Nostromo’s 8th passenger: the secrets of the Entamoeba invadens genome and transcriptome

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Many of the enteric protozoa are dangerous parasites found in a diverse range of animals. One of them, Entamoeba hystolytica, causes colitis and dysentery in humans and affects half a billion people across the planet. However, despite its genome having been sequenced nearly a decade ago (see this article in Nature in 2005), we still don’t understand some of the most important aspects of this parasite’s life.

Entamoeba‘s life cycle comprises two phases: it proliferates inside its host during the first one, while in the other it turns into a non-dividing multinucleate cyst. Cyst formation is absolutely essential to Entamoeba‘s survival, and yet it is a process that we are unable to study in this important human parasite due to the lack of the right tools: we simply don’t have methods to induce encystation and excystation in E. hystolytica in vitro cultures.

A cyst of E.hystolytica. /source: CDC (public domain)

Enter Entamoeba invadens: an equivalent parasite affecting reptiles. One of its strains, IP-1, which was originally isolated from a painted turtle (avid Genome Biology readers should now be reminded of an article published earlier this year, which described a genome of just that reptile), is able to form cysts in axenic culture and the methods for studying this process in vitro have already been developed. One thing has, however, still been missing, hampering the efforts to better understand this process: and that is the E.invadens genome.

In an article published today in Genome Biology, Neil Hall and colleagues provide the answer to these problems through the description of the E.invadens genome assembly. They find that the core gene content of this species is very similar to its close relative, E.hystolytica. Furthermore, they also look at the transcriptome changes in the course of encystation and excystation. They discover that one of the genes with increased expression during encystation encodes phosphoplipase D, an enzyme involved in lipid second messenger signalling. Using activity and inhibition assays, Hall and colleagues were able to confirm the role of phospholipase D in the encystation process.

Of course, phospholipase D is just a starting point. Now, that genomic resources are available for many enteric parasites, we should expect that much more will be revealed by the comparative studies that will surely follow the genome and transcriptome sequences; moreover, E. invadens functional studies could perhaps be translated into the discovery of therapeutic targets for the treatment of human parasitic protozoans.