A bone morphogenetic protein homologue in the parasitic flatworm, Schistosoma mansoni

Members of the bone morphogenetic protein (BMP) subfamily of cytokines control many aspects of metazoan development including patterning and organogenesis. Despite the recognition that schistosomes possess key components of a BMP signaling pathway, a BMP-like ligand in the parasitic flatworm Schistosoma mansoni remained elusive. Here, we describe the cloning and characterisation of an S. mansoni BMP (SmBMP). SmBMP is most closely related to BMP homologues from the free-living flatworms Schmidtea mediterranea and Dugesia japonica, with 51% and 47% identity at the amino acid level, respectively. Based on reverse transcription-PCR, SmBMP is expressed throughout the mammalian life-cycle of the parasite in both male and female schistosomes. In support of these results, antibodies to SmBMP successfully immunoprecipitated the protein in adult male and female antigen preparations with more protein detected in male parasites. Immunofluorescent studies localised SmBMP to the protonephridia of adult parasites, and SmBMP was identified in the excretory/secretory products of adult male parasites via immunoprecipitation. With the previous description of a TGF-β subfamily homologue in S. mansoni, ligands representing both arms of the TGF-β superfamily have now been described in this trematode.