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Un cuerpo transcripcional poli I asociado con la expresión monoalélica de VSG en Trypanosoma brucei
1Present address: Instituto de Parasitología y Biomedicina 'López-Neyra', CSIC, C/ Ventanilla 11, 18001 Granada, Spain. miguel.navarro@ipb.csic.es
Nature
|December 14, 2001
Resumen
Los tripanosomas africanos controlan la expresión génica cambiando su capa superficial. Un cuerpo nuclear recientemente descubierto que contiene ARN polimerasa I (pol I) organiza la expresión activa de la glicoproteína de superficie variante (VSG), asegurando una sola visualización de tipo VSG.
Área de la Ciencia:
- Biología Molecular Biología Molecular
- Parasitología Parasitología.
- Biología celular Biología celular.
Sus antecedentes:
- Los tripanosomas africanos evaden el sistema inmunológico del huésped alterando su capa superficial.
- Esta capa comprende un solo tipo de glicoproteína de superficie variante (VSG) en un momento dado.
- El mecanismo para expresar solo un tipo de VSG de múltiples loci de genes sigue sin estar claro.
Objetivo del estudio:
- Investigar el mecanismo molecular que controla la expresión de la glicoproteína de superficie variante monoalélica (VSG) en los tripanosomas africanos.
- Para identificar las estructuras celulares involucradas en la regulación de la transcripción del gen VSG.
Principales métodos:
- Utilizamos imágenes de células vivas con etiquetado de proteínas fluorescentes verdes para visualizar los loci de genes activos.
- Caracterizó un nuevo cuerpo extranucleolar que contiene ARN polimerasa I (pol I).
- Evaluó la estabilidad y la composición del cuerpo transcripcional.
Principales resultados:
- Se identificó un cuerpo extranucleolar único, transcripcionalmente activo, que contiene ARN polimerasa I (pol I) en trypanosomes en forma de torrente sanguíneo.
- Se demostró que el único sitio activo de expresión de VSG se localiza en esta fábrica transcripcional específica.
- Se demostró que el cuerpo transcripcional es una estructura nuclear estable y coherente presente en los núcleos postmitóticos.
Conclusiones:
- Un cuerpo transcripcional discreto de ARN polimerasa I (pol I) actúa como una "fábrica" para la expresión génica de VSG.
- El reclutamiento de un solo sitio de expresión de VSG en este cuerpo y la exclusión de otros impone la expresión monoalélica.
- Este mecanismo proporciona información crucial sobre la variación antigénica y la supervivencia de los parásitos.
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