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Physical Studies of Cell Division: Statistical Fluctuations; Effects Due to X-Radiation, Temperature, and Hydrostatic Pressure

Description: Thesis discussing "a technique for determining the generation times of individual yeast cells...the effect of x-radiation on the generation times of individual cells and their progeny..." and "attempts to synchronize cell division in a population of cells."
Date: December 9, 1954
Creator: Burns, Victor Will
Partner: UNT Libraries Government Documents Department

Studies on Cell Division, 1. Alpha Radiation as a Division Inhibiting Agent

Description: Report discussing a study aimed at learning about cell division and the effects of radiation alpha radiation on the process of cell division. This was done by correlating changes in the biochemical state of cells and the inhibition of cell division. Materials and methods are included as well as experimental results and data.
Date: unknown
Creator: Spoerl, Edward S. & Balske, R. J.
Partner: UNT Libraries Government Documents Department

brk1 and dcd1 Act Synergistically in Subsidiary Cell Formation in Zea mays

Description: Subsidiary mother cell (SMC) divisions during stomatal complex formation in Zea mays are asymmetric generating a small subsidiary cell (SC) and a larger epidermal cell. Mutants with a high number of abnormally shaped subsidiary cells include the brick1 (brk1) and discordia1 (dcd1) mutants. BRK1 is homologous to HSPC300, an ARP2/3 complex activator, and is involved in actin nucleation while DCD1 is a regulatory subunit of the PP2A phosphatase needed for microtubule generation (Frank and Smith, 2002; Wright et al. 2009). Possible causes of the abnormal SCs in brk1 mutants include a failure of the SMC nucleus to polarize in advance of mitosis, no actin patch, and transverse and/or no PPBs (Gallagher and Smith, 2000; Panteris et al 2006). The abnormal subsidiary mother cell division in dcd1 is due to correctly localized, but disorganized preprophase bands (PPBs; Wright et al. 2009). The observation that brk1 has defects in PPB formation and that the dcd1 phenotype is enhanced by the application of actin inhibitors led us to examine the dcd1; brk1 double mutant (Gallagher and Smith, 1999). We found that dcd1; brk1 double mutants demonstrate a higher percentage of aberrant SCs than the single mutants combined suggesting that these two mutations have a synergistic and additive effect on SC formation. Our observations and results are intriguing and the future step will be to quantitate the abnormal PPBs and phragmoplasts in the double and single mutants using immunolocalization of tubulin and actin as well as observations of live cells expressing tubulin-YFP.
Date: August 2014
Creator: Malhotra, Divya
Partner: UNT Libraries

Methylglyoxal Effects on Cell Division of Scenedesmus quadricauda (Scenedesmaceae)

Description: Cell division of ggeneflesmus quadricauda (Turp.) Breb. (Scenedesmaceae) is enhanced by methylglyoxal, a general inhibitor of cell division, at threshold concentration in conjunction with treatment timing related to growth stage of batch cultures. At 0.5 mM methylglyoxal concentration, cell division was significantly enhanced in algae treated in the logarithmic phase. Specific growth rates of methylglyoxal-treated cultures were rapidly increased at the beginning of logarithmic phase. Cultures inoculated with high cell numbers were less sensitive, but still showed high specific growth rates in logarithmic phase. Cell division in cultures which had low cell numbers was inhibited by 0.5 mM methylglyoxal treatment. Both specific activity of Glyoxalase I and the ratio of Glyoxalase I to Glyoxalase II of methylgloxal-treated cultures were higher than those of controls (1.3 and 2.1- fold, respectively). Pyruvate concentration in treated cultures was increased after methylglyoxal treatment.
Date: August 1990
Creator: Rhie, Kitae
Partner: UNT Libraries

