Showing 1 - 50 of 67 Items

Date: 2013-05-01

Creator: Patrick J Lariviere

Access: Access restricted to the Bowdoin Community

Date: 2022-01-01

Creator: Devaki Rajiv

Access: Open access

The binding of adjacent cells to one another, or cell adhesion, is critical for the growth and development of multicellular organisms. In plant cells, much evidence suggests that the amount and modification of pectin in the cell wall largely determines how well cell adhesion occurs. ELMO1 is a Golgi protein involved in pectin-mediated cellular adhesion, and mutations in ELMO1 lead to disrupted cell organization in Arabidopsis. ELMO1 is predicted to be a scaffold for pectin biosynthesis enzymes, and thus its absence leads to the adhesion-defective phenotype of elmo1-/- plants. There are four other ELMO homologues (ELMO2,3,4 and 5) which remain to be characterized as to their function and role in cell adhesion. This thesis focuses on the characterization of ELMO2, which has 79% amino acid similarity with ELMO1. A genetic analysis that evaluated elmo2 double mutants revealed that ELMO2 and ELMO1 have redundant functions. elmo1-/-/2-/- double mutants, but not elmo2-/- or elmo1-/- single mutants, have reduced tensile strengths. While elmo1-/- phenotypes are most pronounced in liquid media, they are partially rescued by growth on agar, suggesting a role of turgor in maintaining cell adhesion. Like ELMO1, ELMO2-GFP colocalizes with Golgi markers. The results suggest that like ELMO1, ELMO2 also functions as a scaffold for pectin biosynthesis enzymes in the Golgi.

Date: 2023-01-01

Creator: Katharine Barrett

Access: Access restricted to the Bowdoin Community

• Embargo End Date: 2026-05-20

Date: 2021-01-01

Creator: Jialin Xie

Access: Embargoed

• Restriction End Date: 2029-06-01

Date: 2024-01-01

Creator: Olivia Sewon Choi

Access: Access restricted to the Bowdoin Community

Date: 2023-01-01

Creator: Isabella de la Luz Quintana

Access: Access restricted to the Bowdoin Community

• Restriction End Date: 2027-06-01

Date: 2022-01-01

Creator: Phuong Luong

Access: Access restricted to the Bowdoin Community

Date: 2015-05-01

Creator: Jaepil E Yoon

Access: Open access

Date: 2017-05-01

Creator: Arman Ashrafi

Access: Access restricted to the Bowdoin Community

Date: 2024-01-01

Creator: Sophia Elisabeth Nigrovic

Access: Access restricted to the Bowdoin Community

Date: 2021-01-01

Creator: Bethany J. Thach

Access: Open access

The eya gene is essential to development of the Drosophila visual system and eye-specific loss of function mutations in the gene commonly result in the missing eye phenotype. The eya2m35g mutation carries a deletion of exon 1B and adjacent regulatory sequences. Flies carrying the eya2m35g allele exhibit a photoreceptor axon phenotype that has not previously been associated with the eya gene. To determine a potential role for eya in photoreceptor axon targeting, I characterized various phenotypes of eya2m35g mutants and generated additional eya alleles consisting of smaller deletions within the eya2m35g mutation to locate the genetic source of axonal disruption. Using immunofluorescence staining to visualize Eya protein, I found a loss of eya expression in the optic lobe region of eya2m35g stage 9 embryos and third instar larvae. I also observed a loss of retinal basal glial (RBG) cells in the larval eye disc. Finally, I demonstrated that the disconnected axon phenotype is generated when a region of the intron immediately downstream of exon 1B is deleted. These findings suggest that a possible regulatory element for eya that is essential for photoreceptor axon targeting exists in this intronic region.

