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Start date: 2006 × End date: 2009 × search.filters.applied.f.isOrgUnitOfPublicationTitle: School of Biological Sciences ×

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Now showing 1 - 10 of 23
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Nanoparticle-mediated r-depression in the rotifer Brachionus manjavacas

2009-12 , Hicks, Daniel

Nanotechnology research promises novel and practical applications of well-characterized materials. However, responsible development of the nanotechnology industry necessitates proactive research into the ecological responses of communities to the presence of nano-scale materials. I attempt to discern if and how the presence of inert nanoparticles at varying concentrations and size affects the fitness of populations of Brachionus manjavacas (Rotifera). Feeding fluorescently labeled 50 nm latex microspheres to rotifers produced dramatic fluorescence distributed throughout the females and their eggs. Fluorescent intensity was distinct from background epifluorescence exhibited by B. manjavacas, and increased with concentration, availability of food, and duration of exposure. Transfer of exposed maternal females and F1 offspring into nanoparticle-free environments demonstrated that these nanoparticles were rapidly cleared from the animals, and that the offspring suffered no significant effects from parental exposure. However, the population growth rate was depressed 50% in rotifer cultures exposed to 0.30 ug/mL of 50 nm particles, and 89% in cultures with nanoparticle concentrations of 1.14 ìg/mL. Nanoparticles of identical composition but of larger diameter (up to 3000 nm, comparable to algae cells, a natural food source), caused no reduction in population growth rate. These larger particles remained confined in the gut, implicating nanoparticle size as a critical factor in bioactivity. Causes of growth rate depression include, but are not limited to, a marked decrease in feeding behavior. Mode of entry is suspected to be either epithelial digestive-tract phagocytosis or introduction through cellular pores.

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Genetic Mechanisms of Telencephalon Diversification Through Shifts in the Pallial-Subpallial Boundary

2009-05-04 , Rich, Constance Anne

The vertebrate brain develops through the formation of compartments. These compartments are physically separated to allow for the proper differentiation of each structure within the brain. The telencephalon, a compartment analogous to the cerebral cortex of mammals, further subdivides once it is separated from the rest of the developing forebrain. The first division within the telencephalon splits it into the ventral and dorsal divisions, or the subpallial and pallial regions, respectively. The pallial-subpallial boundary (PSB) separates these regions to ensure proper development of each telencephalic structure. The pallium develops into memory storage and processing centers, and the subpallium further divides into the pallidum and the olfactory bulbs, which are involved in motor coordination and scent processing, respectively. Because of the different ecological niches occupied by cichlid species, they utilize certain telencephalic structures moreso than others and because of the space constraints, telencephalic morphology reflects these preferences. Mbuna species, which feed among the rocks scraping algae, utilize their sense of smell and have large olfactory bulbs. Non-mbuna species, which feed in the water column and utilize eyesight and possibly memory for recognition of prey, have larger pallial structures. These differences in structures are observed early in development shortly after the telencephalon separates from the remainder of the forebrain. Upon formation of the PSB, placement and angle of the boundary are distinctly different in mbuna and non-mbuna species. In mbuna species compared to non-mbuna species, the PSB is shifted dorsally, allowing more tissue to be allocated to the developing olfactory bulbs. The PSB is shifted ventrally in nonmbuna species to allocate more tissue to the progenitor cells that develop into the memoryx processing center and structures that process visual input. These observed shifts in the developmental boundaries within the brain may provide insight into the evolution of structures such as the cerebral cortex.

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Density-dependent Stiffness in Petiole Biomechanics

2008-05-05 , Wilson, Christina

Morphological features of plants vary with increasing size. This relationship between different physical characteristics and size is referred to as allometry. Recently allometric research focused on plants and in particular plant leaves due to their importance in nutrient flow and gas exchange. Allometric plant research aims to enhance our understanding of the ontogeny of plants and offers a tool for ecological modeling. Previous allometric models have glanced over the influence of biomechanics on leaf form and function. This research will test if density-dependent stiffness of petioles is variable or if it scales with leaf mass. In order to test the variance of stiffness in leaf petioles, Young s modulus (E) was measured by modeling the petioles as simply loaded beams. Young s modulus was shown to vary among different species, even those of the same genus. Density-dependent stiffness varied with leaf size for some herbaceous species but not for other woody tree species. Future research should investigate the biomechanical role of a possible redistribution of structural tissue and how this rearrangement would affects petiole stiffness and overall petiole function.

