A Genetic Survey of the Pathogenic Parasite Trypanosoma cruzi

Sammanfattning: Trypanosoma cruzi, the causative agent of Chagas´ disease, is an evolutionarily ancient species with distinct biological and immunological characteristics. A fundamental understanding of the basic biology of the parasite is necessary in order to develop reliable therapeutic and prophylactic agents against T. cruzi. We have, as a part of the T. cruzi genome project launched by the WHO, generated ESTs corresponding to about one third of the functional genes in the parasite. Only about 1/3 of the unique ESTs could be assigned a function upon sequence comparison to all publicly available data. Comparative analysis of the ESTs to functional genes in S. cerevisiae and C. elegans as well as to sequence data from all other kinetoplastids provided primary insights into the evolutionary divergence of T. cruzi. A novel dispersed gene family (DGC3) was identified and shown to be present specifically on chromosome 3 and its homologue. Sequence analysis of ten isolated DGC3 genes revealed a high sequence similarity of almost 98% among copies. The DGC3 genes were transcribed, trans-spliced with the spliced leader and polyadenylated, but did not seem to have any protein-coding property. These data preliminary suggest that it encodes a novel family of functional RNA. In the T. cruzi CL Brener strain, the two alleles of a single copy gene encoding the trypanothione synthetase (TcTRS) enzyme appeared to be highly polymorphic. The divergence of the deduced protein sequence was 4%, almost ten-fold higher than another protein, trypanothione reductase, involved in the same pathway. The observed allelic divergence might influence the TcTRS activity thereby having implications for drug design. Moreover, the TcTRS gene was found to be flanked by a number of genes involved in diverse functions and located to a pair of homologous chromosomes with a size difference of about 2 Mbp. A gene potentially encoding the polypyrimidine-binding protein (TcPTB) was identified and characterised regarding its organisation and function. The deduced amino acid sequence was shown to comprise four RRM domains generally present in other PTBs. Interestingly, the TcPTB gene appeared to be expressed in a stage-specific manner implicating different functions during parasite development.