Alternative mRNA Editing in Trypanosomes Is Extensive and May Contribute to Mitochondrial Protein Diversity

The editing of trypanosome mitochondrial mRNAs produces transcripts necessary for mitochondrial functions including electron transport and oxidative phosphorylation. Precursor-mRNAs are often extensively edited by specific uridine insertion or deletion that is directed by small guide RNAs (gRNAs). Recently, it has been shown that cytochrome c oxidase subunit III (COXIII) mRNAs can be alternatively edited to encode a novel mitochondrial membrane protein composed of a unique hydrophilic N-terminal sequence of unknown function and the C-terminal hydrophobic segment of COXIII. To extend the analysis of alternative editing in Trypanosoma brucei we have constructed libraries with over 1100 full-length mitochondrial cDNAs and the sequences of over 1200 gRNA genes. Using this data, we show that alternative editing of COXIII, ATPase subunit 6 (A6), and NADH dehydrogenase subunits 7, 8 and 9 (ND7, 8, 9) mRNAs can produce novel open reading frames (ORFs). Several gRNAs potentially responsible for the alternative editing of these mRNAs were also identified. These findings show that alternative editing of mitochondrial mRNAs is common in T. brucei and expands the diversity of mitochondrial proteins in these organisms

Mitochondrial genes support a common origin of rodent malaria parasites and Plasmodium falciparum's relatives infecting great apes

<p>Abstract</p> <p>Background</p> <p><it>Plasmodium falciparum </it>is responsible for the most acute form of human malaria. Most recent studies demonstrate that it belongs to a monophyletic lineage specialized in the infection of great ape hosts. Several other <it>Plasmodium </it>species cause human malaria. They all belong to another distinct lineage of parasites which infect a wider range of primate species. All known mammalian malaria parasites appear to be monophyletic. Their clade includes the two previous distinct lineages of parasites of primates and great apes, one lineage of rodent parasites, and presumably <it>Hepatocystis </it>species. <it>Plasmodium falciparum </it>and great ape parasites are commonly thought to be the sister-group of all other mammal-infecting malaria parasites. However, some studies supported contradictory origins and found parasites of great apes to be closer to those of rodents, or to those of other primates.</p> <p>Results</p> <p>To distinguish between these mutually exclusive hypotheses on the origin of <it>Plasmodium falciparum </it>and its great ape infecting relatives, we performed a comprehensive phylogenetic analysis based on a data set of three mitochondrial genes from 33 to 84 malaria parasites. We showed that malarial mitochondrial genes have evolved slowly and are compositionally homogeneous. We estimated their phylogenetic relationships using Bayesian and maximum-likelihood methods. Inferred trees were checked for their robustness to the (i) site selection, (ii) assumptions of various probabilistic models, and (iii) taxon sampling. Our results robustly support a common ancestry of rodent parasites and <it>Plasmodium falciparum's </it>relatives infecting great apes.</p> <p>Conclusions</p> <p>Our results refute the most common view of the origin of great ape malaria parasites, and instead demonstrate the robustness of a less well-established phylogenetic hypothesis, under which <it>Plasmodium falciparum </it>and its relatives infecting great apes are closely related to rodent parasites. This study sheds light on the evolutionary history of <it>Plasmodium falciparum</it>, a major issue for human health.</p

Giardia

The intestinal protozoan parasite Giardia duodenalis (syn. Giardia lamblia , Giardia intestinalis ) causes diarrhoea in humans and animals worldwide. The life cycle of G. duodenalis consists of two stages, the fl agellated trophozoite proliferating in the upper part of the small intestine and the non proliferative cyst representing the infectious stage of the parasite. Both stages can be handled in vitro and in vivo. Trophozoites are pear-shaped, motile cells exhibiting a convex dorsal and a concave ventral side. The cell body is formed by a microtubule cytoskeleton. The whole genome contained in two diploid nuclei per trophozoite has been sequenced and characterised. It has some prokaryote-like features such as short promoter sequences. Moreover, some key enzymes of energy and intermediate metabolisms share common features with prokaryotic enzymes and may have been acquired by lateral transfer. Giardia does not contain mitochondria and peroxisomes, but mitosomes, most likely an evolutionarily reduced version of a mitochondrion. The energy metabolism is chemoheterotrophic and works under anaerobic or semiaerobic conditions with glucose as main energy and carbon source and arginine as another important energy source. The present book chapter selectively reviews current knowledge in Giardia research highlighting its basic genetic, physiological and, to a lower extent, its immunological properties. Furthermore, this chapter also shows that G. duodenalis is a suitable cellular model system for the investigation of fundamental biological principles