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ItemNanoparticle-mediated r-depression in the rotifer Brachionus manjavacas(Georgia Institute of Technology, 2009-12) Hicks, DanielNanotechnology 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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ItemUtilization of Pathway Modeling to Predict Changes in Sphingolipid Content During Granulocytic Differentiation of Retinoic Acid-induced HL60 cells(Georgia Institute of Technology, 2009-05-04) Portz, Brent JamesGenomic 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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ItemThe importance of nitrogen fixation to the nitrogen budget of the North Atlantic Ocean(Georgia Institute of Technology, 2009-05-04) Hall, MadisonSamples 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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ItemGenetic Mechanisms of Telencephalon Diversification Through Shifts in the Pallial-Subpallial Boundary(Georgia Institute of Technology, 2009-05-04) Rich, Constance AnneThe 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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ItemCoupling the Developmental Programs of Teeth and Taste Buds in Malawi Cichlids(Georgia Institute of Technology, 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.