Functional characterization of sensory neuron membrane proteins (SNMPs)

Sensory neuron membrane proteins (SNMPs) play a critical role in insect olfactory system. However, limited functional studies focused on lepidopteran SNMPs. Here we utilised approaches including bioinformatics curation, genome and transcriptome data analysis, phylogeny, expression profiling and gene knockdown techniques to investigate insect SNMPs with a specific focus on moths. We curated 81 genes from 35 insect species and identified a novel lepidopteran SNMP gene family, SNMP3. Phylogenetic analysis shows that lepidopteran SNMP3, but not the previously annotated lepidopteran SNMP2, is the true homologue of the dipteran SNMP2. Digital expression, microarray and qPCR analyses showed the lepidopteran SNMP1 is specifically expressed in adult antennae. SNMP2 is widely expressed in multiple tissues while SNMP3 is specifically expressed in the larval midgut. Microarray analysis suggest SNMP3 may be involved in the silkworm immunity response to virus and bacterial infections. Subsequently we functionally characterised SNMP1 in the silkworm using RNAi and behavioural assays. Our results suggested that Bombyx mori SNMP1 is a functional orthologue of the Drosophila melanogaster SNMP1 and plays a critical role in pheromone detection. Split-ubiquitin yeast hybridization study showed that BmorSNMP1 has a protein-protein interaction with pheromone receptor, BmorOR1 and co-receptor, BmorOrco respectively. Concluding, we propose a novel molecular model in which BmorOrco, BmorSNMP1 and BmorOR1 are three subunits and form a heteromer in the detection of sex pheromone, bombykol.