CELLULAR AND TRANSCRIPTIONAL CHANGES DURING EXCYSTATION OF GIARDIA-LAMBLIA IN-VITRO

Excystation of Giardia lamblia entails differentiation of dormant cyst s into parasitic trophozoites. Despite its importance for infection, t his transformation is not understood at the cellular or molecular leve ls. In these studies, eve report that excystation entails detection of environmental stimuli across the tough extracellular cyst wall leadin g to highly coordinated physiological, structural, and molecular respo nses. We found that novel cytoplasmic rearrangements and changes in in dividual species of mRNA and in cytoplasmic pH occur within the cyst w all in the earliest stage of excystation, in response to conditions mo deling cyst ingestion and passage into the human stomach. This suggest s that cysts do not contain all the mRNA needed for excystation and em ergence and supports our hypothesis that external stimuli, including h ydrogen ions, may penetrate or be perceived across the cyst wall. In c ontrast, changes in cyst wall structure or proteins were detected only later in excystation, in the stage that models passage into the human small intestine, where trophozoites can emerge and survive. These fin dings show that excystation of G. lamblia is a highly complex and acti ve process and provide important insights into its cellular and molecu lar components. (C) 1998 Academic Press.