Product differentiation is a key feature of modern economies. Although its relevance had already been recognized in the XIX century, it is only in the last forty years that a formal treatment has been developed. The 'address approach' distinguishes between horizontal and vertical product differentiation; in the former, consumers do not agree on the quality ranking of commodities, while in the second they do. The first three chapters of this thesis deal with vertical product differentiation in an imperfectly competitive framework. In particular, the first two essays take into account the empirical evidence concerning labor requirements in the production of vertically differentiated goods in order to model labor and product markets in an upstream-downstream relation to each other. The main assumption is that higher variants of vertically differentiated commodities require highly-skilled labor. This allows to study the links between labor markets and vertically differentiated products markets, their equilibrium implications and issues of trade liberalization. The third chapter explores another side of vertical product differentiation, namely the time-to-market of vertically differentiated goods. This interval, which corresponds to the lapse of time for a product to reach the market, is studied under the assumption that firms can make it shorter through costly investments. The analysis compares firms' choices as a function of the parameters characterizing products and technologies and of market structure. The last chapter develops a general equilibrium model with imperfect competition. The concept of monopoly equilibrium is applied to a Ricardian economy in order to study the emergence of trade in that framework.

We previously showed that injury by partial duct ligation (PDL) in adult mouse pancreas activates Neurogenin 3 (Ngn3)(+) progenitor cells that can differentiate to beta cells ex vivo. Here we evaluate the role of Ngn3(+) cells in beta cell expansion in situ. PDL not only induced doubling of the beta cell volume but also increased the total number of islets. beta cells proliferated without extended delay (the so-called 'refractory' period), their proliferation potential was highest in small islets, and 86% of the beta cell expansion was attributable to proliferation of pre-existing beta cells. At sufficiently high Ngn3 expression level, upto 14% of all beta cells and 40% of small islet beta cells derived from non-beta cells. Moreover, beta cell proliferation was blunted by a selective ablation of Ngn3(+) cells but not by conditional knockout of Ngn3 in pre-existing beta cells supporting a key role for Ngn3(+) insulin(-) cells in beta cell proliferation and expansion. We conclude that Ngn3(+) cell-dependent proliferation of pre-existing and newly-formed beta cells as well as reprogramming of non-beta cells contribute to in vivo beta cell expansion in the injured pancreas of adult mice.

Tumor Susceptibility Gene 101, TSG101, exhibits multiple biological functions including the regulation of gene transcription, vesicular trafficking, cellular growth and differentiation. However, the signals involve in the regulation of TSG101 gene functions are unclear. In this present study, we observed congruous TSG101 up-regulation and the differentiation status of keratinocyte in both human foreskin tissue and reconstructed organotypic skin culture. In addition, we found an essential and downstream role of TSG101 in calcium-induced early keratinocyte differentiation since TSG101 siRNA inhibits this process. Our results also indicate a PKC-dependent mechanism is involved based on the following findings. First, a PKC agonist, TPA up-regulates TSG101 and keratin 10 under low calcium condition. Second, co-treatment of keratinocytes with GF 109203X, a PKC inhibitor, blocks TPA-induced TSG101 and keratin 10 up-regulation. Previous report indicates TSG101 gene exhibits a TATA-less and Sp1-containing promoter. Our analysis further shows that both calcium and TPA stimulate phosphorylation of Sp1 and the corresponding TSG101 wild type promoter activity, but not the activity of Sp1 site mutant TSG101 promoter. The co-treatment with GF 109203X blocks the above effects of calcium and TPA, implying that this is a PKC signaling-dependent process. Taken together, these data suggest a PKC-Sp1 signaling is involved in early differentiation switch of keratinocyte through up-regulation of TSG101. Functional inactivation experiment indicates that tsg101 is a tumor suppressor in mouse model. However, many studies using human tumor specimens or conditional knockout mouse give discrepant and contradictive results. Therefore, the role of TSG101 in human cancer remains illusive. Here we demonstrate an inverse correlation between TSG101 and p16INK4a or acetylated- histone H4 protein expression profiles in human head and neck squamous cell carcinomas (HNSCC) (N=98, p<0.001). Using conditioned human HEp2 cells, we confirm that TSG101 negatively modulates p16INK4a expression. Chromatin immunoprecipitation and the subsequent PCR analysis reveal that TSG101 dose-dependently decreases the amount of acetylated histone H4-associated chromatin on p16INK4a promoter. In addition, TSG101 interacts and colocalizes with HDAC1 and SUMO-1 in the nucleus. Furthermore, TSG101 confers a dose-dependent effect on promoting HDAC1 SUMOylation, hence its activity. Taken together, our data demonstrate for the first time that TSG101 can promote SUMO-1 modification of HDAC1, which impacts on down-regulation of p16INK4a gene expression, providing evidence whereby TSG101 might participate in the epigenetic silencing of p16INK4a during the development of HNSCC.

none

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 89-107). Also available in print.

