The minichromosomes of livestock-infecting African Trypanosomes

Abstract

Animal-infecting trypanosomes amongst subgenus Nannomonas pose severe threats to food security across Sub-Saharan Africa, yet the species associated with these infections have been largely left behind in the modern era of trypanosome research, with only a handful of incomplete genomic sequences available. The objective of this investigation was to characterise a similarly ignored portion of the trypanosome genome – the minichromosomes (MCs) - for six taxa within subgenus Nannomonas, and to compare them to the better known T.b. brucei MCs. MCs are highly repetitive, linear chromosomes involved in the process of antigenic variation, acting as VSG gene libraries. The traditional karyotype visualisation technique Pulsed Field Gel Electrophoresis (PFGE) was refined for the comparative analysis of MCs belonging to the Nannomonas species and findings of species-specific MC size classes were used to guide the recovery of minichromosomes from whole genome sequence data. A bioinformatic pipeline for the extraction, assembly and annotation of MCs from PacBio genome data was generated. This was more successful for some species than others, which in itself reflected species-specific differences in MC structure. Statistical comparisons characterised these differences in detail and an-notation of assembled MC contigs showed that they also displayed species-specific differences in gene content. These findings challenge our previous understanding of MC structure and genesis, highlighting the importance of avoiding inter-specific generalisations based on T. brucei and providing direction for further investigation.

Date of Award	23 Mar 2021
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Wendy C Gibson (Supervisor) & Tom Williams (Supervisor)