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Axons are long projections of nerve cells that conduct electrical impulses or action potentials; they are of interest, as an understanding of their dynamics would allow clarification of neural communication. The purpose of this study is to quantify the effects of axonal structural properties on the speed and propagation of action potentials across different brain structures. Based on previous experimental evidence we hypothesize that the diameter distribution of axons in different regions of the brain follows a power-law distribution. This would suggest that synchronously generated action potentials in an axonal bundle could widely desynchronize over long distances, thus affecting coordinated transmission of synaptic information. We are currently studying the effects of different properties such as delays and neural network size on the distribution of action potential propagation velocities by using computer-based models of integrate-and-fire neurons using MATLAB. In order to enhance our data, we have compiled our MATLAB file and are now running more and faster simulations. Subsequently, we intend to test for a power-law emergence by using our models and other scientific data from the literature to link the effects of different delay times with the effects of the diameter distribution of axons on action potential propagation velocities.
LIPOPOLYSACCHARIDE-MEMBRANE INTERACTIONS EXPLORED USING LIPID BILAYER ASSEMBLIESKirstie Swingle1, Gabriel Montano2.
University of New Mexico, Albuquerque, NM, 2Center for Integrated Nanotechnologies, Los Alamos National 1 Laboratory, Los Alamos, NM.
Lipopolysaccharides (LPS) are found in the outer membrane of Gram-negative bacteria and provide stability for the bacteria. LPS is also known to be an endotoxin that can penetrate human cells and induce responses such as toxic shock, which can result in death. Understanding the mechanism of LPS interaction with membranes is crucial in making advances in understanding such pathogenic effects and developing therapeutics. Lipid bilayer assemblies (LBA) can be used as model systems for investigating membrane interactions and responses. In this study, lipid bilayer assemblies were formed using lipids of varying properties and LPS from different species were introduced.
Different ion concentrations (i.e., Ca2+ and Na+) in the presence of LPS were also screened to evaluate LPSmembrane interaction as a result of electrostatic conditions. Depending on LPS, lipid, and environment, a variety of membrane responses were observed such as lipid tubule formation, holes in the lipid bilayer assembly or formation of lamellar sheets that appeared to be mobile. These results indicate that a number and combination of conditions can
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impact the mechanism of LPS-membrane interaction and are under continued exploration. A detailed understanding of such interactions will allow for refined mechanisms of LPS interaction for the biomedical community and aid in design of therapeutics and biosensor design. The results also indicate promise in using LPS in soft-lithography approaches for biomaterials design and are also being explored as such.
EFFECTS OF HIGH CARBON CONCENTRATIONS ON MARINE MICROBIAL COMMUNITIESAmy Duarte1, and Jude Apple2.
Humboldt State University, Arcata, CA, 2Western Washington University, Anacortes, WA.
1 Heterotrophic bacterioplankton are the most abundant microorganism in the ocean and play a major role in global carbon cycling. Heterotrophic microbes consume most of the organic matter in the marine ecosystem and dictate the extent to which CO2 is absorbed or released by the oceans. Despite their importance in ocean carbon cycling, we currently lack an understanding of how heterotrophic microbes will change with ocean acidification. This research aims to determine the response of microbial communities to increased carbon supply. Respiration rates of surface and deep ocean microbes from the Rosario Strait were measured. By supplementing these microbes with different carbon concentrations and comparing respiration rates, we were able to determine the dissolved oxygen consumed and ultimately the CO2 respired. We hypothesize that deep ocean microbes are carbon limited and predict that deep ocean microbial respiration rates will dramatically increase with the introduction of carbon sources while respiration of surface microbes will remain relatively the same. This work will provide valuable insight on microbial response to climate change and more accurate marine food web and earth system modeling.
THE ROLE OF AIRE EXPRESSING CELLS IN SHAPING THE REPERTOIRE OF THYMIC REGULATORY T-CELLRECEPTORS Anael Rizzo, Maria Mouchess.
Diabetes Center, University Of California San Francisco, San Francisco, CA.
