A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, May 23, 2014. / A systematic experimental investigation was performed of the phenomenon of fine structure, with emphasis on the region of the Isoscalar Giant Quadrupole Resonance (ISGQR), in nuclei across stable even-even neodymium isotopes. The 200 MeV proton beams were delivered by the Separated Sector Cyclotron (SSC) facility of iThemba Laboratory for Accelerator Based Sciences (iThemba LABS). Measurements were made using the state-of-the-art K = 600 magnetic spectrometer, where unique high energy-resolution ( E ≈ 42 − 48 keV FWHM) proton inelastic scattering results were obtained on 142Nd, 144Nd, 146Nd, 148Nd and 150Nd targets. All measurements were taken at θLab = 8◦, where the cross-section of the ISGQR is at a maximum. An additional measurement was also made for the 142Nd at θLab = 7◦. Nuclei with mass number A ≈ 150 and neutron number N ≈ 90 are of special interest since they occupy that region of the nuclide chart wherein the onset of permanent prolate deformation occurs. The stable neodymium (Z = 60) isotopes have been chosen in the present study in order to investigate the effects accompanying the onset of deformation on the excitation energy spectra in the ISGQR region (9 ≤ Ex ≤ 15 MeV). The neodymium isotopes extend from the semi-magic N = 82 nucleus (142Nd) to the permanently deformed N = 90 (150Nd) nucleus. In order to emphasize the ISGQR in the measured excitation energy spectra, a Discrete Wavelet Transform (DWT) background subtraction was carried out. This model independent method for background determination decomposes the spectrum into various approximations and details through the application of high pass and low pass filters. A comparison of the resonance widths extracted shows a systematic broadening of the ISGQR (􀀀 = 3.220 MeV to 5.100 MeV), moving from spherical 142Nd to highly deformed 150Nd nuclei as has already been observed for the Isovector Giant Dipole Resonance (IVGDR) excited by γ-capture. Even though it is known that the IVGDR spectacularly splits and shows a double bump for the deformed 150Nd, no obvious splitting of the ISGQR was observed. In order to investigate the fine structure of the ISGQR, a theoretical microscopic calculation termed the Quasiparticle-Phonon Model (QPM) was applied to predict excitation energy spectra for 142−146Nd targets. These calculations were based on the one- plus two-phonon configuration. Characteristic energy scales were extracted for the resonance region using the Continuous Wavelet Transform (CWT) technique, on both experimental data and theoretical predictions. Comparison of the resulting characteristic energy scales suggests the coupling to low-lying collective vibrations as the dominant contributor to the ISGQR decay width. Level densities of 2+ states were extracted through the application of a fluctuation analysis technique, for full spectra from the ground state upwards in all five Nd targets. Comparisons are made with theoretical predictions from the Back Shifted Fermi Gas, Hartree-Fock-BCS and Hartree-Fock-Bogoluibov models. While there is generally an excellent agreement between experimental level densities and theoretical predictions from the ground state up to less than 10 MeV excitation, there is a marked disagreement beyond 10 MeV in all target nuclei. Comparison of the experimental results for the Nd isotope chain shows a clear systematic trend in which the onset of this disagreement occurs at lower and lower excitation energies, moving from low to high mass. For the spherical 142Nd nucleus the deviation occurs at about 9 MeV while in the case of the deformed 150Nd this occurs much earlier at about 4 MeV, all limited to a maximum of 103 MeV−1 by the energy resolution of the present experiment. Additionally, measurements of elastic scattering and inelastic excitation of lowlying collective states in 144−150Nd has also been possible. Excitation energy spectra in all targets predominantly exhibited various 2+ states, owing to the “spin-filter” effects. A single strong 3− 1 state, together with a weak 4+ 1 state were observed in each target nucleus. Angular distributions were obtained for the various ground and excited states by applying the optical model of elastic scattering and Distorted Wave Born Approximation (DWBA) of inelastic scattering. Deformation lengths δL were obtained for most of the states and these were in good agreement with previously obtained results from the literature.

