Biology Commons^™

Effects Of Trophic Relationships On Oyster Reef Restoration Success In The Mississippi Sound, Virginia Robin Fleer

Dissertations

Natural and anthropogenic changes resulting from altered hydrology, hurricanes, variable precipitation, and the BP oil spill have all taken their toll on oyster reefs in Mississippi. In response, oyster reef restoration efforts are currently underway within the Northern Gulf of Mexico. In order to understand why these efforts succeed or fail, it is crucial to consider predator-prey relationships within the context of the trophic dynamics of oyster reefs. Thus, for this dissertation study I integrated a multidisciplinary approach to understanding key trophic interactions affecting oyster recruitment, growth and survival, comprising field sampling, manipulative lab experiments, and individual-based modeling. Spat settlement …

Ecological And Oceanographic Influences On Leatherback Turtle Behavior And Scyphozoan Jellyfish Distributions In The Gulf Of Mexico, Katrina Aleksa

Dissertations

Leatherback turtles (Dermochelys coriacea) are a wide-ranging, oceanic species that feed exclusively on gelatinous zooplankton. Leatherback have been spotted in the Gulf of Mexico (GoM) for several decades and consistently had a high level of interactions with longline fisheries. However, no quantitative studies have been performed to address the spatiotemporal distribution of these turtles in the GoM. This research determines 1) leatherback movements and high-use areas in the GoM, 2) their association with oceanographic features, 3) the distribution and density of two abundant medusae in the northern GoM and any association with biophysical parameters, and 4) the body …

Achilles Is A Circadian Clock-Controlled Gene That Regulates The Immune System And Its Rhythmicity In Drosophila, Jiajia Li

Dissertations

Circadian clock is a transcriptional/translational feedback loop that drives the rhythmic expression of downstream mRNAs. Termed “clock-controlled genes,” these molecular outputs of the circadian clock orchestrate cellular, metabolic, and behavioral rhythms. As part of our on-going work to characterize key upstream regulators of circadian mRNA expression, we have identified a novel clock-controlled gene in Drosophila melanogaster, Achilles (Achl), which is rhythmic at the mRNA level in the brain and represses expression of immune response genes, especially anti-microbial peptides in the immune system. Achl knock-down in the brain dramatically elevates expression of crucial immune response genes, including IM1 …

Regulation Of Voltage-Gated K+ Currents In Motor Neurons: Activity-Dependence And Neuromodulation, Dalia Salloum

Dissertations

Neuronal output is shaped by extrinsic modulation as well as modulation of intrinsic properties of individual neurons, mediated by activity-dependent changes in the expression levels of voltage-gated ionic currents. Activity-dependent regulation of ionic currents is a mechanism by which electrical output of a neuron feeds back onto the expression of its own ion channels to alter cellular excitability in response to stimuli. Neurons alter their intrinsic properties to achieve long lasting changes involved in development, learning and memory formation and vital functions of organ systems such as locomotion and digestion. At the same time, plasticity of neuronal excitability driven by …

Biophysical Mechanisms Of Frequency-Dependence And Its Neuromodulation In Neurons In Oscillatory Networks, David Michael Fox

Dissertations

In response to oscillatory input, many isolated neurons exhibit a preferred frequency response in their voltage amplitude and phase shift. Membrane potential resonance (MPR), a maximum amplitude in a neuron’s input impedance at a non-zero frequency, captures the essential subthreshold properties of a neuron, which may provide a coordinating mechanism for organizing the activity of oscillatory neuronal networks around a given frequency. In the pyloric central pattern generator network of the crab Cancer borealis, for example, the pacemaker group pyloric dilator neurons show MPR at a frequency that is correlated with the network frequency. This dissertation uses the crab …

Evolution Of Caffeine Biosynthetic Enzymes And Pathways In Flowering Plants, Ruiqi Huang

Dissertations

Convergent evolution generally refers to the independent evolution of similar biological function more than once in unrelated species. Caffeine is thought to have evolved by convergence, and is naturally produced through secondary metabolism in plants to defend against pathogen attack and insect feeding or to attract pollinators. The same caffeine biosynthetic pathway has been elucidated in Camellia (tea) and Coffea (coffee), in which xanthosine is sequentially methylated to caffeine via 7-methylxanthine and theobromine. However, although the same catalysis pathway is used, different (paralogous) enzymes in the SAMT/BAMT/theobromine synthase (SABATH) multigene family are used in the two species. In my dissertation, …

An Ecological Examination Of Johnson Bayou (Pass Christian, Ms) With A Reproductive Histological Analysis Of Rangia Cuneata, And A Comparative Morphological Study Of The Foot And Shell Of Rangia Cuneata And Polymesoda Caroliniana, Brandon Drescher

