Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item High Resolution Mapping of Intracellular Mechanical Properties during Key Stages of Cancer Progression(2022) Nikolic, Milos; Scarcelli, Giuliano; Tanner, Kandice; Biophysics (BIPH); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The mechanical phenotype of the living cell is critical for survival following deformations due to confinement and fluid flow. Furthermore, in recent years mechanical interaction between cells and the cellular environment has been implicated as one of the key regulators of cancer progression and malignant transformation. Due to the need to better understand the mechanical properties of invasive cells and how the mechanical phenotype plays a role in cancer progression, several microrheology techniques have been applied to study cell mechanics in a range of in vitro environments. However, many of these techniques have been limited either to studying cells in only one type of environment (e.g. 2D), with limited resolution, or with invasive probes. To begin to address this question, in this dissertation we aim to quantify the mechanical state of cells in a broader range of different contexts and geometries. To do this we use Brillouin microscopy, a non-contact, label free, non-invasive technique which enables us to probe the mechanical response of cells in a wide range of complex microenvironments. Here we introduce an improved Brillouin microscope with improved signal and acquisition speed which enables us to perform biological studies at the single cell level. Using the improved Brillouin microscopy, we find that individual cells can be softer as function of the invasive potential, but that cells are able to dynamically change their mechanical properties across many different contexts. We validate our results using complementary microrheology methods such as atomic force microscopy and broadband optical tweezer microrheology. We directly observe changes in cell mechanics in key processes relevant for metastatic migration, as well as a function of external and internal parameters like morphology, ECM properties, intracellular factors, and cell-cell cooperativity during multicellular tissue organization. These results support the paradigm that the mechanical state of a cell is a dynamic parameter that varies as a consequence of the microenvironmental and functional context, in addition to the observable changes in cell’s mechanical properties due to malignant transformation.Item Role and Regulation of Autophagy During Developmental Cell Death in Drosophila Melanogaster(2010) McPhee, Christina Kary; Mount, Stephen M; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Two prominent morphological forms of programmed cell death occur during development, apoptosis and autophagic cell death. Improper regulation of cell death can lead to a variety of diseases, including cancer. Autophagy is required for survival in response to starvation, but has also been associated with cell death. It is unclear how autophagy is regulated under specific cell contexts in multi-cellular organisms, and what may distinguish autophagy function during cell survival versus cell death. Autophagic cell death is characterized by cells that die in synchrony, with autophagic vacuoles in the cytoplasm, and phagocytosis of the dying cells is not observed. However, little is known about this form of cell death. Autophagic cell death is observed during mammalian development, during regression of the corpus luteum and involution of the mammary and prostate glands. Autophagic cell death is also observed during development of the fruitfly Drosophila melanogaster, during larval salivary gland cell death. Drosophila is an excellent genetic model system to study developmental cell death in vivo. Cells use two main catabolic processes to degrade and recycle cellular contents, the ubiquitin/proteasome system (UPS) and autophagy. Here I investigate the role of the UPS and autophagy in developmental cell death using Drosophila larval salivary glands as an in vivo model. Proteasome inhibitors are being used in anti-cancer therapies; however the cellular effects of proteasome inhibition have not been studied in vivo. Here I demonstrate that the UPS is impaired during developmental cell death in vivo. Taking a proteomics approach to identify proteins enriched in salivary glands during developmental cell death and in response to proteasome impairment, I identify several novel genes required for salivary gland cell death, including Cop9 signalsome subunit 6 and the engulfment receptor Draper. Here I show that the engulfment receptor Draper is required for salivary gland degradation. This is the first example of an engulfment factor that is autonomously required for self-clearance. Surprisingly, I find that Draper is cell-autonomously required for autophagy during cell death, but not for starvation-induced autophagy. Draper is the first factor to be identified that genetically distinguishes autophagy that is associated with cell death from cell survival.