Novel organization of mitochondrial minicircles and guide RNAs in the zoonotic pathogen Trypanosoma lewisi

Abstract

Kinetoplastid flagellates are known for several unusual features, one of which is their complex mitochondrial genome, known as kinetoplast (k) DNA, composed of mutually catenated maxi- and minicircles. Trypanosoma lewisi is a member of the Stercorarian group of trypanosomes which is, based on human infections and experimental data, now considered a zoonotic pathogen. By assembling a total of 58 minicircle classes, which fall into two distinct categories, we describe a novel type of kDNA organization in T. lewisi. RNA-seq approaches allowed us to map the details of uridine insertion and deletion editing events upon the kDNA transcriptome. Moreover, sequencing of small RNA molecules enabled the identification of 169 unique guide (g) RNA genes, with two differently organized minicircle categories both encoding essential gRNAs. The unprecedented organization of minicircles and gRNAs in T. lewisi broadens our knowledge of the structure and expression of the mitochondrial genomes of these human and animal pathogens. Finally, a scenario describing the evolution of minicircles is presented.

Euglenozoa: taxonomy, diversity and ecology, symbioses and viruses

“…Kinetoplastids harbour in their mitochondrial DNA in the form of relaxed (rarely supercoiled) circular molecules, either catenated or free, of two types—maxicircles and minicircles, with the former carrying all protein-coding genes, while the latter encode guide RNA genes required for the editing of the maxicircle transcripts [ 23 ]. The size of maxicircles is rather uniform, while the minicircles come in different variants [ 24 ]. In diplonemids, the single type of non-catenated circles uniquely encodes fragments of protein-coding genes, the transcripts of which have to be massively trans -spliced and edited in order to become translatable [ 25 ].…”

Complete minicircle genome ofLeptomonas pyrrhocorisreveals sources of its non-canonical mitochondrial RNA editing events

“…Indeed, the structure, size and organization of kDNA minicircles vary dramatically among trypanosomatids ( 8 , 27 , 28 ). While there are clearly significant differences in gRNA population and minicircle organization among various trypanosomatids ( 29 ), any comparative analysis suffers from a narrow set of species for which a complete and validated minicircle population is available. Furthermore, no study has directly investigated what the impact of gRNA population complexity might be for a species.…”

First finding of free-living representatives of Prokinetoplastina and their nuclear and mitochondrial genomes

“…A. spiralis gDNA contigs could not be circularized using a seed-and-extend approach, and are likely linear molecules. Confirmation of gRNA gene size and number would benefit from RNA-seq of libraries enriched for small RNAs 42 .…”