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Dissertation
Single Molecule Telomere Length Measurement and Its Application in Investigation Alternative Lengthening of Telomeres (ALT) Pathway
Doctor of Philosophy (Ph.D.), Drexel University
Jun 2024
DOI:
https://doi.org/10.17918/00010460
Abstract
Telomere is a repeated sequence (TTAGGG)N that caps the end of the chromosomes to protect them from damage during DNA replication prior to cell division. Telomere length is essential to the cell's genomic stability and biological function. Each division shortened the telomere by approximately 40 to 200bp. After multiple rounds of cell division, telomere shortening leads to genomic instability, which triggers DNA Damage Response (DDR), leading to senescence or apoptosis. In rare cases, 1 out of 10 million cells activates the telomere maintenance mechanisms (TMMs) to maintain cell immortality and lead to cancer. Approximately 85 to 90% of cancers maintain telomere length by activating telomerase expression, while the remaining 10-15% of cancers use Alternative Lengthening of Telomeres (ALT). Recent studies indicate that Homology- Dependent Repair (HDR) plays a role in the ALT pathway. Unlike Telomerase, HDR doesn't use a standard template; instead, HDR searches for a DNA template complement to the broken DNA strand. As a result, ALT telomeres are characterized by highly heterogeneous telomeres, including very long telomeres and telomere-free chromosome end, and unique telomere structures such as extrachromosomal telomeric DNA. ALT cancers include some of the deadliest and most difficult-to-treat cancers. Understanding telomere repair mechanisms in ALT cancer presents a potential for finding biomarkers for cancer diagnosis and helps explore targets for anticancer therapy. Here, single-molecule telomere assay via Optical Mapping (SMTA-OM), an innovative technology that enables single telomere characterization and measurement, was utilized to study telomere repair and replication in ALT cancer cells. SMTA-OM allowed the identification of ALT- unique telomere structures, such as internal telomere-like sequences (ITS), which other telomere measurement methods couldn't identify. Furthermore, SMTA-OM is utilized to study the effects of inhibiting the replication stress response by depleting DNA2 and FANCM proteins in ALT cancer cells. The result shows that most chromosome arms exhibited longer telomeres increase in fusion/ITS+ frequency in comparison to the control cells, suggesting that the break-induced replication (BIR) pathway may be activated by the damaged telomeres. Additionally, the role of POLD3 and PIF1 in the BIR telomere Repair Pathway in ALT Cancer cells was investigated using SMTA-OM. The results provide insight into telomere maintenance and repair mechanisms in ALT cells and help identify ALT biomarkers and potential anticancer treatment targets.
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Details
- Title
- Single Molecule Telomere Length Measurement and Its Application in Investigation Alternative Lengthening of Telomeres (ALT) Pathway
- Creators
- Heba Zuhair Abid
- Contributors
- Ming Xiao (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xvi, 109 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- School of Biomedical Engineering, Science, and Health Systems (1997-2026); Drexel University
- Other Identifier
- 991021890312604721