The Role of the Actin Cytoskeleton in Asymmetric Cell Division in Maize

Description: Stomata are specialized plant structures required for gaseous exchange with the outer environment. During stomata formation, the cytoskeleton plays an important role in controlling the division of the individual cells leading to the generation of the stomata complex. Two mutants that affect microfilament and microtubule organization in subsidiary mother cells include brk1 and dcd1. While only 20% of the subsidiary cells in the brk1 and dcd1 single mutants are abnormally shaped, it was reported that there is a synergistic effect between the brk1 and dcd1 mutations in the brk1; dcd1 double mutant since 100% of the subsidiary cells are abnormal. The focus of this research is to try to understand this synergistic effect by investigating the actin cytoskeleton and nuclear position in the single and double mutants. The reported results include the observation that the size of actin patch was largest in the wild-type subsidiary mother cells (SMCs) and smallest in dcd1 and brk1; dcd1 SMCs and that brk1 and brk1; dcd1 double mutants had fewer actin patches than wild-type and dcd1 SMCs. Additionally, we observed that some SMCs that did not have actin patches still underwent nuclear migration suggesting that nuclear migration may not be solely dependent on actin patch formation. Finally, during SMC cytokinesis, a large percentage of double mutant (brk1; dcd1) cells showed an off-track development of the phragmoplast as compared to the single mutants and the wild-type plant explaining the large number of abnormally shaped subsidiary cells in the double mutants.
Date: August 2014
Creator: Alhassan, Hassan Hamdan
Partner: UNT Libraries

Designing Tools to Probe the Calcium-dependent Function of Arabidopsis Tonneau2

Description: Plants possess unique features in many aspects of development. One of these features is seen in cell wall placement during cytokinesis, which is determined by the position of the preprophase band (PPB) and the subsequent expansion of the phragmoplast that deposits the new cell wall. During phragmoplast expansion, the phragmoplast tracks to the cortical division site, which was delineated by the PPB. Thus the position of the PPB determines the orientation of the division plane. In Arabidopsis thaliana, TONNEAU2 (TON2) is required for PPB formation and has been shown to interact with a type A subunit of the PP2A phosphatase in the yeast two-hybrid system. In Arabidopsis tonneau2 (ton2) mutants, abnormalities of the cortical microtubule cytoskeleton, such as disorganization of the interphase microtubule array and lack of PPB formation before mitosis markedly affects cell shape and arrangement as well as overall plant morphology. Loss of dcd1/add1, the maize ton2 homologues gives rise to a similar phenotype in Zea mays. The TON2 protein has two EF hand domains which are calcium-binding sites. Since calcium has been known to play key roles in several areas of plant functioning, the following question was raised: “Does calcium binding contribute to the localization and function of TONNEAU at the PPB?” To address this question, a series of constructs were generated to determine if TON2 binds calcium. Additionally, Ca2+ binding sites were mutated in constructs containing the TON2 gene fused to GFP or YPF. These constructs were then transformed into ton2 mutant plants and the localization of TON2 fusion protein and whether the construct is capable of rescuing the mutant phenotype were observed. Although, localization of TON2 to the PPB was not observed, the presence of the constructs were confirmed in the transformed plants using selection markers and by observing fluorescence under a confocal microscope.
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Date: December 2013
Creator: Oremade, Oladapo O.
Partner: UNT Libraries

The Korarchaeota: Archaeal orphans representing an ancestral lineage of life

Description: Based on conserved cellular properties, all life on Earth can be grouped into different phyla which belong to the primary domains Bacteria, Archaea, and Eukarya. However, tracing back their evolutionary relationships has been impeded by horizontal gene transfer and gene loss. Within the Archaea, the kingdoms Crenarchaeota and Euryarchaeota exhibit a profound divergence. In order to elucidate the evolution of these two major kingdoms, representatives of more deeply diverged lineages would be required. Based on their environmental small subunit ribosomal (ss RNA) sequences, the Korarchaeota had been originally suggested to have an ancestral relationship to all known Archaea although this assessment has been refuted. Here we describe the cultivation and initial characterization of the first member of the Korarchaeota, highly unusual, ultrathin filamentous cells about 0.16 {micro}m in diameter. A complete genome sequence obtained from enrichment cultures revealed an unprecedented combination of signature genes which were thought to be characteristic of either the Crenarchaeota, Euryarchaeota, or Eukarya. Cell division appears to be mediated through a FtsZ-dependent mechanism which is highly conserved throughout the Bacteria and Euryarchaeota. An rpb8 subunit of the DNA-dependent RNA polymerase was identified which is absent from other Archaea and has been described as a eukaryotic signature gene. In addition, the representative organism possesses a ribosome structure typical for members of the Crenarchaeota. Based on its gene complement, this lineage likely diverged near the separation of the two major kingdoms of Archaea. Further investigations of these unique organisms may shed additional light onto the evolution of extant life.
Date: May 1, 2007
Creator: Elkins, James G.; Kunin, Victor; Anderson, Iain; Barry, Kerrie; Goltsman, Eugene; Lapidus, Alla et al.
Partner: UNT Libraries Government Documents Department