Nuclear positioning occurs in different cellular contexts: from dividing yeast to more specialized cells like neuronal glial progenitor and skeletal muscle cells. Interestingly, abnormal nuclear positioning is associated with diseases such as muscular dystrophy where nuclei occupy a central rather than peripheral location. Moreover, rearward nuclear positioning is typical of migratory cells. Active nuclear movement in most cases involves coupling of cytoskeletal components with the nucleus by a group of transmembrane proteins in the nuclear envelope called the LINC (linker of nucleoskeleton and cytoskeleton) complex. It is composed of the inner nuclear membrane SUN (Sad1p, UNC-84) proteins associated with nuclear lamins and the outer nuclear membrane KASH (Klarsicht, ANC-1, Syne Homology) proteins, which interact with the cytoskeleton. In my thesis, the murine fibroblast cell line NIH3T3 was used as a model system to study nuclear positioning in states of active movement and static homeostatic positioning. Nuclear positioning and centrosome reorientation are hallmarks of cell polarity in migrating fibroblasts. The Gundersen lab has established that the nucleus moves rearward to orient the centrosome in serum starved fibroblast monolayers stimulated by the serum-derived factor lysophosphatidic acid (LPA). LPA stimulates the GTPase Cdc42, which in turn activates the Cdc42 effector MRCK to phosphorylate myosin II and activate actin retrograde flow to move the nucleus to the rear. A second Cdc42 effector, Par6 functions with Par3 and dynein to maintain the centrosome in the cell centroid. The nucleus is moved rearward by the attachment of retrograde dorsal actin cables to the nucleus through transmembrane actin-associated nuclear (TAN) lines. TAN lines are composed linear arrays of the LINC complex proteins nesprin-2G (N2G) and SUN2 and dorsal actin cables. Disrupting TAN lines components blocks nuclear movement and efficient cell migration. Interestingly, TAN lines are analogous to other membrane adhesions, such as focal adhesions, in that they are transmembrane structures linked to the actin cytoskeleton and transmit force. Given the large number of proteins composing structures such as focal adhesions, we predicted there would be additional components in TAN lines necessary for their formation and function. Thus, I set out to identify and study cytoplasmic factors required for TAN line formation and/or function during active nuclear positioning in fibroblast. A collaborator detected N2G as a hit in a yeast two-hybrid screen for FHOD1 interactors. FHOD1 is an actin regulator and belongs to the formin family. Like other formin family members, it has an FH2 actin binding domain, an FH1 domain and DID and DAD domains that interact to autoinhibit FHOD1. Unlike other formins, FHOD1 is not activated by GTPase binding and contains a second actin binding domain (ABS domain), giving it actin bundling activity. We show that spectrin repeats (SRs) 10-13 of N2G and the N-terminus of FHOD1 interacts with each other directly by biochemical assays with purified proteins. SiRNA against FHOD1 and overexpression of either FHOD1 or N2G interacting domains prevented LPA-stimulated nuclear movement in wounded monolayers of NIH3T3 fibroblasts, suggesting that the interaction between FHOD1 and N2G is required for nuclear movement and centrosome reorientation. FHOD1 was required for TAN line formation, but was dispensable for the formation of dorsal actin cables and retrograde actin flow. By re-expressing an artificial construct containing the N2G-binding domain of FHOD1 and the actin-binding domain of α–actinin in FHOD1 depleted cells, we show that the FHOD1 ABS domain provides N2G with an additional contact to actin filaments required for nuclear movement. This study thus identifies FHOD1 as a new TAN line component and suggests that the interaction of FHOD1 with N2G may reinforce TAN lines so that they can resist the force necessary to move the nucleus. The above study identifies a new component in a pathway that actively moves the nucleus. We have far less knowledge about the mechanism that maintains the nucleus in position when it is not moving. For example, it is unknown whether the static nuclear positioning is an active process or simply an inactivation of mechanisms that actively move nuclei. To answer this question, I developed a novel method to artificially displace the nucleus in adherent cells by centrifugation and used this system to identify active mechanisms of homeostatic nuclear positioning. By subjecting wounded monolayers of starved NIH3T3 fibroblast on coverslips to centrifugal force perpendicular to the wound, I find that nuclei are displaced towards the direction of centrifugal force, so that on one wound edge, the nuclei are in the cell rear while on the other, in the cell front. After returning centrifuged cells to the incubator, I used fixed and live cell recordings to show that the displaced nuclei actively re-center within one hour, although nuclei moving rearward did so faster than those moving forward. Treating centrifuged cells with cytoskeletal drugs, revealed an actin/myosin II-dependent rearward recentration and a microtubule (MT)/dynein-dependent forward recentration. I knocked down LINC complex components to test their involvement in these movements. N2G was required for both rearward and forward movement while SUN1 and SUN2 were required for forward and rearward movement, respectively. Overexpression of different N2G constructs in N2G-depleted cells showed that different regions of N2G were necessary for each direction of movement: N-terminal constructs rescued rearward nuclear recentration whereas C-terminal constructs rescued forward recentration. Based on the minimal N2G construct that rescued forward (MT dependent) nuclear recentration, I identified a dynein and dynactin site in the C terminus of N2G. To test whether the homeostatic nuclear positioning mechanisms were active in uncentrifuged cells, I