Expression of odorant co-receptor Orco in tissues and development stages of Glossina morsitans morsitans, Glossina fuscipies fuscipies and Glossina pallidipies

Abstract

Tsetse flies (Glossina) depend on their olfactory system to identify host, larviposition sites and mates. Previous studies have characterized olfactory organs and evaluated the odorant receptor (OR) expression to host-derived chemicals. However, no studies thus far have investigated the odorant co-receptor (Orco) associated with these olfaction processes in tissues and developmental stages in tsetse flies. In this study, quantitative polymerase chain reaction was done with Glossina morsitans morsitans, Glossina pallidipies and Glossina fuscipes fuscipes tissues (antennae and legs) and developmental stage (larvae and pupae) to quantify Orco expression levels and G. m. morsitans OR genes in G. m. morsitans larvae and pupae. Our findings indicate that expression of Orco were elevated in G. f. fuscipes male antennae and legs relative to G. f. fuscipes female antennae and relative to male antennae in G. m. morsitans and G. pallidipies. However, in female G. m. morsitans antennae, expression of Orco was higher than in female G. pallidipies and G. f. fuscipes. Orco levels were also significantly higher in pupal stages of G. f. fuscipes and G. pallidipies relative to the three larval stages and G. m. morsitans pupae. Two G. m. morsitans OR genes (GmmOR20 and GmmOR28) were highly expressed in G. m. morsitans larvae and pupae respectively. This study demonstrate that the Orco gene was significantly expressed in adult male and female tissues as well as in the developmental stages of Glossina species. The G. m. morsitans OR genes reported in larvae and pupae could mean co-expression of Orco and ORs in developmental stages. These findings pinpointed the olfactory differences that exists amongst G. m. morsitans, G. pallidipies and G. f. fuscipes, and provide valuable information to the probable role of olfactory genes in Glossina contributing further to the understanding of olfactory processes and the evolution of olfactory genes in tsetse flies. Keywords: Glossina, Olfaction, Orco, Odorant receptors, RNA expression