Manning-Cela Rebeca, Jaishankar Sobha, Swindle John
Departamento de Biomedicina Molecular, Centro de Investigación y de Estudios Avanzados del IPN, México, D.F., México.
Arch Med Res. 2006 Jul;37(5):593-601. doi: 10.1016/j.arcmed.2005.11.013.
Trypanosoma cruzi, the causative agent of Chagas disease, exhibits a complex life cycle that is accompanied by the stage-specific gene expression. At the molecular level, very little is known about gene regulation in trypanosomes. Complex gene organizations coupled with polycistronic transcription units make the analysis of regulated gene expression difficult in trypanosomes. The ubiquitin genes of T. cruzi are a good example of this complexity. They are organized as a single cluster containing five ubiquitin fusion (FUS) and five polyubiquitin (PUB) genes that are polycistronically transcribed but expressed differently in response to developmental and environmental changes.
Gene replacements were used to study FUS and PUB gene expression at different stages of growth and at different points in the life cycle of T. cruzi.
Based on the levels of reporter gene expression, it was determined that FUS1 expression was downregulated as the parasites approached stationary phase, whereas PUB12.5 polyubiquitin gene expression increased. Conversely, FUS1 expression increases when epimastigotes and amastigotes differentiate into trypomastigotes, whereas the expression of PUB12.5 decreases when epimastigotes differentiate into amastigotes and trypomastigotes.
Although the level of CAT activity in logarithmic growing epimastigotes is six- to seven-fold higher when the gene was expressed from the FUS1 locus than when expressed from the PUB12.5 locus, the rate of transcription from the two loci was the same implying that post-transcriptional mechanisms play a dominant role in the regulation of gene expression.
克氏锥虫是恰加斯病的病原体，其具有复杂的生命周期，并伴随着阶段特异性基因表达。在分子水平上，对于锥虫中的基因调控知之甚少。复杂的基因组织与多顺反子转录单元使得在锥虫中分析受调控的基因表达变得困难。克氏锥虫的泛素基因就是这种复杂性的一个很好例子。它们被组织成一个单一的簇，包含五个泛素融合（FUS）基因和五个多聚泛素（PUB）基因，这些基因以多顺反子形式转录，但在发育和环境变化时表达不同。
采用基因替换法研究克氏锥虫在不同生长阶段和生命周期不同时间点的FUS和PUB基因表达。
根据报告基因的表达水平，确定随着寄生虫接近稳定期，FUS1表达下调，而PUB12.5多聚泛素基因表达增加。相反，当无鞭毛体和无鞭毛体分化为锥鞭毛体时，FUS1表达增加，而当无鞭毛体分化为无鞭毛体和锥鞭毛体时，PUB12.5的表达降低。
尽管当基因从FUS1基因座表达时，对数生长期无鞭毛体中的CAT活性水平比从PUB12.5基因座表达时高6至7倍，但两个基因座的转录速率相同，这意味着转录后机制在基因表达调控中起主导作用。