depleted cells of nesprin-2 and then re-expressed nesprin-2 constructs capable of interacting with actin, MTs or both cytoskeletal elements. Nuclei in nesprin-2-depleted cells were no longer maintained at the cell centroid and only re-expression of a construct that contained sites for interaction with both actin and MTs rescued this defect. Thus, both actin- and MT- interaction domains of N2G are required for homeostatic nuclear positioning. To test whether the actin and MT activities of N2G were important for cell migration, I depleted NIH3T3 fibroblasts of nesprin-2 and re-expressed N2G constructs capable of interaction with actin, MTs or both and tested these cells in single and collective cell migration assays. I found that only the MT-dependent activity of N2G is required for the directionality of single cell migration while both N- and C- terminal (actin- and MT- dependent) N2G are required for the velocity of collective cell migration. These results show that different cytoskeletal linkages are used in different modes of cell migration. My thesis studies identify the first cytoplasmic factor required for TAN lines structure, establish a novel method to artificially displace the nucleus in adherent cells, and reveal different mechanisms of LINC complex coupling cytoskeletons during active and homeostatic nuclear positioning, as well as specific cytoskeleton-dependent contributions of nuclear envelope protein N2G during cell migration.

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No description available.

The objective of this study was to investigate whether or not the treatment of nuclear donor cells with inhibitors of protein synthesis and cyclin-dependent kinases (CDKs) affect the development of swine embryos produced by somatic cell nuclear transfer. Host oocytes were derived from pre-pubertal females and matured in vitro for 42-46 h under standard conditions. Nuclear donor cells were fetal fibroblasts maintained in culture for 2 to 6 passages. Oocytes were reconstructed with cells treated for 22-24 hours with cycloheximide (CHX; 10mug/ml), roscovitine (ROS; 25 muM), the combination of CHX + ROS (CR), or untreated cells. Two hours after reconstruction, the oocytes were activated using ionomycin (15muM/5 min) and strontium chloride (10mM/4h), maintained for 6 h in the presence of cytochalasin B (7.5mug/ml) and CHX (10mug/ml), and then cultured in porcine zygote medium (PZM3) for 6 days. The cleavage rate, 63.7% (n=318), 55.2% (n=99), 56.7% (n=107) and 60.6% (n=347), at 48 h post-fusion were not significantly different between embryos derived from ROS, CHX, CR and control cells, respectively. Developmental rate to blastocyst stage was higher for embryos reconstructed with ROS (12.2%) and untreated cells (12.1%) when compared to CHX (5.7%) and CR (4.9%). Blastocysts produced with ROS treated cells had similar number of nuclei compared to embryos reconstructed with untreated donor cells (30.9+/-10.4 vs. 32.2+/-8.0). Phosphorylated H2A.X (gammaH2A.X) was highly expressed in donor cells treated with CR compared to non treated cells, but it was similarly expressed in most of 1-cell stage embryos reconstructed with control or treated cells. Flow cytometry analysis showed that the majority of the fibroblasts were at G 0/G1 phase of the cell cycle at the time of nuclear transfer. It was concluded that the treatment of nuclear donor cells with inhibitors of protein synthesis and CDKs did not improve the in vitro development of somatic cell nuclear transfer embryos in pigs.

This thesis develops image segmentation methods for the application of automated cervical cancer screening. The traditional approach to automating this task has been to emulate the human method of screening, where every one of the hundreds of thousands of cells on each slide is analysed for abnormality. However, due to the complexity of cervical smear images and the low error tolerance imposed upon the segmentation stage, only limited success has previously been found. A different approach is to detect malignancy associated changes (MACs) in a relatively small sample of the total population of cells. Under this paradigm, the requirement to segment every cell is loosened, but delineation accuracy and error checking become essential. Following a review of generic and cervical smear segmentation, it is concluded that prior work on the traditional approach to automation is not suitable for a MACs solution. However, the previously proposed framework of a dual-magnification system is found to be relevant and is therefore adopted. Here, scene images are first captured at low resolution in order to rapidly locate the cells on a slide. Cells that are deemed to be suitable for further analysis are then imaged at high resolution for the more accurate segmentation of their nuclei. A water immersion algorithm is developed for low resolution scene segmentation. This method achieves a rapid and robust initial segmentation of the scene without the requirement of incorporating extensive a priori knowledge of the image objects. A global minimum searching contour is presented as a top-down method for segmenting the high resolution cell nucleus images where the image objects are well characterised by shape and appearance. This latter method is tested upon 20,000 images and found to achieve an accurate segmentation rate of 99.47%. An error checking method, that uses segmentation stability as an indicator of segmentation success, is developed that is capable of detecting 100% of the failures of the nucleus segmenter, at the expense of discarding only 9% of the data. Throughout this work, contemporary issues in the field of generic image segmentation are presented and some of these are addressed for the cervical smear application. Finally, an avenue of future work is proposed which may lead to the much wider proliferation of computer vision solutions to everyday problems.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 130-161). Also available via the Internet.

