Abstracts for Thursday, February 21
Katie Kaugars, Heritable Variation in Responsiveness to Photoperiod, Reproduction, and Immune Function
Biological functions, like the immune response or reproduction, change in response to the environment to optimize survival. Closely related organisms have similar endocrine signaling pathways that regulate these biological functions. However, within a single population of individuals from one species, signaling pathways can vary to produce drastically different phenotypes when under certain environmental conditions. In order to understand the causes and consequences of heritable variation in signaling pathways, our lab studies the differences between the most extreme phenotypes of the population. In Dr. Heideman’s lab, we use two lines of mice that have been artificially selected to have different responses to an important environmental cue, the length of day, also known as the photoperiod. Generally, our lab has studied how variation in response to photoperiod can cause seasonal differences in the ability to reproduce. In this honors thesis, I used our two lines of mice – that have differences in brain morphology and hormone secretion – to investigate if heritable variation affecting reproduction can affect other biological systems as well, such as the immune system. I sorted mice from both lines and two photoperiods (long-day and short-day) into four groups. I then used delay-type hypersensivity, a test that measures the strength of the cell-mediated immune response, to compare the strength of the immune response in the groups.
Eva Szymanski, A Tale of Two Proteins: The Budding Yeast STUbL Slx5 Functionally Interacts with the SUMO Ligase Siz1
Ubiquitin and SUMO (Small Ubiquitin-like Modifier) are two structurally similar small peptides that post-translationally modulate the function of their target proteins. The recent discovery of SUMO-targeted ubiquitin ligases (STUbLs), E3 ligases that ubiquitylate sumoylated targets, offers an additional layer of protein regulation. STUbLs are crucial for the response to genotoxic stress and preventing gross chromosomal rearrangements, but currently only a few STUbL substrates are known. Here we describe the interaction of the yeast STUbL Slx5/Slx8 with a new target, the SUMO ligase Siz1. Several lines of evidence suggest that Slx5 and Siz1 physically and functionally interact . First, Slx5 and Siz1 interact in yeast two hybrid assays, and we identify specific domains of Slx5 required for that interaction. Second, Slx5 and Siz1(delta)440 co-purify in both in vitro and in vivo pulldown experiments, offering further evidence of a physical interaction. Third, functionally, Slx5 appears to influence the steady state levels and phosphorylation of Siz1. Fourth, Siz1(delta)440 is a substrate for ubiquitylation by Slx5 both in vitro and in vivo. We present a model in which the Slx5 STUbL subunit modulates Siz1-mediated sumoylation activity in the cell.
Daniel Hodges, Les Français au Congo/Zaïre: Une histoire de convoitise
The Democratic Republic of the Congo, formerly known as Zaire, was a Belgian colony that came into being during the Berlin Conference of 1885. This specific territory was endowed with immense natural resources and represented a promising source of revenue for rival European powers. However, aside from King Leopold’s Belgium, the titular colonizing power, one other country, France, held a keen interest in the Congo basin and sought to expand its influence in the region. This interest has exerted itself numerous times throughout history, most notably during the founding of the country at the Berlin Conference (France helped Leopold consolidate his power via diplomatic maneuvers and le droit de preference in the hopes of later taking over his possession), shortly after the Second World War (in the period of decolonization, de Gaulle made advances to Congo/Zaire and sought to incorporate the country into the francophone community), and the period associated with Zaïrianisation (1973-74) under the corrupt and dictatorial presidency of Mobutu Sese Seko. These three periods mark significant turning points in the history of the Democratic Republic of the Congo, and further, they allow scholars to draw insightful analyses of how French influence has maintained itself and flourished in this African nation that was once the colony of a rival power. In more recent times, however, France has had to rethink its African policy in the present-day DRC due to changing international norms and increasing levels of globalization. A multipolar world order has replaced the bipolar system of the Cold War, and countries are becoming more and more interconnected in terms of ideological and economic linkages. Old ties have broken down—one can see this with Rwanda defining itself as an Anglophone country or the Eastern European countries defining themselves as members of the EU—and countries are shedding the ideological conceptions of traditional postcolonialism. In the DRC, Mobutu and his predecessors started to identify itself with France instead of Belgium due to common linguistic and cultural norms. Beginning with de Gaulle’s two famous speeches at Brazzaville in 1944 and 1960, and cemented during the period of Zaïrianisation, one can see a change of patrons in the patron-client relationship as Zaire responded favorably to French advances in terms of cooperation, which can be defined as economic, cultural, and military aid/alliances. This is unusual in that France maintains a kind of de facto rivaling of the Belgium’s traditional role of European metropole to the former colony. In sum, France still maintains a strong interest in the country, but this interest has shifted from the archetypical metropole-colony relationship (which is based on traditional principles of exploitation of the colony by the European power) pioneered by the influential Chief Advisor on African Policy, Jacques Foccart to an alternative approach of coopération that focuses more on language and economic policy than on classical bilateral post-colonial ties. Instead of continuing a strict international patron-client network, France is increasing its influence by expanding access to French instruction and by increasing Franco-Congolese economic ties. In this way, France has maintained a neocolonialist approach throughout the centuries and continues to perpetuate a common culture—or identity—that facilitates exploitation well into the 21st century.
