SNMP1 and odorant receptors are co-expressed in olfactory neurons of the labial and maxillary palps from the desert locust Schistocerca gregaria (Orthoptera: Acrididae).

In insects, pheromones are detected by olfactory sensory neurons (OSNs) of the antennae that co-express pheromone receptors (PRs) and the "sensory neuron membrane protein 1" (SNMP1). Beyond its relevance for pheromone detection via the antenna, little is known about a potential expression and functional role of SNMP1 in cells of other chemosensory appendages. Here, we report that in the desert locust Schistocerca gregaria, SNMP1 is also expressed in the labial and maxillary palps of the mouthparts. In the palps, the SNMP1-positive cells were situated next to the so-called terminal sensilla that are considered as chemosensory. Moreover, the SNMP1-positive cells of the palps expressed the "odorant receptor co-receptor" (Orco), a marker for OSNs endowed with odorant receptors (ORs), suggesting that these cells are olfactory. With respect to an olfactory function of the SNMP1-positive cells, further analyses examining a possible expression of ORs (notably putative PRs) in the labial and maxillary palps revealed that several members of a particular OR subfamily from S. gregaria, the b-OR group, are co-expressed with SNMP1 in cells of the palps. Interestingly, b-OR types co-expressed with SNMP1 in antennal OSNs were also co-expressed with SNMP1 in cells of the palps, indicating a specific pairing in the expression of SNMP1 and given ORs in both antennae and palps. The co-expression of SNMP1 and certain b-ORs that are regarded as candidate PRs opens up the possibility that chemosensory cells on the palps of the desert locust may contribute to pheromone detection.