A comparison of adult and larval Manduca sexta apolipophorin-III

Abstract

Apolipophorin-III (apoLp-III) is known to be present in the hemolymph of larval and adult Manduca sexta, but is associated with lipophorin only in the adult. We tested two hypotheses which might account for the lack of apoLp-III in larval lipophorin: (1) there might be a difference in processing of the prepro precursor between adult and larval fat body; (2) there might be larval and adult specific transcription of the apoLp-III gene. ApoLp-III isolated from adult or larval hemolymph has exactly the same amino acid composition and therefore there is not a significant amount of the pro precursor present in hemolymph in either case. We did confirm the presence of the pro precursor in the fat body and showed the site of cleavage of the prepro precursor is between ser (−6) and ala (−5). Restriction mapping, cDNA sequencing and primer extension analysis all indicated that both larval and adult apoLp-III have the same mRNA transcripts and utilize the same coding sequences of a single apoLp-III gene. The data show that neither hypothesis can explain the lack of apoLp-III in larval lipophorin and that other explanations, perhaps involving the mechanism of lipophorin assembly in the fat body, will have to be sought. It was shown that the apoLp-III gene is expressed in a cyclic manner during larval development with maximum expression occurring during the feeding period and that adult fat body contains 2- to 10-fold higher levels of the apoLp-III mRNA.