Browsing by Subject "cell migration"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item HEM-protein regulates cell migration and asymmetric cell division during development of the ventral nerve cord in Drosophila melanogaster(2010-07-08) Zengrong Zhu; Krishna M. Bhat; Pomila Singh; Ping Wu; Kathleen M. Beckingham; Javier V. NavarroCell migration and asymmetric cell division are two of the key events during development of the nervous system. I have focused on a typical neuronal lineage, NB4-2→GMC-1→RP2/sib, in the ventral nerve cord (VNC) of the Drosophila embryo to investigate the regulation of neuronal migration and asymmetric cell division during development of the nervous system. I have discovered a migration defect of RP2 neurons in HEM-protein (Hem) mutants: RP2 neurons cross the midline and migrate from the initial hemi-segment to the opposite hemi-segment. The same migration defect is observed in WASP-family verprolin-homologous protein (WAVE/SCAR) and Abl tyrosine kinase (Abl) mutants, suggesting that these three genes might act together to regulate neuronal migration in the VNC. I have found that Hem is required for maintaining the protein level of WAVE in vivo and is necessary for its proper localization in the cell. In Hem mutants, WAVE is down regulated and mis-localized in RP2 neurons, resulting in the migration defect of RP2 neurons. Abl on the other hand negatively regulates the protein level of WAVE. When Abl is ectopically expressed, WAVE protein is down regulated. In Abl mutants, WAVE is up regulated and its hyperactivity may be responsible for the migration defect of RP2 neurons. Meanwhile, instead of asymmetric division in wild type embryos, a symmetric division of GMC-1 is observed in the “strong phenotype embryo†of HemJ4-48 mutants. It was not observed in other Hem mutants and Hem deficiency alleles. The truncated Hem protein (∆HemJ4-48) in HemJ4-48 allele may behave as a neomorphic protein, resulting in the symmetric division of GMC-1. In HemJ4-48 mutants, the apical localization of Inscuteable (Insc) is disrupted, suggesting that regulation of the asymmetric division of GMC-1 by Hem is mediated by Insc. The same symmetric division of GMC-1s was also observed in Abl mutants but not WAVE mutants, suggesting that Abl may act together with Hem to regulate the asymmetric division of GMC-1s. This study uses the Drosophila VNC as a model system and describes how neuronal migration and asymmetric cell division are regulated by Hem during development of the nervous system.Item Integrin alpha6beta4 contributions in pancreatic adenocarcinoma(2007-06-11) Zobeida Cruz-Monserrate; Kathleen L. O'Connor Ph.D.; Xiadong Cheng Ph.D; Panagiotis Z. Anastasiadis Ph.D.; Lisa Elferink Ph.D.; Claire E. Hulsebosch Ph.D.; B. Mark Evers MDPancreatic adenocarcinomas are among the most lethal human cancers due to an elevated incidence of tumor cell invasion and metastasis for reasons that are currently unclear. In this dissertation, I determined how the pro-invasive integrin alpha6beta4 expression was related to pancreatic adenocarcinoma tumor progression in tumor samples and assessed in-vitro if the expression of this integrin was required for the migration and invasion of pancreatic cancer cells. In addition, I explored the mechanisms of how the alpha6beta4 integrin could contribute to an invasive and migratory phenotype. To examine if integrin alpha6beta4 expression was related to cancer progression, immunohistochemical analysis was performed in normal pancreas, pancreatic intraepithelial neoplasia (PanIN) lesions, pancreatic adenocarcinomas, and chronic pancreatitis. In normal pancreatic ducts, integrin alpha6beta4 was noted only at the cell’s basal interface with the basement membrane. In pancreatic adenocarcinomas, 92% (104/113) demonstrated overexpression of integrin alpha6beta4 and altered localization to the cytoplasm and membranous regions. This pattern of expression was observed in all PanIN lesions as early as PanIN-1A. In contrast, 93% (13/14) of chronic pancreatitis samples resembled the staining pattern of normal pancreas. When cancer was present in areas of chronic pancreatitis, this altered expression of alpha6beta4 integrin identified the cancer. These results indicate that the early overexpression of the alpha6beta4 integrin in pancreatic adenocarcinoma progression may contribute to the malignancy of this disease. \r\nTo understand the contribution of integrin alpha6beta4 expression in cell migration and invasion, cell lines were screened for the presence of integrin alpha6beta4 by immunoblotting and fluorescence activated cell sorting and correlated with their ability to migrate towards hepatocyte growth factor (HGF), a known mitogenic and motility factor of pancreatic carcinomas. I found that cell surface expression positively correlated with the cell line ability to migrate and invade towards HGF. When cells expressing high levels of integrin alpha6beta4 were treated with siRNAs targeting the alpha6 or beta4 integrin subunits, I observed a reduction in HGF-induced migration and invasion. Furthermore, the activity of the small GTPase Rac-1 decreased when alpha6beta4 integrin expression was reduced. In addition, expression of the Rac-specific nucleotide exchange factor, Tiam-1 was upregulated by the integrin alpha6beta4 and required for Rac-1 activity. These results suggest that the integrin alpha6beta4 plays an important role in the migratory and invasive phenotype of pancreatic carcinoma cells and that the Tiam-1-Rac1 pathway is an important mediator of integrin alpha6beta4-mediated HGF-induced migration and invasion. Overall this study provided evidence that integrin alpha6beta4 is an important contributor to the migratory and invasive phenotype that characterize pancreatic adenocarcinomas.