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 MOLECULAR MECHANISMS UNDERLYING CADHERIN-6B INTERNALIZATION IN PREMIGRATORY CRANIAL NEURAL CREST CELLS DURING THEIR EPITHELIAL-TO-MESENCHYMAL TRANSITION(2015) Padmanabhan, Rangarajan; Taneyhill, Lisa A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The generation of migratory cells from immotile precursors occurs frequently throughout development and is crucial to the formation and maintenance of a functioning organism. This phenomenon, called an epithelial-to-mesenchymal transition (EMT), involves the disassembly of intercellular adhesions and cytoskeletal rearrangements in order to promote migration. Importantly, aberrant EMTs and cell migration can lead to devastating human conditions including cancer metastasis and fibrosis. How cells accomplish EMT to become migratory is still an unanswered question in the biomedical field. To this end, we use chick neural crest cells as an in vivo model to elucidate the molecules and pathways that regulate EMT and migration. Neural crest cells are a population of embryonic cells that are originally stationary within the dorsal neural tube but later migrate to form a variety of adult derivatives, such as the craniofacial skeleton, skin pigment cells and portions of the heart. To facilitate EMT, chick premigratory neural crest cells lose intercellular contacts mediated, in part, by the transmembrane cell adhesion protein Cadherin-6B (Cad6B). While Cad6B mRNA is transcriptionally repressed in premigratory neural crest cells, loss of Cad6B protein does not directly follow and instead occurs ~90 minutes later, just prior to migration. This rapid depletion of Cad6B is all the more striking given that the half-life of most cadherins, including Cad6B, is ~6-8 hours in vitro. As such, unique post- translational mechanisms must exist to remove Cad6B from premigratory neural crest cell plasma membranes to facilitate neural crest EMT. Since cadherins are known to be downregulated through internalization mechanisms (e.g., endocytosis, macropinocytosis) in other in vitro systems, the hypothesis of this dissertation is that Cad6B is internalized, and that this process plays a critical function to enable neural crest EMT. To this end, we document the existence of Cad6B cytoplasmic puncta in cultured cells, cultured neural crest cells and transverse sections of chick embryos. We subsequently identified a p120-catenin binding motif in the Cad6B cytoplasmic tail and demonstrated its functionality through site-directed mutagenesis, revealing a role in enhancing Cad6B internalization and reducing the stability of membrane-bound Cad6B. Furthermore, we uncover for the first time that Cad6B is removed from premigratory cranial neural crest cells through cell surface internalization events that include clathrin-mediated endocytosis and macropinocytosis. Both of these processes are dependent upon the function of dynamin, and inhibition of Cad6B internalization abrogates neural crest cell EMT and migration. Collectively, our findings provide a molecular blueprint for how cadherins are dynamically regulated during the formation of migratory cell types required for normal embryonic development and tissue repair as well as those generated during human diseases and cancers. Importantly, our research is multi-disciplinary, integrating cell biology and physiology to reveal how a cellular event, the active downregulation of a membrane protein, results in a physiological event, neural crest EMT and migration.Item Phylogenetic analysis of swine influenza viruses isolated from humans in Alma-Ata, Kazakhstan(2009) Padmanabhan, Rangarajan; Perez, Daniel; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Continuous surveillance of influenza becomes important considering the economic, epidemic and pandemic implications of influenza infections. This study details phylogenetic & molecular analysis of the genes of four swine influenza viruses isolated from humans in Alma-Ata, Kazakhstan. Phylogenetic analysis placed the eight segments of the four viruses in the classical H1N1 swine clade, along with the isolate A/sw/Jamesburg/1942, except for the HA of A/Alma-Ata/32/98, which was placed in the human H1N1 lineage, along with the isolate A/WS/1933. On amino acid analysis, the viruses displayed mutations on HA and ribonucleoproteins which putatively disrupt antigenic recognition of the virus by the host immune system. The presence of these viruses relatively unchanged for 6 decades after their initial isolation could be speculated to be a combination of laboratory leaks in southern USSR in 1980s, low divergence of classical H1N1 viruses in pigs, and the low population density of Kazakhstan.