Tag: Biological Science

Investigating the Role of Transposons in Temperature-Induced DNA Damage During Spermatogenesis

Presenter(s):  Colin Maxwell − Biology

Faculty Mentor(s): Diana Libuda, Nicole Kurhanewicz Codd

Oral Session 3M

Research Area: Biological Science

Meiosis is a specialized form of cell division that sexually reproducing organisms use to generate haploid sex cells. Developing sperm are particularly sensitive to temperature fluctuations, with some studies indicating that exposure to elevated temperature increases DNA damage in spermatocytes, but not oocytes. Although temperature-induced DNA damage has been observed, the underlying molecular mechanisms remain unknown. DNA transposons are mobile genetic elements that produce double-strand DNA breaks (DSBs) when excised from the genome. Additionally, transposons can excise from the genome under heat stress.

I hypothesize that heat stress causes transposon excision which may be observed as a linear relationship between transposon copy number and the quantity of DSBs in developing spermatocytes exposed to elevated temperature. To test this hypothesis, I conducted an immunofluorescence screen of wild type Caenorhabditis elegans strains with varying transposon copy numbers. Using deconvolution microscopy, DSBs were visualized via the recombinase RAD-51, a protein involved in the early stages of meiotic DSB repair. Quantification of RAD-51 foci was performed to determine the frequency of temperature-induced DSB formation. Preliminary results demonstrate that the CB4856 strain with ~15 copies of Tc1, a class of transposons active in C. elegans, exhibited half the amount of DSBs as the Bristol N2 strain with ~30 copies of Tc1 displayed upon heat shock. In contrast, comparisons of DSB quantities between additional strains with varying Tc1 copy numbers show no clear relationships. Taken together, these results indicate temperature-induced DNA damage in spermatocytes has multiple mechanisms, with excision of Tc1 transposons as one possible mechanism.

Ethanol Tolerance in Caenorhabditis elegans

Presenter(s): Lucy Kelly − Geography

Faculty Mentor(s): Alex De Verteuil, Patrick Phillips

Poster 55

Research Area: Biological Science

Funding: Knight Campus Funding

SCORE (Students of Color Opportunities in Research Enrichment) is a mentorship program aimed at engaging underrepresented groups with original scientific research. To this end, we utilized an established biological model system to investigate an unexplored question. The nematode C. elegans is a classic genetic system, and its well-defined stress response network makes it ideal for evaluating the effects of ethanol on stress responses. In C. elegans, daf-16 is a transcription factor critical for regulating stress-response genes. In addition, at high concentrations, ethanol absorption leads to high rates of lethality in nematodes. It is then possible that daf-16 is critical for surviving this stress. To investigate this, we exposed both wild-type and daf-16 mutant animals to an acute ethanol stress following pre-exposure to a low concentration ethanol solution and measured survivorship. Additionally, we measured survivorship in both genotypes across multiple ethanol concentrations. In our conditions, high concentration ethanol exposure promotes widespread mortality in both daf-16 and wild-type animals. Furthermore, we found no significant difference in ethanol-induced mortality between genotypes at any ethanol concentration. These results suggest that daf-16 may not be implicated in ethanol-induced stress-responses. Here, programs like SCORE can achieve their educational missions while concurrently making advances in original research.

Investigating the Role Of Genomic Positioning in Directing Meiotic Double-Strand DNA Break Repair

Presenter(s): Rachel David − Biochemistry

Faculty Mentor(s): Diana Libuda, Erik Toraason

Oral Session 3M

Research Area: Biological Sciences

Funding: UO Alden Scholar Research Award, NICHD Grant

During meiosis, the specialized form of cell division that produces gametes, cells utilize recombination to maintain genomic integrity and promote proper chromosome segregation, ensuring fertility. Double-strand DNA breaks (DSBs), which serve as substrates for homologous recombination, are intentionally induced during meiosis. A fraction of DSBs must be repaired
as crossover recombination events with the homologous chromosome to forge a physical connection required to facilitate proper chromosome segregation. Although DSBs are induced across the genome, crossovers in C. elegans are preferentially formed along chromosome arms and not the center of chromosomes. What determines this crossover preference along chromosome arms is not well known. Intriguingly, previous studies in C. elegans have indicated that the crossover landscape is not determined by chromatin marks or specific sequence motifs. However, proximity of a DSB to the synaptonemal complex (SC), a meiosis-specific proteinaceous structure that connects homologous chromosomes together, has been suggested to influence DSB repair outcomes. To determine how genomic positioning of a DSB affects its repair outcome, I am exploiting genetic assays developed by the Libuda lab that enable controlled induction of a single DSB at a known genomic location and assess how that induced DSB was repaired. Utilizing CRISPR/Cas9 genome editing, I have targeted these assays to four unique loci that differ in position both along the chromosome length and in proximity to the SC. Together, our studies will elucidate how the position of a DSB within the genome influences how it is repaired to maintain genome integrity.

