Essays in game theory

This dissertation studies the nature and the role of strategic uncertainty, which is uncertainty about the strategy choice of the other players. This uncertainty is typically represented by the player's probabilistic belief about the other players. In these models, analysts rely on the expected utility hypothesis to predict players' behavior. However, the expected utility model is often criticized since it excludes much interesting behavior. In the first chapter of the dissertation, I analyze a very general class of games and study a notion of rationalizability, showing it captures rationality and common knowledge of rationality in this framework. The framework is general enough to accommodate many non-expected utility models. I show that any rationalizable action profile can be made uniquely so by perturbing higher order uncertainty slightly. This result implies that the set of the rationalizable action profiles is generically a singleton. When there are multiple rationalizable action profiles, any refinement is not stable because there is another model with slightly different higher order beliefs where another action profile is uniquely rationalizable. This result also suggests that relaxing the expected utility axioms such as independence does not change behavior of the rational agents very much in strategic settings. In particular, if an action profile is uniquely rationalizable in the expected utility model, this action profile is still uniquely rationalizable even if the agents' risk attitude or ambiguity attitude changes slightly. In the second chapter, I propose a new framework to study the role of strategic uncertainty in the information design problem while maintaining the expected utility hypothesis about the players' behavior. In the information design problem, a designer chooses an information structure, which is a probability distribution over signals she discloses to the player about the state. The designer's goal is to affect the players' decisions and implement her preferred outcome. After receiving information, the players update their belief about the other players. I characterize what is implementable when the designer takes into account potential misunderstandings of information and misspecification of beliefs of the players. In particular, I require that an outcome close to the desired one is implementable in every nearby information structure. I show that under a richness condition, an outcome is robustly implementable if and only if it is strictly dominant for all realizations of the signal. As a result, the designer's ability to affect the outcome is severely restricted and she cannot gain by disclosing information in many interesting cases. Another main result suggests that the designer has to send a more informative signal to implement a particular outcome compared to the standard case

Mature natural killer cell and lymphoid tissue–inducing cell development requires Id2-mediated suppression of E protein activity

The Id2 transcriptional repressor is essential for development of natural killer (NK) cells, lymphoid tissue–inducing (LTi) cells, and secondary lymphoid tissues. Id2 was proposed to regulate NK and LTi lineage specification from multipotent progenitors through suppression of E proteins. We report that NK cell progenitors are not reduced in the bone marrow (BM) of Id2−/− mice, demonstrating that Id2 is not essential for NK lineage specification. Rather, Id2 is required for development of mature (m) NK cells. We define the mechanism by which Id2 functions by showing that a reduction in E protein activity, through deletion of E2A, overcomes the need for Id2 in development of BM mNK cells, LTi cells, and secondary lymphoid tissues. However, mNK cells are not restored in the blood or spleen of Id2−/−E2A−/− mice, suggesting a role for Id2 in suppression of alternative E proteins after maturation. Interestingly, the few splenic mNK cells in Id2−/− and Id2−/−E2A−/− mice have characteristics of thymus-derived NK cells, which develop in the absence of Id2, implying a differential requirement for Id2 in BM and thymic mNK development. Our findings redefine the essential functions of Id2 in lymphoid development and provide insight into the dynamic regulation of E and Id proteins during this process

Identification of the nuclear export signal in the helix–loop–helix inhibitor Id1

AbstractId proteins play important roles in cellular differentiation and proliferation by negatively regulating basic helix–loop–helix transcription factors. Although their intracellular localization may change depending on the biological situation, little is known about the molecular determinants underlying such changes. Here we report the identification of a nuclear export signal (NES) in Id1. The identified NES was different from that of Id2, but had the ability to confine heterologous green fluorescent protein to the cytoplasm. Thus, our results indicate that the intracellular localization of Id1 is regulated differently from that of Id2

Regulation of Id2 expression by CCAAT/enhancer binding protein β

Mice deficient for Id2, a negative regulator of basic helix–loop–helix (bHLH) transcription factors, exhibit a defect in lactation due to impaired lobuloalveolar development during pregnancy, similar to the mice lacking the CCAAT enhancer binding protein (C/EBP) β. Here, we show that Id2 is a direct target of C/EBPβ. Translocation of C/EBPβ into the nucleus, which was achieved by using a system utilizing the fusion protein between C/EBPβ and the ligand-binding domain of the human estrogen receptor (C/EBPβ-ERT), demonstrated the rapid induction of endogenous Id2 expression. In reporter assays, transactivation of the Id2 promoter by C/EBPβ was observed and, among three potential C/EBPβ binding sites found in the 2.3 kb Id2 promoter region, the most proximal element was responsible for the transactivation. Electrophoretic mobility shift assay (EMSA) identified this element as a core sequence to which C/EBPβ binds. Chromatin immunoprecipitation (ChIP) furthermore confirmed the presence of C/EBPβ in the Id2 promoter region. Northern blotting showed that Id2 expression in C/EBPβ-deficient mammary glands was reduced at 10 days post coitus (d.p.c.), compared with that in wild-type mammary glands. Thus, our data demonstrate that Id2 is a direct target of C/EBPβ and provide insight into molecular mechanisms underlying mammary gland development during pregnancy