Katherine Hoptay, Analyzing Ancient DNA by Sequencing Mitochondrial DNA Hypervariable Regions I and II to Determine Origin of Fontabelle Emergency Excavation Site Remains
Molecular archaeology utilizes mitochondrial DNA (mtDNA) extracted from ancient remains to provide information regarding kinship patterns, genealogies, and evidence of migration. mtDNA is inherited maternally. Mitochondrial genomes of siblings and all maternal relatives are identical, thus mtDNA can be used to confirm lineages. Two regions in the mitochondrial genome, hypervariable regions I and II, have a higher mutation rate than the rest of the mitochondrial genome. Certain mutations in these regions are more likely to be found in certain ethnic groups than others, to the extent that ethnic groups can be identified by their specific mitochondrial sequence, or haplotype. Haplotypes are confirmed by comparing sample sequences to the Cambridge Reference Sequence (CRS); mutations from the CRS at specific locations correspond with certain haplotypes. Successful extraction of ancient mtDNA is more likely than extraction of ancient nuclear DNA due to the high copy number of mtDNA: Cells contain as many as 1,000 mitochondria, and each mitochondrion contains between two and 10 copies of its DNA. Our bone samples include 10 teeth samples, four long bone fragments, and four to six cranial fragments previously dated back to the mid 17th to 18th century. The samples were found in an unmarked burial site during an emergency excavation in Fontabelle, St. Michael, Barbados. Two different methods are used to extract the mtDNA in order to optimize extraction. Any isolated mtDNA is amplified using PCR and sequenced in order to determine the haplotype of each sample and the origin of the unidentified remains.
Hallie Nelson, Characterization of Thyroid Hormone Receptor Export Pathways
Thyroid hormone receptor alpha (TRα) and beta (TRβ) are critical in many aspects of metabolic control and development. TRα can use a CRM1-dependent or a CRM1-independent pathway for nuclear export. To determine if exportin 5 mediates TR’s export by the latter pathway, Myc-tagged exportin 5 was over-expressed in HeLa cells. The distribution and transcriptional activity of GFPTRα or TRβ was analyzed by fluorescence microscopy and CATELISA, respectively. TR is primarily nuclear at steady-state, but TR had a more cytoplasmic distribution when exportin 5 was overexpressed. In addition, CAT reporter gene expression under control of a thyroid hormone response element was markedly decreased when exportin 5 was over-expressed, indicating less TR was present in the nucleus. TR has multiple nuclear export sequences (NESs) in the ligand-binding domain. We tested the helix 12 NES (NES-H12) and the NES located in the 3rd and 6th helices (NESH3/ H6) on their direct interactions with exportin 5. TR with a NES-H12-disrupting mutation had a more cytoplasmic distribution when exportin 5 was over-expressed, suggesting that exportin 5 utilizes NES-H3/H6 during export. By determining the nuclear export mechanism of TR by exportin 5 and other exportins, further knowledge into regulation of thyroid hormone-responsive gene expression will be gained. This work was funded in part by NSF MCB 10144844 and NIH 2R15DKO58028-03 to L.A.A.