Selectivity of lynx proteins on insect nicotinic acetylcholine receptors in the brown planthopper,Nilaparvata lugens

Neuronal nicotinic acetylcholine receptors (nAChRs) are major excitatory neurotransmitter receptors in both vertebrates and invertebrates. Two lynx proteins (Nl‐lynx1 and Nl‐lynx2) have been identified in the brown planthopper, Nilaparvata lugens, which act as modulators on insect nAChRs. In the present study, two lynx proteins were found to act on the triplet receptor Nlα1/Nlα2/β2 expressed in Xenopus oocytes, increasing agonist‐evoked macroscopic currents, but not changing agonist sensitivity and desensitization properties. Nl‐lynx1 and Nl‐lynx2 increased I_max (maximum responses) of acetylcholine to 4.85‐fold and 2.40‐fold of that of Nlα1/Nlα2/β2 alone, and they also increased I_max of imidacloprid to 2.57‐fold and 1.25‐fold. Although, on another triplet nAChRs Nlα3/Nlα8/β2, Nl‐lynx2 increased I_max of acetylcholine and imidacloprid to 3.63‐fold and 2.16‐fold, Nl‐lynx1 had no effects on I_max of either acetylcholine or imidacloprid. The results demonstrate the selectivity of lynx proteins for different insect nAChR subtypes. This selectivity was also identified in native N. Lugens. Co‐immunoprecipitation was found between Nlα1/Nlα2‐containing receptors and both Nl‐lynx1 and Nl‐lynx2, but was only found between Nlα3/Nlα8‐containing receptors and Nl‐lynx2. When the previously identified Nlα1^Y151S and Nlα3^Y151S mutations were included (Nlα1^Y151S/Nlα2/β2 and Nlα3^Y151S/Nlα8/β2), the increase in I_max of imidacloprid, but not acetylcholine, caused by co‐expression of Nl‐lynx1 and Nl‐lynx2 was more noticeable than that of their wildtype counterparts. Taken together, these data suggest that two modulators, Nl‐lynx1 and Nl‐lynx2, might serve as an influencing factor in target site insensitivity in N. lugens, such as Y151S mutation.     

Molecular cloning and immunolocalization of a diuretic hormone receptor in rice brown planthopper (Nilaparvata lugens)

RNA extracted from guts of rice brown planthopper, Nilaparvata lugens, was used to clone cDNA predicted to encode a diuretic hormone receptor (DHR). The DHR, a member of the calcitonin/secretin/corticotropin-releasing factor family of G-protein-coupled receptors, contains seven transmembrane domains and a large N-terminal extracellular domain potentially involved in hormone binding. The N-terminal domain was expressed as a recombinant protein, purified and used to raise antibodies. Anti-DHR IgG bound specifically to Malpighian tubules in immunolocalization experiments using dissected guts, and to a putative DHR polypeptide from N. lugens gut on Western blots. Anti-DHR IgG delivered orally to insects was not detected in the haemolymph, and showed no binding to gut or tubules, confirming that DHR N-terminal hormone-binding domain is not exposed to the gut lumen.