G protein subunits and the stimulation of phospholipase C by Gs-and Gi-coupled receptors: Lack of receptor selectivity of Galpha(16) and evidence for a synergic interaction between Gbeta gamma and the alpha subunit of a receptor activated G protein.

Stimulatory guanine nucleotide binding protein (Gs)-coupled receptors activated by luteinizing hormone, vasopressin, and the catecholamine isoproterenol (luteinizing hormone receptor, type 2 vasopressin receptor, and types 1 and 2 beta-adrenergic receptors) and the Gi-coupled M2 muscarinic receptor (M2R) were expressed transiently in COS cells, alone and in combination with Gbeta gamma dimers, their corresponding Galphas (Galpha(s), or Galpha(i3)) and either Galpha(q) or Galpha(16). Phospholipase C (PLC) activity, assessed by inositol phosphate production from preincorporated myo[3H]inositol, was then determined to gain insight into differential coupling preferences among receptors and G proteins. The following were observed: (i) All receptors tested were able to stimulate PLC activity in response to agonist occupation. The effect of the M2R was pertussis toxin sensitive. (ii) While, as expected, expression of Galpha(q) facilitated an agonist-induced activation of PLC that varied widely from receptor to receptor (400% with type 2 vasopressin receptor and only 30% with M2R), expression of Galpha(16) facilitated about equally well the activation of PLC by any of the tested receptors and thus showed little if any discrimination for one receptor over another. (iii) Gbeta gamma elevated basal (agonist independent) PLC activity between 2- and 4-fold, confirming the proven ability of Gbeta gamma to stimulate PLCbeta. (iv) Activation of expressed receptors by their respective ligands in cells coexpressing excess Gbeta gamma elicited agonist stimulated PLC activities, which, in the case of the M2R, was not blocked by pertussis toxin (PTX), suggesting mediation by a PTX-insensitive PLC-stimulating Galpha subunit, presumably, but not necessarily, of the Gq family. (v) The effects of Gbeta gamma and the PTX-insensitive Galpha elicited by M2R were synergistic, suggesting the possibility that one or more forms of PLC are under conditional or dual regulation of G protein subunits such that stimulation by one sensitizes to the stimulation by the other.

Gain and kinetics of activation in the G-protein cascade of phototransduction.

The guanine nucleotide binding protein (G protein) cascade underlying phototransduction is one of the best understood of all signaling pathways. The diffusional interactions of the proteins underlying the cascade have been analyzed, both at a macroscopic level and also in terms of the stochastic nature of the molecular contacts. In response to a single activated rhodopsin (R*) formed as a result of a single photon hit, it can be shown that molecules of the G-protein transducin will be activated approximately linearly with time. This, in turn, will cause the number of activated molecules of the effector protein (the phosphodiesterase) also to increase linearly with time. These kinetics of protein activation provide an accurate description of the time course of the rising phase of the photoreceptor's electrical response over a wide range of flash intensities. Recent estimates indicate that at room temperature each R* triggers activation of the phosphodiesterase at a rate of 1000-2000 subunits.s-1. Now that a quantitative description of the activation steps in transduction has been obtained, perhaps the greatest challenge for the future is to provide a comprehensive description of the shutoff reactions, so that a complete account of the photoreceptor's response to light can be achieved.

Gain of chromosome 3q defines the transition from severe dysplasia to invasive carcinoma of the uterine cervix.

We have chosen tumors of the uterine cervix as a model system to identify chromosomal aberrations that occur during carcinogenesis. A phenotype/genotype correlation was established in defined regions of archived, formalin-fixed, and hematoxylin/eosin-stained tissue sections that were dissected from normal cervical epithelium (n = 3), from mild (n = 4), moderate (n = 6), and severe dysplasias/carcinomas in situ (CIS) (n = 13), and from invasive carcinomas (n = 10) and investigated by comparative genomic hybridization. The same tissues were analyzed for DNA ploidy, proliferative activity, and the presence of human papillomavirus (HPV) sequences. The results show that an increase in proliferative activity and tetraploidization had occurred already in mildly dysplastic lesions. No recurrent chromosomal aberrations were observed in DNA extracted from normal epithelium or from mild and moderate dysplasias, indicating that the tetraploidization precedes the loss or gain of specific chromosomes. A gain of chromosome 3q became visible in one of the severe dysplasias/CIS. Notably, chromosome 3q was overrepresented in 90% of the carcinomas and was also found to have undergone a high-level copy-number increase (amplification). We therefore conclude that the gain of chromosome 3q that occurs in HPV16-infected, aneuploid cells represents a pivotal genetic aberration at the transition from severe dysplasia/CIS to invasive cervical carcinoma.

The angiotensin II type 2 (AT2) receptor antagonizes the growth effects of the AT1 receptor: gain-of-function study using gene transfer.

