Transcriptional and post-transcriptional gene regulatory mechanisms in the malaria parasite, Plasmodium falciparum

Abstract

Malaria is a devastating disease which affects almost half of the world’s population. Since the description of the malaria genome sequence, various aspects of the parasite have been studied, including drug resistance mechanisms, epidemiology and surveillance systems. Alarmingly, very little is known about the basic biological processes such as the regulation of the expression of parasite genes. The parasite, Plasmodium falciparum, has developed highly specialized methods of regulating the transcription of genes, starting at the regulation of genes controlling basic cellular processes such as protein synthesis and erythrocyte invasion, followed by the transcriptional regulation of more specialized genes, such as those aiding in immune evasion and pathogenesis. The description of the P. falciparum transcriptome by Bozdech et al. in 2003 revealed a complex, just-in-time and tightly regulated transcription profile of P. falciparum genes. This suggests that the most probable Achilles heel for Plasmodium may be its unique mechanisms of regulating gene expression. Various cis- and trans-regulatory sequences have been identified in P. falciparum, along with possible DNA (and RNA) binding proteins. The first part of this research focussed on transcriptional regulatory mechanisms in which an in silico search identified cis-regulatory sequences in the 5’ untranslated region of the antigenically variant var gene family. Electrophoretic mobility shift assays (EMSA) were used to identify protein binding partners of these sequences, which could ultimately act as transcription factors in regulating the expression of this essential gene family. The second part of the research investigated the involvement of post-transcriptional regulatory mechanisms in the polyamine biosynthetic pathway of P. falciparum. Polyamines have been proven to be crucial for the parasite’s development and therefore, an RNA interference knock-down strategy was used to verify the importance of the polyamine biosynthetic enzymes S-Adenosylmethionine decarboxylase (AdoMetDC), Ornithine decarboxylase (ODC) and Spermidine synthase. It is clear that various mechanisms for gene regulation are used by the parasite and that this is critical for the survival of this organism. The results of this study suggest the potential presence of both double-stranded and single-stranded DNA regulatory proteins within P. falciparum nuclear extract. As controversial as RNA interference remains in P. falciparum, this technique was used as a plausible knock-down strategy of parasite specific genes and certain trends, regarding the visible decreases in gene transcript level after double-stranded RNA treatment, were observed. However, final conclusions as to the feasibility of using RNA interference in P. falciparum remain to be elucidated. This study therefore ultimately lends insight into the transcriptional and post-transcriptional levels of P. falciparum gene regulation.