Investigating the Molecular Mechanism of TSO1 Function in Arabidopsis cell division and meristem development

Description: Unlike animals, plants are constantly exposed to environmental mutagens including ultraviolet light and reactive oxygen species. Further, plant cells are totipotent with highly plastic developmental programs. An understanding of molecular mechanisms underlying the ability of plants to monitor and repair its DNA and to eliminate damaged cells are of great importance. Previously we have identified two genes, TSO1 and TSO2, from a flowering plant Arabidopsis thaliana. Mutations in these two genes cause callus-like flowers, fasciated shoot apical meristems, and abnormal cell division, indicating that TSO1 and TSO2 may encode important cell cycle regulators. Previous funding from DOE led to the molecular cloning of TSO1, which was shown to encode a novel nuclear protein with two CXC domains suspected to bind DNA. This DOE grant has allowed us to characterize and isolate TSO2 that encodes the small subunit of the ribonucleotide reductase (RNR). RNR comprises two large subunits (R1) an d two small subunits (R2), catalyzes a rate-limiting step in the production of deoxyribonucleotides needed for DNA replication and repair. Previous studies in yeast and mammals indicated that defective RNR often led to cell cycle arrest, growth retardation and p53-dependent apoptosis while abnormally elevated RNR activities led to higher mutation rates. Subsequently, we identified two additional R2 genes, R2A and R2B in the Arabidopsis genome. Using reverse genetics, mutations in R2A and R2B were isolated, and double and triple mutants among the three R2 genes (TSO2, R2A and R2B) were constructed and analyzed. We showed that Arabidopsis tso2 mutants, with reduced dNTP levels, were more sensitive to UV-C. While r2a or r2b single mutants did not exhibit any phenotypes, tso2 r2b double mutants were embryonic lethal and tso2 r2a double mutants were seedling lethal indicating redundant functions among the three R2 genes. Furthermore, tso2 r2a double mutants exhibited increased DNA dam ...
Date: October 1, 2004
Creator: Liu, Zhongchi
Partner: UNT Libraries Government Documents Department

Regulatory role of AINTEGUMENTA in organ initiation and growth

Description: Although several members of the plant-specific AP2/ERF family of transcription factors are important developmental regulators, many genes in this large protein family remain uncharacterized. Here, we present a phylogenetic analysis of the18 genes that make up the AP2 subgroup of this family. We report expression analyses of seven Arabidopsis genes most closely related to the floral development gene AINTEGUMENTA and show that all AINTEGUMENTA-like (AIL) genes are transcribed in multiple tissues during development. They are expressed primarily in young actively dividing tissues of a plant and not in mature leaves or stems. The spatial distribution of AIL5, AIL6, and AIL7 mRNA in inflorescences was characterized by in situ hybridization. Each of these genes is expressed in a spatially and temporally distinct pattern within inflorescence meristems and flowers. Ectopic expression of AIL5 resulted in a larger floral organ phenotype, similar to that resulting from ectopic expression of ANT. Our results are consistent with AIL genes having roles in specification of meristematic or division-competent states.
Date: March 1, 2005
Creator: Krizek, Beth Allyn & Lebioda, Lukasz
Partner: UNT Libraries Government Documents Department

Regulation of cell division in higher plants. Final technical report

Description: Research in the latter part of the grant period was divided into two parts: (1) expansion of the macromolecular tool kit for studying plant cell division; (2) experiments in which the roles played by plant cell cycle regulators were to be cast in the light of the emerging yeast and animal cell paradigm for molecular control of the mitotic cycle. The first objectives were accomplished to a very satisfactory degree. With regard to the second part of the project, we were driven to change our objectives for two reasons. First, the families of cell cycle control genes that we cloned encoded such closely related members that the prospects for success at raising distinguishing antisera against each were sufficiently dubious as to be impractical. Epitope tagging is not feasible in Pisum sativum, our experimental system, as this species is not realistically transformable. Therefore, differentiating the roles of diverse cyclins and cyclin-dependent kinases was problematic. Secondly, our procedure for generating mitotically synchronized pea root meristems for biochemical studies was far too labor intensive for the proposed experiments. We therefore shifted our objectives to identifying connections between the conserved proteins of the cell cycle engine and factors that interface it with plant physiology and development. In this, we have obtained some very exciting results.
Date: February 29, 2000
Creator: Jacobs, Thomas W.
Partner: UNT Libraries Government Documents Department

