Heteroplasmy in the mitochondrial genomes of human lice and ticks revealed by high throughput sequencing.

Haoyu Xiong,Stephen C Barker,Renfu Shao,Thomas D Burger,Didier Raoult

doi:10.1371/journal.pone.0073329

Abstract

The typical mitochondrial (mt) genomes of bilateral animals consist of 37 genes on a single circular chromosome. The mt genomes of the human body louse, Pediculus humanus, and the human head louse, Pediculus capitis, however, are extensively fragmented and contain 20 minichromosomes, with one to three genes on each minichromosome. Heteroplasmy, i.e. nucleotide polymorphisms in the mt genome within individuals, has been shown to be significantly higher in the mt cox1 gene of human lice than in humans and other animals that have the typical mt genomes. To understand whether the extent of heteroplasmy in human lice is associated with mt genome fragmentation, we sequenced the entire coding regions of all of the mt minichromosomes of six human body lice and six human head lice from Ethiopia, China and France with an Illumina HiSeq platform. For comparison, we also sequenced the entire coding regions of the mt genomes of seven species of ticks, which have the typical mitochondrial genome organization of bilateral animals. We found that the level of heteroplasmy varies significantly both among the human lice and among the ticks. The human lice from Ethiopia have significantly higher level of heteroplasmy than those from China and France (Pt<0.05). The tick, Amblyomma cajennense, has significantly higher level of heteroplasmy than other ticks (Pt<0.05). Our results indicate that heteroplasmy level can be substantially variable within a species and among closely related species, and does not appear to be determined by single factors such as genome fragmentation.

Highlights

Mitochondrial genomes exist usually in multiple copies per cell and vary in copy number among different cells and organisms
Of the 494 heteroplasmic sites, 374 sites are in the protein-coding genes, 21 heteroplasmic sites in the rRNA genes, and 99 heteroplasmic sites in the tRNA genes (Table 2, Table S2)
Heteroplasmy occurs at a relatively low level in humans, with 32 heteroplasmic sites revealed in a human individual by high throughput sequencing at 16,700x coverage [9]

Summary

Introduction

Mitochondrial (mt) genomes exist usually in multiple copies per cell and vary in copy number among different cells and organisms. A mouse sperm has ,100 copies of mt DNA molecules whereas a mouse oocyte can have up to 100,000 copies of mt DNA molecules [2]. A sperm has 100 to 1,500 copies of mt DNA molecules whereas an oocyte can have up to 400,000 copies [3,4,5,6]. The multiple copies of mt DNA molecules in a cell or an organism often are not identical in sequence. Heteroplasmy, i.e. variation in mt genome sequence within a cell, an organism or an individual, is common in bilateral animals but usually occurs at very low levels [7,8,9,10,11]

Methods

Results

Conclusion