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The nucleus circularis has been linked to a role in regulating osmotic thirst but evidence has also shown that full bilateral destruction of the nucleus circularis was not necessary to achieve a deficit in drinking behavior after an osmotic challenge. The present study attempted to answer two primary research questions. The first question was whether osmoreceptive cells existed around the nucleus circularis in a homogeneous fashion or if these cells existed in a structured fashion stretching from the nucleus circularis forward. The second question was whether animals with lesions of the nucleus circularis and the surrounding areas were different in normal daily water intake than animals with no lesions. The first question was approached by lesioning the nucleus circularis, the area one millimeter anterior to the nucleus circularis, one millimeter posterior to the nucleus circularis, one half of a millimeter medial to the nucleus circularis and using a sham group which had the electrode passed through the brain to a spot one millimeter above the nucleus circularis but passing no current. All animals were then given an osmotic challenge which consisted of half of each group with an injection of hypertonic saline while the other half of each group was given isotonic saline. After a five-day recovery period, the injection procedure was reversed. Water consumption on each test day was measured at ten-minute intervals for one hour. Difference scores were then computed by subtracting the amount of water consumed after hypertonic saline injection from the amount of water consumed after isotonic saline injection. The difference scores were then used in an analysis of variance which revealed a significant difference between groups. A subsequent post hoc test showed that the nucleus circularis group was different from all other groups except for the anterior lesion group which showed a trend in the same direction as the nucleus circularis group. The second research question was approached in two ways. The first way was to simply record the amount of water consumed in each twenty-four hour period. An analysis of variance showed no significant difference between any of the groups. The second method for testing the second research question was to put the animals on a twenty-three hour water deprivation schedule and measure the amount of water consumed during the one hour when water was available. Once again, no significant differences were observed.

Polyglutamine (polyQ) diseases are a group of progressive neurodegenerative disorders, which are caused by the expansion of an existing glutamine-coding CAG repeat in the coding region of disease genes. The cell nucleus is a major site of polyQ toxicity, and gene transcription is compromised in polyQ-induced neurodegeneration. Understanding the nuclear translocation of mutant polyQ proteins is therefore crucial to unfold the complex pathogenic mechanisms that underlie the neuronal toxicity of polyQ disease. The polyQ domain is the only common sequence found among different mutant disease proteins. Nuclear transport signals have been identified in some, but not all, polyQ disease proteins. The detection of those mutant polyQ proteins that carry no classical nuclear transport signal, but not their normal counterparts, in the cell nucleus suggests the existence of uncharacterized nuclear transport signals in mutant polyQ proteins. Thus, the objective of the present study is to elucidate the nuclear transport pathway(s) adopted by an expanded polyQ domain and determine its correlation with polyQ toxicity. / Through a series of genetic and biochemical studies in cell culture, mouse and transgenic Drosophila models, exportin-1 was found to modulate the nucleocytoplasmic localization of mutant polyQ protein and its toxicity. Further, mutant polyQ protein was also demonstrated to be a novel transport substrate of exportin-1. By promoting the nuclear export of mutant polyQ protein, exportin-1 suppressed polyQ toxicity by reducing the interference of mutant polyQ protein on gene transcription. It was found that the protein level of exportin-1 diminished in the normal ageing process, which would result in an exaggeration of nuclear mutant polyQ toxicity. Thus, the age-dependent decline of exportin-1 level, at least in part, accounts for the progressive degeneration observed in polyQ patients. Results obtained from this project first demonstrated that expanded polyQ domain is a nuclear export signal, and further provided mechanistic explanation of how protein nuclear transport receptors modulate polyQ toxicity. / Chan, Wing Man. / Source: Dissertation Abstracts International, Volume: 71-01, Section: B, page: 0113. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 189-203). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese.