Avaliação de testes estatísticos em dados de Q-PCR.

A Q-PCR (Quantitative Polymerase Chain Reaction) é uma técnica que permite quantificar de forma precisa, especifica e indireta a quantidade de RNA mensageiro presente em uma determinada amostra. A Q-PCR apresenta vantagens metodológicas para a quantificação do RNA mensageiro quando comparada às técnicas de Northern Blot e Reverse Transcription Polymerase Chain Reaction, facilitando estudos de expressão gênica diferenciada. No entanto, experimentos de Q-PCR freqüentemente apresentam limitações amostrais (6= N =12) e são analisados por testes estatísticos tradicionais (paramétricos) sem a devida verificação da condição de normalidade da variável resposta e de homogeneidade das variâncias dos grupos experimentais, exigidas nesses testes. O presente trabalho avaliou quatro testes estatísticos de comparação de médias e/ou medianas, entre os grupos controle(C) e tratado (T), com objetivo de propor o teste mais adequado para estudar expressão gênica com dados de Q-PCR. O experimento foi realizado na Embrapa Pecuária Sudeste ? São Carlos, Brasil, utilizando 10 bezerros Nelore (Bos indicus), divididos aleatoriamente em dois grupos de cinco animais: grupo tratado (T) infestado artificialmente com carrapatos Rhipicephalus (Boophilus) microplus e grupo controle (C) livre de infestação. Os dados foram submetidos a quatro diferentes testes estatísticos, sendo o primeiro paramétrico (ANOVA com teste t) e os demais não-paramétricos (teste de mediana, boot strap, e Rest.). Quando o gene referência (gene de expressão constitutiva) apresentou pequena variação entre os tratamentos (0,6 = P = 1) os testes estatísticos, com exceção do teste de mediana, apresentaram valores de probabilidade confiáveis e semelhantes. Porém, quando o gene referência apresentou variação entre os tratamentos (P = 0,6) todos os testes apresentaram resultados distintos, e o teste Rest©, não-paramétrico, de comparações das médias e com ajustes para eficiência de amplificação do primer e valores de probabilidade do gene referência, foi o mais adequado para analisar dados de Q-PCR

Quantificação de mRNA de genes relacionados a resposta imune em abomaso de bovinos infectados com endoparasitos Haemonchus spp.

No sudeste brasileiro os endoparasitos que causam maiores perdas na produção de bovinos são do gênero Haemonchus spp e Cooperia spp. Esses são responsáveis por uma série de alterações tanto na imunidade inata quanto adquirida do hospedeiro. Desta maneira, o objetivo deste trabalho foi verificar a diferença na abundância de RNA mensageiro de genes relacionados à resposta imune no abomaso de bovinos submetidos a 1ª infecção com Haemonchus spp. Foi obtido RNA total de dois grupos de cinco bezerros da raça Nelore, um grupo desafio infectado com Haemonchus spp e um grupo controle, sem infecção. A quantificação dos genes foi feita pela técnica de transcrição reversa seguida de reação em cadeia da polimerase em tempo real (RT-PCR), utilizando o gene constitutivo RPL-19, como controle e SYBR Green, como corante. Os resultados Obtidos foram analisados pelo programa computacional REST (Relative Expression Software Tool). Não foram encontradas diferenças significativas (P > 0,05) de abundância de mRNA para os genes de interleucinas (IL-2, IL-8 e IL-13), lisozima, proteína de atração de monócitos (MCP-1) e pepsinogênio entre os grupos tratamento e controle analisados. Pode-se concluir que para o tecido analisado, assim como para o tempo de infecção e número de indivíduos por grupo não houve alteração na abundância de transcritos destes genes relacionados à resposta imune

Quantum spin pumping mediated by magnon

We theoretically propose quantum spin pumping mediated by magnons, under a time-dependent transverse magnetic field, at the interface between a ferromagnetic insulator and a non-magnetic metal. The generation of a spin current under a thermal equilibrium condition is discussed by calculating the spin transfer torque, which breaks the spin conservation law for conduction electrons and operates the coherent magnon state. Localized spins lose spin angular momentum by emitting magnons and conduction electrons flip from down to up by absorbing the momentum. The spin transfer torque has a resonance structure as a function of the angular frequency of the applied transverse field. This fact is useful to enhance the spin pumping effect induced by quantum fluctuations. We also discuss the distinction between our quantum spin pumping theory and the one proposed by Tserkovnyak et al.Comment: 27 pages, 2 figures. v2; the detail of the calculation has been added in Appendix. The distinction from the spin pumping theory proposed by Tserkovnyak et al. has been clarified in section 5. v3; typos correcte

