Elias M C, Marques-Porto R, Freymüller E, Schenkman S
Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, R. Botucatu 8628A, 04023-062 São Paulo S.P., Brazil.
Mol Biochem Parasitol. 2001 Jan 15;112(1):79-90. doi: 10.1016/s0166-6851(00)00349-2.
In trypanosomes transcription occurs as large polycistronic units, with trans-splicing and polyadenylation generating each individual mRNA. There are no defined RNA polymerase II promoters and mRNA stabilisation is most likely the process controlling levels of differentially expressed mRNAs, since no selective modulation of gene activity has even been reported at the transcriptional level. Here, we show a large decrease in the transcription rates by RNA polymerases I and II when proliferative forms of Trypanosoma cruzi (epimastigotes and amastigotes) transform into non-proliferative and infective forms (trypomastigotes). We also show that these changes in transcription occur in parallel with modifications in the nuclear structure. While nuclei of proliferative forms are round, contain small amounts of peripheral heterochromatin and a large nucleolus, nuclei of trypomastigotes are elongated, the nucleolus disappears and the heterochromatin occupies most of the nuclear compartment. The decrease in the transcription parallels the nucleolus disassembly, as seen by the dispersion of nucleolar antigens. As T. cruzi cycles continuously through proliferative and infective forms, the molecular mechanisms involved in the control of nuclear organisation and chromatin remodelling can be revealed by this system.
在锥虫中，转录以大型多顺反子单位进行，通过反式剪接和多聚腺苷酸化产生每个单独的mRNA。不存在明确的RNA聚合酶II启动子，mRNA稳定性很可能是控制差异表达mRNA水平的过程，因为甚至在转录水平上都未曾报道过基因活性的选择性调节。在此，我们发现当克氏锥虫的增殖形式（前鞭毛体和无鞭毛体）转变为非增殖性感染形式（ trypomastigotes ）时，RNA聚合酶I和II的转录速率大幅下降。我们还表明，这些转录变化与核结构的改变同时发生。增殖形式的细胞核呈圆形，含有少量外周异染色质和一个大核仁，而 trypomastigotes 的细胞核则拉长，核仁消失，异染色质占据了大部分核区室。转录的减少与核仁解体平行，这可通过核仁抗原的分散看出。由于克氏锥虫不断循环通过增殖和感染形式，该系统可以揭示参与核组织控制和染色质重塑的分子机制。
