Fine structure immunocytochemistry permitted the localization of proteins, which are presumably relevant to olfactory signal transduction in the olfactory sensilla of the silkmoths Bombyx mori (Lepidoptera: Bombycidae), Antheraea pernyi and Antheraea polyphemus (Lepidoptera: Saturniidae). Odorant-binding proteins of different classes, pheromone-binding protein and general odorant-binding protein 2, were localized in different olfactory sensilla. The expression pattern of these proteins among the population of olfactory sensilla was analysed and correlated with the olfactory specificity of sensilla. The results support the notion that odorant-binding proteins may play a multifunctional role in olfactory signal transduction. Further immunocytochemical experiments concerned the intracellular signalling pathways. A G-protein of the G(q)-family and an inositol 1,4,5-trisphosphate-receptor, which is an inositol 1,4,5-trisphosphate-dependent Ca2+-channel, were localized in the receptive dendrites of olfactory receptor cells and other parts of the neuroepithelium. Both molecules are involved in the inositol 1,4,5-trisphosphate/diacylglycerol second messenger pathway, which is supposed to mediate olfactory signal transduction in insects. Calmodulin, an ubiquitous calcium-binding protein, and calcineurin, a Ca2+/calmodulin-regulated phosphatase, were also localized at high labelling densities in the dendrites of olfactory receptor cells. This co-expression and the finding that a Ca2+-channel (the inositol 1,4,5-trisphosphate-receptor) is localized in the receptor cell dendrites supports the notion that calcium plays a role in olfactory signal transduction. Finally, a possible nitric oxide-synthase was localized in the haemolymph, which suggests that the localized form of the enzyme has no functional relevance for olfactory signal transduction. (C) 1997 Elsevier Science Ltd. All rights reserved.