The Cotton Kinesin-Like Calmodulin-Binding Protein Associates with Cortical Microtubles in cotton Fibers

Description: Microtubules in interphase plant cells form a cortical array, which is critical for plant cell morphogenesis. Genetic studies imply that the minus end-directed microtubule motor kinesin-like calmodulin-binding protein (KCBP) plays a role in trichome morphogenesis in Arabidopsis. However, it was not clear whether this motor interacted with interphase microtubules. In cotton (Gossypium hirsutum) fibers, cortical microtubules undergo dramatic reorganization during fiber development. In this study, cDNA clones of the cotton KCBP homolog GhKCBP were isolated from a cotton fiber-specific cDNA library. During cotton fiber development from 10 to 21 DPA, the GhKCBP protein level gradually decreases. By immunofluorescence, GhKCBP was detected as puncta along cortical microtubules in fiber cells of different developmental stages. Thus the results provide evidence that GhKCBP plays a role in interphase cell growth likely by interacting with cortical microtubules. In contrast to fibers, in dividing cells of cotton, GhKCBP localized to the nucleus, the microtubule preprophase band, mitotic spindle, and the phragmoplast. Therefore KCBP likely exerts multiple roles in cell division and cell growth in flowering plants.
Date: May 1, 2003
Creator: L., Preuss M.; Delmar, D.P. & Liu, Bo
Partner: UNT Libraries Government Documents Department

Identifying genetic interactions of the spindle checkpoint in Caenorhabditis elegans.

Description: Faithful segregation of chromosomes is ensured by the spindle checkpoint. If a kinetochore does not correctly attach to a microtubule the spindle checkpoint stops cell cycle progression until all chromosomes are attached to microtubules or tension is experienced while pulling the chromosomes. The C. elegans gene, san-1, is required for spindle checkpoint function and anoxia survival. To further understand the role of san-1 in the spindle checkpoint, an RNAi screen was conducted to identify genetic interactions with san-1. The kinetochore gene hcp-1 identified in this screen, was known to have a genetic interaction with hcp-2. Interestingly, san-1(ok1580);hcp-2(ok1757) had embryonic and larval lethal phenotypes, but the phenotypes observed are less severe compared to the phenotypes of san-1(ok1580);hcp-1(RNAi) animals. Both san-1(ok1580);hcp-1(RNAi) and san-1(ok1580);hcp-2(RNAi) produce eggs that may hatch; but san-1(ok1580):hcp-1(RNAi) larvae do not survive to adulthood due to defects caused by aberrant chromosome segregations during development. Y54G9A.6 encodes the C. elegans homolog of bub-3, and has spindle checkpoint function. In C.elegans, bub-3 has genetic interactions with san-1 and mdf-2. An RNAi screen for genetic interactions with bub-3 identified that F31F6.3 may potentially have a genetic interaction with bub-3. This work provided genetic evidence that hcp-1, hcp-2 and F31F6.2 interact with spindle checkpoint genes.
Date: May 2009
Creator: Stewart, Neil
Partner: UNT Libraries


Description: A study of the incorporation of {sup 14}CO{sub 2} into cell components of synchronously growing Chlorella pyrenoidosa has shown that DNA is synthesized primarily during the latter stages of the cell cycle prior to cell division. RNA was synthesized at an approximately equal rate during each of the three phases of the cell growth studied. No major differences were noted in the incorporation of {sup 14}CO{sub 2} into the soluble cell components in these long-term incorporation studies.
Date: March 8, 1962
Creator: Stange, Luise; Kirk, Martha; Bennett, Edward L. & Calvin, M.
Partner: UNT Libraries Government Documents Department

Elucidation of the Mechanism of Gene Silencing using Small Interferin RNA: DNA Hybrid Molecules

