Encystation of Giardia intestinalis—a Journey from the Duodenum to the Colon
The intestinal protozoan parasite Giardia intestinalis has a simple life cycle consisting of disease-causing trophozoites and infectious cysts. The parasite differentiates into the cyst stage (encystation) when duodenal trophozoites are swept further down in the small intestine. The encystation process can be divided into an early and a late phase. Expressions of cyst wall sugars and proteins are induced early during encystation, and Giardia has developed special transport systems for cyst wall material. This is combined with disassembly of the flagella and adhesive disc. In the later phase of encystation, nuclei are divided, DNA is replicated, and the parasites prepare for the next step in differentiation (excystation) via large changes in gene expression. Even if many aspects of the encystation process have been studied and much information has been gained during the last years, much still remains to be explored regarding this highly complex process.