The type 1 angiotensin II (AT1) receptor is well characterized but the type 2 (AT2) receptor remains an enigma. We tested the hypothesis that the AT2 receptor can modulate the growth of vascular smooth muscle cells by transfecting an AT2 receptor expression vector into the balloon-injured rat carotid artery and observed that overexpression of the AT2 receptor attenuated neointimal formation. In cultured smooth muscle cells, AT2 receptor transfection reduced proliferation and inhibited mitogen-activated protein kinase activity. Furthermore, we demonstrated that the AT2 receptor mediated the developmentally regulated decrease in aortic DNA synthesis at the latter stages of gestation. These results suggest that the AT2 receptor exerts an antiproliferative effect, counteracting the growth action of AT1 receptor.

Transgenic mice carrying the diphtheria toxin A chain gene under the control of the granzyme A promoter: expected depletion of cytotoxic cells and unexpected depletion of CD8 T cells.

We have generated transgenic mice bearing the diphtheria toxin A chain (DTA) gene under the control of granzyme A (GrA) promoter sequences (GrA-DTA). GrA is expressed in activated cytotoxic cells but not in their immediate progenitors. These GrA-DTA mice are deficient in cytotoxic functions, indicating that most cytotoxic cells express GrA in vivo. Surprisingly, one founder strain containing a multicopy GrA-DTA insert show a marked and selective deficiency in CD8+ cells in peripheral lymphoid organs. This depletion was not observed in thymus, where the distribution of CD4+ and CD8+ cells is normal. Moreover, the emigration of T cells from thymus is normal, indicating that the depletion occurs in the periphery. GrA-DTA mice should be useful as models to dissect the role of cytotoxic cells in immune responses and as recipients of normal and neoplastic hematopoietic cells. The selective depletion of CD8+ cells in one founder strain could have implications for postthymic T-cell development.

Rapid genome change in synthetic polyploids of Brassica and its implications for polyploid evolution.

Although the evolutionary success of polyploidy in higher plants has been widely recognized, there is virtually no information on how polyploid genomes have evolved after their formation. In this report, we used synthetic polyploids of Brassica as a model system to study genome evolution in the early generations after polyploidization. The initial polyploids we developed were completely homozygous, and thus, no nuclear genome changes were expected in self-fertilized progenies. However, extensive genome change was detected by 89 nuclear DNA clones used as probes. Most genome changes involved loss and/or gain of parental restriction fragments and appearance of novel fragments. Genome changes occurred in each generation from F2 to F5, and the frequency of change was associated with divergence of the diploid parental genomes. Genetic divergence among the derivatives of synthetic polyploids was evident from variation in genome composition and phenotypes. Directional genome changes, possibly influenced by cytoplasmic-nuclear interactions, were observed in one pair of reciprocal synthetics. Our results demonstrate that polyploid species can generate extensive genetic diversity in a short period of time. The occurrence and impact of this process in the evolution of natural polyploids is unknown, but it may have contributed to the success and diversification of many polyploid lineages in both plants and animals.

Gain of function mutations for paralogous Hox genes: implications for the evolution of Hox gene function.

To investigate the functions of paralogous Hox genes, we compared the phenotypic consequences of altering the embryonic patterns of expression of Hoxb-8 and Hoxc-8 in transgenic mice. A comparison of the phenotypic consequences of altered expression of the two paralogs in the axial skeletons of newborns revealed an array of common transformations as well as morphological changes unique to each gene. Divergence of function of the two paralogs was clearly evident in costal derivatives, where increased expression of the two genes affected opposite ends of the ribs. Many of the morphological consequences of expanding the mesodermal domain and magnitude of expression of either gene were atavistic, inducing the transformation of axial skeletal structures from a modern to an earlier evolutionary form. We propose that regional specialization of the vertebral column has been driven by regionalization of Hox gene function and that a major aspect of this evolutionary progression may have been restriction of Hox gene expression.

Psychological and Social Perspectives on Malingering and Symptom Exaggeration: Conceptualization and Interventions Using Acceptance and Commitment Therapy

Malingering and the production of false symptoms seen in such disorders as Factitious Disorder are an ongoing mystery to medical and mental health professionals. Historically, these presentations have been difficult to identify and treat. As might be expected, individuals with such symptomology rarely agree to participate in research, possibly because of a reluctance to admit to the feigning or exaggerating behaviors and a fear of reprisals. Many different etiologies have been proposed, including the assumption of roles in order to manage impressions, taking control of symptoms in order to gain attention or other rewards or avoid aversive events, and even the production of symptoms that is largely out of awareness such as is seen in conversion or somatoform presentations. By examining historical and present-day beliefs about etiology and treatment interventions, professionals can explore what new types of effective treatment might look like. The behaviorist philosophy that underlies Acceptance and Commitment Therapy proposes a perspective emphasizing effective working in context. This philosophy also suggests individuals sometimes engage in behavior in order to escape from or avoid aversive experiences. Utilizing case examples and fresh behavioral perspectives provides insight and ideas for conceptualization of these behaviors of interest. Using the above conceptualizations, an ACT based treatment of those who produce false symptoms is introduced.