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Sustained Delivery of Thermally Stabilized chABC by Lipid Microtubules

2008-05-05 , Kumar, Nathan

Our knowledge of spinal cord injury repair is broadening with the developing technology for nerve regeneration and drug delivery. In this paper we discuss the current capabilities for spinal cord repair as well as those that are in development. We develop protocols for determining the thermal stability of chondroitinase ABCI and its ability to be implanted into a microtubule-hydrogel drug delivery vehicle as well as the release profile that results from this implantation. After the use of sodium dodecyl electrophoresis, we determined that the disaccharide trehalose has the capacity to thermally stabilize our therapeutic enzyme in vitro. We also determined that the microtubules are effective for sustaining the release of our enzyme while the hydrogel is effective for localizing its effects. The deactivation profile was experimentally quantified to allow for complete diffusion of our enzyme over the course of a two-week implantation. Our thermally stabilized enzyme and drug delivery system can be used for the purpose of facilitating nerve regeneration at the site of an injury.

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Utilization of Pathway Modeling to Predict Changes in Sphingolipid Content During Granulocytic Differentiation of Retinoic Acid-induced HL60 cells

2009-05-04 , Portz, Brent James

Genomic analyses have the potential to provide insight to metabolic pathways and biomolecules that are important in cellular processes. This study used a recently developed tool (GenMAPP v2.1, www.genmapp.org adapted for the human sphingolipid biosynthesis pathway, www.sphingomap.org) to compare published gene expression data for HL60 cells, a human promyelocytic leukemia cell line, treated with retinoic acid to induce granulocytic differentiation. Based on the location and magnitude of changes in expression of genes for enzymes of sphingolipid metabolism in the context of this pathway model, granulocytic differentiation would be predicted to elevate de novo sphingolipid biosynthesis due to higher expression of serine palmitoyltransferase, with some interesting shifts in the way that the sphingoid base (sphinganine) is subsequently metabolized—such as that some may be incorporated into downstream metabolites such as ganglioside GD3. These predictions were tested and confirmed using thin layer chromatography. It is hoped this approach will help translate changes in gene expression for this pathway into a sphingolipidomic profile for the cells, and perhaps uncover interesting changes that can explain the behavior of these cells and possible therapeutic targets or biomarkers.

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Coupling the Developmental Programs of Teeth and Taste Buds in Malawi Cichlids

2009-05-04 , MacDougall, Alexander I.

Epithelial tissue of vertebrate organisms serves as the interface between them and the immediate environment with which they interact. Transformation of this outer tissue layer generates specialized structures that allow organisms to make enhanced or entirely new interactions with its ecological niche. This study examines two structures derived from the oropharyngeal cavity epithelium: teeth and taste buds. Using cichlids from Lake Malawi in eastern Africa as a model, this study seeks to show the co-evolutionary relationship that likely exists between teeth and taste buds. Based on the observations that both teeth and taste buds are derived from the epithelium, are colocalized sensory organs within the oropharyngeal cavity, have very similar structures in early development, and share certain patterns in gene expression, we hypothesize that the gene networks governing tooth and taste bud development are similar. Through comparative morphology and molecular developmental biology, this study shows that both teeth and taste buds share similarities of gene expression in both spatial and temporal patterns.

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Rotifer Ecotoxicology: Behavioral Avoidance of Toxicants

2008-05-05 , Weigel, Emily G.

Previous rotifer ecotoxicology studies have shown varied effects of sublethal concentrations of hormones and metals on species but have largely ignored toxicant effects on behavior. Given the importance of chemical cues for mating, grazing, and predator avoidance, the phenomenon of behavioral response to pollutants is a critical topic impacting rotifer survival and reproduction. Dual- and tri-chamber test slides similar to Y-tubes were developed to test rotifer behavioral responses to sublethal concentrations of several toxicants. Rotifers were placed in a start chamber between a control chamber and test chamber containing a toxicant, and after fifteen minutes, rotifer distribution in all chambers was recorded. No significant distributional effects were observed for cadmium (2μg/L), pentochlorophenol (2μg/L), flutamide (8μg/L) nor progesterone (8μg/L). Significant deviation from a random distribution was recorded for selenium (2μg/L), lead (8μg/L), and rotifer conditioned medium. In addition, significant avoidance was found for copper (2μg/L) and mercury (0.2μg/L), even in tests with the start chamber containing the toxicant. These data suggest that rotifers can detect and avoid certain toxicants at sublethal levels. Avoidance often occurs at levels below published lethal concentrations (LC50s) on which many water quality criteria are based. Avoidance can alter rotifer survival and reproduction, leading to reductions in rotifer abundance and energy transfer to higher trophic levels.

