Differential expression of two novel odorant receptors in the locust (Locusta migratoria)

Abstract

BackgroundOlfaction in animals is important for host localization, mating and reproduction in heterogeneous chemical environments. Studying the molecular basis of olfactory receptor neurons (ORNs) systems can elucidate the evolution of olfaction and associated behaviours. Odorant receptors (ORs) in insects have been identified, particularly in the holometabolous model Drosophila, and some of them have been functionally studied. However, ORs in the locust—a hemimetabolous model insect and the most important insect crop pest—have not yet been identified, hindering our understanding of locust olfaction. Here, we report for the first time four putative ORs in Locusta migratoria: LmigOR1, LmigOR2, LmigOR3 and LmigOR4.ResultsThese four putative OR genes encoded proteins with amino acids of 478, 436, 413 and 403 respectively. Sequence identity among them ranged from 19.7% to 35.4%. All ORs were tissue-specifically expressed in olfactory organs, without sex-biased characteristics. However, LmigOR1, LmigOR3 and LmigOR4 were only expressed in the antenna, while LmigOR2 could also be detected in mouthparts. In situ hybridization demonstrated that the LmigOR1antisense probe labelled olfactory receptor neurons (ORNs) in almost all segments of the antenna, but only a few segments housed ORNs expressing LmigOR2. The number of neurons labelled by LmigOR1 antisense probes in each antennal segment was much greater (>10 neurons/segment) than that labelled by LmigOR2 probes (generally 1–3 neurons/segment). Furthermore, some of the labelled neurons could be attributed to the basiconic sensilla, but LmigOR1 and LmigOR2 were expressed in different subtypes.ConclusionsOur results strongly suggested that these newly discovered genes encode locust ORs and the differential expression patterns of LmigOR1 and LmigOR2 implied distinct functions. These results may offer insights into locust olfaction and contribute to the understanding of the evolution of insect chemoreception.

A broadly tuned odorant receptor in neurons of trichoid sensilla in locust, Locusta migratoria

“…Previous PCR experiment results showed that LmigOR3 was specifically expressed in the antennae of locust from nymph to adult at high levels (Xu et al, 2013). To localize LmigOR3 expression to a type of sensillum, we performed in situ hybridization experiments with DIG-labeled LmigOR3 sense and antisense probes.…”

“…Adult locusts ( L. migratoria ) in this study were obtained and raised as previously described (Xu et al, 2013). Intact antennae were dissected using forceps and stored at −80°C until further processing for in situ hybridization or to recover mRNA.…”

“…Digoxigenin (DIG)-labeled LmigOR3 antisense and sense probes were generated from linearized recombinant pGem-T Easy plasmids using the T7/SP6 RNA transcription system (Roche, Basel, Switzerland) following recommended protocols, as described previously, except that the probes were not fragmented by incubation in carbonate buffer (Xu et al, 2013). RNA in situ hybridization and analysis was also performed as described previously (Xu et al, 2013).…”

“…There is very limited knowledge on molecular mechanisms of olfaction which mediates locust behaviors though many locust OR genes have been identified (Xu et al, 2013; Wang et al, 2015). Understanding the molecular olfaction mechanisms that underlie these behaviors will be helpful to develop new locust control methods based on the functions of odorant receptors.…”

“…Some types of ORNs in locust trichoid sensilla were identified with single sensilla recording technology (Cui et al, 2011; Ochieng and Hansson, 1999). Recently, locust odorant receptors, LmigOR1 and LmigOR2 have been demonstrated to be expressed in different neurons housed in basiconic sensilla (Xu et al, 2013). To date, no locust ORs have been localized in trichoid sensilla and functionally studied so far.…”