• Embargo End Date: 2027-05-19

Date: 2022-01-01

Creator: Usira Ahmed Ali

Access: Embargoed

• Restriction End Date: 2026-06-01

Date: 2021-01-01

Creator: Nicholas J. Purchase

Access: Access restricted to the Bowdoin Community

Date: 2021-01-01

Creator: Kamyron Anthony Speller

Access: Open access

Pharmaceuticals and personal care products (PPCPs) are contaminating natural bodies of water and are problematic for aquatic organisms and ecosystems. Generally, PPCPs are introduced to water systems due to incomplete removal by wastewater treatment plants (WWTPs). As such, it is vital to find ways to remediate these problematic contaminants before they are discharged into the environment. In this study, two photocatalysts¾titanium dioxide (TiO2) and bismuth oxychloride (BiOCl)¾were compared to determine their relative efficiencies (degradation rates) and dominant degradation mechanism (hydroxyl radical production or direct oxidation) with the goal of photocatalytically degrading two pharmaceuticals, atenolol and ibuprofen, using UV (254 nm) light. While TiO2 has been used extensively for photocatalytic degradation, BiOCl is a newer photocatalyst. The two pharmaceuticals selected for study represent two large classes of drugs (aryloxypropanolamine and propionic acid derivatives, respectively) that have been detected in the influent into and effluent from wastewater treatment plants and in the environment. When irradiated at 254 nm, BiOCl degrades ibuprofen with a rate constant 15 times greater than TiO2. On the other hand, TiO2 degrades atenolol with a rate constant 2.2 times greater than BiOCl. LCMS analysis of photodegradation products reveals different products produced by the two photocatalysts, providing evidence for the dominance of different degradation mechanisms for the two photocatalysts. In summary, this work suggests that BiOCl, potentially used in combination with TiO2, holds potential for degrading PPCPs in natural bodies of water.

Date: 2021-01-01

Creator: Alicia G. Edwards

Access: Open access

The adult auditory system of the cricket, Gryllus bimaculatus, exhibits a rare example of neuronal plasticity. Upon deafferentation, we observe medial dendrites that normally respect the midline of the PTG in the central nervous system sprouting across the boundary and forming synaptic connections with the contralateral auditory afferents. The Horch Lab has investigated key molecular factors that might play a causal role in this paradigm. Specifically, the protein Sema1a.2 comes from a guidance molecule family and has a role in developmental neuronal plasticity in other organisms. In this study, I explored the role of Sema1a.2 in the neuronal plasticity of the adult auditory system of the cricket by conducting a series of dsRNA knockdown experiments targeting Sema1a.2 followed by backfill procedures in which we iontophoresed dye into the Ascending Neurons (ANs) to visualize the anatomical effects of the knockdown experiments using confocal microscopy. We found that there were no significant differences between animals injected with dsRNA against GFP and Sema1a.2 volume, with respect to qualitative and quantitative data. However, we believe with an increase in cohort size, the trends observed, particularly the effect of Sema1a.2 knockdowns on CWM and CBM volumes, will become more pronounced and significant. Potential future pathways could include conducting double knockdowns of Sema1a.2 and Sema2a to observe if these two proteins are working together to create a more obvious effect on midline crossing and branching. Other options also include looking into other protein families that might be the causing factor in this rare phenomenon (toll-like receptors).

Date: 2024-01-01

Creator: Daniel Chi

Access: Access restricted to the Bowdoin Community

Date: 2024-01-01

Creator: Maryam Akramova

Access: Open access

The main cause of the ongoing global climate crisis is the emission of greenhouse gases, and current climate reports emphasize the need to transition to low-emission renewable energy sources. Urgently needed are methods for storing renewable energy, such as synthetic fuels like hydrogen (H2) gas; however, a challenge to the widespread implementation of hydrogen fuel is its low volumetric energy density. This thesis describes an effort to synthesize a catalyst that takes advantage of hard-soft acid-base (HSAB) mismatches to activate H2 and facilitate its reaction with CO2 to form hydrocarbon fuels, thereby providing a sustainable means of storing renewable energy in high-density carbon-neutral fuels. The catalyst design features an exceptionally bulky N-heterocyclic carbene (NHC) ligand known as IPr** (3-Bis[2,6-bis[bis(4-tert-butylphenyl)methyl]-4-methylphenyl]-1H-imidazol-3-ium chloride), a coinage metal acting as a soft acid, and a hard base such as an alkoxide ion. Herein is reported a modified synthetic route of IPr**, along with its metalation with silver, and preliminary results of the addition of an alkoxide base. The ligand and its complex with silver are structurally characterized by nuclear magnetic resonance (NMR) spectroscopy. Further work is needed to complete the characterization of IPr**-supported HSAB mismatch complexes and investigate their potential to activate H2.

