Characterization of assemblage specific genes in Giardia intestinalis
Franziska Pietsch
Giardia intestinalis is a unicellular parasite and an important pathogen, which accounts for approximately 280 million symptomatic human infections (giardiasis) every year. In addition to humans, more than 40 mammalian species can be infected by this protozoan.
The parasite passes through two life cycle stages: an infectious, robust cyst and a disease causing trophozoite, which, upon infection, leads to symptom such as watery diarrhea, epigastric pain, nausea and vomiting.
Today, G. intestinalis is described as a species complex, consisting of eight different variant genotypes (known as assemblages A to H). So far, the genomes of three different isolates belonging to assemblage A, B, and E have been sequenced. Around 91% of the genes are shared between the three isolates, but there is also significant variation between the genomes, which might be linked to host specificity and assemblage‐specific pathogenicity. More precisely, a set of 102 putative genes predicted to be unique to one or two of the so far sequenced genotypes have been identified.
The aim of this project was to verify and characterize those newly identified assemblage specific genes by analysis of gene expression control and by localization of the relevant proteins during the different life stages of the parasite. In addition, the relative efficiency of different protocols for triggering the formation of cysts was tested. Within the parameters of this study, a comprehensive new approach for development of diagnostic and epidemiologic tools for G. intestinalis has been proposed and tested.
In total, thirteen genes were found to be uniquely expressed in the three isolates examined. At least one specific gene was shown to be expressed in trophozoites of each assemblage and most of the proteins could be localized in trophozoites. Where stable transfectants were achieved, localization of the protein was also performed in other life cycle stages of the parasite. Hence, the expression of the putative genes identified in the comparative genomics has been verified in this study and the unique proteins expressed have subsequently been localized in the original isolates. Those unique proteins are promising candidates to be used as marker proteins for genotyping in epidemiological studies and in clinical settings.
Degree Project in Biology
Examensarbete i biologi, 45hp, Uppsala universitet, 2010
Biology Education Centre and the Department of Cell and Molecular Biology, Uppsala University Supervisor: Staffan Svärd
