Comparative transcriptome analysis of small non-coding RNAs in different life stages of Trypanosoma bruce

Trypanosoma brucei, a pathogen of human and domestic animals, is an early evolved protozoan with a complex life cycle. Most genes of this parasite are post-transcriptionally regulated. But the mechanisms and the molecules involved remain largely unknown. We have deep-sequenced the small RNAs of two life stages of this parasite, the blood slender and the insect procyclic form. Surprisedly, there is a significant difference of small RNA types and expressions during different environment stages. The dominant part of small RNAs in both stages are siRNAs, our results shown that siRNAs could derive from multiple sources and have uniform features in two life stages, but the expressions are more abundant in the slender-form stage. Dicer knockdown evidence shows that the endo-siRNAs could regulate the expression of genes in this parasite. In addition, the results showed the production of an abundant class of small RNAs preferentially restricted to the specific position of rRNA and tRNA molecules. These small RNAs are not meaningless random degradation producers but specially processed molecules. All the three types of small RNAs have significant dynamic change between two life stages. Our results show the sources, features and functions of small RNAs in T. brucei, which amount to a more complex picture than previously thought. The results also shed light on questions regarding the origins and evolution of small RNA-based mechanisms in early eukaryotes.