Description: The recent discovery that short hybrid RNA:DNA molecules (siHybrids) induce long-term silencing of gene expression in mammalian cells conflicts with the currently hypothesized mechanisms explaining the action of small, interfering RNA (siRNA). As a first step to elucidating the mechanism for this effect, we set out to quantify the delivery of siHybrids and determine their cellular localization in mammalian cells. We then tracked the segregation of the siHybrids into daughter cells after cell division. Markers for siHybrid delivery were shown to enter cells with and without the use of a transfection agent. Furthermore, delivery without transfection agent only occurred after a delay of 2-4 hours, suggesting a degradation process occurring in the cell culture media. Therefore, we studied the effects of nucleases and backbone modifications on the stability of siHybrids under cell culture conditions.
Date: February 8, 2006
Creator: Dugan, L
Partner: UNT Libraries Government Documents Department

Modeling the Mechano-Chemistry of NTPases

Description: This project is to develop theoretical framework for protein motors based on experimental data. Protein motors use chemical and electrochemical energies to perform mechanical work. Protein motors are machines of life. They are essential for many biological processes, including cell division, DNA transcription, replication, etc. Understanding the working mechanisms of protein motors has both scientific and medical/clinical significances, including revealing the physiological origins of certain diseases, designing of drugs against pathogens. Experiments with new techniques, especially recent advances in single molecule force measurements, have accumulated a large amount of experimental data that requires systematic theoretical analysis. We worked out a theoretical analysis on protein fluctuations to explain the recent single molecule experiment on dynamic disorders, proposed a new mechanism to explain mechanical signal propagation through the allosteric effect, a fundamental property of proteins, and examined the dynamic disorder effects on protein interaction networks. We also examined various theoretical formulations describing mechanical stress propagation in proteins, and derived mathematical formula for various approximate methods solving the mathematical equations.
Date: February 21, 2007
Creator: Xing, J
Partner: UNT Libraries Government Documents Department

A hybrid parallel framework for the cellular Potts model simulations

Description: The Cellular Potts Model (CPM) has been widely used for biological simulations. However, most current implementations are either sequential or approximated, which can't be used for large scale complex 3D simulation. In this paper we present a hybrid parallel framework for CPM simulations. The time-consuming POE solving, cell division, and cell reaction operation are distributed to clusters using the Message Passing Interface (MPI). The Monte Carlo lattice update is parallelized on shared-memory SMP system using OpenMP. Because the Monte Carlo lattice update is much faster than the POE solving and SMP systems are more and more common, this hybrid approach achieves good performance and high accuracy at the same time. Based on the parallel Cellular Potts Model, we studied the avascular tumor growth using a multiscale model. The application and performance analysis show that the hybrid parallel framework is quite efficient. The hybrid parallel CPM can be used for the large scale simulation ({approx}10{sup 8} sites) of complex collective behavior of numerous cells ({approx}10{sup 6}).
Date: January 1, 2009
Creator: Jiang, Yi; He, Kejing & Dong, Shoubin
Partner: UNT Libraries Government Documents Department

Integrated analysis of breast cancer cell lines reveals unique signaling pathways

Description: Cancer is a heterogeneous disease resulting from the accumulation of genetic defects that negatively impact control of cell division, motility, adhesion and apoptosis. Deregulation in signaling along the EGFR-MAPK pathway is common in breast cancer, though the manner in which deregulation occurs varies between both individuals and cancer subtypes. We were interested in identifying subnetworks within the EGFR-MAPK pathway that are similarly deregulated across subsets of breast cancers. To that end, we mapped genomic, transcriptional and proteomic profiles for 30 breast cancer cell lines onto a curated Pathway Logic symbolic systems model of EGFR-MEK signaling. This model was comprised of 539 molecular states and 396 rules governing signaling between active states. We analyzed these models and identified several subtype specific subnetworks, including one that suggested PAK1 is particularly important in regulating the MAPK cascade when it is over-expressed. We hypothesized that PAK1 overexpressing cell lines would have increased sensitivity to MEK inhibitors. We tested this experimentally by measuring quantitative responses of 20 breast cancer cell lines to three MEK inhibitors. We found that PAK1 over-expressing luminal breast cancer cell lines are significantly more sensitive to MEK inhibition as compared to those that express PAK1 at low levels. This indicates that PAK1 over-expression may be a useful clinical marker to identify patient populations that may be sensitive to MEK inhibitors. All together, our results support the utility of symbolic system biology models for identification of therapeutic approaches that will be effective against breast cancer subsets.
Date: March 31, 2009
Creator: Heiser, Laura M.; Wang, Nicholas J.; Talcott, Carolyn L.; Laderoute, Keith R.; Knapp, Merrill; Guan, Yinghui et al.
Partner: UNT Libraries Government Documents Department

