When One Is Enough: The Only Gα Subunit Governs Encystation and Other Cellular Processes in Entamoeba invadens

Gα, Gβ, and Gγ-the heterotrimeric G protein subunits transmit signals from G-protein coupled receptors (GPCRs) to downstream pathways. The causative agent of Amoebiasis, Entamoeba, has been presumed to contain a GPCR signaling pathway playing a role in its encystation, phagocytosis, and motility. A Gα subunit, EhGα1, has been characterized earlier in Entamoeba histolytica , which is involved in its different pathogenic processes. Here, we have characterized its ortholog, EiGα1, in the reptilian model, Entamoeba invadens , which expresses both in trophozoites and during encystation. Silencing EiGα1 through trigger-mediated knockdown reduces efficiency and leads to improper cell aggregation and abnormal chitin wall formation during encystation. Downregulation of EiGα1 results in anomalous F-actin polymerization. EiGα1 silenced cells also exhibit loss of polarity and reduced motility. Furthermore, EiGα1 knockdown also results in decreased phagocytosis of bacteria. Our findings indicate that EiGα1 controls the expression of two vital proteins in Entamoeba-the atypical EiMAPK15 and the homeobox transcription factor EiHbox1-which modulates cyst-wall development and actin reorganization. In conclusion, our findings provide strong evidence for a GPCR signaling network in Entamoeba and highlight the essential function of the Gα subunit in stage conversion and actin cytoskeleton rearrangement.