Boram Hong

Reactivity of Ferrihydrite Nanoparticles

Ferrihydrite (Fe5HO8 · 4H2O) is a poorly crystalline iron oxide that typically occurs  in the 2-10 nm size range and is initially formed during precipitation of iron in soils and sediments. Ferrihydrite is metastable and serves as a precursor for transformation to more  crystalline iron oxide phases such as goethite or hematite. Using surface-area normalized rates of reduction by hydroquinone, results demonstrate that, contrary to expectation, redox reactivity increases with increasing particle size. In addition, monitoring the rate at which ferrihydrite transforms to goethite by way of transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS)  demonstrates that growth rates increase with decreasing primary nanoparticle size. Finally, combining results from TEM with those from SAXS demonstrate that the latter method is an efficient means by which the formation of goethite from ferrihydrite can be quantified.

Notch Signaling Determines Regional Specifity and Promotes Epithelial-Mesenchymal Transformation in the AV Canal During Cardiac Development

The development of cardiac valves arises from precursor structures called cardiac cushions. Following myocardial signaling, endothelial cells lining the atrioventricular region separate and populate the cell-free extracellular matrix (ECM) of the cardiac cushions in a process known as epithelial-mesenchymal transformation (EMT) which ultimately leads to the generation of valvular structures of the mature heart. Notch signaling regulates EMT by interacting with the TGFß family pathway which determines the separation and invasion steps of EMT. We suggested that Notch signaling regulates TGFßs by setting up a capability for EMT in AV canal endothelium at an early stage. This hypothesis was tested by dissecting AV canals from chicks, inhibiting Notch with DAPT and growing cultures in a collagen gel. Results were analyzed by performing RT-PCR and photographic analysis. It was found that Notch signaling establishes EMT’s localized specificity in the AV canal by strongly regulating ligands and receptors that are most critically involved in the process of invasion. Moreover, it was found that Notch inhibition has a stronger effect on AV canal markers at an earlier stage, this effect wearing off as stages advance.

Regulation of Cell Invasion in the Developing Heart by Sox E genes

Cell invasion is a fundamental process in embryological development and a component of epithelial-mesenchymal transformation (EMT). Birth defects often occur due to the perturbation of EMT, but the process itself is poorly understood. Using in vitro model of EMT during heart valve formation, the laboratory previously resolved EMT in two steps, activation and invasion. Activation is characterized by the expression of the transcription factor slug. Although it has been argued that slug is sufficient to regulate EMT, it appears that the second step of EMT, cell invasion, requires further gene transcription. Overexpression of Sox E genes in neural tubes of embryos appears to produce increased delamination of neural crest cells in neural crest cell forming regions. This suggests that these transcription factors, that are normally expressed in the heart at the time of EMT, but have not been investigated, could be central mediators of embryonic cell invasion. The purpose of this study is to determine whether a loss of one or more Sox E genes blocks EMT.

Honolulu REU

This project involved analyzing the mineral content in meteorites to draw conclusions about the distribution of heat and water in the early solar system. I spent a lot of time at an SEM and electron microprobe getting at the composition of the meteorites which tells you how much water has helped the meteorite altered.

Subcloning and Evaluating Functionality of Estrogen and Androgen Responsive Positive Controls

In the past, reporter vectors such as chloramphenicol acetyltransferase, luciferase and beta-galactosidase were used in order to study the responsiveness of certain regions of genes that are suspected to be hormone-regulated. However, recent studies have concluded that in some types of cells the plasmid backbone also responds to steroid hormones, particularly estrogen and glucocorticoids. We created two constructs containing steroid hormone-responsive regulatory sequences from mouse mammary tumor virus (MMTV) and vitellogenin genes. The first contained the promoter MMTV, which is known to respond to androgens and glucocorticoids. The second construct, derived from TK101, contained a region of the vitellogenin gene ligated to the thymidine kinase (TK) promoter and is responsive to estrogen. The regulatory sequences were subcloned into pSEAP-Basic, a new vector that uses a secreted form of human placental alkaline phosphatase as a reporter protein. The vector is used to monitor the effect of enhancers and promoters. The pSEAP-MMTV construct was then transfected into the androgen-responsive cell line PC3/AR, along with numerous controls. The media was then assayed for the reporter protein (alkaline phosphatase) and the results were standardized to the endogenous protein levels. The results showed that the PC3/AR cells were unresponsive to androgens.

Regultaion of INSM-1 in Small Cell Lung Cancer

During the 8 week NCI Short Summer Experience Program, it was the goal of Mary Breslin, Ph.D. (mentor) and Stephanie Abascal (mentee) to investigate the gene INSM1 further. INSM1 is already known to be regulated by transcription factors Neuro D and NGN3. NGN 2 is also thought to be another transcription factor that regulates INSM1 and is upstream of Neuro D and NGN3. Our goal was to look at different transcription factors similar to Neuro D and NGN3 to see if INSM1 expression correlates to other transcription factors and determine which transcription factors may regulate INSM-1. INSM1 has been discovered to help with fetal pancreatic and brain development but is silenced in normal adults and reappears in neuroendocrine tumors. INSM1 is an insullinoma-associated antigen 1 that was originally isolated from a human insulinoma subtraction library (Breslin et al., 2001). Using reverse transcriptase polymerase chain reaction and various primers and cell lines, we were able to determine which gene sequences were present in each of the cell lines. The presence of Neurogenin 2 correlated well with the presence of INSM1 in the cell lines. The lab is now in the process co-transfecting cells to determine further is NGN2 could possibly be a regulator of INSM1. These findings are not definite but INSM1 continues to be under investigation in the Breslin Laboratory.

Construction of Recombinant GST Fusion Proteins

Recent studies have shown the ability of the oubain-activated Na/K-ATPase to act as a signalplex and tether Phospholipase C and IP3R into a regulatory complex. It is important to understand the detailed mechanism of this pathway that results in increased [Ca2+]i. The compound that provides the substrate for IP3R, PIP2 is hydrolyzed by PLC-γ1 in rat kidney cells. This project worked to find the binding site for PIP2 to the Na/K-ATPase given strong experimental suggestions that PIP2 interacts with the pump. The experiment involved working with α-subunit of the Na/K-ATPase, mutated at the suspected binding site, to create a vector carrying the mutated motif, fused with the GST protein and expressing the corresponding protein, in order to observe any change in protein interaction via GST-pull down assays.

Investigating Auxin Metabolism in Arabidopsis Mutants with Altered Adventitious Rooting Via High Throughput Quantification of Indolealkanoic Acids

Auxins are a class of plant hormones, or phytohormones, that mediate the coordination of a number of important growth and behavioral processes in plants. Two important auxins are indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA). Interestingly, IBA can be converted to IAA and IAA can serve as a precursor to IBA. This work aims to identify and characterize enzymes involved in catalyzing the interconversion of IBA and IAA through the quantification of these auxins within lines of Arabidopsis mutated in genes that have been positively or negatively correlated with adventitious rooting and/or endogenous auxin levels.  Endogenous auxin levels are determined by a high-throughput solid-phase extraction purification method and GC-SIM-MS analysis that utilizes a novel IBA internal standard, 13C815N1-[Indole Ring]-3-butyric acid.  Specifically, this work focuses on the potential of the auxin-conjugating enzymes GH3-3, AtGH3a, and GH3-6/DFL1 in the role of IBA/IAA metabolism and adventitious rooting.

I researched at the University of Toledo in Toledo, OH, as a part of the REU program there.  I worked in a Magnetic Thin Films lab, researching micromagnetic fields of cobalt nanostructures.