Plerocercoid larvae of the tapeworm Spirometra mansonoides produce a factor which is very similar to human growth hormone (hGH). The analogy has been based on similarities in biological actions. A very important difference is the lack of any anti-insulin/diabetogenic activity in PGF. Recently plerocercoid growth factor (PGF) has been shown to share significant antigenic homology with hGH, and plerocercoid genomic DNA exhibits extensive homology with a hGH cDNA. These data suggest that this tapeworm possesses and expresses a hGH-like gene. While this hypothesis alone warrants thorough investigation, the fact that PGF stimulates growth with fattening while suppressing endogenous GH makes this proposal even more significant. A """"""""hGH-like"""""""" factor without anti-insulin activities would be of enormous value in treatment of human disorders requiring hGH therapy. Recombinant DNA techniques will be used to clone both genomic sequences and cDNA for PGF. The approach taken is based on the assumption that the sequences in plerocercoid DNA and poly(A)+ RNA that hybridize to hGH cDNA are likely to be those coding for PGF. Thus, a plerocercoid genomic library has been constructed in Charon 4A and will be screened for recombinants which hybridize to hGH cDNA. The cloned inserts will be mapped for restriction sites and those fragments hybridizing to hGH cDNA will be determined by Southern blot analysis. Restriction fragments will be subcloned into appropriate plasmid vectors and sequenced by the Maxam and Gilbert technique. Reverse transcripts (cDNA) will be generated from total plerocercoid poly(A)-containing RNA, cloned into expression vectors, and used to transform appropriate hosts. Recombinants containing PGF sequences will be detected by hybridization of colony lifts to hGH cDNA or by immunoblotting using an hGH monoclonal antibody that cross reacts with PGF. The cDNA sequence will be determined and compared to that of hGH; similarities may suggest corresponding protein domains involved in receptor binding and growth promotion, whereas differences may indicate regions of the growth hormone molecule responsible for diabetogenic activity.