The T cell repertoire (variation) in T cell receptors (TCRs) is shaped by the interactions between antigen presenting cells and T cells in the thymus. Regulatory T cells (Tregs) are one type of T cell that plays a vital role in preventing autoimmunity through suppression of autoreactive T cells (non-Tregs). Dysfunctional Tregs can lead to a vast number of autoimmune diseases. Medullary thymic epithelial cells (mTECs) are among these thymic antigen-presenting cells that influence the TCR repertoire. mTECs lead to the deletion of autoreactive T-cells through their unique ability to express the autoimmune regulator (Aire), which allows them to upregulate the expression of tissue-specific antigens (i.e., insulin) and thus delete autoreactive T cells. Although Aire expressing cells are important for deletion of self-reactive T cells, the question of their influence in specifically shaping the repertoire of thymic regulatory T cells still remains. We hypothesize that mTECs shape the repertoire of Treg TCRs. To test our hypothesis, we have taken AIRE-DTR transgenic mice, and administered diphtheria toxin to selectively delete Aire-expressing cells.
This approach allowed us to look at the influence of mTECs on Tregs. After isolating Tregs and non-Tregs from DTR- and DTR+ mice, we obtained DNA to sequence the TCR receptors from each pool of T cells. Analysis of the sequences using IMGT software allowed us to determine the CDR3 region of the thymic regulatory T cell receptor.
Upon repertoire analysis, our data suggests that mTECs play a role in influencing the development of Tregs and also influencing the decision of the type of T cell that is made.
CHARACTERIZATION OF TISSUE-SPECIFIC EXPRESSION OF NDI1 IN LONG-LIVED DROSOPHILA
MELANOGASTERJacqueline Graniel, Jae Hur, David Walker.
University of California, Los Angeles, Los Angeles, CA.
As organisms age, mitochondrial activity is reduced, which is thought to be a major cause of aging. Previous studies have shown that the alternative internal NADH-ubiquinone oxidoreductase (ndi1), a yeast gene that can functionally substitute for some complex I functions of the electron transport chain in metazoans, can increase mitochondrial activity in Drosophila melanogaster and extend life when expressed in neurons. Dietary restriction (DR), reduced fertility, and beneficial bacteria have been correlated with lifespan extension and we set out to determine if the mechanisms involved in ndi1-mediated lifespan extension overlap with these paradigms. We examined the influence of tissue-specific ndi1 expression on lifespan, feeding behavior, fertility, and gut flora. We show that ndi1 flies live
ARSENATE RESPIRATORY REDUCTASE: BIOMARKER FOR DETECTION OF ENVIRONMENTAL THREATLirianys Figueroa-Vélez1, José R. Pérez-Jiménez2.
Universidad del Turabo, Gurabo, PR, 2Puerto Rico Institute for Microbial Ecology Research, Universidad del Turabo, 1 Gurabo, PR.
Arsenic is a toxic element found in nature which affects human health by causing different types of cancer, neurological, and skin disorders. Arsenic is an odorless, colorless, and tasteless toxin capable of being dissolved in water. For these reasons, arsenic species are almost impossible to detect when present in food, water, and gasses.
Recent discoveries have shown that some bacteria can transform arsenic species into more toxic compounds through reductive mechanisms. Dissimilatory arsenate-reducing prokaryotes, DARPs, respire arsenate, mobilizing arsenic into water.The non-Firmicutes DARPs represent several phyla inChrysiogenes arsenatis, Geobacter uraniireducens, Alkalilimnicola, Bacillus, Halanaerobiaceaesp. strain SLAS-1, Sulfurospirillum arsenophilum,Shewanella sp. ANA-3, and Wolinella succinogenes. Our goal is to strengthen screening tools with a new method in order to examine the prevalence and diversity of DARPs in nature through the employment of bioinformatics analyses. The prevalence of DARPs in nature is being assessed by the presence of the arrA gene among microbial genomes. The arrA gene from Sulfurospirillum barnesii was subjected to blast analyses among 1470 non-Firmicutes genomes. So far, the highest homology was found for three genomes: 71% for Wolinella succinogenes, 74% for Shewanella putrefaciens, and 74% for Shewanella sp. ANA-3. Shewanella species demonstrated large centers of divergence in the middle, about 80% coverage. Less homology was detected at nucleotide level than the amino acid sequence. The arrA genes are highly divergent to find sites that flank central islands of difference to support a new detection method. Conserved sequences are useful biomarkers to ascertain prokaryotes capable of arsenate respiration; this will allow us to monitor the risk of arsenate mobilization in nature.