Date: 2019-05-01

Creator: Natasha Ann Belsky

Access: Access restricted to the Bowdoin Community

Date: 2014-05-01

Creator: Divya Hoon

Access: Access restricted to the Bowdoin Community

Date: 2022-01-01

Creator: Garrison Asper

Access: Open access

The Extracellular Matrix (ECM) between plant cells is vital for structure, development, and intercellular adhesion. A pectin rich layer in between cells, the middle lamella, is largely responsible for regulating the adhesive properties of adjacent plant cells. Homogalacturonan (HG) pectin, the most common, is synthesized in the Golgi and secreted into the ECM where it undergoes calcium crosslinking, increasing its adhesive properties. Mutations in proteins essential for HG synthesis can reveal a severe adhesion defective phenotype, where the hypocotyls of dark grown Arabidopsis exhibit cell sloughing, curling, and general disorganization. A family of five ELMO proteins are suspected to act as scaffolds for pectin biosynthesis enzymes. ELMO1 and ELMO4 mutants exhibit an adhesion deficient phenotype, and a double mutant provides evidence of redundancy in function between ELMO1 and ELMO2. ELMO1-GFP co-immunoprecipitated with enzymes required for HG synthesis indicating its role as a scaffold protein. Double mutants of the other ELMO homologues were created to determine if they exhibit functional redundancy, and ELMO1 and ELMO3 appear partially redundant. A gene deletion of ELMO3 was also created using the CRSPR/Cas9 system, resulting in two distinct elmo3 deletion alleles, which were phenotypically identical to the original elmo3-/- mutant. All adhesion defective phenotypes can be partially suppressed by altering the osmoticum and hence turgor that provides pressure on adhesive cells. Lastly, ELMO3-GFP was localized to the Golgi, the site of pectin biosynthesis, further supporting a common role of the ELMOs in pectin biosynthesis.

Date: 2021-01-01

Creator: Alejandro Garcia

Access: Open access

The negative environmental impact and the diminishing supply of fossil fuels demand a renewable alternative. Pyrolysis oils produced from the decomposition of biomass, like wood, are a potential fuel substitute for energy production and a feedstock alternative for manufacturing value-added chemicals. The possibilities offered by pyrolysis oils are offset by oil instability. The oils contain reactive compounds, such as small aldehydes, conjugated aromatics, and acids that over time react and produce higher molecular mass products. This instability manifests as an increase in viscosity by a process referred to as aging. One chemical component, coniferyl alcohol, is proposed to react with formaldehyde under the acidic oil conditions to produce a dimer. In our lab, researchers have detected the coniferyl alcohol dimer in authentic oil samples and have simulated the reaction under conditions that removes the complexity of the pyrolysis oil matrix. This study focused on the synthesis, isolation, and characterization of the dimer structure by employing NMR analysis. GC/MS analysis of a successful synthesis of the dimer showed multiple dimers were produced, but there was one principal product. The NMR analysis of this dimer was used to elucidate the geometry, providing evidence that the product has E stereochemistry for the double bond and trans stereochemistry in the acetal ring. Confirmation of the principal structure provides support for the dimerization mechanism and will allow for future research to address instability of pyrolysis oils.

Date: 2015-05-01

Creator: Joshua A Benton

Access: Access restricted to the Bowdoin Community

• Embargo End Date: 2027-05-16

Date: 2024-01-01

Creator: Joanne Du

Access: Embargoed

Date: 2024-01-01

Creator: Panhasith Ung

Access: Access restricted to the Bowdoin Community

Date: 2017-01-01

Creator: Jack Ryan Mitchell

Access: Open access

Wall associated kinases (WAKs) are cell membrane bound receptor kinases that bind pectin and pectin fragments (OGs).The binding of WAKs to pectin sends a growth signal required for cell elongation and plant development. WAKs bind OGs with higher affinity than native pectin and instead activate a stress response. Glycine rich proteins (GRPs) are secreted cell wall proteins of unknown function. Seven GRPs with 65% sequence similarity are coded on a 90kb locus of Arabidopsis chromosome 2. GRP3 and WAK1 have been shown to bind in vitro, but single null mutations have no discernible phenotype, suggesting that the GRPs are redundant. Low recombination frequency has made multiple mutations difficult to achieve, but in this thesis, CRISPR/Cas9 technology was used to induce deletions of the GRP locus. The promoters pYAO and pICU2 drove Cas9 expression in transformed Arabidopsis plants. The presence of a deletion and Cas9 were detected by PCR. While somatic mutations were induced, there was no inheritance of the GRP deletion, indicating that pYAO and pICU2 do not drive Cas9 to induce deletions in progenitor cells. LIK1 is a CERK1 interacting kinase implicated in mediating response to various microbe associated molecular patterns (MAMP) such as chitin, flagellin, and peptidoglycans. LIK1 exhibits a drastic increase in phosphorylation in response to OG treatment, making it a candidate for a co-receptor to WAK. T-DNA insertions to the 5’UTR of LIK1 were used to examine the effect of a lik1 mutation on the OG induced stress response. lik1/lik1 mutant seedlings were grown in the presence and absence of OGs, and RNA was isolated. qPCR was used on cDNA to examine FADLOX expression, a reporter for the transcriptional response to OGs. The lik1/lik1 mutant caused a reduction in the OG induced transcriptional response. However, increased LIK1 expression was associated with the T-DNA insertion indicating that LIK1 inhibits the WAK stress response pathway. Understanding the roles of GRP and LIK1 in moderating WAK mediated pathogenic response in Arabidopsis will enable a better understanding of plant resistance to pathogen invasion in the greater plant kingdom.

