COMPLETE CDNA-SEQUENCE OF THE RECEPTOR RESPONSIBLE FOR ARYLPHORIN UPTAKE BY THE LARVAL FAT-BODY OF THE BLOWFLY, CALLIPHORA-VICINA

In late larvae of the blowfly Calliphora vicina the storage protein arylphorin is selectively taken up by the fat body cells from the haemolymph. We have demonstrated that arylphorin incorporation is mediated by a specific membrane-bound receptor which is activated by 20-hydroxyecdysone. In this study we report the construction of a cDNA expression library from mRNA isolated from 8-day-old Calliphora larvae. Using affinity-purified antibodies against the arylphorin receptor we identified two cDNA clones of 4044 and 4043 bp, respectively, Both clones code for a 1253 amino acid protein with a deduced molecular mass of 142 kDa, the potential arylphorin receptor precursor, as confirmed by immunoprecipitation of translation products in vitro. Southern blot analysis indicated a single copy gene with multiple alleles; Northern blotting revealed a single mRNA of about 4.5 kb that appeared stage specifically from day 4 to day 8 during larval development. The deduced amino acid sequence exhibits significant similarities to arylphorin, the ligand, as well as to Fbp 1, the product of an ecdysteroid-inducible gene in Drosophila melanogaster larval fat body.