| Start Date: | 9/9/2024 | Start Time: | 1:00 PM |
| End Date: | 9/9/2024 | End Time: | 3:00 PM |
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Event Description
BIOMED PhD Thesis Defense
Title:
Alternative Lengthening of Telomeres in Cancer
Speaker:
Kaitlin Elizabeth Raseley, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University
Advisor:
Ming Xiao, PhD
Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University
Details:
In humans, telomeres are nucleoprotein complexes of tandem 5′TTAGGG3′ DNA repeats and associated proteins at the ends of all 46 chromosomes. Telomere loss beyond a certain threshold causes telomere dysfunction, leading to senescence or apoptosis. Cancer cells utilize one of the two Telomere Maintenance Mechanisms (TMM) to maintain their telomeres during uncontrolled proliferation; telomerase or alternative lengthening of telomeres (ALT). ALT cancers are thought to occur in about 10–20% of all tumors and rely on many DNA damage response (DDR) proteins, including those involved in break-induced repair (BIR) in the homology-dependent repair (HDR) pathway.
We developed the Single Molecule Telomere Assay Optical Mapping (SMTA-OM) assay to analyze individual telomeres to detect the telomeric features in ALT+ cancer cells, such as fused DNA molecules with internal telomere-like sequence (ITS+), fusions with loss of internal telomere-like sequence (ITS-), telomere-free ends (TFEs), superlong telomeres, and elevated telomere length heterogeneity. We compared telomeric features in telomerase-positive cancers (TEL+) and ALT cancers. ALT+ cancer cells exhibited increased telomeric features such as fusion/ITS+, fusion/ITS-, and TFEs, as well as increased telomere length heterogeneity (CV) compared to TEL+ cells. Additionally, we compared our SMTA assay with the C-circle assay which is the gold standard for ALT-cancer diagnosis. Since SMTA-OM utilizes multiple parameters for the determination of ALT activity, it decreased the false positives than the C-circle assay. Based on these results, SMTA-OM readouts can be used as potential biomarkers for ALT+ cancer.
Finally, we applied the SMTA-OM to further construe the underlying mechanisms of ALT pathways. Our results show that targeting telomeric sequence with a catalytically inactive Cas9 (dCas9) physically prevents the progression of DNA replication machinery. The blocked replication machinery led to an increase in ITS+, likely resulting from the upregulation of the ALT pathways. These studies also provide substantial insight into the breakage-fusion-bridge cycle and how telomeric structural changes and molecular fusions are formed. Despite recent advances in this area of research, there are still critical unanswered questions and a need for a reliable diagnostic method for ALT cancer. |
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Audience:
Undergraduate StudentsGraduate StudentsFacultyStaff |
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