• Embargo End Date: 2025-05-14

Date: 2020-01-01

Creator: Jacob Dexter-Meldrum

Access: Embargoed

Date: 2021-01-01

Creator: Sheikh Omar Kunjo

Access: Access restricted to the Bowdoin Community

• Embargo End Date: 2027-05-19

Date: 2022-01-01

Creator: Yucheng Hua

Access: Embargoed

Date: 2023-01-01

Creator: Lucas John DiCerbo

Access: Access restricted to the Bowdoin Community

Date: 2024-01-01

Creator: Andre Eden

Access: Open access

During every second of a human’s life, the cardiovascular system is modulated by factors both intrinsic and extrinsic to the physiology of the heart. We can uncover new insights regarding the nature of our system through investigations of similar systems in other model species. One example materializes itself in the form of the American Lobster (Homarus americanus) whose single-chambered heart finds resemblance to the function and anatomy to that of humans. The lobster heart is powered by the cardiac ganglion (CG), a group of neurons that drive contractions of surrounding heart muscles, known as the myocardium. Both the CG and myocardium work in a feedback loop, with both intrinsic (afterload and preload) and extrinsic (temperature and neuropeptides) factors affecting cardiac output (CO) or the overall ability of the heart to carry out its primary function of nutrient distribution. In this paper, we examine how the addition of these factors into in vitro whole heart preparations affect CO and other associated variables. From experimentation, we conclude that the neuropeptide SGRNFLRFamide (SGRN) increases the heartbeat frequency and the active force exerted by the heart. We also conclude that increases in temperature decrease CO as higher temperatures decrease heartbeat frequency and the active force exerted by the heart. Lastly, we conclude that the effect of preload and afterload combined produce more robust effects on the CO and active force of the heart, potentially painting a better picture of what may happen in vivo.

Date: 2024-01-01

Creator: Devin Kathleen O’Loughlin

Access: Access restricted to the Bowdoin Community

Date: 2024-01-01

Creator: Ayanna S Hatton

Access: Open access

When photons from sunlight are absorbed by plants, they can take paths of photosynthesis, fluorescence, or energy dissipation. Instruments to quantify fluorescence have expanded in scale to allow measurements from satellites and flux towers using Solar-Induced Chlorophyll Fluorescence (SIF). Studies have found a positive correlation between SIF and gross primary productivity (GPP; representative of photosynthesis), suggesting SIF is a proxy for GPP. This conclusion encourages the use of SIF to inform decisions about carbon budgets and responding to climate change. Studies of fluorescence on the single-leaf scale have revealed that SIF measurements do not account for all variables nor is there an understanding of the impact of environmental factors, such as drought, on these measurements. In this project, tall fescue turfgrass was placed in one of four differing drought severities for 19 days. Leaf-level measurements of photosynthesis and pulse-amplitude modulated fluorescence were made, demonstrating stomatal closure and inhibition of photosynthesis. This physiological change caused greater photon allocation to energy dissipation. Changes in greenness and the utilization of photoprotective mechanisms such as senescence and anthocyanin accumulation were observed. This study has provided an understanding of the temporal, physiological, and visible impacts of drought on turfgrass to inform interpretations of SIF in future experiments. Caution is crucial in utilizing SIF as a proxy for GPP before further research into the impact of drought on SIF is completed.

