Ecdysteroid-mediated uptake of arylphorin by larval fat bodies of Calliphora vicina: Involvement and developmental regulation of arylphorin binding proteins

Abstract

In the final larval instar of the blowfly Calliphora vicina the storage protein arylphorin is stage-specifically and selectively taken up by the fat body cells from the haemolymph. Previously, we have identified three arylphorin binding proteins (ABP 130, ABP 96, ABP 65) in the membrane fraction of late larvae and white puparia. Here we demonstrate that all ABPs derive from a single translation product (ABP 130) that we consider as arylphorin receptor precursor. The appearance of the ABPs is developmentally regulated throughout the last larval instar. While ABP 130 and ABP 96 appear at day 4, ABP 65 emerges at the end of last larval instar, coinciding with the rise in ecdysteroid titre and the beginning of arylphorin incorporation. We showed that 20HE induces stage-specifically arylphorin uptake and is responsible for the transformation of ABP 96 into ABP 65 plus a 30 kDa protein, which does not bind arylphorin.