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There are numerous situations in which a polarity occurs, several of these being pointed out by G. Birkhoff [2] who first discussed polarities and formulated some of the elementary results. R.M. Thrall examined more closely a polarity between the subspaces of a vector space and the algebra of linear transformations [8]. Another important application arises in lattice completions [2]. [...]

This work is concerned with the automatic understanding of evaluative text. We investigate sentence level opinion polarity prediction by assigning lexical polarities and deriving sentence polarity from these with the use of contextual valence shifters. A methodology for iterative failure analysis is developed and used to refine our lexicon and identify new contextual shifters. Algorithms are presented that employ these new shifters to improve sentence polarity prediction accuracy beyond that of a state-of-the-art existing algorithm in the domain of consumer product reviews. We then apply the best configuration of our algorithm to the domain of movie reviews.

Septins are a group of filament forming proteins that act as scaffolds and diffusion barriers that regulate various cellular functions, such as cytokinesis. Recently, evidence was obtained in our laboratory that septins may also regulate mammalian cell polarity through their interaction with Par3, an important metazoan polarity regulator. In this thesis I sought to examine whether septins regulated the polarization of migrating cells through their interaction with Par3 as well as how this interaction occurred. I demonstrated that the C terminus of Sept7 was capable of binding to Par3 in vitro. Sept7 was also able to colocalize with Par3, but an interaction between the two proteins could not be detected by immunoprecipitation. Migration assays used to examine the significance of Sept7 in polarization showed a small decrease in polarization after Sept7 depletion. This suggests that septins may play a non-essential role in regulating the polarization of migrating cells.

Septins are a group of filament forming proteins that act as scaffolds and diffusion barriers that regulate various cellular functions, such as cytokinesis. Recently, evidence was obtained in our laboratory that septins may also regulate mammalian cell polarity through their interaction with Par3, an important metazoan polarity regulator. In this thesis I sought to examine whether septins regulated the polarization of migrating cells through their interaction with Par3 as well as how this interaction occurred. I demonstrated that the C terminus of Sept7 was capable of binding to Par3 in vitro. Sept7 was also able to colocalize with Par3, but an interaction between the two proteins could not be detected by immunoprecipitation. Migration assays used to examine the significance of Sept7 in polarization showed a small decrease in polarization after Sept7 depletion. This suggests that septins may play a non-essential role in regulating the polarization of migrating cells.

Planar cell polarity (PCP) provides positional information to a field of cells, coordinating the orientation of polarized structures or the direction of polarized cell movements. An evolutionarily conserved signalling pathway regulates PCP, however, the cue that establishes PCP is unknown. There is a strong precedent for Wnt signalling to act as the cue to establish PCP. Here I perform in vivo assays of cell polarity to examine the role of non-canonical Wnt signalling in regulating PCP, using zebrafish neural progenitor cells and asymmetric membrane localization of GFP-Prickle (a PCP cytoplasmic effector molecule) as a model system. My preliminary evidence suggests Wnt4a provides positional information to cells in the neural tube. In addition, using a membrane-yeast-two-hybrid approach to discover novel regulators of PCP, I identified Ring Finger 41 as a new binding partner to Van-gogh-like-2 (an essential PCP signalling molecule) and a novel regulator of vertebrate PCP.

Epithelial sheets line the surfaces of the body, forming a barrier between the external environment and internal tissues. During development, regulation of epithelial architechture can drive morphogenesis and build the three-dimensional structures of the body. Epithelial form and function derive from the polarized morphology of epithelial cells, which have apical surfaces that face the external environment, lateral surfaces containing cell-cell junctions and basal surfaces that connect to the underlying tissue. A network of polarity proteins establishes the apico-basolateral axis, while a system of polarized membrane traffic ensures delivery of specialized cargo to distinct membrane surfaces. How these systems of polarity and trafficking are integrated is still poorly understood. The focus of my study was to investigate how the apical polarity proteins Cdc42, Par6, Bazooka and aPKC (the “Par complex”) regulate polarity and adherens junction (AJ) integrity during Drosophila development. Upon perturbation of Cdc42/Par activity during embryogenesis, apical membrane proteins accumulate in sorting endosomes. This trafficking defect occurs throughout the ectoderm, but in the ventral neuroectoderm (VNE) is accompanied by a concomitant depletion of the apical proteins from the plasma membrane (PM) and a loss of AJ integrity. I have demonstrated that the VNE phenotype is a consequence of the relatively high morphogenetic activity of this tissue. Furthermore, I have shown that the AJ defects are likely a downstream consequence of the depletion of important apical polarity factors, such as Crumbs, from the PM. To further characterize the mechanism of apical trafficking, I searched for interactors of Cdc42/Par in the membrane trafficking machinery. I describe interactions between several trafficking genes and Cdc42/Par and provide evidence that Vps26, a component of the retromer complex that retrieves proteins from endosomal membrane and delivers them to the Golgi for re-secretion, is phosphorylated by aPKC and acts as an aPKC effector in the recycling of apical membrane proteins. I propose that Cdc42/Par regulate the retromer to promote the PM localization of apical proteins, which is important to maintain AJ integrity in morphogenetically active tissues.

Planar cell polarity (PCP) provides positional information to a field of cells, coordinating the orientation of polarized structures or the direction of polarized cell movements. An evolutionarily conserved signalling pathway regulates PCP, however, the cue that establishes PCP is unknown. There is a strong precedent for Wnt signalling to act as the cue to establish PCP. Here I perform in vivo assays of cell polarity to examine the role of non-canonical Wnt signalling in regulating PCP, using zebrafish neural progenitor cells and asymmetric membrane localization of GFP-Prickle (a PCP cytoplasmic effector molecule) as a model system. My preliminary evidence suggests Wnt4a provides positional information to cells in the neural tube. In addition, using a membrane-yeast-two-hybrid approach to discover novel regulators of PCP, I identified Ring Finger 41 as a new binding partner to Van-gogh-like-2 (an essential PCP signalling molecule) and a novel regulator of vertebrate PCP.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Stanley J. Roux, Jr. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 190-217). Available also in a digital version from Dissertation Abstracts.