Date: 2024-01-01

Creator: William Joseph Surks

Access: Access restricted to the Bowdoin Community

• Embargo End Date: 2025-05-14

Date: 2020-01-01

Creator: Zachary C. LeBlanc

Access: Embargoed

Date: 2021-01-01

Creator: Andrew James Mulholland

Access: Access restricted to the Bowdoin Community

• Restriction End Date: 2025-06-01

Date: 2020-01-01

Creator: Rebecca Londoner

Access: Access restricted to the Bowdoin Community

Date: 2020-01-01

Creator: Edward Myron Bull

Access: Open access

Neuropeptides are a class of small peptides that govern various neurological functions, and the American lobster (Homarus americanus) provides a model system for their characterization. Neuropeptides are commonly post-translationally modified (PTM), and one common PTM is glycosylation. Past research in the Stemmler lab has found glycosylated neuropeptides in H. americanus; however, the extent and biological role of this modification has not been well characterized. This study was undertaken to determine the number of glycosylated peptides in the sinus glands of H. americanus and to develop an approach to tag the site of glycosylation using beta-elimination chemistry. LC-MS paired with high pH reverse phase fractionation was used to survey for glycosylated neuropeptides and beta elimination with an amine tag was used as an approach to characterize the site of glycosylation. Our results indicate that high pH fractionation is a useful approach to simplify complex mixtures of neuropeptides and improve glycopeptide detection. Efforts to use beta elimination and tagging to characterize glycosylated neuropeptides have been less successful. Beta elimination of full length peptides resulted in peptide degradation. An approach utilizing chymotrypsin to reduce peptide size coupled with beta elimination and labeling with 2-dimethylaminoethanethiol showed less evidence for degradation, and this approach yielded data isolating two potential serine residues for the site of glycosylation; however, the data was not sufficient to distinguish the two sites. Work to optimize reaction conditions using a glycopeptide standard showed that multiple isomeric products were formed during beta elimination. With the goal of optimizing reaction conditions, future work will further examine reaction kinetics to eventually apply the approach to the entire sinus gland

Date: 2023-01-01

Creator: Emma Straw Noel

Access: Access restricted to the Bowdoin Community

Date: 2021-01-01

Creator: Ruby Chimereucheya Ahaiwe

Access: Open access

The American lobster Homarus americanus uses its innate immune system for protection against foreign bodies and diseases. Hemocytes in the innate immune system are responsible for the rapid and effective cellular response against pathogens and infections observed in lobsters. These hemocytes, particularly semi-granulocytes and granulocytes, store antimicrobial peptides (AMPs) which specifically target and destroy microbes. Hemocyte samples from the American lobster Homarus americanus hemolymph or circulatory fluid, mixed and fractionated into separated semi-granular and granular cell samples, were analyzed for possible AMP presence. A defensin AMP, Hoa-D1, (SYVRSCSSNGGDCVYRCYGNIINGACSGSRVCCRSGGGYamide; with C representing a cysteine participating in a disulfide bond) was successfully isolated and identified by mass using reversed-phase high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS/MS). Preliminary results also show the defensin AMP to be concentrated in the semi-granulocytes and granulocytes.Hoa-D1 was isolated via HPLC fractionation. Isolated Hoa-D1 and semi-granular and granular hemocyte extracts were tested for bioactivity against the gram-negative bacteria, Escherichia coli, using the Kirby-Bauer disk diffusion assay. The assay did not show any activity, an outcome attributed to concentrations of the AMP that were too low to have any antimicrobial effect on E. coli. Subsequent work on this study should involve increasing the concentration of Hoa-D1 in test samples. Studying function of AMPs in the American lobster can provide more information on the depth of their cellular immune responses in other crustaceans, and possibly contribute to the development of novel antibiotics for treating diseases in humans.

Date: 2024-01-01

Creator: Foje-Geh Robert Tendoh

Access: Access restricted to the Bowdoin Community

Date: 2025-01-01

Creator: Elisabeth C. Chan

Access: Access restricted to the Bowdoin Community

Date: 2025-01-01

Creator: Katie Lynn Rea

Access: Access restricted to the Bowdoin Community

• Restriction End Date: 2025-06-01

Date: 2020-01-01

Creator: Boris S. Dimitrov

Access: Access restricted to the Bowdoin Community

Date: 2020-01-01

Creator: Frances DeCamp Hobart Zorensky

Access: Access restricted to the Bowdoin Community

Date: 2020-01-01

Creator: Owen Templeton Tuck

Access: Access restricted to the Bowdoin Community

Date: 2021-01-01

Creator: Melissa G. Demczak

Access: Access restricted to the Bowdoin Community

• Restriction End Date: 2027-06-01

Date: 2022-01-01

Creator: Michael Christopher Dean

Access: Access restricted to the Bowdoin Community

• Embargo End Date: 2027-05-19

Date: 2022-01-01

Creator: Justin K. Yang

Access: Embargoed

• Restriction End Date: 2026-06-01

Date: 2021-01-01

Creator: Kodie R Garza

Access: Access restricted to the Bowdoin Community

Date: 2022-01-01

Creator: Adedunmola Praise Adewale

Access: Access restricted to the Bowdoin Community