Odor-detection in the
malaria mosquito Anopheles gambiae involves large families of diverse
proteins, including multiple odorant
binding proteins (AgOBPs) and
olfactory receptors (AgORs). The receptors AgOR1 and AgOR2, as well as the
binding protein AgOBP1, have been implicated in the recognition of human host odors. In this study, we have explored the expression of these olfactory
proteins, as well as the ubiquitous
odorant receptor heteromerization partner AgOR7, in the thirteen flagellomeres (segments) of female and male antenna. Expressing cells were visualized by adapting a whole mount fluorescence in situ hybridization method. In female mosquitoes, AgOR1-expressing olfactory receptor neurons (ORNs) were almost exclusively segregated in segments 3 to 9, whereas AgOR2-expressing ORNs were distributed over flagellomeres 2 to 13. Different individuals comprised a similar number of cells expressing a distinct
AgOR type, although their antennal topography and number per flagellomere varied. AgOBP1-expressing support cells were present in segments 3 to 13 of the female antenna, with increasing numbers towards the distal end. In male mosquitoes, total numbers of
AgOR- and AgOBP1-expressing cells were much lower. While AgOR2-expressing cells were found on both terminal flagellomeres, AgOR1 cells were restricted to the most distal segment. High densities of AgOBP1-expressing cells were identified in segment 13, whereas segment 12 comprised very few. Altogether, the results demonstrate that both sexes express the two
olfactory receptor types as well as the
binding protein AgOBP1 but there is a significant sexual dimorphism concerning the number and distribution of these cells. This may suggest gender-specific differences in the ability to detect distinct odorants, specifically human host-derived volatiles.