The influence of magnetic field geometry on magnetars X-ray spectra

Nowadays, the analysis of the X-ray spectra of magnetically powered neutron stars or magnetars is one of the most valuable tools to gain insight into the physical processes occurring in their interiors and magnetospheres. In particular, the magnetospheric plasma leaves a strong imprint on the observed X-ray spectrum by means of Compton up-scattering of the thermal radiation coming from the star surface. Motivated by the increased quality of the observational data, much theoretical work has been devoted to develop Monte Carlo (MC) codes that incorporate the effects of resonant Compton scattering (RCS) in the modeling of radiative transfer of photons through the magnetosphere. The two key ingredients in this simulations are the kinetic plasma properties and the magnetic field (MF) configuration. The MF geometry is expected to be complex, but up to now only mathematically simple solutions (self-similar solutions) have been employed. In this work, we discuss the effects of new, more realistic, MF geometries on synthetic spectra. We use new force-free solutions [14] in a previously developed MC code [9] to assess the influence of MF geometry on the emerging spectra. Our main result is that the shape of the final spectrum is mostly sensitive to uncertain parameters of the magnetospheric plasma, but the MF geometry plays an important role on the angle-dependence of the spectra.

Essays on the Effects of Corporate Taxation

Cette thèse est une collection de trois articles en macroéconomie et finances publiques. Elle développe des modèles d'Equilibre Général Dynamique et Stochastique pour analyser les implications macroéconomiques des politiques d'imposition des entreprises en présence de marchés financiers imparfaits. Le premier chapitre analyse les mécanismes de transmission à l'économie, des effets d'un ré-échelonnement de l'impôt sur le profit des entreprises. Dans une économie constituée d'un gouvernement, d'une firme représentative et d'un ménage représentatif, j'élabore un théorème de l'équivalence ricardienne avec l'impôt sur le profit des entreprises. Plus particulièrement, j'établis que si les marchés financiers sont parfaits, un ré-échelonnement de l'impôt sur le profit des entreprises qui ne change pas la valeur présente de l'impôt total auquel l'entreprise est assujettie sur toute sa durée de vie n'a aucun effet réel sur l'économie si l'état utilise un impôt forfaitaire. Ensuite, en présence de marchés financiers imparfaits, je montre qu'une une baisse temporaire de l'impôt forfaitaire sur le profit des entreprises stimule l'investissement parce qu'il réduit temporairement le coût marginal de l'investissement. Enfin, mes résultats indiquent que si l'impôt est proportionnel au profit des entreprises, l'anticipation de taxes élevées dans le futur réduit le rendement espéré de l'investissement et atténue la stimulation de l'investissement engendrée par la réduction d'impôt. Le deuxième chapitre est écrit en collaboration avec Rui Castro. Dans cet article, nous avons quantifié les effets sur les décisions individuelles d'investis-sement et de production des entreprises ainsi que sur les agrégats macroéconomiques, d'une baisse temporaire de l'impôt sur le profit des entreprises en présence de marchés financiers imparfaits. Dans un modèle où les entreprises sont sujettes à des chocs de productivité idiosyncratiques, nous avons d'abord établi que le rationnement de crédit affecte plus les petites (jeunes) entreprises que les grandes entreprises. Pour des entreprises de même taille, les entreprises les plus productives sont celles qui souffrent le plus du manque de liquidité résultant des imperfections du marché financier. Ensuite, nous montré que pour une baisse de 1 dollar du revenu de l'impôt, l'investissement et la production augmentent respectivement de 26 et 3,5 centimes. L'effet cumulatif indique une augmentation de l'investissement et de la production agrégés respectivement de 4,6 et 7,2 centimes. Au niveau individuel, nos résultats indiquent que la politique stimule l'investissement des petites entreprises, initialement en manque de liquidité, alors qu'elle réduit l'investissement des grandes entreprises, initialement non contraintes. Le troisième chapitre est consacré à l'analyse des effets de la réforme de l'imposition des revenus d'entreprise proposée par le Trésor américain en 1992. La proposition de réforme recommande l'élimination des impôts sur les dividendes et les gains en capital et l'imposition d'une seule taxe sur le revenu des entreprises. Pour ce faire, j'ai eu recours à un modèle dynamique stochastique d'équilibre général avec marchés financiers imparfaits dans lequel les entreprises sont sujettes à des chocs idiosyncratiques de productivité. Les résultats indiquent que l'abolition des impôts sur les dividendes et les gains en capital réduisent les distorsions dans les choix d'investissement des entreprises, stimule l'investissement et entraîne une meilleure allocation du capital. Mais pour être financièrement soutenable, la réforme nécessite un relèvement du taux de l'impôt sur le profit des entreprises de 34\% à 42\%. Cette hausse du taux d'imposition décourage l'accumulation du capital. En somme, la réforme engendre une baisse de l'accumulation du capital et de la production respectivement de 8\% et 1\%. Néanmoins, elle améliore l'allocation du capital de 20\%, engendrant des gains de productivité de 1.41\% et une modeste augmentation du bien être des consommateurs.