Expression of Odorant Receptor Genes in Savannah Tsetse Fly Glossina morsitans morsitans Westwood, 1850 (Diptera: Glossinidae

Abstract

Tsetse flies are the sole cyclical vectors of African trypanosomes with negative agricultural and economic impacts in sub-Saharan Africa, yet management of their populations has not been adequately addressed. Ecologically relevant molecules like odorant receptors and gustatory receptors were recently identified computationally. However, understanding the ecological behaviour of the tsetse remains limited because of absence to informative expression of the molecular data. This experimental study aimed to establish the expression levels of Glossina morsitans morsitans odorant receptor (OR) genes in the antennae and legs at different developmental stages of adults’ for sexes. Whole tissue mRNA was extracted from fresh samples of G. m. morsitans larvae, pupae, adults’ antennae and legs and used to synthesise cDNA. The Glossina morsitans morsitans Odorant Receptor genes expression levels were quantified from the cDNA relative amounts. Glossina morsitans morsitans protein sequences and Drosophila melanogaster orthologs in FlyBase and mosquitoes and other sequenced Glossina sequences from VectorBase were aligned for conserved sequences using MUSCLE alignment tool and their transmembrane domains ascertained with TMHMM tool. All the GmmORs had the 7-transmembrane domain, a hallmark feature for ORs, except GmmOR20. In adults, the OR genes were highly expressed in antennae than in the legs. GmmOR3 and GmmOR45 were dimorphically expressed in antennae in females and males respectively, while GmmOR26 and GmmOR20 were differentially expressed at high levels in female and male tsetse legs respectively. High expression OR genes in developmental stages, and particularly GmmOR28 in pupae, may suggest their involvement in development. The exclusive expression of GmmOR20 in larvae is indicative of the role this gene may play especially on feeding habits of the larvae. Higher expression of GmmOR15 in larvae also suggested that the gene product is critical in escape responses similar to confirmed role of its homolog in D. melanogaster, DmOR45. These results open avenues to determine functional roles of tsetse ORs by matching the receptors to their ecological odor ligands. This knowledge of ecologically active ORs will aid in designing effective tsetse control targets. Accordingly, the expressed OR genes established in this study should be subjected to functional studies to determine their specificity and, subsequently, their suitability to be used to be targeted in developing pest control measures.