402 amino acids with a predicted molecular mass of 45.9 kDa, which shares high amino acid identities with the Aurora/Ipl1 protein kinase family; hence the cDNA is designated as aik (aurora/IPL1-related kinase). Amino acid sequence of C-terminal kinase domain of Aik shares 86, 86, 72, 59, and 49% identity with those of Xenopus XLP46APK and XLP46BPK, mouse STK-1, Aurora of Drosophila, and yeast Ipl1, respectively, whereas N-terminal domain of Aik shares high homology only with those of XLP46APK and XLP46BPK. Northern and Western blotting analyses revealed that Aik is expressed highly in testis and various proliferating cells including HeLa cells. In HeLa cells, the endogenous levels of aik mRNA and protein contents are tightly regulated during cell cycle progression. Both of these levels are low in G1/S, accumulate during G2/M, and reduce rapidly after mitosis. Its protein kinase activity is also enhanced at mitosis as inferred by exogenous casein phosphorylation. Immunofluorescence studies using a specific antibody have shown that Aik is localized to the spindle pole during mitosis, especially from prophase through anaphase. These results strongly suggest that Aik is a novel member of a protein kinase family possibly involved in a centrosome function(s) such as chromosome segregation or spindle formation.
Cytokinesis and septation in the fission yeast Schizosaccharomyces pombe are studied as a model for mammalian cell division. In fission yeast, septation is positively regulated by Spg1, a Ras family GTPase that localizes to spindle-pole bodies (SPBs) throughout the cell cycle. As cells enter mitosis, Spg1 accumulates in an active, GTP-bound form and binds the Cdc7 protein kinase to cause Cdc7 translocation to SPBs. Cdc7 disappears from one SPB in mid-anaphase and from the second SPB in late mitosis. Byr4 plus Cdc16 negatively regulate septation by forming a two-component GTPase-activating protein for Spg1. These results led us to hypothesize that Byr4 localization to SPBs regulated the nucleotide state of Spg1, due to its ability to form Spg1GAP activity with Cdc16 and thus the binding of Cdc7 to Spg1 at SPBs. To test this hypothesis, Byr4 localization was determined using indirect immunofluorescence. This analysis revealed that Byr4 was localized to SPBs that did not contain Cdc7. In byr4(-) mutants, Cdc7 localized to interphase SPBs and only symmetrically localized to mitotic SPBs. In contrast, Byr4 overexpression prevented Spg1 and Cdc7 localization to SPBs. These results suggest that Byr4 localization to SPBs maintains Spg1 in an inactive form, presumably by stimulating Spg1 GTPase activity with Cdc16, and that loss of Byr4 from mitotic SPBs increases the active fraction of Spg1 and thereby increases Spg1-Cdc7 binding. Byr4 localization to SPBs was decreased in spg1, cdc16, sid4, and cdc11 mutants as well as in several mutants that affect medial F-actin structures, suggesting that multiple pathways regulate Byr4 localization to SPBs.
Enamel biomineralization is a complex process that involves interactions between extracellular matrix proteins. To identify proteins interacting with tuftelin, a potential nucleator of enamel crystallites, the yeast two-hybrid system was applied to a mouse tooth expression library and a tuftelin-interacting protein (TIP) was isolated for further characterization. Polyclonal antibodies were prepared against two recombinant variants of this protein. Both antibodies identified a major protein product in tooth organs at 39 kDa, and this protein has been called TIP39. Northern analysis showed TIP39 messenger RNA in multiple organs, a pattern similar to that of tuftelin messenger RNA. In situ hybridization of mandibles of 1-day-old mice detected TIP39 RNA in secretory ameloblasts and odontoblasts. Immunolocalization of TIP39 and tuftelin in cultured ameloblast-like cells showed that these two proteins colocalize. Within the developing tooth organ, TIP39 and tuftelin immunolocalized to the apical pole of secretory ameloblasts (Tomes' processes) and to the newly secreted extracellular enamel matrix. TIP39 amino acid sequence appears to be highly conserved with similarities to proteins in species as diverse as yeast and primates. Available sequence data and the findings reported here suggest a role for TIP39 in the secretory pathway of extracellular proteins.