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The importance of nitrogen fixation to the nitrogen budget of the North Atlantic Ocean

2009-05-04 , Hall, Madison

Samples of seawater and suspended particles in the mixed layer (top 100m) were collected on Seward Johnson cruises SJ9603, SJ9612, and SJ0005 to the tropical and subtropical North Atlantic Ocean. Deep-water nitrate has been proposed to provide most nitrogen to the upper water column of the North Atlantic Ocean. Recent evidence has shown that N2 fixation is plays a significant role in supplying nitrogen for new production. The ratio of 15N: 14N, referred to as δ15N, provides a useful tracer for identifying major sources to new nitrogen in the upper water column. Persistently low δ15N values coupled with high N* values imply a large contribution of N2 fixation, with 83 of 85 stations suggesting some contribution of N2 fixation. The highest levels of diazotrophic contribution were recorded in the southwestern tropical Atlantic Ocean, where a large bloom of the N2 fixing diatom/ cyanobacterial association Hemiaulus/ Richelia association in addition to the N2 fixing cyanobacterium Trichodesmium was previously recorded. The isotopic data, N* data, and diazotrophic contribution estimates show N2 fixation is making a significant contribution to the nitrogen budget of the nutrient-poor North Atlantic Ocean.

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Lateral gene transfer of pandemic Vibrio parahaemolyticus genomic island genes

2008-12-15 , Silberger, Daniel James

Vibrio parahaemolyticus is an emerging enteric pathogen. The O3:K6 serotype has become pandemic, and the genome has been sequenced for the RIMD2210633 strain of this serotype (20). The thermostabile direct hemolysin (tdh), thermostabile related hemolysin (trh), and two distinct Type III Secretion Systems (T3SS) have been implicated in virulence. Deletion studies have determined that the T3SS alone are sufficient to induce eukaryotic cell apoptosis. The T3SS loci are found within two separate genomic islands. Because genomic islands are known to be disseminated by Lateral Gene Transfer (LGT), we examined the distribution of the pandemic genomic island genes among clinical and environmental V. parahaemolyticus isolates and also among closely-related environmental Vibrio spp. using primers designed to amplify hemolysins and T3SS effectors previously characterized for V. parahaemolyticus strain RIMD2210633 (23). We also examined the distribution of a hypothetical bacteriocin, encoded by vpa1263, within another genomic island that is similar to the bacteriocins produced by Escherichia coli. Preliminary screens for the bacteriocin gene suggest that many clinical strains and some environmental strains contain vpa1263. PCR screens for the T3SS effector genes have shown that 22% of closely-related environmental Vibrio spp. contain at least one T3SS1 or one T3SS2 effector gene. Sequencing of housekeeping genes is ongoing to confirm these findings.

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Förster Resonance Energy Transfer and Fluorescence Quenching Based Low-density Lipoprotein Probes for Visualizing Transcytosis

2008-05-05 , Fay, Nicole C.

Transcytosis is the process by which macromolecules are transported across a polarized cell. It is one of the main methods of nutrient absorption from the blood stream as well as the only means past the blood brain barrier. Insight into the transcytic route has enormous medical potential where drug delivery methods stand to be significantly optimized. Despite the importance of this fundamental biological process, the mechanism of transcytosis is not well understood. Previously, fluorescence microscopy has allowed the tracking of fluorescently labeled low-density lipoprotein (LDL) intracellularly. However, this labeled LDL is not able to distinguish LDL particles undergoing transcytosis versus degradation. LDL is an ideal cargo for observing intracellular processes due to its vital role in transporting cholesterol for cell membrane fluidity. In order to differentiate transcytosis from degradation, I have produced two probes sensitive to degradation. The two probes are based on the principles of 1.) Förster resonance energy transfer (FRET) and 2.) fluorescence quenching. LDL degradation of the FRET-based or the fluorescence-quenching-based probe results in a significant increase in fluorescent activity. I have used several methods to assess the functionality of these probes including fluorescence measurements of detergent and enzyme degradations, SDS-PAGE analysis of degradations, and in vivo flow cytometry. Additionally, I have optimized the growth conditions for maintaining polarity in a cell line (MDCK) known to undergo transcytosis. The time and location of LDL degradation in a cell can be resolved through the use of these probes. Future work includes single-particle tracking of LDL as it is being degraded versus actively transcytosing across a cell layer. This process is critical to understanding transcytosis as well as LDL regulation in the human body.

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