Subolesin gene structure and mRNA isoform diversity in South African R. microplus ticks: Relevance for understanding subolesin-based tick vaccines

Abstract

Designing a universal vaccine against ticks, capable of protecting a wide range of species, has long been an appealing goal. One antigen that has been proposed for a universal tick vaccine is Subolesin. Despite its intracellular and mostly nuclear location, this antigen has seen some success in bovine vaccine trials. The mechanism behind the observed efficacy remains elusive and may be due to various isoforms being produced in tick cells. By means of RNA sequencing and mapping to the annotated genome of R. microplus, this study confirms the presence of a single subolesin gene along with four distinct transcripts, resulting in three protein variants. However, none of the putative protein variants have extracellular location signals or known functional motifs. Furthermore, this study offers insights into the antigenic diversity of Subolesin isoforms and their expression across multiple life stages in R. microplus ticks from South Africa. This study also raise the question regarding the contrast between Subolesin's nuclear location, function, and its observed efficacy in bovine vaccine trials as an antigen accessible to the host immune system. Future studies evaluating antisera cross-reactivity with other tick proteins is therefore essential to fully understand subolesin as a protective antigen.