Telomerase activity in human cancer

Description: The overall goal of this collaborative project was to investigate the role in malignant cells of both chromosome telomeres, and telomerase, the enzyme that replicates telomeres. Telomeres are highly conserved nucleoprotein complexes located at the ends of eucaryotic chromosomes. Telomere length in somatic cells is reduced by 40--50 nucleotide pairs with every cell division due to incomplete replication of terminal DNA sequences and the absence of telomerase, the ribonucleoprotein that adds telomere DNA to chromosome ends. Although telomerase is active in cells with extended proliferative capacities, including more than 85% of tumors, work performed under this contract demonstrated that the telomeres of human cancer cells are shorter than those of paired normal cells, and that the length of the telomeres is characteristic of particular types of cancers. The extent of telomere shortening ostensibly is related to the number of cell divisions the tumor has undergone. It is believed that ongoing cell proliferation leads to the accumulation and fixation of new mutations in tumor cell lineages.Therefore, it is not unreasonable to assume that the degree of phenotypic variability is related to the proliferative history of the tumor, and therefore to telomere length, implying a correlation with prognosis. In some human tumors, short telomeres are also correlated with genomic instabilities, including interstitial chromosome translocation, loss of heterozygosity, and aneuoploidy. Moreover, unprotected chromosome ends are highly recombinogenic and telomere shortening in cultured human cells correlates with the formation of dicentric chromosomes, suggesting that critically short telomeres not only identify, but also predispose, cells to genomic instability, again implying a correlation with prognosis. Therefore, telomere length or content could be an important predictor of metastatic potential or responsiveness to various therapeutic modalities.
Date: October 2000
Creator: Griffith, J.
Partner: UNT Libraries Government Documents Department

Distinct constrictive processes, separated in time and space,divide Caulobacter inner and outer membranes

Description: Cryo-electron microscope tomography (cryoEM) and a fluorescence loss in photobleaching (FLIP) assay were used to characterize progression of the terminal stages of Caulobacter crescentus cell division. Tomographic cryoEM images of the cell division site show separate constrictive processes closing first the inner, and then the outer, membrane in a manner distinctly different from septum-forming bacteria. The smallest observed pre-fission constrictions were 60 nm for both the inner and outer membrane. FLIP experiments had previously shown cytoplasmic compartmentalization, when cytoplasmic proteins can no longer diffuse between the two nascent progeny cell compartments, occurring 18 min before daughter cell separation in a 135 min cell cycle. Here, we used FLIP experiments with membrane-bound and periplasmic fluorescent proteins to show that (1) periplasmic compartmentalization occurs after cytoplasmic compartmentalization, consistent with the cryoEM observations, and (2) inner membrane and periplasmic proteins can diffuse past the FtsZ constriction site, indicating that the cell division machinery does not block membrane diffusion.
Date: May 1, 2005
Creator: Judd, Ellen M.; Comolli, Luis R.; Chen, Joseph C.; Downing,Kenneth H.; Moerner, W.E. & McAdams, Harley H.
Partner: UNT Libraries Government Documents Department

Symposium on Plant Protein Phosphorylation

Description: Protein phosphorylation and dephosphorylation play key roles in many aspects of plant biology, including control of cell division, pathways of carbon and nitrogen metabolism, pattern formation, hormonal responses, and abiotic and biotic responses to environmental signals. A Symposium on Plant Protein Phosphorylation was hosted on the Columbia campus of the University of Missouri from May 26-28, 2010. The symposium provided an interdisciplinary venue at which scholars studying protein modification, as it relates to a broad range of biological questions and using a variety of plant species, presented their research. It also provided a forum where current international challenges in studies related to protein phosphorylation could be examined. The symposium also stimulated research collaborations through interactions and networking among those in the research community and engaged students and early career investigators in studying issues in plant biology from an interdisciplinary perspective. The proposed symposium, which drew 165 researchers from 13 countries and 21 States, facilitated a rapid dissemination of acquired knowledge and technical expertise regarding protein phosphorylation in plants to a broad range of plant biologists worldwide.
Date: November 1, 2011
Creator: Walker, John C.
Partner: UNT Libraries Government Documents Department