Inhibitor of differentiation (Id) family helix-loop-helix proteins regulate the proliferation, survival and differentiation of numerous cell types during development, however their function during retinal development has not been analyzed. Using loss-of-function and overexpression assays in zebrafish, I demonstrate that Id2a levels modulate retinoblast cell cycle kinetics and thereby influence neuron and glia formation in the retina. Id2a-deficient retinas possess increased numbers of cells occupying S phase, at the expense of mitotic cells, and kinetic analyses demonstrate that Id2a is required for S-phase progression and/or the transition from S to M phase. Id2a-dependent defects in retinoblast proliferation lead to microphthalmia and to an absence of nearly all differentiated inner and outer nuclear layer cell types. Overexpression of id2a has the opposite effect on retinoblast cell cycle kinetics: id2a-overexpressing retinoblasts progress from S to M phase more rapidly and they undergo mitosis more frequently, which results in macrophthalmia. Mosaic analyses reveal that Id2a function in facilitating both cell cycle progression and neuronal differentiation in the retina is non-cell-autonomous, suggesting that Id2a functions upstream of the extrinsic pathways that regulate retinogenesis. In an effort to identify which extrinsic pathways function downstream of Id2a, I discovered that Id2a function is necessary and sufficient to limit Notch pathway activity during retinogenesis. Id2a-deficient retinae possess elevated levels of Notch pathway component gene expression, while retinae overexpressing id2a possess reduced expression of Notch pathway component genes. Attenuation of Notch signaling activity by DAPT or by morpholino knockdown of Notch1a is sufficient to rescue both the proliferative and differentiation defects in Id2a-deficient retinae. In addition to regulating Notch pathway activity, through an RNA-Seq and differential gene expression analysis of Id2a-deficient retinae, I identified a number of additional intrinsic and extrinsic regulatory pathway components whose expression is regulated by Id2a. These data highlight the integral role played by Id2a in the gene regulatory network governing the transition from retinoblast proliferation to terminal differentiation during vertebrate retinogenesis. / text

My dissertation features three essays in industrial organization. The first two investigate aspects of potentially anticompetitive firm behavior in differentiated product markets. Contrary to previous analyses, requirements tying and bundled rebates by a firm with a monopoly in one market that competes in another may increase total surplus when product differentiation in the competitive market is endogenous. This result is stronger for tying than for bundled rebates, and holds for both horizontal and vertical differentiation (essays 1 and 2, respectively). Under requirements tying or bundled rebates, a multiproduct firm (horizontally) differentiates its product less from its rival's product than it would under independent pricing, suggesting a new efficiency consideration for requirements tying: a reduction in transport costs. A similar result prevails under vertical differentiation: when the tying firm controls either quality niche, it reduces the quality of its tied product; however, the rival may invest in the quality of its competing product. Hence, the effect on total surplus is ambiguous when tying or bundled rebates arrangements are permitted. The second essay employs an empirical model typically used to analyze differentiated product markets analyze a different economic environment: parents' decision to home school their children. Home schooling has grown in popularity as an alternative to public or private schools; some estimates place growth at 15 to 40% per year in the U.S. I empirically estimate the demand for home schooling as an alternative to these other modes of education, focusing on potential network effects in household decisions to home-school. I find support for the hypothesis that home schooling 'support groups' mitigate the cost of home schooling relative to the alternatives, but only occur in areas with a critical mass of home-schooling households. The data also suggest that as interest in home schooling grows, the local community's school district spending per child declines, increasing the probability that more parents will take their children out of public schools. Both phenomena suggest the existence of network effects in the market for primary and secondary education. / text

This report articulates some of the recent research on different methods of optimization. Topics discussed include an implicit differentiation process in which the primary substitution method is not used and a relationship among variables method is introduced. In addition, a finding extrema without limits method is explored. Also included is a discussion on the depth of optimization taught in secondary schools and the different methods and levels of instruction on this topic. / text

No description available.

The intracellular pathogen Legionella pneumophila thrives in both natural and man-made water habitats where it replicates inside freshwater amoebae. L. pneumophila follows a developmental cycle as it grows in amoebae. The actively-multiplying intracellular replicative forms (RFs) differentiate into highly virulent mature infectious forms (MIFs) late in the amoeba infection, and are then released extracellularly. L. pneumophila accidentally infects susceptible humans causing the non-communicable Legionnaires’ disease (LD). MIFs play a central role in the life cycle of L. pneumophila and are thought to be responsible for the transmission of LD. Early reports demonstrated that MIFs were poorly produced inside human macrophages, suggesting that the L. pneumophila progeny from human macrophages has fitness and infectivity disadvantages. Direct comparisons of the L. pneumophila progenies from amoebae and human macrophages have demonstrated that the progeny from amoebae is more morphologically differentiated, resistant to antibiotic challenges, and able to adhere to and initiate infections in host cells than the progeny from macrophages. Analysis of the transcriptomic and proteomic profiles of L. pneumophila inside different hosts has revealed a specific set of genes that are upregulated during differentiation of L. pneumophila into MIFs inside freshwater protozoa but not inside human macrophages, suggesting that these genes may be required for the full differentiation of L. pneumophila and, therefore, for the transmission of LD to susceptible humans. Since the expression of the gene lpg1669, which encodes a putative α-amylase, was upregulated in amoebae (highest level of upregulation among the tested genes) and inside Tetrahymena ciliates, but not inside human macrophages, the role of lpg1669 in the differentiation of L. pneumophila into MIFs was investigated. An isogenic lpg1669 deletion mutant did not display defects in morphological differentiation, in vitro (BYE broth) or in vivo (A. castellanii or U937 human macrophages) growth when compared to its parent strain, suggesting that the gene lpg1669 is not essential for the intracellular differentiation of L. pneumophila. Collectively, these findings demonstrate that L. pneumophila can reach different developmental end points in different hosts and could also provide a clue for the lack of transmission of LD among humans.