Mixed perturbative expansion: the validity of a model for the cascading

A new type of perturbative expansion is built in order to give a rigorous derivation and to clarify the range of validity of some commonly used model equations. This model describes the evolution of the modulation of two short and localized pulses, fundamental and second harmonic, propagating together in a bulk uniaxial crystal with non-vanishing second order susceptibility $\chi^(2)$ and interacting through the nonlinear effect known as ``cascading'' in nonlinear optics. The perturbative method mixes a multi-scale expansion with a power series expansion of the susceptibility, and must be carefully adapted to the physical situation. It allows the determination of the physical conditions under which the model is valid: the order of magnitude of the walk-off, phase-mismatch,and anisotropy must have determined values.Comment: arxiv version is already officia

Far-ultraviolet Spectroscopy of Venus and Mars at 4 A Resolution with the Hopkins Ultraviolet Telescope on Astro-2

Far-ultraviolet spectra of Venus and Mars in the range 820-1840 A at 4 A resolution were obtained on 13 and 12 March 1995, respectively, by the Hopkins Ultraviolet Telescope (HUT), which was part of the Astro-2 observatory on the Space Shuttle Endeavour. Longward of 1250 A, the spectra of both planets are dominated by emission of the CO Fourth Positive band system and strong OI and CI multiplets. In addition, CO Hopfield-Birge bands, B - X (0,0) at 1151 A and C - X (0,0) at 1088 A, are detected for the first time, and there is a weak indication of the E - X (0,0) band at 1076 A in the spectrum of Venus. The B - X band is blended with emission from OI 1152. Modeling the relative intensities of these bands suggests that resonance fluorescence of CO is the dominant source of the emission, as it is for the Fourth Positive system. Shortward of Lyman-alpha, other emission features detected include OII 834, OI lambda 989, HI Lyman-beta, and NI 1134 and 1200. For Venus, the derived disk brightnesses of the OI, OII, and HI features are about one-half of those reported by Hord et al. (1991) from Galileo EUV measurements made in February 1990. This result is consistent with the expected variation from solar maximum to solar minimum. The ArI 1048, 1066 doublet is detected only in the spectrum of Mars and the derived mixing ratio of Ar is of the order of 2%, consistent with previous determinations.Comment: 8 pages, 5 figures, accepted for publication in ApJ, July 20, 200

Scaling and Crossover to Tricriticality in Polymer Solutions

We propose a scaling description of phase separation of polymer solutions. The scaling incorporates three universal limiting regimes: the Ising limit asymptotically close to the critical point of phase separation, the "ideal-gas" limit for the pure-solvent phase, and the tricritical limit for the polymer-rich phase asymptotically close to the theta point. We have also developed a phenomenological crossover theory based on the near-tricritical-point Landau expansion renormalized by fluctuations. This theory validates the proposed scaled representation of experimental data and crossover to tricriticality.Comment: 4 pages, 3 figure

Oncogenic ras induces gastrin gene expression in colon cancer

AbstractBackground & Aims: The expression of gastrin, as a tumor growth factor, is significantly increased in some colon cancers compared with the low levels found in normal mucosa. The aim of this study was to elucidate the transcriptional mechanisms of gastrin induction in colon cancer. Methods: Gastrin messenger (mRNA) levels and K-ras genotype were determined in colon cancer cell lines and surgical specimens. Colon cancer cells were transfected with oncogenic ras expression vectors, and transcriptional activity was assayed with gastrin-luciferase reporter genes. Results: Colon cancer cell lines and tissues with K-ras mutations all had significantly higher gastrin mRNA levels than those that were ras wild type. Treatment of several ras mutant cell lines with PD98059, an inhibitor of mitogen-activated protein kinase kinase, resulted in a decrease in endogenous gastrin mRNA levels. The effects of ras on gastrin expression appeared to be mediated through the gastrin promoter because transfection of oncogenic ras and activated raf expression vectors both induced gastrin-promoter, luciferase-reporter genes. The inductive effects of oncogenic ras could be blocked by the coexpression of dominant negative forms of raf and extracellular regulated kinase. Conclusions: Oncogenic ras induces gastrin gene expression through activation of the Raf-MEK-ERK signal transduction pathway.GASTROENTEROLOGY 1998;115:1144-115