Nongyrotropic electron velocity distribution functions near the lunar surface

We have analyzed nongyrotropic electron velocity distribution functions (VDFs) obtained near the lunar surface. Electron VDFs, measured at ∼10–100 km altitude by Kaguya in both the solar wind and the Earth's magnetosphere, exhibit nongyrotropic empty regions associated with the ‘gyroloss’ effect; i.e., electron absorption by the lunar surface combined with electron gyromotion. Particle-trace calculations allow us to derive theoretical forbidden regions in the electron VDFs, thereby taking into account the modifications due to nonuniform magnetic fields caused by diamagnetic-current systems, lunar-surface charging, and electric fields perpendicular to the magnetic field. Comparison between the observed empty regions with the theoretically derived forbidden regions suggests that various components modify the characteristics of the nongyrotropic electron VDFs depending on the ambient-plasma conditions. On the lunar nightside in the magnetotail lobes, negative surface potentials slightly reduce the size of the forbidden regions, but there are no distinct effects of either the diamagnetic current or perpendicular electric fields. On the dayside in the solar wind, the observations suggest the presence of either the diamagnetic-current or solar wind convection electric field effects, or both. In the terrestrial plasma sheet, all three mechanisms can substantially modify the characteristics of the forbidden regions. The observations imply the presence of a local electric field of at least 5 mV/m although the mechanism responsible for production of such a strong electric field is unknown. Analysis of nongyrotropic VDFs associated with the gyroloss effect near solid surfaces can promote a better understanding of the near-surface plasma environment and of plasma–solid-surface interactions

Initiation of NALT Organogenesis Is Independent of the IL-7R, LTβR, and NIK Signaling Pathways but Requires the Id2 Gene and CD3−CD4+CD45+ Cells

AbstractInitiation of nasopharyngeal-associated lymphoid tissue (NALT) development is independent of the programmed cytokine cascade necessary for the formation of Peyer's patches (PP) and peripheral lymph nodes (PLN), a cytokine cascade which consists of IL-7R, LTα1β2/LTβR, and NIK. However, the subsequent organization of NALT seems to be controlled by these cytokine signaling cascades since the maturation of NALT structure is generally incomplete in those cytokine cascade-deficient mice. NALT as well as PP and PLN are completely absent in Id2−/− mice. NALT organogenesis is initiated following the adoptive transfer of CD3−CD4+CD45+ cells into Id2−/− mice, constituting direct evidence that CD3−CD4+CD45+ inducer cells can provide an IL-7R-, LTα1β2/LTβR-, and NIK-independent tissue organogenesis pathway for secondary lymphoid tissue development

Id2-, RORγt-, and LTβR-independent initiation of lymphoid organogenesis in ocular immunity

The eye is protected by the ocular immunosurveillance system. We show that tear duct–associated lymphoid tissue (TALT) is located in the mouse lacrimal sac and shares immunological characteristics with mucosa-associated lymphoid tissues (MALTs), including the presence of M cells and immunocompetent cells for antigen uptake and subsequent generation of mucosal immune responses against ocularly encountered antigens and bacteria such as Pseudomonas aeruginosa. Initiation of TALT genesis began postnatally; it occurred even in germ-free conditions and was independent of signaling through organogenesis regulators, including inhibitor of DNA binding/differentiation 2, retinoic acid–related orphan receptor γt, lymphotoxin (LT) α1β2–LTβR, and lymphoid chemokines (CCL19, CCL21, and CXCL13). Thus, TALT shares immunological features with MALT but has a distinct tissue genesis mechanism and plays a key role in ocular immunity

Lactation defect in mice lacking the helix–loop–helix inhibitor Id2

Id proteins are thought to be negative regulators of cell differentiation and positive regulators of cell proliferation. Mammary glands of Id2(–/–) female mice reveal severely impaired lobulo-alveolar development during pregnancy. Id2(–/–) mammary epithelia show no precocious maturation, but instead exhibit intrinsic defects in both cell proliferation and cell survival, implying that the role of Id2 in pregnant mammary epithelia is mainly stimulation of cell proliferation and support of cell viability. Expression studies of genes required for mammary gland development suggest Id2 to be a downstream or parallel factor of these genes. A decrease in the DNA binding activity of Stat5 was also observed in Id2(–/–) mammary glands at 7 days post-coitus. Our results indicate an indispensable role of Id2 in pregnant mammary glands

Backscattered energetic neutral atoms from the Moon in the Earth's plasma sheet observed by Chandarayaan-1/Sub-keV Atom Reflecting Analyzer instrument

We present the observations of energetic neutral atoms (ENAs) produced at the lunar surface in the Earth's magnetotail. When the Moon was located in the terrestrial plasma sheet, Chandrayaan-1 Energetic Neutrals Analyzer (CENA) detected hydrogen ENAs from the Moon. Analysis of the data from CENA together with the Solar Wind Monitor (SWIM) onboard Chandrayaan-1 reveals the characteristic energy of the observed ENA energy spectrum (the e-folding energy of the distribution function) ∼100 eV and the ENA backscattering ratio (defined as the ratio of upward ENA flux to downward proton flux) <∼0.1. These characteristics are similar to those of the backscattered ENAs in the solar wind, suggesting that CENA detected plasma sheet particles backscattered as ENAs from the lunar surface. The observed ENA backscattering ratio in the plasma sheet exhibits no significant difference in the Southern Hemisphere, where a large and strong magnetized region exists, compared with that in the Northern Hemisphere. This is contrary to the CENA observations in the solar wind, when the backscattering ratio drops by ∼50% in the Southern Hemisphere. Our analysis and test particle simulations suggest that magnetic shielding of the lunar surface in the plasma sheet is less effective than in the solar wind due to the broad velocity distributions of the plasma sheet protons