RESUMO
The Id proteins are inhibitors of basic-Helix-Loop-Helix transcription factor function that have been implicated in the control of cell differentiation and proliferation. To study the role of Id proteins in the control of T cell development, we generated transgenic mice that overexpress the Id2 protein in thymocytes. We detect a significant expansion of the early CD4(-)CD8(+)TCR(-) thymocyte stage and a depletion of the thymocytes of the subsequent developmental stages. These data indicate that the overexpression of Id2 leads to a stage-specific developmental block early in thymopoiesis. In addition, progeny mice from five of the six Id2 transgenic founder lines succumb to aggressive T cell hyperproliferation that resembles lymphoma. Thus, overexpression of the Id2 protein has profound effects on T cell development and oncogenesis, consistent with the hypothesis that the bHLH proteins play critical roles in these processes.
Assuntos
Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/imunologia , Proteínas Repressoras/genética , Proteínas Repressoras/imunologia , Linfócitos T/citologia , Linfócitos T/imunologia , Fatores de Transcrição , Animais , Linfócitos T CD8-Positivos/citologia , Linfócitos T CD8-Positivos/imunologia , Diferenciação Celular/genética , Diferenciação Celular/imunologia , Divisão Celular/genética , Divisão Celular/imunologia , Feminino , Sequências Hélice-Alça-Hélice/genética , Sequências Hélice-Alça-Hélice/imunologia , Células-Tronco Hematopoéticas/citologia , Células-Tronco Hematopoéticas/imunologia , Proteína 2 Inibidora de Diferenciação , Ativação Linfocitária/genética , Linfoma de Células T/etiologia , Linfoma de Células T/genética , Linfoma de Células T/imunologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos CBA , Camundongos Transgênicos , Baço/citologia , Baço/imunologia , Subpopulações de Linfócitos T/citologia , Subpopulações de Linfócitos T/imunologia , Timo/citologia , Timo/imunologiaRESUMO
The ground level concentrations of methane in the atmosphere have been measured to be in the range from 1.45 to 1.62 parts per million by volume (ppmv) of dry air in remote locations between 62 degrees N and 54 degrees S latitudes during the time period from November 1977 to July 1979. The average (+/-rms) concentration for the northern hemisphere was 1.57 +/- 0.02 ppmv in January 1978 and 1.59 +/- 0.02 in July 1979. The average concentration in the southern hemisphere was lower-1.47 +/- 0.02 in January 1978 and 1.51 +/- 0.01 in July 1979. The ratio of concentrations between the two hemispheres was 1.068 +/- 0.016 in January 1978 and 1.055 +/- 0.013 in July 1979, for an average of 1.06 +/- 0.01. The higher concentrations in the northern hemisphere require either that the sources of methane lie preferentially in the northern hemisphere or that the removal processes operate more rapidly in the southern hemisphere or both. The primary removal process for CH(4) is reaction with tropospheric OH radicals and its estimated atmospheric lifetime is 10.5 +/- 1.8 yr. The observed interhemispheric gradient is consistent with this lifetime and preferential release of methane in the northern hemisphere. Measurements taken in the Amazon basin region indicate the presence of a substantial source of methane in that area.