Control of gene expression and genetic manipulation in the Trypanosomatidae

Mechanisms controlling gene expression in trypanosomatids depend on several layers of regulation, with most regulatory pathways acting at a post-transcriptional level. Consequently, these parasites can follow the rapid changes associated with transitions between the insect vector and the mammalian host, with instant reprogramming of genetic expression. Using primarily Trypanosoma brucei as a model, the basic controlling mechanisms have been elucidated and now researchers are beginning to define the cellular factors involved in the transcription, processing and translation of the mRNAs in these parasites. We describe some of the studies made on a subset of genes that are differentially expressed during the life cycles of T. brucei and T. cruzi. It is becoming evident that the regulatory strategies chosen by different species of trypanosomatids are not the same, and therefore, the lessons learned from one species do not necessarily apply to the others. Some of the tools available for genetic manipulation that have been developed along with these studies are also described. Two of them are of particular interest in this postgenomic period: inducible systems to express foreign genes and specific inhibition of gene expression by RNA interference

Control of gene expression in Trypanosomatidae

The study of mechanisms which control gene expression in trypanosomatids has developed at an increasing rate since 1989 when the first successful DNA transfection experiments were reported. Using primarily Trypanosoma brucei as a model, several groups have begun to elucidate the basic control mechanisms and to define the cellular factors involved in mRNA transcription, processing and translation in these parasites. This review focuses on the most recent studies regarding a subset of genes that are expressed differentially during the life cycle of three groups of parasites. In addition to T. brucei, I will address studies on gene regulation in a few species of Leishmania and the results obtained by a much more limited group of laboratories studying gene expression in Trypanosoma cruzi. It is becoming evident that the regulatory strategies chosen by different species of trypanosomatids are not similar, and that for these very successful parasites it is probably advantageous to employ multiple mechanisms simultaneously. In addition, with the increasing numbers of parasite genes that have now been submitted to molecular dissection, it is also becoming evident that, among the various strategies for gene expression control, there is a predominance of regulatory pathways acting at the post-transcriptional level

A comparison of counterimmunoelectrophoresis and indirect haemagglutination tests for the immunoepidemiological investigation of kala-azar.

Counterimmunoelectrophoresis (CIE) using cell-free extracts of Leishmania donovani promastigotes and Trypanosoma brucei as antigens and indirect haemagglutination (IHA) using commercially prepared reagents were compared for their diagnostic efficacy and applicability to immunoepidemiological studies in an area of Bangladesh where kala-azar is present. The CIE was positive for all parasitologically confirmed cases whereas the IHA positivity was only 60%. The T. brucei antigen was equally as good, if not better, than the L. donovani antigen for CIE. The CIE test was negative for all of 34 apparently healthy villagers. For this same group of individuals, 10 (29%) were low titre-IHA positive. The findings suggest that CIE is the more reliable diagnostic test but both methods should be employed for immunoepidemiological investigations.