Putative EGF ligand and receptor of Echinococcus multilocularis that are critical for parasite development

The neglected zoonosis alveolar echinococcosis (AE) is caused by infiltrative growth of the metacestode larval stage of the cestode Echinococcus multilocularis within host organs. We previously demonstrated that metacestode growth depends on the mitotic activity of a population of parasite stem cells, called germinative cells, but it is not yet clear which molecular mechanisms govern Echinococcus stem cell dynamics such as cell-cycle progression, self-renewal and differentiation. Based on previous reports showing that epidermal growth factor (EGF) signalling contributes to Echinococcus stem cell regulation, we herein characterized three EGF receptors of the parasite and demonstrated by RNAi and inhibitor assays that one of these, EmER1, is crucial for the development of metacestode vesicles from parasite stem cells. We also showed that EmER1 serves as a target for afatinib, an EGF receptor inhibitor with profound anti-parasitic activities in vitro and in vivo. By bioinformatic analyses and membrane-bound yeast two-hybrid assays, we identified a parasite-derived, neuregulin-like cognate ligand for EmER1, EmNRG, the expression of which is strongly upregulated in metacestode vesicles during clonal expansion of germinative cells. Furthermore, we demonstrate that RNAi knockdown of the EmNRG encoding gene drastically affects the ability of germinative cells to produce metacestode vesicles. We propose that EmNRG and EmER1 form a cognate ligand-receptor system utilized by E. multilocularis to regulate asymmetric versus symmetric division decisions of stem cells. These data are relevant for further studies into Echinococcus stem cell dynamics and for the development of EGF signalling-based anti-infectives against echinococcosis.