Drosophila embryonic dorsal-ventral (D-V) polarity is defined by the expression of the gene pipe in the ventral cells of the follicular epithelium surrounding the developing oocyte. pipe encodes a sulfotransferase that transfers sulfate groups to several protein components of the vitelline membrane layer of the eggshell, including Vitelline Membrane-Like protein (VML). These sulfated proteins represent a ventral cue embedded in the eggshell, which, during embryogenesis, leads to the spatially-restricted activation of a serine protease cascade involving Gastrulation Defective (GD), Snake and Easter. Several important pieces of information missing from our understanding of Drosophila D-V patterning include the structures of the carbohydrates borne by the Pipe targets that represent the direct substrates for Pipe and how the Pipe-sulfated ventral cue triggers the spatially-regulated activation of the serine protease cascade. Two major goals of my studies on VML are to elucidate the structures of Pipe-sulfated carbohydrates associated with VML and to identify proteins that interact with VML in a Pipe-dependent manner. To achieve the first goal, I explored different purification systems to isolate VML and eventually found a way of partially purifying VML from Drosophila ovaries. Mass spectrometric analysis of the purified VML is underway to determine the carbohydrate structures on VML and the sites of Pipe-mediated sulfation. Future experiments will involve identification of putative enzymes responsible for the glycosylation of VML and examination of their requirements in D-V patterning. To identify interacting partners of VML, a strategy combining in vivo biotinylation of VML, reversible protein crosslinking and Streptavidin purification of crosslinked complexes will be used. In the second section of my studies, I have demonstrated that VML bearing a biotin acceptor peptide (BAP) tag can be efficiently biotinylated in vivo by co-expressing it with a biotin protein ligase BirA in the follicle cells. As an extension of the application of the approach, I also show that the Torso-like protein, which is localized to the poles of the vitelline membrane and whose polar localization is crucial for Drosophila terminal patterning, can also be biotinylated in vivo when the BAP-tagged protein is co-expressed with BirA in the follicle cells. / text

This dissertation investigates the peculiar behavior of negative polarity items in questions and argues that a unified account of their distribution across declarative and interrogative constructions is feasible. These items are acceptable in questions, despite the fact that questions do not prima facie share anything in common with the other environments in which NPIs surface. Specifically, given current analyses of questions there is no way to argue that questions give rise to downward-entailing inferences, which is what otherwise unifies all other NPI licensing environments. In Chapter 2 I argue for a new semantics of questions wherein strength of exhaustivity is encoded not in different answer-hood operators (cf. Heim 1994), but rather in terms of the presence/absence of a null only that adjoins at the level of the question nucleus, building on an observation by Guerzoni and Sharvit (2007) that question strength appears to be the determining factor in whether or not a question allows NPIs. Chapter 3 focuses specifically on the distribution of NPIs in constituent questions and shows how the analysis put forward in Chapter 2 can account for an array of facts, namely their distribution both in the question nucleus, and in the restrictor of the wh-phrase. Further predictions related to NPIs that had not been discussed before are examined, such as how their scope relative to adjunct wh-phrases affects their acceptability, as well as the distributional differences between weak and strong NPIs. In Chapters 4 and 5 we turn to non-wh questions, namely alternate and polar questions. In Chapter 4 I argue that alternate questions can and should be given an analysis akin to that of wh-questions based on both old and new empirical evidence that the distribution of NPIs is sensitive to the same set of restrictions. In Chapter 5 I argue, contrary to previous analyses, that the acceptability of NPIs is not a function of strength, but rather of how polar questions are interpreted, namely as speech act conditionals. Lastly, Chapter 6 focuses on complex questions and puts forward an analysis of these questions that sets the stage for an arguably unified semantics of all types of questions. / Linguistics

Rho GTPases are highly conserved regulators of cell polarity and the actin cytoskeleton. The role of the Rho GTPase Cdc42 and its regulation during cell division is not well understood. Using biochemical and imaging approaches in budding yeast, I demonstrate that Cdc42 activation peaks during the G1/S transition and during anaphase, but drops during mitotic exit and cytokinesis. Cdc5/Polo kinase is an important upstream cell cycle regulator that suppresses Cdc42 activity. Failure to downregulate Cdc42 during mitotic exit prevents the normal localization of key cytokinesis regulators - Iqg1 and Inn1- at the division site, and results in an abnormal septum. The effects of Cdc42 hyperactivation are largely mediated by the Cdc42 effector p21-activated kinase (PAK) kinase, Ste20. Inhibition of Cdc42 and related Rho GTPases may be a general feature of cytokinesis in eukaryotes.