Dissertations

Johnson Bayou is an estuarine system located in Pass Christian, MS. Research involved a biotic and abiotic examination of Johnson Bayou, resulting in the identification of numerous species of plants and animals, including Rangia cuneata (Mactridae) and Polymesoda caroliniana (Cyrenidae), sympatric species of infaunal bivalves. Environmental factors (e.g., water temperature, salinity) were measured over three years to describe the system from an abiotic standpoint, and used in a qualitative and quantitative reproductive histological study on R. cuneata. Results revealed differences in timing of gamete production and spawning between three subpopulations of this species. Sediment samples taken from the study …

Solution Of Pdes For First-Order Photobleaching Kinetics Using Krylov Subspace Spectral Methods, Somayyeh Sheikholeslami

Dissertations

We solve the first order reaction-diffusion equations which describe binding-diffusion kinetics using a photobleaching scanning profile of a confocal laser scanning microscope approximated by a Gaussian laser profile. We show how to solve these equations with prebleach steady-state initial conditions using a time-domain method known as a Krylov Subspace Spectral (KSS) method. KSS methods are explicit methods for solving time- dependent variable-coefficient partial differential equations (PDEs). KSS methods are advantageous compared to other methods because of their stability and their superior scalability. These advantages are obtained by applying Gaussian quadrature rules in the spectral domain developed by Golub and Meurant. …

Oncolytic Tanapoxvirus For Melanoma Therapy, Tiantian Zhang

Dissertations

Oncolytic viruses (OVs), which preferentially infect cancer cells and induce host anti- tumor immune responses, have emerged as an effective melanoma therapy. Tanapoxvirus (TPV), which possesses a large genome and causes mild self-limiting disease in humans, is potentially an ideal OV candidate. The purposes of our studies are to engineer TPV into effective OVs via arming immumo-stimulatory proteins and/or manipulating the virokines, and to explore the immuno-modulatory activities of TPV.

Interleukin-2 (IL-2) plays a critical role in activating T cells, natural killer cells and macrophages in both the innate and adaptive immune systems. In our study, a recombinant TPV expressing …

Regulation Of Mtorc1 By Homocysteine And Its Effects On Autophagy In Human And Mouse Neuronal Tissues, Khoosheh Khayati

Dissertations

The molecular mechanisms leading to and responsible for age-related, sporadic Alzheimer’s disease (AD) remain largely unknown. It is well documented that aging patients with elevated levels of the amino acid metabolite homocysteine (Hcy) are at high risk of developing AD. The impact of Hcy on molecular clearance pathways in mammalian cells, including in-vitro cultured induced pluripotent stem cell-derived forebrain neurons and in-vivo neurons in mouse brains is investigated in this research project. Exposure to high Hcy levels results in up-regulation of the mechanistic target of rapamycin complex 1 (mTORC1) activity, one of the major kinases in cells that is tightly …

In Vivo Characterization Of The Drosophila Mrna 3’-End Processing Core Cleavage Complex: Poly(A) Mrna & Histone Mrna 3’-End Processing, Daniel Michalski

Dissertations

A core cleavage complex (CCC) consisting of CPSF73, CPSF100 and Symplekin is required for co-transcriptional 3’ end processing of all metazoan pre-mRNAs, yet little is known about the in vivo molecular interactions within this complex. The CCC is a component of two distinct complexes, the cleavage/polyadenylation complex and the complex that processes non-polyadenylated histone pre-mRNAs. RNAi-depletion of CCC factors in Drosophila culture cells causes reduction of CCC processing activity on histone mRNAs, resulting in read through transcription. In contrast, RNAi-depletion of factors only required for histone mRNA processing allows use of downstream cryptic polyadenylation signals to produce polyadenylated histone mRNAs. …

The Role Of Notch-1-Mediated Repression Of Pten On Growth And Cancer Stem Cell Survival In Trastuzumab Resistant, Her2+ Breast Cancer, Andrew Thomas Baker

Dissertations

Trastuzumab targets the ErbB2 (HER2) receptor on breast cancer cells to attenuate HER2 driven tumor formation. Trastuzumab reduces both downstream PI3K/Akt and MAPK pathway signaling as well as the breast cancer stem cell (BCSC) population. BCSCs are hypothesized to be responsible for tumor recurrence, metastasis, as well as drug resistance. Today, resistance to trastuzumab remains a major clinical problem for women diagnosed with HER2+ breast cancer. Attenuation of PI3K/Akt and MAPK pathways may occur through the tumor suppressor, PTEN. Women with HER2+ breast tumors expressing less PTEN and increased PI3K/Akt or MAPK activity have worse overall outcome. Previously we have …