FIG. 8.

Integrated model proposing the functions of SL genes in giardial encystation. The model proposes that ceramide uptake by Giardia is regulated by SPTs encoded by the gspt-1 and gspt-2 genes in nonencysting trophozoites. During encystation, the expression of gglct-1, which encodes GlcT-1, is upregulated. gGlcT-1 catalyzes the production of GlcCer by combining ceramide with glucose that is required for encystation. To ensure a steady supply of ceramide, Giardia synthesizes gSmases during encystation (encoded by gsmase B and gsmase 3b) to hydrolyze sphingomyelin to generate additional ceramide. gSmases were annotated as acid sphingomyelinase-like phosphodiesterases (ASPD) in the genome database. CoA, coenzyme A.