Developmental regulation of protein synthesis in schistosomes

Soon after infecting a mammalian host, cercariae of Schistosoma mansoni rapidly undergo a series of morphologic and biochemical adaptations associated with transformation to their next developmental stage, the schistosomulum. Few of these changes are associated with alterations in gene expression except for an apparent increase in protein synthesis. By pulse-labeling, we demonstrate that there is a gradual rise in methionine incorporation after transformation, and that the rise is not due to increasing amino acid uptake or increasing protein stability. This pattern of protein synthesis did not result from a general increase in transcription of mRNA. There was likewise no evidence of a rise in the availability of selected rate limiting components of the translational machinery such as rRNA or elongation factor 1 alpha as a mechanism for increasing levels of translation. Transcription of HSP 70 appears to be induced in both cercariae and schistosomula, though translation of this message was not detected. A comparison between the level of in vivo synthesis of proteins and the level of their corresponding mRNAs suggests that following transformation of cercariae to schistosomula the translation of most mRNAs is blocked and that this block is gradually reversed during the first 24 h.