IMMUNOCYTOCHEMICAL LOCALIZATION OF LIPOPHORIN IN THE FAT-BODY OF DRAGONFLY LARVAE (AESHNA-CYANEA)

Immunocytochemistry using affinity-purified polyclonal antilipophorin revealed extracellular and intracellular locations of lipophorin in the fat body of dragonfly larvae. Lipophorin was associated with the external surface of the superficial and lateral plasma membranes which are directly exposed to the haemolymph. This location probably plays a role in the extracellular lipid-loading and unloading of lipophorin. Lipophorin was detected in the endoplasmic reticulum, Golgi apparatus and small vesicles located in the trans Golgi network region. These locations were interpreted as the secretory pathway of nascent lipophorin. Lipophorin was localized in various membrane-bound compartments which were identified as endosomes using biotinyl lipophorin and horseradish peroxidase as endocytotic markers. These results clearly suggested that circulating lipophorin was endocytosed by the adipocytes. Lipophorin endocytosis might serve the removal and lysosomal degradation of old lipophorin and/or provide an additional or alternative intracellular recycling mechanism of lipid-loading and unloading.