Immunocytochemical localization of pheromone-binding protein in moth antennae

Abstract

Odorant-binding proteins are supposed to play an important role in stimulus transport and/or inactivation in olfactory sense organs. In an attempt to precisely localize pheromone-binding protein in the antenna of moths, post-embedding immunocytochemistry was performed using an antiserum against purified pheromone-binding protein of Antheraea polyphemus. In immunoblots of antennal homogenates, the antiserum reacted exclusively with pheromone-binding protein of A. polyphemus, and cross-reacted with homologous proteins of Bombyx mori and Autographa gamma. On sections of antennae of male A. polyphemus and B. mori, exclusively the pheromone-sensitive sensilla trichodea are labelled; in A. gamma, label is restricted to a subpopulation of morphologically similar sensilla trichodea, which indicates that not all pheromone-sensitive sensilla contain the same type of pheromone-binding protein and accounts for a higher specificity of pheromone-binding protein than hitherto assumed. Within the sensilla trichodea, the extracellular sensillum lymph of the hair lumen and of the sensillum-lymph cavities is heavily labelled. Intracellular label is mainly found in the trichogen and tormogen cells: in endoplasmic reticulum, Golgi apparatus, and a variety of dense granules. Endocytotic pits and vesicles, multivesicular bodies and lysosome-like structures are also labelled and can be observed not only in these cells, but also in the thcogen cell and in the receptor cells. Cell membranes are not labelled except the border between thecogen cell and receptor cell and the autojunction of the thecogen cell. The intracellular distribution of label indicates that pheromone-binding protein is synthesized in the tormogen and trichogen cell along typical pathways of protein secretion, whereas its turnover and decomposition does not appear to be restricted to these cells but may also occur in the thecogen and receptor cells. The immunocytochemical findings are discussed with respect to current concepts of the function of pheromone-binding protein.