Orco-dependent survival of odorant receptor neurons in ants.

Abstract

Olfaction is essential for complex social behavior in insects. To discriminate complex social cues, ants evolved an expanded number of <i>odorant receptor</i> (<i>Or</i>) genes. Mutations in the obligate odorant co-receptor gene <i>orco</i> lead to the loss of ~80% of the antennal lobe glomeruli in the jumping ant <i>Harpegnathos saltator</i>. However, the cellular mechanism remains unclear. Here, we demonstrate massive apoptosis of odorant receptor neurons (ORNs) in the mid to late stages of pupal development, possibly due to ER stress in the absence of Orco. Further bulk and single-nucleus transcriptome analysis shows that, although most <i>orco</i>-expressing ORNs die in <i>orco</i> mutants, a small proportion of them survive: They express <i>ionotropic receptor</i> (<i>Ir</i>) genes that form IR complexes. In addition, we found that some <i>Or</i> genes are expressed in mechanosensory neurons and nonneuronal cells, possibly due to leaky regulation from nearby non-<i>Or</i> genes. Our findings provide a comprehensive overview of ORN development and <i>Or</i> expression in <i>H. saltator</i>.