Loss of polarity is a defining characteristic of epithelial cancers. The cytoskeletal proteins, HUGL1 and HUGL2, mediate polarity in epithelial cells through diversified roles in defining membrane identity and trafficking to the basolateral membrane. Importantly, an ortholog of these molecules can inhibit tumor growth in Drosophila, although the mechanisms of their tumor suppressive functions in mammary epithelial cells are unknown. Here, we show nonredundant tumor protective roles for HUGL1 and HUGL2 in human mammary epithelial cells. Using a three dimensional culture system, we report that loss of HUGL1 or HUGL2 causes loss of apicobasal polarity, aberrant growth of multilayered epithelium, nuclear enlargement, loss of membrane identity, and cellular overgrowth. Experiments on plastic also revealed that HUGL1 or HUGL2 loss results in induction of a phenotypic EMT in breast epithelial cells and overexpression of HUGL1 in breast cancer cells reduces proliferation.In a Drosophila model of cancer driven by loss of lgl, we have discovered the consistent dysregulation of a number of miRNAs and mRNAs including the loss of let-7 and miR-9a, which are implicated in breast cancer and associated with the suppression of stem cells. Cross comparisons revealed a set of mRNAs that are both dysregulated in vivo and represent putative targets of the miRNAs changed in lgl mutants. Among these, Thrombospondin, a component of the extracellular matrix was found to be misexpressed in both flies and human cells lacking Lgl. Moreover, genetic interaction experiments showed miR-9a to be a functional effector of lgl in controlling proliferation in the wing. Taken together, the findings reported in this dissertation suggest that HUGL1 and HUGL2 function as tumor suppressors through their roles in polarity and miRNA regulation. These two proteins, functioning as modulators of cell plasticity and promoters of differentiation, are potentially able to control the transition between a differentiated epithelial cell and a cancer stem cell. This research offers new insight into the role of HUGL1 and HUGL2 in breast cancer and reveals novel targets downstream of polarity proteins for therapeutic intervention.

Fragile X Protein (FMRP) is an RNA binding protein linked to the most common form of inherited mental retardation, Fragile X syndrome (FraX). Despite its ubiquitous expression and presence of non-neuronal phenotypes, FMRP function remains understudied outside of neural and synaptic development. In addition to severe cognitive deficits, FraX etiology also includes postpubescent macroorchidism, which is thought to occur due to overproliferation of the germline. Using a Drosophila model for FraX, I have shown that FMRP controls germline proliferation as well as dorso-ventral polarity during oogenesis. dFmr1 null ovaries exhibit egg chambers with increased numbers of germ cells and ventralized embryos. The number of cyclin E and phosphohistone H3 positive cells is increased in dFmr1 germaria compared to wild-type, suggesting that the mutant germline cells exhibit defects in proliferation. In addition, BrdU incorporation is increased during vitellogenesis, consistent with a prolonged S phase for endoreplicating nurse cells. Here I report the FMRP controls the levels of cbl mRNA in the ovary and that the overproliferation and polarity defects found in dFmr1 ovaries can be rescued by reducing cbl dosage in half. These data suggest a model whereby FMRP regulates cellular proliferation and polarity during oogenesis by controlling the E3 ubiquitin ligase cbl.

In a targeted proteomic screen to identify polarity protein complexes, a number of Scribble (Scrib) -associating proteins were identified; of particular interest was the Nitric Oxide Synthase 1 Adaptor Protein (NOS1AP). NOS1AP contains an N-terminal phosphotyrosine binding (PTB) domain and a C-terminal PSD-95/Dlg homology/ZO-1 (PDZ) binding motif that associates with neuronal NOS (NOS1). We show that the PTB domain of NOS1AP associates with the fourth PDZ domain of Scrib. We identified NOS1AP binding partners including three key regulators of dendritic spine formation, beta-Pix, Git1, and PAK, which require Scrib to associate with NOS1AP. Overexpression of NOS1AP in cultured hippocampal neurons increases dendritic protrusions, a process dependent on the PTB domain. The increase in dendritic protrusions can be blocked by the co-expression of a dominant negative Rac construct. NOS1AP, and the PTB domain of NOS1AP influence Rac activity. Together these data suggest that Scrib and NOS1AP function as important scaffolding proteins in the mammalian synapse and that NOS1AP functions in the dendritic spine by influencing Rho GTPase activity.

The Par6-polarity pathway regulates breast cancer metastasis, and more recently has been shown to regulate transforming growth factor β (TGFβ)-induced apoptosis. Integrins may mediate the regulation of TGFβ-induced apoptosis by Par6, as they are key regulators of cell polarity, survival and death. First, we confirmed that blocking Par6 activation significantly inhibits TGFβ-induced apoptosis in both monolayer and three-dimensional NMuMG (Normal Murine Mammary Gland) cell culture models. TGFβ altered the expression of β1 and β4 integrins in NMuMG monolayers. In addition, TGFβ significantly reduced the basal localization of α6 and β4 integrins in NMuMG three-dimensional acini-like structures (p < 0.001), which was dependent on both Par6 and TGFβ receptor I (TβRI)/SMAD activation. We went on to show that the activities of integrin pro-survival signaling mediators, NF-κB and FAK, were altered in response to TGFβ, and that blocking Par6 activation in the Par6/S345A mutant maintained polarity and basal α6 and β4 integrin expression in the presence of TGFβ in NMuMG three-dimensional structures, in addition to a significant increase in FAK activation. This suggests that TGFβ alters the expression, localization and downstream signaling of integrins, which may contribute to TGFβ-induced apoptosis

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Through his work in ludics and Geometry of Interaction, Jean-Yves Girard invites us to a change of paradigm in the study of logic: the quest for a transcendental syntax, some kind of idealized language that emerges from the rules of logic. Amongst these rules, "testing" plays a leading role in defining a duality for the interpretation of negation. The present work focuses on a notion of polarity which is a central technique used throughout Girard's work to express linear negation. We describe some properties and illustrate them with examples with the purpose of getting acquainted with the technique. We also highlight how the classical connectives (conjunction and disjunction) arise from an interpretation based on testing. In a sense, this work is intended to provide an alternative introduction to Girard's ideas and we hope it can have some pedagogical value.