The transcriptional response to encystation stimuli in Giardia lamblia is restricted to a small set of genes
2010-07,
Morf, Laura,
Spycher, Cornelia,
Rehrauer, Hubert,
Fournier, Catharine Aquino,
Morrison, Hilary G.,
Hehl, Adrian B.
The protozoan parasite Giardia lamblia undergoes stage-differentiation in the small intestine of
the host to an environmentally resistant and infectious cyst. Encystation involves secretion of
an extracellular matrix comprised of cyst wall proteins (CWPs) and a β(1-3)-GalNAc
homopolymer. Upon induction of encystation, genes coding for CWPs are switched on, and
mRNAs coding for a transcription factor Myb and enzymes involved in cyst wall glycan synthesis
are upregulated. Encystation in vitro is triggered by several protocols, which call for changes in
bile concentrations or availability of lipids, and elevated pH. However, the conditions for
induction are not standardized and we predicted significant protocol-specific side effects. This
makes reliable identification of encystation factors difficult. Here, we exploited the possibility
to induce encystation with two different protocols, which we show to be equally effective, for a
comparative mRNA profile analysis. The standard encystation protocol induced a bipartite
transcriptional response with surprisingly minor involvement of stress genes. A comparative
analysis revealed a core set of only 18 encystation genes and showed that a majority of genes
was indeed upregulated as a side effect of inducing conditions. We also established a Myb
binding sequence as a signature motif in encystation promoters, suggesting coordinated
regulation of these factors.