DRUG STUDIES: AGED-RELATED HEARING CHANGES INDUCED BY D-GALACTOSECharneka Hopkins1, Julie Luna2, Aravindakshan Parthasarathy3, Edward Bartlett3.
Rust College, Chicago, IL, 2University of Puerto Rico in Aguadilla, Aguadilla, PR, 3Purdue University, West Lafayette, 1 IN.
Age-related hearing loss may be caused by deficits in both peripheral (cochlear) and central auditory structures.
Deficiency in either peripheral or central auditory pathways makes it difficult to hear and process sound stimuli. These deficiencies can be caused by oxidative stress or other cellular damage. D-galactose has been shown to induce oxidative stress and cause changes in auditory brainstem responses in young animals. The aim of this study was to investigate whether D-galactose serves as a reasonable aging model that can induce changes in sustained responses to sound in young rats. Eight young (3-5 months old) rats were injected subcutaneously with D-galactose for multiple weeks. Auditory, evoked responses were compared to naturally aged rats using three evoked potential tests: the auditory brainstem responses (ABRs), middle latency responses (MLRs), and frequency following responses (FFRs) obtained from both groups of rats using subdermal needle electrodes. ABRs to brief click and tone pips measured peripheral sensitivity by measuring the threshold sound level to evoke ABRs. MLRs measure the thalamocortical responses to brief sounds, and FFRs measure sustained auditory processing in central brainstem and mid-brain nuclei. The stimuli consisted of sinusoidally amplitude modulated tones with the same carrier frequency but different modulation frequencies. If D-galactose serves as a reasonable aging model for hearing we expect to see a delay in ABR responses and/or FFR responses similar to those found in naturally aged animals.
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DESIGN OF AN INFRARED FLUORESCENT PROTEIN MARKER FOR IN VIVO IMAGING IN MAMMALSAlexandra Cabanov1, Stephanie Puetz1, Jacqueline Meraz1, Angela E. Varela1, Anna Baker1, John T. M. Kennis2, Aaron Schirmer1 and Emina A. Stojkovic1.
Northeastern Illinois University, Chicago, IL, 2Vrije Universiteit, Amsterdam, NL.
1 The fluorescent signal in the infrared (IR) range has minimal absorption by hemoglobin and water making it optimal for in vivo imaging in mammals. Bacteriophytochromes (BphPs), bacterial red-light photoreceptors, have been engineered as infrared fluorescent proteins (IFPs) and used as liver markers in mouse models. BphP photochemistry depends on biliverdin (BV), an organic cofactor naturally abundant in mammals as a by-product of heme metabolism.
Our goal is to develop an IFP marker using the naturally fluorescent RpBphP3 (P3) from Rhodopseudomonas palustris. P3 in tandem with classical RpBphP2 (P2) modulates the synthesis of light-harvesting complexes in R.
palustris. P2 and P3 share a 52% amino acid sequence identity and bind the same BV chromophore, yet they have different photochemistry. P2 was recently engineered as an IFP, but has a fluorescence quantum yield of less than 10%. To optimize the naturally fluorescent P3 as an IFP, we conducted comparative sequence and structural analyses of homologous BphPs. A highly conserved Asp (D216), found in the PASDIP motif, is essential for stabilization of BV in the chromophore-binding domain. Using site-directed mutagenesis we introduced single point mutations, Asp216His or Asp216Thr, effectively disrupting the photochemistry of P3. Both mutants were cloned into the mammalian expression vector, Adtrack-CMV, and expressed in HeLa cells. Preliminary results include the in vitro characterization and comparison of the P3 Asp216His and Asp216Thr mutants with the P2-derived IFP. Subsequent research goals include further optimization of P3-derived IFP through secondary mutations on the Asp216His and/or Asp216Thr templates to improve fluorescence quantum yield.
MOLECULAR CHARACTERIZATION OF IRON STRESS RESPONSE IN SOYBEANLeorrie Atencio1, Adrienne Moran Lauter2, Michelle Graham2.
Northern New Mexico College, Espanola, NM, 2Corn Insects and Crop Genetics Research Unit, USDA-ARS, Ames, IA.