SMC-5/6 Facilitates Efficient DSB Repair During Meiosis in C. elegans

Presenter(s): Cordell Clark − Biology

Faculty Mentor(s): Diana Libuda, Erik Toraason

Poster 73

Oral Session 3M

Research Area: Biological Science

Funding: OURS Program Summer 2017, Dr. Diana Libuda’s laboratory is funded in part by an NICHD grant

Sexually reproducing organisms depend upon meiosis to form haploid sex cells necessary for reproduction. Despite the inherent risks of DNA damage to genome integrity, meiotic cells intentionally induce double strand DNA breaks (DSBs) throughout the genome. A specific and limited number of DSBs must be repaired as crossovers with the homologous chromosome to promote proper chromosome segregation. DSBs are induced in excess of the permitted number of crossovers. DSBs not repaired as crossovers must be repaired to maintain genomic integrity. In the Libuda lab, we have designed an assay to determine the repair outcome of a single induced DSB. We have demonstrated that in addition to the homologous chromosome, the sister chromatid is used as a repair template during DSB repair in C. elegans meiosis. My research aims to uncover the mechanisms that facilitate intersister repair, which are currently unknown. Experiments in multiple species have demonstrated that SUMOylation is required for crossover formation. Our preliminary immunofluorescence experiments in SUMO deficient mutants reveal SUMOylation is required for DSB repair in C. elegans oocytes. Prior research has hypothesized that the SMC5/6 complex, which contains a SUMO ligase subunit (NSE-2), facilitates intersister recombination. Using our intersister repair assay, I have demonstrated that the SMC5/6 complex is required for efficient intersister repair and intersister crossovers. My ongoing experiments are directly testing whether the SMC5/6 complex promotes intersister recombination via the NSE-2 SUMO ligase subunit. Overall, our studies are defining the mechanisms that facilitate intersister recombination to ensure genome integrity during sperm and egg development.

Identifying Fossils: Horses of Kyrgyzstan in the Miocene

Presenter(s): Dylan Carlini − Geology

Faculty Mentor(s): Samantha Hopkins, Win Mclaughlin

Oral Session 4O

Research Area: Earth and Biological Science

In paleontology, correct identification of fossils is of paramount importance to the scientific process. In locations with sparse fossil records and little preexisting literature, such as Kyrgyzstan, fossil identification can be particularly difficult. For this study, I identified two previously unidentified specimens from the University of Oregon Kyrgyz fossil collection as a mandible and a cheek tooth from the genus Hipparion, a member of family Equidae. Following a review of relevant paleontological literature, I used digital calipers to gather precise measurements of the specimens and conducted a careful analysis of tooth cusp morphology in order to make the determination. While the two specimens cannot be definitively attributed to the same individual, I determined that both came from adult individuals of the genus Hipparion. Using tooth morphology from the mandible, I also estimated the age of the individual at the time of death. These identifications add to our knowledge of the biodiversity of Miocene central Asia. Additionally, this study serves to demonstrate the process of fossil identification.

Fossils of Oregon: Mammalian Body Mass Communities in the Miocene

Presenter(s): Dylan Carlini − Geology

Faculty Mentor(s): Samantha Hopkins, Dana Reuter

Poster 9

Research Area: Earth and Biological science

Funding: Presidential Undergraduate Research Scholarship
UROP Mini-Grant

The size of an organism relates to a host of other characteristics about a species such as diet, metabolism, and trophic level. Changes in body mass through deep time are often the result of changing environments and climates. Previous research has examined how the patterns of mammalian body size at a community scale are shaped by the environments the organisms inhabit. However, the fossil record of Eastern Oregon has never been investigated through that lens. The extensive fossil record and well-studied long-term environmental shifts in Eastern Oregon make it an ideal location to study the effects of environmental changes on mammalian body masses. This study intends to classify and quantify the effects of the spread of grasslands on body size structure of mammals in the Miocene. I estimated body mass for Miocene mammals using measurements from fossil teeth as a proxy. These estimates derive from measurements taken with digital calipers and from the computer program Image J. I then organized the body masses into size categories and compared the changes in size structures as Oregon developed from a closed woodland in the middle Miocene to a more open, grassland environment in the late Miocene. If a pattern is discovered, it could help inform biologists and ecologists which varieties of mammal are at the greatest risk of climate-change related extinction in the near future.