Protein synthesis and its regulation was studied for the first time in the rat tapeworm, Hymenolepis diminuta, during strobilization. Parasites were metabolically labelled with (\u2735)S-methionine and the pattern of gene products synthesized was obtained for the scolex/neck region, male proglottids, female proglottids and onchospheres by high resolution 2-dimensional polyacrylamide gel electrophoresis and fluorography. Gene products unique to different sexually differentiated proglottids were localized to the nuclear, brush border, mitochondrial, microsomal and cytosolic fractions obtained by detergent treatment and osmotic shock, followed by differential centrifugation. The purity of different fractions was monitored by transmission electron microscopy and enzyme marker studies. Total RNAs extracted from the specific regions of the worm were translated in vitro in a reticulocyte lysate system. The patterns of protein synthesis obtained following in vitro translations were compared with the patterns obtained by metabolic labelling with (\u2735)S-methionine. The results indicated a post-transcriptional control of protein synthesis during strobilization in H. diminuta.;Protein synthesis and its regulation was also studied in H. diminuta obtained from non-permissive hosts (mice) and immunosuppressed mice and compared with the parasites of the same age obtained from permissive rat hosts. (\u2735)S-methionine labelled proteins were extracted from the different groups of parasites and analysed by 2-dimensional polyacrylamide gel electrophoresis and fluorography. The in vitro translation products obtained by translating the total RNA of different groups of worms were compared with the patterns of protein synthesis obtained from parasites using (\u2735)S-methionine metabolic labelling. The results indicated a massive post-transcriptional regulation of protein synthesis which was inhibited in parasites obtained from mice, but not in immunosuppressed mice.;The results of this study provide a basic framework on which future studies dealing with post-transcriptional regulation of protein synthesis can be based. The ease of maintenance of this parasite in the lab combined with almost overwhelming post-transcriptional regulation of protein synthesis make H. diminuta an excellent model for developmental studies