Effect of passage number on cellular response DNA-damaging agents: cell survival and gene expression

Description: The effect of different passage numbers on plating efficiency, doubling time, cell growth, and radiation sensitivity was assessed in Syrian hamster embryo (SHE) cells. Changes in gene expression after UV or {gamma}-ray irradiation at different passage numbers were also examined. The SHE cells were maintained in culture medium for up to 64 passages. Cells were exposed to {sup 60}Co {gamma} rays or 254-m UV radiation. Differential display of cDNAs and Northern blots were used for the study of gene expression. With increasing passage number, SHE cells demonstrated decreased doubling time, increased plating efficiency, and a decreased yield in the number of cells per plate. Between passages 41 and 48 a ``crisis`` period was evident during which time cell growth in high serum (20%) was no longer optimal, and serum concentrations were reduced (to 10%) to maintain cell growth. Sensitivity to ionizing radiation was no different between early- and intermediate-passage cells. However, after UV exposure at low passages (passage 3), confluent cells were more sensitive to the killing effects of UV than were log-phase cells. At intermediate passages (passages 43, 48), confluent cells were slightly more radioresistant- than were log-phase cells. By passage 64, however, both confluent and log-phase cells showed similar patterns of UV sensitivity. Expression of {gamma}-actin, PCNA, and p53 transcripts did not change following UV exposure. p53 mRNA was induced following {gamma}-ray exposure of the intermediate (passage 45) epithelial cells. Differential display, however, revealed changes in expression of several transcripts following exposure to ionizing and ultraviolet radiations. The observed differences in radiation sensitivity associated with increasing passage number may be influenced by radiation-induced gene expression. We are conducting experiments to identify these genes.
Date: March 1, 1996
Creator: Chang-Liu, Chin-Mei & Wolschak, G.E.
Partner: UNT Libraries Government Documents Department

Life Sciences Division and Center for Human Genome Studies 1994

Description: This report summarizes the research and development activities of the Los Alamos National Laboratory`s Life Sciences Division and the biological aspects of the Center for Human Genome Studies for the calendar year 1994. The technical portion of the report is divided into two parts, (1) selected research highlights and (2) research projects and accomplishments. The research highlights provide a more detailed description of a select set of projects. A technical description of all projects is presented in sufficient detail so that the informed reader will be able to assess the scope and significance of each project. Summaries useful to the casual reader desiring general information have been prepared by the group leaders and appear in each group overview. Investigators on the staff of the Life Sciences Division will be pleased to provide further information.
Date: September 1, 1995
Creator: Cram, L.S. & Stafford, C.
Partner: UNT Libraries Government Documents Department

Structure, Function, and Evolution of Rice Centromeres

Description: The centromere is the most characteristic landmark of eukaryotic chromosomes. Centromeres function as the site for kinetochore assembly and spindle attachment, allowing for the faithful pairing and segregation of sister chromatids during cell division. Characterization of centromeric DNA is not only essential to understand the structure and organization of plant genomes, but it is also a critical step in the development of plant artificial chromosomes. The centromeres of most model eukaryotic species, consist predominantly of long arrays of satellite DNA. Determining the precise DNA boundary of a centromere has proven to be a difficult task in multicellular eukaryotes. We have successfully cloned and sequenced the centromere of rice chromosome 8 (Cen8), representing the first fully sequenced centromere from any multicellular eukaryotes. The functional core of Cen8 spans ~800 kb of DNA, which was determined by chromatin immunoprecipitation (ChIP) using an antibody against the rice centromere-specific H3 histone. We discovered 16 actively transcribed genes distributed throughout the Cen8 region. In addition to Cen8, we have characterized eight additional rice centromeres using the next generation sequencing technology. We discovered four subfamilies of the CRR retrotransposon that is highly enriched in rice centromeres. CRR elements are constitutively transcribed and different CRR subfamilies are differentially processed by RNAi. These results suggest that different CRR subfamilies may play different roles in the RNAi-mediated pathway for formation and maintenance of centromeric chromatin.
Date: February 4, 2010
Creator: Jiang, Jiming
Partner: UNT Libraries Government Documents Department